WO2013006442A2 - Method for handling a wafer - Google Patents

Method for handling a wafer Download PDF

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Publication number
WO2013006442A2
WO2013006442A2 PCT/US2012/044955 US2012044955W WO2013006442A2 WO 2013006442 A2 WO2013006442 A2 WO 2013006442A2 US 2012044955 W US2012044955 W US 2012044955W WO 2013006442 A2 WO2013006442 A2 WO 2013006442A2
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WO
WIPO (PCT)
Prior art keywords
wafer
shape memory
polymer film
memory polymer
film
Prior art date
Application number
PCT/US2012/044955
Other languages
French (fr)
Other versions
WO2013006442A3 (en
Inventor
Maria Parals SENDIN
Terry Sterrett
Albert P. Perez
Dave PEARD
Ciaran Mcardle
Original Assignee
Henkel Ag & Co. Kgaa
Henkel Ireland Limited
Henkel Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Henkel Ag & Co. Kgaa, Henkel Ireland Limited, Henkel Corporation filed Critical Henkel Ag & Co. Kgaa
Publication of WO2013006442A2 publication Critical patent/WO2013006442A2/en
Publication of WO2013006442A3 publication Critical patent/WO2013006442A3/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H01L21/6835—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support
    • H01L21/6836—Wafer tapes, e.g. grinding or dicing support tapes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2221/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof covered by H01L21/00
    • H01L2221/67—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere
    • H01L2221/683—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H01L2221/68304—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support
    • H01L2221/68327—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support used during dicing or grinding
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2221/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof covered by H01L21/00
    • H01L2221/67—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere
    • H01L2221/683—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H01L2221/68304—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support
    • H01L2221/6834—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support used to protect an active side of a device or wafer
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2221/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof covered by H01L21/00
    • H01L2221/67—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere
    • H01L2221/683—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H01L2221/68304—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support
    • H01L2221/68381—Details of chemical or physical process used for separating the auxiliary support from a device or wafer
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2221/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof covered by H01L21/00
    • H01L2221/67—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere
    • H01L2221/683—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H01L2221/68304—Apparatus for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support
    • H01L2221/68381—Details of chemical or physical process used for separating the auxiliary support from a device or wafer
    • H01L2221/68386—Separation by peeling

Definitions

  • the present invention relates to a method for handling a wafer which comprises a plurality of grooves on its surface.
  • the invention further relates to an assembly, comprising a wafer and a shape memory polymer film and to the use of said film as a fixing device in dicing before grinding (DBG) processes.
  • the wafer thinning is performed by bringing the back side of the wafer in contact with a hard and flat rotating horizontal platter that contains a liquid slurry.
  • the slurry may contain abrasive media with chemical etchants such as ammonia, fluoride, or combinations thereof.
  • the wafer is maintained in contact with the media until an amount of substrate has been removed to achieve a targeted thickness.
  • adhesive materials also known as back grinding tapes or protection tapes
  • back grinding tapes or protection tapes can be laminated to the top side of the wafer to protect this active side during the thinning process.
  • such materials are used as fixing devices to hold semiconductor wafers during the thinning process.
  • US2006/0046433 A1 teaches a method for handling a wafer comprising the steps of forming a plurality of protrusions on a wafer and engaging said protrusions in a fixture; and exposing the wafer to a grinding operation to thin said wafer.
  • the fixing device has a series of protrusions that form an interference fit with surface features extending outwardly from the non- thinned surface of the wafer to be thinned.
  • wafers As wafers are made thinner and thinner, the severity of wafer damage may increase dramatically. At thicknesses below 100 ⁇ , wafers are prone to cracking, surface burnishing, and surface irregularities. Semiconductor wafers having a plurality of grooves on the top side, such as partially diced wafers may have the additional problem of die shifting during the thinning process and/or wafer deformation after the completion of the thinning process. Especially with very thin wafers, the wafers are prone to damage during removal from the thinning fixing device.
  • the present invention provides a method for handling a wafer, such as a method for thinning a wafer, in which a wafer, having a plurality of grooves on its top side, is effectively held by a shape memory polymer film as a fixing device.
  • a shape memory polymer film as a fixing device.
  • the occurrence of wafer defects and/or wafer deformations is reduced by the method of the present invention.
  • said shape memory polymer film can be removed substantially completely from the wafer surface in a stress-free process by applying a low peel force.
  • the shape memory polymer film is therefore reusable, which reduces waste and overall cost.
  • the present invention provides a method for handling a wafer, comprising the steps of:
  • the wafer has a plurality of grooves on the top side of the wafer.
  • Another aspect of the present invention relates to an assembly, comprising a wafer and a shape memory polymer film, wherein the wafer has a plurality of grooves on the top side of the wafer and the shape memory polymer film is attached to the top side of the wafer.
  • a further aspect of the present invention relates to an assembly, comprising a wafer and a shape memory film, wherein the assembly is obtained by the method of the present invention.
  • the present invention relates to the use of a shape memory polymer film as a fixing device for a wafer having a plurality of grooves on one side of the wafer and to the use of said polymer film as a fixing device in dicing before grinding (DBG) processes.
  • DBG dicing before grinding
  • shape memory polymer refers to stimuli-responsive polymeric materials.
  • shape memory polymer refers to thermo-responsive shape memory polymers which have the ability to change their shape upon application of heat as an external stimulus.
  • Shape memory polymers are characterized by having a permanent shape, which can be formed during the production of these polymers. Above a specific temperature (transition temperature Ttrans) the shape memory polymers can be deformed to a temporary shape, wherein said temporary shape is fixed by cooling the SMPs below the transition temperature (Ttrans). Heating up the shape-memory polymers above the transition temperature (Ttrans) induces the shape memory effect. As a consequence, the recovery of the stored permanent shape can be observed.
  • the shape memory effect is not related to a specific material property of single polymers; it rather may result from the polymer ' s structure, its morphology in combination with a certain processing and programming technology. Therefore, the shape memory behavior can be observed for several polymers that may differ significantly in their chemical composition.
  • transition temperature (Ttrans) can vary widely, wherein it is preferred that the transition temperature Ttrans of the shape memory film is in the range of 20°C to 200°C, more preferably in the range of 40°C to 180°C, and particularly preferably in the range of 60°C to 140°C.
  • the transition temperature (Ttrans) of the shape memory polymer film is preferably determined by DMA (Dynamic mechanical analysis).
  • the transition temperature (Ttrans) is preferably defined as the temperature which corresponds to an elastic modulus E ' trans which has a value of 70% of the initial elastic modulus E ' lnit determined at -40°C.
  • the initial elastic modulus E'lnit as well as the elastic modulus E'trans are derived from an elastic modulus ( ⁇ ' ) versus temperature plot.
  • the transition temperature (Ttrans) is preferably determined by using a Rheometrics solids Analyzer (RSA-3) from TA Instruments-Waters LLC, New Castle, wherein the samples for the dynamic mechanical analysis are prepared by cutting specimens to a size of 30 mmx5 mmx1 mm, followed by equilibrating these samples at a temperature of -40°C for 2 min before the temperature is raised to 200°C at a heating rate of 10°C/min.
  • RSA-3 Rheometrics solids Analyzer
  • the wafer used in the method of the present invention is made of a semiconductor material, typically silicon and exhibits a plurality of grooves on its top side.
  • the grooves formed into the top side of the wafer are also known as dicing lines, dicing streets or trenches.
  • the terms "grooves” and “dicing lines” are used interchangeably in the present invention.
  • the means for forming the dicing lines include, for example, wet or dry etching, and laser drilling.
  • the purpose of the grooves/dicing lines is to facilitate and guide the dicing of the wafer into individual semiconductor dies.
  • the dicing lines separate a plurality of fabrication regions on the top side of the wafer, wherein the term "fabrication regions" , as used in the present invention, includes circuitry, through-silica-vias, micro bumps and other fabrication elements on the wafer.
  • the formation of the plurality of fabrication regions, such as circuits on the top side of the wafer is made according to semiconductor fabrication methods well documented in industry literature.
  • the shape memory film is applied by bringing the top side of the wafer into contact with the shape memory polymer film at a contact pressure of 0.1 to 100 MPa and at a temperature above the transition temperature (Ttrans) of the shape memory polymer film.
  • the shape memory film and the top side of the wafer are contacted at a temperature of more than 10°C, preferably at a temperature of more than 20°C, and particularly preferably at a temperature of more than 40°C above the transition temperature (Ttrans) of the shape memory polymer film and/or at a contact pressure of 0.2 to 5 MPa, more preferably at a contact pressure of 0.5 to 2 MPa.
  • the contact pressure for pressing the shape memory film against the top side of the wafer can be achieved by any suitable means known in the art, such as stamps, rolls and the like.
  • the method of the present invention comprises the additional step c) of cooling the formed assembly to a temperature below the transition temperature (Ttrans) of the shape memory polymer film at a contact pressure of 0.1 to 100 MPa.
  • the formed assembly is cooled to a temperature of more than 20°C, preferably of more than 30°C, and particularly preferably of more than 40°C below the transition temperature (Ttrans) of the shape memory polymer film at a contact pressure of 0.2 to 5 MPa, and more preferably at a contact pressure of 0.5 to 2 MPa.
  • Ttrans transition temperature
  • the shape memory polymer film is cooled to a temperature of 0°C to 35°C, more preferably to a temperature of 10°C to 27°C in step c) of the method of the present invention.
  • the shape memory polymer film used in the method of the present invention may comprise a single polymer or a mixture of two or more different polymers.
  • the shape memory film can also comprise or consist of a single layer or two of more different layers.
  • the shape memory polymer film used in the method of the present invention is the cured product of a composition A, comprising
  • polymeric particles which are distributed within said one or more crosslinkable polyorganosiloxanes and which remain discrete in the cured elastomer and have a melting temperature below the degradation temperature of the cured elastomer.
  • melting temperature of the polymeric particles preferably refers to the temperature at which the polymeric particles undergo a change of state from a solid to liquid.
  • the melting temperature can be determined by DSC where the melting temperature is defined as the inflection point of the DSC curve.
  • the term "degradation temperature" of the cured elastomer refers to the temperature at which the elastomer undergoes a weight loss of more than 10 wt.-%, preferably more than 20 wt.-%.
  • the degradation temperature can be determined by TGA (Thermogravimetric Analysis).
  • polymeric particles are polymeric powders, wherein the polymeric particles are preferably selected from polyolefins and/or copolyolefins, such as polyethylene, polypropylene, polyethylene-co-propylene, polybutadiene, polycapralactone, isotactic poly(1- butene), syndiotactic polypropylene, poly(l-decene), poly(ethylene-co-l-butene), poly(ethylene- co-viny I acetate) , polybutylene adipic acid), poly(a-methyl styrene-co-methylstyrene), polyethylene oxide, trans-1 ,4-polybutadiene or trans-1 ,4-polyisoprene.
  • polyolefins and/or copolyolefins such as polyethylene, polypropylene, polyethylene-co-propylene, polybutadiene, polycapralactone, isotactic poly(1- butene
  • the particle size of the polymeric particles of the present invention may vary widely, such as, for example, from 50 nm up to about 100 ⁇ . Desirably, the polymeric particles have a particle size from about 5 ⁇ to about 10 ⁇ .
  • the particle size is preferably determined by laser diffraction using a Mastersizer 2000 (produced by Malvern instruments Ltd, calculation according to Mie).
  • particle size refers to the d50 volume average particle diameter.
  • the d50 volume average particle diameter is defined as that particle diameter at which 50% by volume of the particles have a larger diameter than the d50 value.
  • the polymeric particles are distributed within the crosslinkable polyorganosiloxanes of composition A in a shape-holding amount, preferably in an amount of 1 to 80 wt.-%, more preferably in an amount of 20 to 60 wt.-%, and particularly preferably in an amount of 30 to 50 wt.-%, based on the total amount of the curable composition A.
  • the shape memory polymer film used in the method of the present invention is the cured product of a composition B, comprising
  • (meth)acrylic acid esters is intended to include methacrylic acid esters and acrylic acid esters, and reference to one of methacrylates or acrylates is intended to embrace the other as well, unless specifically noted otherwise.
  • the (meth)acrylic acid esters may be selected from a wide variety of compounds.
  • a desirable class of (meth)acrylic acid esters useful as liquid fillers in composition B include poly- and/or mono-functional (meth)acrylic acid esters.
  • One class of (meth)acrylic acid esters useful in the present invention have the general structure:
  • R a is H, halogen, or to C 20 hydrocarbyl; and R is H or to C 20 hydrocarbyl.
  • Rb is at least C4 or greater.
  • hydrocarbyl (hydrocarbon group) is intended to refer to branched and unbranched radicals or diradicals, respectively, which are primarily composed of carbon and hydrogen atoms.
  • the terms encompass aliphatic groups such as alkyl, alkenyl, and alkynyl groups; aromatic groups such as phenyl; and alicyclic groups such as cycloalkyi and cycloalkenyl.
  • Hydrocarbon radicals of the invention may include heteroatoms to the extent that the heteroatoms do not detract from the hydrocarbon nature of the groups.
  • hydrocarbon groups may include such functionally groups as ethers, alkoxides, carbonyls, esters, amino groups, cyano groups, sulfides, sulfates, sulfoxides, sulfones, and sulfones.
  • hydrocarbon radicals and diradicals of the present invention may be optionally substituted to the extent that the substituent does not detract from the hydrocarbon nature of the hydrocarbyl group.
  • the term "optionally substituted” is intended to mean that one or more hydrogens on a group may be replaced with a corresponding number of substituents preferably selected from halogen, nitro, azido, amino, carbonyl, ester, cyano, sulfide, sulfate, sulfoxide, sulfone, and/or sulfone groups.
  • Other desirable (meth)acrylic acid esters of composition B are urethane (meth)acrylates having the general structur
  • R c is H, Ci to C 4 alkyl, or halogen
  • R d is (i) a C n to C 8 hydroxyalkylene or aminoalkylene group, or (ii) a C ⁇ to C 6 alkylamino-C 1 to C e alkylene, a hydroxyphenylene, aminophenylene, hydroxynaphthalene or amino-naphthalene optionally substituted by Ci to C 3 alkyl, Ci to C 3 alkylamino or di-Ci to C 3 alkylamino group
  • R e is C 2 to C 20 alkylene, C 2 to C 2 oalkenylene or C 2 to C 20 cycloalkylene, C 6 to C 40 arylene, alkarylene, C 2 to C 40 aralkarylene, C 2 to C 40 alkyloxyalkylene or C 2 to C 40 aryloxyarylene, optionally substituted by 1 to 4 halogen atoms or by 1 to 3 amino or mono- or di
  • R c , R d , and R e are as described herein above and R f is an w-valent residue obtained by the removal of w amino or hydroxy groups from a polyamine or a polyhydric alcohol having at least two amino or hydroxy groups;
  • X is O or NR 9 where R 9 is H or Ci to C 7 alkyl; and
  • w is an integer from 2 to 20.
  • Suitable monofunctional (meth)acrylic acid esters are selected from isobornyl
  • (meth)acrylate adamantly (meth)acrylate, dicyclopentenyl (meth)acrylate, trimethylcyclohexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, iso-octyl (meth)acrylate, n- nonyl (meth)acrylate, iso-nonyl (meth)acrylate, n-decyl (meth)acrylate, iso-decyl (meth)acrylate, n-undecyl (meth)acrylate, iso-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, iso-dodecyl (meth)acrylate, 2(2-ethoxyethoxy)ethylacrylate, and/or combinations thereof.
  • the (meth)acrylic acid ester may be isobornyl acrylate, iso-octyl acrylate, and/or isodecyl 2(2-ethyxyethoxy) ethylacrylate.
  • the (meth)acrylic acid ester component of composition B comprises a combination of isobornyl (meth)acrylate with n-decyl (meth)acrylate, isobornyl (meth)acrylate with iso-decyl (meth)acrylate, isobornyl (meth)acrylate with n-undecyl (meth)acrylate, isobornyl (meth)acrylate with iso-undecyl (meth)acrylate, isobornyl
  • Specific polyfunctional (meth)acrylic acid esters which are desirable include polyethylene glycol dimethacrylate and dipropylene glycol dimethacrylate.
  • Other desirable (meth)acrylic acid esters are selected from the acrylate, methacrylate and glycidyl methacrylate esters of bisphenol A. Desirable among these free-radical polymerizable components mentioned is ethoxylated bisphenol-A-dimethacrylate ( ⁇ ").
  • composition B Mixtures of any of the above-mentioned (meth)acrylic acid esters may be employed in composition B.
  • One or more (meth)acrylic acid esters may be added in amounts of at least 5 percent by weight of the total composition B. Desirably, one or more (meth)acrylic acid esters are present in an amount of 15% to 80% by weight of the total composition B, and more desirably in an amount of 20% to 70% by weight of the total composition B.
  • composition A as well as composition B comprises one or more crosslinkable polyorganosiloxanes which form an elastomer when cured.
  • the crosslinkable polyorganosiloxanes used in the method of the present invention are preferably selected from curable silicone compositions.
  • curable silicone compositions Various types may be employed. For example, heat curing silicone compositions, moisture curing silicone compositions and photocuring silicone compositions may be employed.
  • Polymodal curing silicone compositions for example photo and moisture dual curing
  • compositions or heat and moisture dual curing silicone compositions are also useful.
  • Suitable crosslinkable polyorganosiloxanes are selected from compounds of formula (I),
  • R 1 , R 2 and R 5 independently of one another are selected from hydrogen, C r
  • R 6 is C -20 hydrocarbyl
  • R 4 is H or C 1-4 alkyl
  • crosslinkable polyorganosiloxanes are selected from compounds of formula (II):
  • MA is a methacryloxypropyl group
  • n is from 1 to 1200 and c is 0 or 1
  • each R 5 independently of one another is Ci. 2 o hydrocarbyl or Ci. 20 hydrocarboxyl.
  • R1 , R2, R3, and R5 groups are alkyl (e.g. methyl, propyl, butyl and pentyl), alkenyl (e.g. vinyl and allyl), cycloalkyl (e.g. cyclohexyl and cycloheptyl), aryl (e.g. phenyl), arylalkyl (e.g. betaphenylethyl), alkylaryl, and hydrocarbonoxy (e.g. alkoxy, aryloxy, alkaryloxy, aryalkoxy, and in particular, methoxy, ethoxy or hydroxyl). Any of the foregoing groups may have some or all of the hydrogen atoms substituted by a halogen, such as fluorine or chlorine.
  • a halogen such as fluorine or chlorine.
  • the number of repeating units in the crosslinkable polyorganosiloxanes can be varied to achieve specific molecular weights, viscosities and other chemical or physical properties.
  • the crosslinkable polyorganosiloxanes may be present in amounts of about 20% to about 95% by weight, based on the total weight of the curable composition A or based on the total weight of the curable composition B.
  • composition A and/or composition B may include one or more silicon hydride crosslinkers and/or one or more organo- metallic hydrosilation catalysts.
  • the silicon hydride crosslinkers are selected from compounds of formula (III)
  • R 7 , R 9 and R 10 are H; otherwise R, R 7 , R 9 , and R 10 are the same or different and are C 1-20 hydrocarbyl, preferably methyl; x is an integer from 10 to 1000; and y is an integer from 1 to 20.
  • One or more silicon hydride crosslinkers may be present in an amount sufficient to achieve the desired amount of crosslinking, and in one embodiment in an amount of 1% to 10% by weight, based on the total weight of the composition A or based on the total weight of the composition B.
  • Useful organo-metallic hydrosilation catalysts may be selected from any precious metal or precious metal-containing catalyst effective for initiating a thermal hydrosilation cure reaction. Especially useful are platinum and rhodium catalysts that are effective for catalyzing the addition reaction between silicone-bonded hydrogen atoms and silicone-bonded olefinic groups. Other classes of catalysts useful in the present invention include organo rhodium and platinum alcoholates. Complexes of ruthenium, palladium, osmium and iridium are also contemplated.
  • One or more organo metallic hydrosilation catalyst may be used in any effective amount to effectuate thermal curing.
  • the catalyst is present in amounts of 0.025% to 1.0% by weight, based on the total weight of composition A or based on the total weight of composition B.
  • compositions A or B may include one or more initiators, wherein the terms “initiator” and “catalyst” are used interchangeably in the present invention.
  • Suitable initiators for use in the present method include moisture cure initiators, photoinitiators, free radical initiators, heat cure catalysts, and/or combinations thereof.
  • One or more initiators may be present in composition A or composition B in an amount of 0.01% to 10% by weight, preferably in an amount of 0.1 % to 5% by weight, each based on the total weight of composition A or composition B.
  • a number of photoinitiators may be employed as part of composition A and/or composition B. Any known free radical type photoinitiator which promotes crosslinking, may be used in the method of the present invention. Photoinitiators enhance the rapidity of the curing process when the photocurable compositions as a whole are exposed to electromagnetic radiation.
  • Non-limiting examples of UV photoinitiators that are useful in composition A and/or composition B include pyruvates, acetophenones, phosphine oxides, benzoins, benzophenone, dialkoxy-benzophenones, Michler's ketone (4,4'-bis(dimethylamino)benzophenone),
  • diethoxyacetophenone and/or any combination thereof.
  • the shape memory film used in the method of the present invention is the cured product of a composition C, comprising i) one or more epoxy resins selected from aromatic epoxy resins, aliphatic epoxy resins, and/or combinations thereof, and
  • crosslinking agents selected from multi-amines, multi-carboxylic acids and anhydrides and/or combinations thereof.
  • Suitable aromatic epoxy resins include aromatic diepoxides, such as the diglycidyl ether of bisphenol A, which is commercially available under the tradename EPON 826 from Hexion Speciality Chemicals.
  • Suitable aliphatic epoxy resins include aliphatic diepoxides, such as neopentyl glycol diglycidyl ether (NGDE), which is commercially available from TCI America.
  • NGDE neopentyl glycol diglycidyl ether
  • composition C comprises a combination of one or more aromatic epoxy resins with one or more aliphatic epoxy resins, wherein a mixture of diglycidyl ether of bisphenol A and neopentyl glycol diglycidyl ether (NGDE) is particularly preferably used as the epoxy resin component of composition C.
  • NGDE neopentyl glycol diglycidyl ether
  • multi-amines refers to compounds having at least two amine groups
  • multi-carboxylic acids refers to compounds having at least two carboxylic acid groups
  • Suitable initiators for composition C include alkoxylated di-or tri-amines, such as poly(propylene glycol)bis(2-aminopropyl)ether, which is commercially available under the tradename Jeffamine D-230 from Hexion Specialty Chemicals and Huntsman.
  • the shape memory polymer film used in the method of the present invention can be prepared according to any method. Particularly preferred methods to prepare said shape memory polymer film are described in US patent application Nos. 2004/0266940 A1 ,
  • the shape memory polymer film can be used to support and/or hold the wafer during a backside grinding process.
  • the shape memory polymer film protects the top side of the wafer during a backside grinding process.
  • the shape memory film used in the method of the present invention has an average film thickness T of 10 ⁇ to 1200 ⁇ , preferably of 15 ⁇ to 500 pm, and particularly preferably of 30 ⁇ to 300 pm.
  • the average thickness T of the shape memory polymer film refers to the thickness of the SMP film before said film is applied to the top side of the wafer in step b) of the method of the present invention.
  • the average film thickness T of the shape memory polymer film can be determined as shown in figure 5.
  • the average film thickness T is the arithmetic average of a multitude of film thickness values Tn, wherein each film thickness value Tn is measured in a substantially orthogonal direction to the longitudinal extension 22 of the shape memory film 20 between two opposing points on two opposing sides of the shape memory polymer film 20.
  • multitude refers, for example, to at least 10 different measuring points at 10 different positions along a profile section of the SMP film 20.
  • the average film thickness T is determined, for example, by using a section of the SMP film 20 (1 cm*1 cm in size) divided into 5 equal strips (each 2 mm) and in each case the average film thickness T of the shape memory polymer film is determined along the profile.
  • the average film thickness T along the profile is preferably determined by scanning electron microscopy (SEM) using a scanning electron microscope JEOL JSM-6060 SEM.
  • shape memory polymer films of the above average film thickness in the method of the present invention, because said shape memory polymer films can be removed easily from the top side of the wafer and these films significantly reduce wafer defects and/or wafer deformations which could occur in the course of a wafer thinning process.
  • the shape memory polymer film which is used in the method of the present invention, can be attached or laminated to a carrier film.
  • a support structure By attaching the shape memory film to a carrier film a support structure is formed, wherein the carrier film imparts structural integrity and/or stiffness to the support structure and/or ensures the reusability of the support structure.
  • the carrier film may be UV transparent and/or may comprise at least one polymer selected from polyethylenes, polypropylenes, polycarbonates, polyesters,
  • the carrier film can comprise or consist of one, two or more than two different layers, wherein each layer can comprise or consist of at least one of the
  • the average thickness of the carrier film is in the range of 20 ⁇ to
  • the surface structure of the shape memory polymer film can be modified.
  • the shape memory polymer film used in the method of the present invention has two opposing surfaces and the surface which is applied to the top side of the wafer (exterior surface) is flat. It is advantageous to use a shape memory film having a flat exterior surface as a fixing device in the method of the present invention, because the resulting assemblies exhibit a good stability during wafer handling operations, wherein the bonding strength between the wafer surface and the shape memory film is particularly high.
  • flat preferably refers to surfaces which exhibit a flatness index (Fl) of less than 0.02.
  • the "flatness index”, as used in the present invention, is defined as the ratio of roughness of the exterior surface of the SMP film to the average film thickness of the shape memory polymer film.
  • the flatness index can be determined as shown in Fig. 3 to 5.
  • the term roughness as used in the present invention, means the roughness average, which is defined as the arithmetic average of peak Pn and valley Vn distances Dn.
  • peak Pn refers to any protruding area of the exterior surface
  • valley Vn refers to any recess between protruding areas of the exterior surface 21 of the SMP film 20.
  • distance Dn means the difference in height of a peak Pn and neighbored valley Vn measured in a substantially orthogonal direction to the longitudinal extension 22 of the shape memory film 20.
  • the distance Dn is defined as the distance, measured in a substantially orthogonal direction to the longitudinal extension 22, of two straight lines extending substantially parallel to the longitudinal extension 22, wherein one straight line subtends a peak Pn and the other straight line subtends a neighbored valley Vn.
  • longitudinal extension refers to a plane extending substantially parallel to the surfaces of the shape memory polymer, wherein the asperity of the surfaces of the shape memory film is not taken into account.
  • the roughness is measured, for example, along a line of usually 0.08 cm on the exterior surface 21 of the shape memory polymer film 20.
  • the roughness is the arithmetic average of 15 different measurements at 15 different positions on the exterior surface 21 of the shape memory polymer film 20.
  • the roughness is preferably determined at a measurement speed of 0.5 mm/s by using a Solarius non-contacting Laser Profilometer equipped with an AF2000 autofocus sensor.
  • the obtained data is analyzed by using solar map universal 3.1.10 image analysis software (Gaussian filter 0.8 mm), wherein a microroughness filtering is used, with a cutoff of 2.5 ⁇ .
  • the shape memory polymer film used in the method of the present invention has two opposing surfaces and the surface which is applied to the top side of the wafer (exterior surface) is microstructured. It is advantageous to use shape memory films having a microstructured exterior surface as a fixing device in the method of the present invention, because said SMP films are easily releasable in a residue free-manner from the wafer surface by applying a temperature above the transition temperature (Ttrans) of the shape memory polymer film.
  • Ttrans transition temperature
  • microstructured refers to surfaces, comprising microstructured features, wherein the term “microstructured features” refers to features of a surface that have at least one, preferably all three dimensions (e.g., height, length, width, or diameter) of less than one millimeter.
  • microstructured features can include one or more projections, one or more depressions, a combination of projections and depressions, ridges, posts, pyramids,
  • projections and/or depressions can also vary.
  • some embodiments of projections and/or depressions can be rounded in shape (e.g., circular, semicircular, spherical,
  • the projections and/or depressions may include or define one or more channels, valleys, wells, ridges, and the like, combinations thereof, or any other configuration.
  • Microstructured features on the exterior surface of the shape memory polymer film may be formed through the use of a microstructured molding tool.
  • Microstructured molding tools can be in the form of a planar stamping press, a flexible or inflexible belt, a roller, or the like.
  • the depth of the grooves on the top side of the wafer can vary widely.
  • the grooves on the top side of the wafer have a depth of 20 ⁇ to 150 ⁇ , preferably of 30 ⁇ to 120 ⁇ , and particularly of 40 ⁇ to 100 ⁇ .
  • the shape memory polymer film is capable of penetrating or extending into the grooves on the top side of the wafer after step b) and step c) of the method of the present invention have been carried out.
  • the penetration depth can be controlled by proper selection of manufacturing parameters, such as contact pressure, temperature and/or contact time in step b) of the method of the present invention.
  • the SMP film fills out at least 10 vol.-%, more preferably at least 20 vol.-%, and particularly preferably at least 30 vol.-% of the total volume of the grooves on the top side of the wafer.
  • a particularly good stabilization is achieved, when the SMP film fills out the grooves completely.
  • the volume fraction of the grooves on the top side of the wafer which is filed out by the SMP film is preferably determined by scanning electron microscopy (SEM).
  • the method of the present invention can further comprise the additional step d) of exposing the back side of the wafer to a grinding operation to thin said wafer to a chosen thickness.
  • the back side of the wafer is subjected to a grinding operation.
  • this back- grinding is done to a level to meet the depth of the dicing lines.
  • the dicing lines are cut slightly deeper into the front side of the wafer than the target depth of the backside grinding. This slight over cutting facilitates the eventual separation of the individual dies and allows to singulate the wafer into individual dies in the course of the grinding operation.
  • an adhesive coating can be applied to the back side of the wafer.
  • This adhesive wafer back side coating is used to attach the individual dies to their substrates.
  • the application of the wafer back side coating is performed by any effective method, such as by spin coating, screen or stencil printing, or spray or jet printing.
  • the chemical composition of the wafer back side coating is any adhesive that will meet the subsequent processing requirements.
  • Such adhesives are known in the art.
  • the wafer back side coating is a B-stageable liquid, meaning it can be heated to remove solvent and/or to partially cure. After B-staging the wafer back side coating is relatively tack-free at room temperature. In the later die attach operation, the coating can be heated to soften and flow during die attach, and then be heated at an elevated temperature for final cure. Finally, a support tape can be applied on top of the B-staged coating on the back side of the wafer for subsequent handling purposes
  • the method of the present invention can comprises the additional step e) of releasing the shape memory polymer film from the top side of the wafer by exposing said film to a temperature above its transition temperature (Ttrans).
  • Ttrans transition temperature
  • the application of heat as an external stimulus induces the shape memory effect of the SMP film.
  • the SMP film used in the method of the present invention can be removed substantially completely from the top side of the wafer in a stress-free process by applying a low peel force.
  • peel force as used in the present invention preferably refers to the 90° peel force needed for peeling the adhered surfaces apart. Said 90° peel force is preferably determined at 23°C according to ASTM D6862-04 test method using a TXT plus tensile tester (available from Stable Micro Systems, Surrey UK) using 5 Kg load cell and a crosshead speed of 25 mm/min.
  • a peel force such as the 90° peel force
  • the peel force is regarded as being low, if the peel force, such as the 90° peel force, needed to separate the SMP film and the wafer at 23°C is less than 0.1 N/mm, preferably less than 0.05 N/mm, more preferably less than 0.01 N/mm, and particularly preferably less than 0.001 N/mm.
  • the shape memory polymer film is released by exposing it to a temperature of at least 10°C, more preferably to a temperature of at least 20°C, and particularly preferably to a temperature of at least 30°C above the transition temperature (Ttrans) of the shape memory polymer film.
  • Ttrans transition temperature
  • the shape memory polymer film can be removed substantially completely from the wafer surface in short time periods, preferably in less than 15 minutes, more preferably in less than 10 minutes, and particularly preferably in less than 5 minutes.
  • substantially completely preferably means, that less than 5 wt.-%, preferably less than 1 wt.-%, more preferably less than 0.5 wt.-%, and particularly preferably less than 0.1 wt.-%, based on the total weight of the shape memory polymer film remain on the wafer surface after the shape memory polymer film is removed from the top side of the wafer.
  • a further aspect of the invention is an assembly, comprising a wafer and a shape memory polymer film, wherein the assembly is obtained by the method of the present invention.
  • Another aspect of the present invention is an assembly, comprising a wafer and a shape memory polymer film, wherein the wafer has a plurality of grooves on the top side of the wafer and the shape memory polymer film is attached to the top side of the wafer.
  • the wafer and the shape memory film correspond to the SMP films and wafers which are described in the method of the present invention.
  • the present invention also relates to the use of a shape memory polymer film as a fixing device for a wafer having a plurality of grooves on one side of the wafer and to the use of a shape memory polymer film as a fixing device in dicing before grinding (DBG) processes, wherein the wafer and the shape memory film preferably correspond to the SMP films and wafers which are described in the method of the present invention.
  • Dicing before grinding (DBG) processes are known in the art and are for example described in U.S. patent No. 7,074,695 B2 in figures 1 to 7 and column 1 , lines 13 to 44.
  • Figure 1 shows a sectional view of the assembly formed in step b) of the method of the present invention.
  • Figure 2 shows an enlarged sectional view of a part A of the assembly shown in figure 1.
  • Figure 3 shows a sectional view of a flat shape memory polymer film 20 as provided in step a) of the method of the present invention.
  • Figure 4 shows an enlarged sectional view of a part B of the shape memory polymer film 3 shown in figure 3.
  • Figure 5 shows an additional enlarged sectional view of a part C of the shape memory polymer film 3 shown in figure 3.
  • Fig. 1 shows a sectional view of an assembly as formed in step b) of the method of the present invention.
  • Said assembly comprises a wafer 10 having a top side 11 and a back side 12, wherein the wafer 10 has a plurality of grooves 13 on the top side of the wafer 11.
  • the assembly further comprises a shape memory film 20 which has an exterior surface 21 which is attached to the top side 11 of the wafer 10.
  • FIG. 2 an enlarged sectional view of a part A of the assembly shown in figure 1 is depicted.
  • the shape memory polymer film 20 penetrates or extends into the grooves 13 on the top side 11 of the wafer 10, wherein the penetration depth can be controlled by proper selection of manufacturing parameters, such as contact pressure, contact time and/or temperature in step b) of the method of the present invention.
  • the SMP film 20 effectively stabilizes said wafer 10 during wafer handling operations, such as grinding operations, wherein the occurrence of wafer defects and/or wafer deformations is reduced.
  • FIG. 3 shows a sectional view of a flat shape memory polymer film 20 as provided in step a) of the method of the present invention.
  • FIG 4 an enlarged sectional view of a part B of the SMP film 20 shown in figure 3 is depicted.
  • the shape memory polymer film 20 has a flatness index of less than 0.02, wherein the flatness index is defined as the ratio of a roughness of the exterior surface 21 of the shape memory polymer film to an average thickness T of the shape memory polymer film 20.
  • the average film thickness T of the shape memory polymer film 20 can be determined as shown in figure 4.
  • the average film thickness T is the arithmetic average of a multitude of film thickness values Tn, wherein each film thickness value Tn is measured in a substantially orthogonal direction to the longitudinal extension 22 of the shape memory film 20 between two opposing points, wherein one point is located on the inner surface of the shape memory polymer film, and the corresponding point is located on the opposing exterior surface 21 of the shape memory polymer film.
  • the term multitude, as used above, can refer, for example, to at least 10 different measuring points at 10 different positions along a profile section of the SMP film 20.
  • the average film thickness T can be determined, for example, by using a section of the SMP film 20 (1 cm*1 cm in size) divided into 5 equal strips (each 2 mm) and in each case the average film thickness T of the shape memory polymer film 20 is determined along the profile.
  • the average film thickness T along the profile is determined by scanning electron microscopy (SEM) using a scanning electron microscope JEOL JSM-6060 SEM.
  • Figure 5 shows an enlarged sectional view of a part C of the shape memory polymer film 20 shown in figure 3 with an indication of the roughness of the shape memory polymer film 20.
  • the exterior surface 21 is of course not completely flat and shows a special asperity.
  • the asperity of the exterior surface 21 of the shape memory polymer film 20 is reflected in sections of the shape memory polymer film 20 having a more or less minor variable thickness. This variable thickness is reflected in the sectional view of the SMP film shown in fig. 5 in the form of peaks P1 , P2, P3 and valleys V1 , V2, V3, V4 in the exterior surface 21 of the shape memory polymer film 20.
  • roughness means the roughness average, which is defined as the arithmetic average of peak Pn and valley Vn distances Dn.
  • peak Pn refers to any protruding area of the exterior surface 21
  • valley Vn refers to any recess between protruding areas of the exterior surface 21 of the shape memory polymer film 20.
  • distance Dn means the difference in height of a peak Pn and neighbored valley Vn measured in a substantially orthogonal direction to the longitudinal extension 22 of the shape memory film 20.
  • the roughness is determined at a measurement speed of 0.5 mm/s by using a Solarius non-contacting Laser Profilometer equipped with an AF2000 autofocus sensor.
  • the obtained data is analyzed by using solar map universal 3.1.10 image analysis software (Gaussian filter 0.8 mm), wherein a microroughness filtering is used, with a cutoff of 2.5 ⁇ .

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Abstract

The present invention relates to a method for handling a wafer which comprises a plurality of grooves on its surface. The invention further relates to an assembly, comprising a wafer and a shape memory polymer film and to the use of said film as a fixing device device in dicing before grinding (DBG) processes.

Description

METHOD FOR HANDLING A WAFER
CROSS-REFERENCE TO RELATED APPLICATION
[001] This application claims the benefit of United States Provisional Application No.
61/503,796 filed July 1 , 2011 , the contents of which are incorporated herein by reference.
[002] The present invention relates to a method for handling a wafer which comprises a plurality of grooves on its surface. The invention further relates to an assembly, comprising a wafer and a shape memory polymer film and to the use of said film as a fixing device in dicing before grinding (DBG) processes.
[003] Miniaturization and slimming of electrical and electronic equipment has led to a need for thinner semiconductor wafers. One way to produce thinner wafers is to remove excess material from the back side of the wafer, the side without any circuitry, before the wafer is separated into the individual dies. This removal is typically done by a grinding process and is known as back side grinding, although it can be anticipated that methods other than grinding might be used.
[004] Normally, the wafer thinning is performed by bringing the back side of the wafer in contact with a hard and flat rotating horizontal platter that contains a liquid slurry. The slurry may contain abrasive media with chemical etchants such as ammonia, fluoride, or combinations thereof. The wafer is maintained in contact with the media until an amount of substrate has been removed to achieve a targeted thickness.
[005] It is known that adhesive materials (also known as back grinding tapes or protection tapes) can be laminated to the top side of the wafer to protect this active side during the thinning process. In addition such materials are used as fixing devices to hold semiconductor wafers during the thinning process.
[006] US2006/0046433 A1 teaches a method for handling a wafer comprising the steps of forming a plurality of protrusions on a wafer and engaging said protrusions in a fixture; and exposing the wafer to a grinding operation to thin said wafer. The fixing device has a series of protrusions that form an interference fit with surface features extending outwardly from the non- thinned surface of the wafer to be thinned.
[007] As wafers are made thinner and thinner, the severity of wafer damage may increase dramatically. At thicknesses below 100 μητι, wafers are prone to cracking, surface burnishing, and surface irregularities. Semiconductor wafers having a plurality of grooves on the top side, such as partially diced wafers may have the additional problem of die shifting during the thinning process and/or wafer deformation after the completion of the thinning process. Especially with very thin wafers, the wafers are prone to damage during removal from the thinning fixing device.
[008] Notwithstanding the state of technology, it would be desirable to provide better methods for handling wafers having a plurality of grooves on their top side, especially better methods for thinning such wafers, in which the mechanical force needed to remove the fixing device from the wafer is low, no subsequent cleaning step is needed to remove residues of the fixing device from the wafer surface, and the occurrence of wafer defects and/or wafer deformations, such as die shifting and wafer warpage is reduced.
[009] The present invention provides a method for handling a wafer, such as a method for thinning a wafer, in which a wafer, having a plurality of grooves on its top side, is effectively held by a shape memory polymer film as a fixing device. Notably, the occurrence of wafer defects and/or wafer deformations is reduced by the method of the present invention. Subsequent to processing, said shape memory polymer film can be removed substantially completely from the wafer surface in a stress-free process by applying a low peel force. The shape memory polymer film is therefore reusable, which reduces waste and overall cost.
[0010] In its broadest sense, the present invention provides a method for handling a wafer, comprising the steps of:
a) providing i) a wafer having a top side and a back side and ii) a shape memory polymer film, and
b) applying the shape memory film to the top side of the wafer to form an assembly,
wherein the wafer has a plurality of grooves on the top side of the wafer.
[0011] Another aspect of the present invention relates to an assembly, comprising a wafer and a shape memory polymer film, wherein the wafer has a plurality of grooves on the top side of the wafer and the shape memory polymer film is attached to the top side of the wafer.
[0012] A further aspect of the present invention relates to an assembly, comprising a wafer and a shape memory film, wherein the assembly is obtained by the method of the present invention.
[0013] In another aspect, the present invention relates to the use of a shape memory polymer film as a fixing device for a wafer having a plurality of grooves on one side of the wafer and to the use of said polymer film as a fixing device in dicing before grinding (DBG) processes.
[0014] The term "shape memory polymer" (SMP), as used herein, refers to stimuli-responsive polymeric materials. In particular, the term "shape memory polymer", as used in the present invention, refers to thermo-responsive shape memory polymers which have the ability to change their shape upon application of heat as an external stimulus. [0015] Shape memory polymers are characterized by having a permanent shape, which can be formed during the production of these polymers. Above a specific temperature (transition temperature Ttrans) the shape memory polymers can be deformed to a temporary shape, wherein said temporary shape is fixed by cooling the SMPs below the transition temperature (Ttrans). Heating up the shape-memory polymers above the transition temperature (Ttrans) induces the shape memory effect. As a consequence, the recovery of the stored permanent shape can be observed.
[0016] The shape memory effect is not related to a specific material property of single polymers; it rather may result from the polymer's structure, its morphology in combination with a certain processing and programming technology. Therefore, the shape memory behavior can be observed for several polymers that may differ significantly in their chemical composition.
[0017] Depending on the chemical structure of the shape memory polymer film the transition temperature (Ttrans) can vary widely, wherein it is preferred that the transition temperature Ttrans of the shape memory film is in the range of 20°C to 200°C, more preferably in the range of 40°C to 180°C, and particularly preferably in the range of 60°C to 140°C.
[0018] The transition temperature (Ttrans) of the shape memory polymer film is preferably determined by DMA (Dynamic mechanical analysis). The transition temperature (Ttrans) is preferably defined as the temperature which corresponds to an elastic modulus E'trans which has a value of 70% of the initial elastic modulus E'lnit determined at -40°C. The initial elastic modulus E'lnit as well as the elastic modulus E'trans are derived from an elastic modulus (Ε') versus temperature plot.
[00 9] The transition temperature (Ttrans) is preferably determined by using a Rheometrics solids Analyzer (RSA-3) from TA Instruments-Waters LLC, New Castle, wherein the samples for the dynamic mechanical analysis are prepared by cutting specimens to a size of 30 mmx5 mmx1 mm, followed by equilibrating these samples at a temperature of -40°C for 2 min before the temperature is raised to 200°C at a heating rate of 10°C/min.
[0020] The wafer used in the method of the present invention is made of a semiconductor material, typically silicon and exhibits a plurality of grooves on its top side. The grooves formed into the top side of the wafer are also known as dicing lines, dicing streets or trenches. The terms "grooves" and "dicing lines" are used interchangeably in the present invention.
[0021] The means for forming the dicing lines include, for example, wet or dry etching, and laser drilling. The purpose of the grooves/dicing lines is to facilitate and guide the dicing of the wafer into individual semiconductor dies. [0022] Preferably, the dicing lines separate a plurality of fabrication regions on the top side of the wafer, wherein the term "fabrication regions" , as used in the present invention, includes circuitry, through-silica-vias, micro bumps and other fabrication elements on the wafer. The formation of the plurality of fabrication regions, such as circuits on the top side of the wafer is made according to semiconductor fabrication methods well documented in industry literature.
[0023] In one embodiment of the method of the present invention the shape memory film is applied by bringing the top side of the wafer into contact with the shape memory polymer film at a contact pressure of 0.1 to 100 MPa and at a temperature above the transition temperature (Ttrans) of the shape memory polymer film. Preferably, the shape memory film and the top side of the wafer are contacted at a temperature of more than 10°C, preferably at a temperature of more than 20°C, and particularly preferably at a temperature of more than 40°C above the transition temperature (Ttrans) of the shape memory polymer film and/or at a contact pressure of 0.2 to 5 MPa, more preferably at a contact pressure of 0.5 to 2 MPa.
[0024] The contact pressure for pressing the shape memory film against the top side of the wafer can be achieved by any suitable means known in the art, such as stamps, rolls and the like.
[0025] It is advantageous to form the assembly in the step b) of the method of the present invention under the aforementioned process conditions, because said conditions cause a particularly good adhesion between the top side of the wafer and the shape memory polymer film.
[0026] In a further embodiment, the method of the present invention comprises the additional step c) of cooling the formed assembly to a temperature below the transition temperature (Ttrans) of the shape memory polymer film at a contact pressure of 0.1 to 100 MPa.
[0027] Preferably, the formed assembly is cooled to a temperature of more than 20°C, preferably of more than 30°C, and particularly preferably of more than 40°C below the transition temperature (Ttrans) of the shape memory polymer film at a contact pressure of 0.2 to 5 MPa, and more preferably at a contact pressure of 0.5 to 2 MPa. For ease of handling, it is preferred that the shape memory polymer film is cooled to a temperature of 0°C to 35°C, more preferably to a temperature of 10°C to 27°C in step c) of the method of the present invention.
[0028] In the present invention the shape memory polymer film used in the method of the present invention may comprise a single polymer or a mixture of two or more different polymers. The shape memory film can also comprise or consist of a single layer or two of more different layers. [0029] In one embodiment the shape memory polymer film used in the method of the present invention is the cured product of a composition A, comprising
i) one or more crosslinkable polyorganosiloxanes which form an elastomer when cured, and
ii) polymeric particles which are distributed within said one or more crosslinkable polyorganosiloxanes and which remain discrete in the cured elastomer and have a melting temperature below the degradation temperature of the cured elastomer.
[0030] As used in the present invention, the term "melting temperature" of the polymeric particles preferably refers to the temperature at which the polymeric particles undergo a change of state from a solid to liquid. The melting temperature can be determined by DSC where the melting temperature is defined as the inflection point of the DSC curve.
[0031] As used in the present invention, the term "degradation temperature" of the cured elastomer refers to the temperature at which the elastomer undergoes a weight loss of more than 10 wt.-%, preferably more than 20 wt.-%. The degradation temperature can be determined by TGA (Thermogravimetric Analysis).
[0032] Among useful polymeric particles are polymeric powders, wherein the polymeric particles are preferably selected from polyolefins and/or copolyolefins, such as polyethylene, polypropylene, polyethylene-co-propylene, polybutadiene, polycapralactone, isotactic poly(1- butene), syndiotactic polypropylene, poly(l-decene), poly(ethylene-co-l-butene), poly(ethylene- co-viny I acetate) , polybutylene adipic acid), poly(a-methyl styrene-co-methylstyrene), polyethylene oxide, trans-1 ,4-polybutadiene or trans-1 ,4-polyisoprene.
[0033] The particle size of the polymeric particles of the present invention may vary widely, such as, for example, from 50 nm up to about 100 μητι. Desirably, the polymeric particles have a particle size from about 5 μπι to about 10 μηη. The particle size is preferably determined by laser diffraction using a Mastersizer 2000 (produced by Malvern instruments Ltd, calculation according to Mie).
[0034] The term "particle size", as used in the present invention, refers to the d50 volume average particle diameter. The d50 volume average particle diameter is defined as that particle diameter at which 50% by volume of the particles have a larger diameter than the d50 value.
[0035] It is desirable that the polymeric particles are distributed within the crosslinkable polyorganosiloxanes of composition A in a shape-holding amount, preferably in an amount of 1 to 80 wt.-%, more preferably in an amount of 20 to 60 wt.-%, and particularly preferably in an amount of 30 to 50 wt.-%, based on the total amount of the curable composition A. [0036] In another embodiment the shape memory polymer film used in the method of the present invention is the cured product of a composition B, comprising
i) one or more crosslinkable polyorganosiloxanes which form an elastomer when cured, and ii) one or more (meth)acrylic acid esters.
[0037] As used herein, the term "(meth)acrylic acid esters" is intended to include methacrylic acid esters and acrylic acid esters, and reference to one of methacrylates or acrylates is intended to embrace the other as well, unless specifically noted otherwise.
[0038] The incorporation of the (meth)acrylic acid esters (here liquid filler) in to the curable composition B, followed by the curing of the (meth)acrylic acid esters lead to phase separation, thereby forming polymeric (meth)acrylate domains in the cured product of composition B.
[0039] The (meth)acrylic acid esters may be selected from a wide variety of compounds. A desirable class of (meth)acrylic acid esters useful as liquid fillers in composition B include poly- and/or mono-functional (meth)acrylic acid esters. One class of (meth)acrylic acid esters useful in the present invention have the general structure:
Figure imgf000007_0001
where Ra is H, halogen, or to C20 hydrocarbyl; and R is H or to C20 hydrocarbyl. Desirably Rb is at least C4 or greater.
[0040] As used herein, the term "hydrocarbyl" (hydrocarbon group) is intended to refer to branched and unbranched radicals or diradicals, respectively, which are primarily composed of carbon and hydrogen atoms. Thus, the terms encompass aliphatic groups such as alkyl, alkenyl, and alkynyl groups; aromatic groups such as phenyl; and alicyclic groups such as cycloalkyi and cycloalkenyl. Hydrocarbon radicals of the invention may include heteroatoms to the extent that the heteroatoms do not detract from the hydrocarbon nature of the groups. Accordingly, hydrocarbon groups may include such functionally groups as ethers, alkoxides, carbonyls, esters, amino groups, cyano groups, sulfides, sulfates, sulfoxides, sulfones, and sulfones.
[0041] The hydrocarbon radicals and diradicals of the present invention may be optionally substituted to the extent that the substituent does not detract from the hydrocarbon nature of the hydrocarbyl group. As used herein the term "optionally substituted" is intended to mean that one or more hydrogens on a group may be replaced with a corresponding number of substituents preferably selected from halogen, nitro, azido, amino, carbonyl, ester, cyano, sulfide, sulfate, sulfoxide, sulfone, and/or sulfone groups. [0042] Other desirable (meth)acrylic acid esters of composition B are urethane (meth)acrylates having the general structur
Figure imgf000008_0001
where Rc is H, Ci to C4 alkyl, or halogen; Rd is (i) a Cn to C8 hydroxyalkylene or aminoalkylene group, or (ii) a C^ to C6 alkylamino-C1 to Ce alkylene, a hydroxyphenylene, aminophenylene, hydroxynaphthalene or amino-naphthalene optionally substituted by Ci to C3 alkyl, Ci to C3 alkylamino or di-Ci to C3 alkylamino group; and Re is C2to C20 alkylene, C2to C2oalkenylene or C2to C20 cycloalkylene, C6to C40 arylene, alkarylene, C2to C40 aralkarylene, C2to C40 alkyloxyalkylene or C2to C40 aryloxyarylene, optionally substituted by 1 to 4 halogen atoms or by 1 to 3 amino or mono- or di-Ci to C3 alkylamino or Ci to C3 alkoxy groups.
[0043] Other desirable (meth)acrylic acid esters, include, without limitation, urethane
(meth)acrylates within the general structure:
Figure imgf000008_0002
where Rc, Rd, and Re are as described herein above and Rf is an w-valent residue obtained by the removal of w amino or hydroxy groups from a polyamine or a polyhydric alcohol having at least two amino or hydroxy groups; X is O or NR9 where R9 is H or Ci to C7 alkyl; and w is an integer from 2 to 20.
[0044] Suitable monofunctional (meth)acrylic acid esters are selected from isobornyl
(meth)acrylate, adamantly (meth)acrylate, dicyclopentenyl (meth)acrylate, trimethylcyclohexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, iso-octyl (meth)acrylate, n- nonyl (meth)acrylate, iso-nonyl (meth)acrylate, n-decyl (meth)acrylate, iso-decyl (meth)acrylate, n-undecyl (meth)acrylate, iso-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, iso-dodecyl (meth)acrylate, 2(2-ethoxyethoxy)ethylacrylate, and/or combinations thereof.
[0045] Advantageously, the (meth)acrylic acid ester may be isobornyl acrylate, iso-octyl acrylate, and/or isodecyl 2(2-ethyxyethoxy) ethylacrylate.
[0046] In one preferred embodiment the (meth)acrylic acid ester component of composition B comprises a combination of isobornyl (meth)acrylate with n-decyl (meth)acrylate, isobornyl (meth)acrylate with iso-decyl (meth)acrylate, isobornyl (meth)acrylate with n-undecyl (meth)acrylate, isobornyl (meth)acrylate with iso-undecyl (meth)acrylate, isobornyl
(meth)acrylate with n-dodecyl (meth)acrylate, or isobornyl (meth)acrylate with iso-dodecyl (meth)acrylate.
[0047] Specific polyfunctional (meth)acrylic acid esters which are desirable include polyethylene glycol dimethacrylate and dipropylene glycol dimethacrylate.
[0048] Other desirable (meth)acrylic acid esters are selected from the acrylate, methacrylate and glycidyl methacrylate esters of bisphenol A. Desirable among these free-radical polymerizable components mentioned is ethoxylated bisphenol-A-dimethacrylate (ΈΒΙΡΜΑ").
[0049] Mixtures of any of the above-mentioned (meth)acrylic acid esters may be employed in composition B.
[0050] One or more (meth)acrylic acid esters may be added in amounts of at least 5 percent by weight of the total composition B. Desirably, one or more (meth)acrylic acid esters are present in an amount of 15% to 80% by weight of the total composition B, and more desirably in an amount of 20% to 70% by weight of the total composition B.
[0051] As mentioned above, composition A as well as composition B comprises one or more crosslinkable polyorganosiloxanes which form an elastomer when cured.
[0052] The crosslinkable polyorganosiloxanes used in the method of the present invention are preferably selected from curable silicone compositions. Various types of curable silicone compositions may be employed. For example, heat curing silicone compositions, moisture curing silicone compositions and photocuring silicone compositions may be employed.
Polymodal curing silicone compositions, for example photo and moisture dual curing
compositions or heat and moisture dual curing silicone compositions are also useful.
[0053] Suitable crosslinkable polyorganosiloxanes are selected from compounds of formula (I),
Figure imgf000009_0001
(I)
in which R1, R2 and R5 independently of one another are selected from hydrogen, Cr
20alkoxyl or C -20acyl; and R3 is
Figure imgf000009_0002
in which R6 is C -20 hydrocarbyl, and R4 is H or C1-4 alkyl.
[0054] In another embodiment, the crosslinkable polyorganosiloxanes are selected from compounds of formula (II):
Figure imgf000010_0001
in which MA is a methacryloxypropyl group, n is from 1 to 1200 and c is 0 or 1; and each R5 independently of one another is Ci.2o hydrocarbyl or Ci.20 hydrocarboxyl.
[0055] Examples of the above R1 , R2, R3, and R5 groups are alkyl (e.g. methyl, propyl, butyl and pentyl), alkenyl (e.g. vinyl and allyl), cycloalkyl (e.g. cyclohexyl and cycloheptyl), aryl (e.g. phenyl), arylalkyl (e.g. betaphenylethyl), alkylaryl, and hydrocarbonoxy (e.g. alkoxy, aryloxy, alkaryloxy, aryalkoxy, and in particular, methoxy, ethoxy or hydroxyl). Any of the foregoing groups may have some or all of the hydrogen atoms substituted by a halogen, such as fluorine or chlorine.
[0056] The number of repeating units in the crosslinkable polyorganosiloxanes can be varied to achieve specific molecular weights, viscosities and other chemical or physical properties.
[0057] The crosslinkable polyorganosiloxanes may be present in amounts of about 20% to about 95% by weight, based on the total weight of the curable composition A or based on the total weight of the curable composition B.
[0058] In addition to the crosslinkable polyorganosiloxanes, the composition A and/or composition B may include one or more silicon hydride crosslinkers and/or one or more organo- metallic hydrosilation catalysts.
[0059] In one embodiment the silicon hydride crosslinkers are selected from compounds of formula (III)
Figure imgf000010_0002
Figure imgf000010_0003
(formula III) in which at least two of R7, R9 and R10 are H; otherwise R, R7, R9, and R10 are the same or different and are C1-20 hydrocarbyl, preferably methyl; x is an integer from 10 to 1000; and y is an integer from 1 to 20. [0060] One or more silicon hydride crosslinkers may be present in an amount sufficient to achieve the desired amount of crosslinking, and in one embodiment in an amount of 1% to 10% by weight, based on the total weight of the composition A or based on the total weight of the composition B.
[0061] Useful organo-metallic hydrosilation catalysts may be selected from any precious metal or precious metal-containing catalyst effective for initiating a thermal hydrosilation cure reaction. Especially useful are platinum and rhodium catalysts that are effective for catalyzing the addition reaction between silicone-bonded hydrogen atoms and silicone-bonded olefinic groups. Other classes of catalysts useful in the present invention include organo rhodium and platinum alcoholates. Complexes of ruthenium, palladium, osmium and iridium are also contemplated.
[0062] One or more organo metallic hydrosilation catalyst may be used in any effective amount to effectuate thermal curing. In one embodiment, the catalyst is present in amounts of 0.025% to 1.0% by weight, based on the total weight of composition A or based on the total weight of composition B.
[0063] Depending on the chemical nature of the crosslinkable polyorganosiloxane component of composition A or B and depending on the intended cure mechanism, each of said
compositions A or B may include one or more initiators, wherein the terms "initiator" and "catalyst" are used interchangeably in the present invention.
[0064] Suitable initiators for use in the present method include moisture cure initiators, photoinitiators, free radical initiators, heat cure catalysts, and/or combinations thereof.
[0065] One or more initiators may be present in composition A or composition B in an amount of 0.01% to 10% by weight, preferably in an amount of 0.1 % to 5% by weight, each based on the total weight of composition A or composition B.
[0066] A number of photoinitiators may be employed as part of composition A and/or composition B. Any known free radical type photoinitiator which promotes crosslinking, may be used in the method of the present invention. Photoinitiators enhance the rapidity of the curing process when the photocurable compositions as a whole are exposed to electromagnetic radiation.
[0067] Non-limiting examples of UV photoinitiators that are useful in composition A and/or composition B include pyruvates, acetophenones, phosphine oxides, benzoins, benzophenone, dialkoxy-benzophenones, Michler's ketone (4,4'-bis(dimethylamino)benzophenone),
diethoxyacetophenone and/or any combination thereof.
[0068] In another embodiment of the present invention, the shape memory film used in the method of the present invention is the cured product of a composition C, comprising i) one or more epoxy resins selected from aromatic epoxy resins, aliphatic epoxy resins, and/or combinations thereof, and
ii) one or more crosslinking agents selected from multi-amines, multi-carboxylic acids and anhydrides and/or combinations thereof.
[0069] Suitable aromatic epoxy resins include aromatic diepoxides, such as the diglycidyl ether of bisphenol A, which is commercially available under the tradename EPON 826 from Hexion Speciality Chemicals.
[0070] Suitable aliphatic epoxy resins include aliphatic diepoxides, such as neopentyl glycol diglycidyl ether (NGDE), which is commercially available from TCI America.
[0071] In a particular preferred embodiment composition C comprises a combination of one or more aromatic epoxy resins with one or more aliphatic epoxy resins, wherein a mixture of diglycidyl ether of bisphenol A and neopentyl glycol diglycidyl ether (NGDE) is particularly preferably used as the epoxy resin component of composition C.
[0072] The term "multi-amines", as used in the present invention refers to compounds having at least two amine groups, whereas the term "multi-carboxylic acids", as used in the present invention, refers to compounds having at least two carboxylic acid groups.
[0073] Suitable initiators for composition C include alkoxylated di-or tri-amines, such as poly(propylene glycol)bis(2-aminopropyl)ether, which is commercially available under the tradename Jeffamine D-230 from Hexion Specialty Chemicals and Huntsman.
[0074] The shape memory polymer film used in the method of the present invention can be prepared according to any method. Particularly preferred methods to prepare said shape memory polymer film are described in US patent application Nos. 2004/0266940 A1 ,
2008/0064815 A1 , and 2008/0262188 A1 , the disclosure of each of which being hereby expressly incorporated herein by reference in their entirety.
[0075] The shape memory polymer film can be used to support and/or hold the wafer during a backside grinding process. In addition, the shape memory polymer film protects the top side of the wafer during a backside grinding process.
[0076] In one embodiment of the present invention the shape memory film used in the method of the present invention has an average film thickness T of 10 μιη to 1200 μιη, preferably of 15 μιη to 500 pm, and particularly preferably of 30 μηη to 300 pm. As used herein, the average thickness T of the shape memory polymer film refers to the thickness of the SMP film before said film is applied to the top side of the wafer in step b) of the method of the present invention.
[0077] The average film thickness T of the shape memory polymer film can be determined as shown in figure 5. The average film thickness T is the arithmetic average of a multitude of film thickness values Tn, wherein each film thickness value Tn is measured in a substantially orthogonal direction to the longitudinal extension 22 of the shape memory film 20 between two opposing points on two opposing sides of the shape memory polymer film 20.
[0078] The term "multitude", as used above, refers, for example, to at least 10 different measuring points at 10 different positions along a profile section of the SMP film 20.
[0079] The average film thickness T is determined, for example, by using a section of the SMP film 20 (1 cm*1 cm in size) divided into 5 equal strips (each 2 mm) and in each case the average film thickness T of the shape memory polymer film is determined along the profile. The average film thickness T along the profile is preferably determined by scanning electron microscopy (SEM) using a scanning electron microscope JEOL JSM-6060 SEM.
[0080] It is advantageous to use shape memory polymer films of the above average film thickness in the method of the present invention, because said shape memory polymer films can be removed easily from the top side of the wafer and these films significantly reduce wafer defects and/or wafer deformations which could occur in the course of a wafer thinning process.
[0081] The shape memory polymer film, which is used in the method of the present invention, can be attached or laminated to a carrier film.
[0082] By attaching the shape memory film to a carrier film a support structure is formed, wherein the carrier film imparts structural integrity and/or stiffness to the support structure and/or ensures the reusability of the support structure.
[0083] The carrier film may be UV transparent and/or may comprise at least one polymer selected from polyethylenes, polypropylenes, polycarbonates, polyesters,
polyethyleneterephthalates, polyvinylchlorides, copolymers of ethylene and vinyl acetate and/or combinations thereof. The carrier film can comprise or consist of one, two or more than two different layers, wherein each layer can comprise or consist of at least one of the
aforementioned polymers.
[0084] It is desirable that the average thickness of the carrier film is in the range of 20 μτη to
200 μΐτι, preferably in the range of 300 μιτι to 175 μηι, and more preferably in the range of 50 to
120 μπι, wherein the average film thickness is determined as described above.
[0085] In order to better control the bonding strength between the shape memory polymer film and the top side of the wafer, the surface structure of the shape memory polymer film can be modified.
[0086] In one embodiment the shape memory polymer film used in the method of the present invention has two opposing surfaces and the surface which is applied to the top side of the wafer (exterior surface) is flat. It is advantageous to use a shape memory film having a flat exterior surface as a fixing device in the method of the present invention, because the resulting assemblies exhibit a good stability during wafer handling operations, wherein the bonding strength between the wafer surface and the shape memory film is particularly high.
[0087] The term "flat", as used herein, preferably refers to surfaces which exhibit a flatness index (Fl) of less than 0.02.
[0088] The "flatness index", as used in the present invention, is defined as the ratio of roughness of the exterior surface of the SMP film to the average film thickness of the shape memory polymer film.
[0089] The flatness index can be determined as shown in Fig. 3 to 5. The term roughness, as used in the present invention, means the roughness average, which is defined as the arithmetic average of peak Pn and valley Vn distances Dn.
[0090] The term peak Pn, as used in the present invention, refers to any protruding area of the exterior surface, whereas the term valley Vn, as used in the present invention, refers to any recess between protruding areas of the exterior surface 21 of the SMP film 20.
[0091] The term distance Dn, as used in the present invention, means the difference in height of a peak Pn and neighbored valley Vn measured in a substantially orthogonal direction to the longitudinal extension 22 of the shape memory film 20.
[0092] In other words the distance Dn is defined as the distance, measured in a substantially orthogonal direction to the longitudinal extension 22, of two straight lines extending substantially parallel to the longitudinal extension 22, wherein one straight line subtends a peak Pn and the other straight line subtends a neighbored valley Vn.
[0093] The term longitudinal extension, as used in the present invention, refers to a plane extending substantially parallel to the surfaces of the shape memory polymer, wherein the asperity of the surfaces of the shape memory film is not taken into account.
[0094] The roughness is measured, for example, along a line of usually 0.08 cm on the exterior surface 21 of the shape memory polymer film 20. Preferably the roughness, as used in the present invention, is the arithmetic average of 15 different measurements at 15 different positions on the exterior surface 21 of the shape memory polymer film 20. The roughness is preferably determined at a measurement speed of 0.5 mm/s by using a Solarius non-contacting Laser Profilometer equipped with an AF2000 autofocus sensor. The obtained data is analyzed by using solar map universal 3.1.10 image analysis software (Gaussian filter 0.8 mm), wherein a microroughness filtering is used, with a cutoff of 2.5 μιη.
[0095] In an alternative embodiment the shape memory polymer film used in the method of the present invention has two opposing surfaces and the surface which is applied to the top side of the wafer (exterior surface) is microstructured. It is advantageous to use shape memory films having a microstructured exterior surface as a fixing device in the method of the present invention, because said SMP films are easily releasable in a residue free-manner from the wafer surface by applying a temperature above the transition temperature (Ttrans) of the shape memory polymer film.
[0096] The term "microstructured" refers to surfaces, comprising microstructured features, wherein the term "microstructured features" refers to features of a surface that have at least one, preferably all three dimensions (e.g., height, length, width, or diameter) of less than one millimeter.
[0097] For example, microstructured features can include one or more projections, one or more depressions, a combination of projections and depressions, ridges, posts, pyramids,
hemispheres, cones, protrusion, or any other suitable feature. The shapes of the various projections and/or depressions can also vary. For example, some embodiments of projections and/or depressions can be rounded in shape (e.g., circular, semicircular, spherical,
hemispherical, oval, pill-shaped, partially pili-shaped, etc.) or include a rounded portion, polygonal in shape or include a polygonal portion (e.g., triangular, squared, cubed including cube corners, tetrahedrical, rectangular, paralleopiped, pentagonal, hexagonal, etc.), an irregular shape, a regular shape, a pointed shape, a truncated shape, combinations thereof, or any other suitable shape. In at least some of these as well as in other embodiments, the projections and/or depressions may include or define one or more channels, valleys, wells, ridges, and the like, combinations thereof, or any other configuration.
[0098] Microstructured features on the exterior surface of the shape memory polymer film may be formed through the use of a microstructured molding tool. Microstructured molding tools can be in the form of a planar stamping press, a flexible or inflexible belt, a roller, or the like.
[0099] Depending on the application profile of the wafer the depth of the grooves on the top side of the wafer can vary widely. In one embodiment of the present invention the grooves on the top side of the wafer have a depth of 20 μιη to 150 μηι, preferably of 30 μιτι to 120 μιη, and particularly of 40 μπι to 100 μηι.
[00100] One particular advantage of the present invention is that the shape memory polymer film is capable of penetrating or extending into the grooves on the top side of the wafer after step b) and step c) of the method of the present invention have been carried out. The penetration depth can be controlled by proper selection of manufacturing parameters, such as contact pressure, temperature and/or contact time in step b) of the method of the present invention. By extending into or partially filling the grooves on the top side of the wafer, the SMP films effectively stabilize said wafer during wafer handling operations, such as grinding operations, thereby reducing the occurrence of wafer defects and/or wafer deformations.
[00101] To achieve a good stabilization, it is preferred that the SMP film fills out at least 10 vol.-%, more preferably at least 20 vol.-%, and particularly preferably at least 30 vol.-% of the total volume of the grooves on the top side of the wafer. A particularly good stabilization is achieved, when the SMP film fills out the grooves completely. The volume fraction of the grooves on the top side of the wafer which is filed out by the SMP film is preferably determined by scanning electron microscopy (SEM).
[00102] The method of the present invention can further comprise the additional step d) of exposing the back side of the wafer to a grinding operation to thin said wafer to a chosen thickness.
[00 03] Any process effective to thin down the wafer can be used. In a particular embodiment, the back side of the wafer is subjected to a grinding operation. Typically, this back- grinding is done to a level to meet the depth of the dicing lines. In some operations the dicing lines are cut slightly deeper into the front side of the wafer than the target depth of the backside grinding. This slight over cutting facilitates the eventual separation of the individual dies and allows to singulate the wafer into individual dies in the course of the grinding operation.
[00104] After the back side thinning/grinding operation, an adhesive coating can be applied to the back side of the wafer. This adhesive wafer back side coating is used to attach the individual dies to their substrates. The application of the wafer back side coating is performed by any effective method, such as by spin coating, screen or stencil printing, or spray or jet printing. The chemical composition of the wafer back side coating is any adhesive that will meet the subsequent processing requirements. Such adhesives are known in the art. In one embodiment the wafer back side coating is a B-stageable liquid, meaning it can be heated to remove solvent and/or to partially cure. After B-staging the wafer back side coating is relatively tack-free at room temperature. In the later die attach operation, the coating can be heated to soften and flow during die attach, and then be heated at an elevated temperature for final cure. Finally, a support tape can be applied on top of the B-staged coating on the back side of the wafer for subsequent handling purposes
[00 05] In order to remove/release the shape memory polymer film from the top side of the wafer, the method of the present invention can comprises the additional step e) of releasing the shape memory polymer film from the top side of the wafer by exposing said film to a temperature above its transition temperature (Ttrans). [00106] The application of heat as an external stimulus induces the shape memory effect of the SMP film. As a consequence the SMP film used in the method of the present invention can be removed substantially completely from the top side of the wafer in a stress-free process by applying a low peel force.
[00107] The term "peel force" as used in the present invention preferably refers to the 90° peel force needed for peeling the adhered surfaces apart. Said 90° peel force is preferably determined at 23°C according to ASTM D6862-04 test method using a TXT plus tensile tester (available from Stable Micro Systems, Surrey UK) using 5 Kg load cell and a crosshead speed of 25 mm/min.
[00108] As used in the present invention a peel force, such as the 90° peel force, is regarded as being low, if the peel force, such as the 90° peel force, needed to separate the SMP film and the wafer at 23°C is less than 0.1 N/mm, preferably less than 0.05 N/mm, more preferably less than 0.01 N/mm, and particularly preferably less than 0.001 N/mm.
[00109] Preferably the shape memory polymer film is released by exposing it to a temperature of at least 10°C, more preferably to a temperature of at least 20°C, and particularly preferably to a temperature of at least 30°C above the transition temperature (Ttrans) of the shape memory polymer film.
[00110] By applying an appropriate temperature, the shape memory polymer film can be removed substantially completely from the wafer surface in short time periods, preferably in less than 15 minutes, more preferably in less than 10 minutes, and particularly preferably in less than 5 minutes.
[00 11] The term "substantially completely", as used in the present invention, preferably means, that less than 5 wt.-%, preferably less than 1 wt.-%, more preferably less than 0.5 wt.-%, and particularly preferably less than 0.1 wt.-%, based on the total weight of the shape memory polymer film remain on the wafer surface after the shape memory polymer film is removed from the top side of the wafer.
[00112] A further aspect of the invention is an assembly, comprising a wafer and a shape memory polymer film, wherein the assembly is obtained by the method of the present invention.
[00113] Another aspect of the present invention is an assembly, comprising a wafer and a shape memory polymer film, wherein the wafer has a plurality of grooves on the top side of the wafer and the shape memory polymer film is attached to the top side of the wafer.
Preferably, the wafer and the shape memory film correspond to the SMP films and wafers which are described in the method of the present invention. [00114] The present invention also relates to the use of a shape memory polymer film as a fixing device for a wafer having a plurality of grooves on one side of the wafer and to the use of a shape memory polymer film as a fixing device in dicing before grinding (DBG) processes, wherein the wafer and the shape memory film preferably correspond to the SMP films and wafers which are described in the method of the present invention.
[00115] Dicing before grinding (DBG) processes are known in the art and are for example described in U.S. patent No. 7,074,695 B2 in figures 1 to 7 and column 1 , lines 13 to 44.
[00116] Preferred embodiments of the invention are described with the figures.
[00117] Figure 1 shows a sectional view of the assembly formed in step b) of the method of the present invention.
[00118] Figure 2 shows an enlarged sectional view of a part A of the assembly shown in figure 1.
[00119] Figure 3 shows a sectional view of a flat shape memory polymer film 20 as provided in step a) of the method of the present invention.
[00120] Figure 4 shows an enlarged sectional view of a part B of the shape memory polymer film 3 shown in figure 3.
[00121] Figure 5 shows an additional enlarged sectional view of a part C of the shape memory polymer film 3 shown in figure 3.
[00 22] Fig. 1 shows a sectional view of an assembly as formed in step b) of the method of the present invention. Said assembly comprises a wafer 10 having a top side 11 and a back side 12, wherein the wafer 10 has a plurality of grooves 13 on the top side of the wafer 11. The assembly further comprises a shape memory film 20 which has an exterior surface 21 which is attached to the top side 11 of the wafer 10.
[00123] With figure 2 an enlarged sectional view of a part A of the assembly shown in figure 1 is depicted. The shape memory polymer film 20 penetrates or extends into the grooves 13 on the top side 11 of the wafer 10, wherein the penetration depth can be controlled by proper selection of manufacturing parameters, such as contact pressure, contact time and/or temperature in step b) of the method of the present invention. By extending into or partially filling the grooves 3 on the top side 11 of the wafer 10, the SMP film 20 effectively stabilizes said wafer 10 during wafer handling operations, such as grinding operations, wherein the occurrence of wafer defects and/or wafer deformations is reduced.
[00124] Fig. 3 shows a sectional view of a flat shape memory polymer film 20 as provided in step a) of the method of the present invention. With figure 4 an enlarged sectional view of a part B of the SMP film 20 shown in figure 3 is depicted. The shape memory polymer film 20 has a flatness index of less than 0.02, wherein the flatness index is defined as the ratio of a roughness of the exterior surface 21 of the shape memory polymer film to an average thickness T of the shape memory polymer film 20.
[00125] The average film thickness T of the shape memory polymer film 20 can be determined as shown in figure 4. The average film thickness T is the arithmetic average of a multitude of film thickness values Tn, wherein each film thickness value Tn is measured in a substantially orthogonal direction to the longitudinal extension 22 of the shape memory film 20 between two opposing points, wherein one point is located on the inner surface of the shape memory polymer film, and the corresponding point is located on the opposing exterior surface 21 of the shape memory polymer film.
[00126] The term multitude, as used above, can refer, for example, to at least 10 different measuring points at 10 different positions along a profile section of the SMP film 20.
[00127] The average film thickness T can be determined, for example, by using a section of the SMP film 20 (1 cm*1 cm in size) divided into 5 equal strips (each 2 mm) and in each case the average film thickness T of the shape memory polymer film 20 is determined along the profile. The average film thickness T along the profile is determined by scanning electron microscopy (SEM) using a scanning electron microscope JEOL JSM-6060 SEM.
[00128] Figure 5 shows an enlarged sectional view of a part C of the shape memory polymer film 20 shown in figure 3 with an indication of the roughness of the shape memory polymer film 20. The exterior surface 21 is of course not completely flat and shows a special asperity. The asperity of the exterior surface 21 of the shape memory polymer film 20 is reflected in sections of the shape memory polymer film 20 having a more or less minor variable thickness. This variable thickness is reflected in the sectional view of the SMP film shown in fig. 5 in the form of peaks P1 , P2, P3 and valleys V1 , V2, V3, V4 in the exterior surface 21 of the shape memory polymer film 20. The term roughness, as used in the present invention, means the roughness average, which is defined as the arithmetic average of peak Pn and valley Vn distances Dn. The term peak Pn, as used in the present invention, refers to any protruding area of the exterior surface 21, whereas the term valley Vn, as used in the present invention, refers to any recess between protruding areas of the exterior surface 21 of the shape memory polymer film 20. The term distance Dn, as used in the present invention, means the difference in height of a peak Pn and neighbored valley Vn measured in a substantially orthogonal direction to the longitudinal extension 22 of the shape memory film 20.
[00129] The roughness is determined at a measurement speed of 0.5 mm/s by using a Solarius non-contacting Laser Profilometer equipped with an AF2000 autofocus sensor. The obtained data is analyzed by using solar map universal 3.1.10 image analysis software (Gaussian filter 0.8 mm), wherein a microroughness filtering is used, with a cutoff of 2.5 μιη.

Claims

1. A method for handling a wafer, comprising the steps of:
a) providing i) a wafer having a top side and a back side and ii) a shape memory polymer film, and
b) applying the shape memory film to the top side of the wafer to form an assembly, wherein the wafer has a plurality of grooves on the top side of the wafer.
2. The method of claim 1 , wherein the shape memory film is applied by bringing the top side of the wafer into contact with the shape memory polymer film at a contact pressure of 0.1 to 100 MPa and at a temperature above the transition temperature (Ttrans) of the shape memory polymer film.
3. The method of claim 2, further comprising the additional step c ) of cooling the formed assembly to a temperature below the transition temperature (T!rans) of the shape memory polymer film at a contact pressure of 0.1 to 100 MPa.
4. The method of any one of claims 1 to 3, wherein the shape memory polymer film is the cured product of a composition A, comprising
i) one or more crosslinkable polyorganosiloxanes which form an elastomer when cured, and
ii) polymeric particles which are distributed within said one or more crosslinkable polyorganosiloxanes and which remain discrete in the cured elastomer and have a melting temperature below the degradation temperature of the cured elastomer.
5. The method of any one of claims 1 to 3, wherein the shape memory polymer film is the cured product of a composition B, comprising
i) one or more crosslinkable polyorganosiloxanes which form an elastomer when cured, and
ii) one or more (meth)acrylic acid esters.
6. The method of claim 4 or 5, wherein the crosslinkable polyorganosiloxane is selected from compounds of formula (I),
Figure imgf000022_0001
in which R\ R2 and R5 independently of one another are selected from hydrogen, Ci
2o alkoxyl or Ci.20 acyl; and R3 is
Figure imgf000022_0002
in which R6 is C -20 hydrocarbyl, and R4 is H or d.4 alkyl.
7. The method of any one of claims 1 to 3, wherein the shape memory film is the cured product of a composition C, comprising
i) one or more epoxy resins selected from aromatic epoxy resins, aliphatic epoxy resins, and/or combinations thereof, and
ii) one or more crosslinking agents selected from multi-amines, multi-carboxylic acids and anhydrides and/or combinations thereof.
8. The method of any one of claims 1 to 7, wherein the shape memory polymer film, before being applied to the top side of the wafer, has an average film thickness T of 10 μηι to 1200 μηι.
9. The method of any one of claims 1 to 8, wherein the shape memory polymer film is attached to a carrier film.
10. The method of claim 9, wherein the carrier film comprises at least one polymer selected from polyethylenes, poly propylenes, polycarbonates, polyesters, polyethyleneterephthalates, polyvinylchlorides, copolymers of ethylene and vinyl acetate and/or combinations thereof.
1 1. The method of any one of claims 1 to 10, wherein the shape memory polymer film has two opposing surfaces and the surface which is applied to the top side of the wafer is flat.
12. The method of any one of claims 1 to 10, wherein the shape memory polymer film has two opposing surfaces and the surface which is applied to the top side of the wafer is
microstructured.
13. The method of any one of claims 1 to 12, wherein the grooves on the top side of the wafer have a depth of 20 μηι to 150 μπι.
14. The method of claim 3, wherein, after step b) and step c) have been carried out, the grooves on the top side of the wafer are at least partially filled with the shape memory film.
15. The method of any one of claims 1 to 14, further comprising the additional step d) of exposing the back side of the wafer to a grinding operation to thin said wafer to a chosen thickness.
16. The method of claim 15, wherein the wafer is singulated into individual dies in the course of the grinding operation,
17. The method of claim 15 or 16, wherein an adhesive coating is applied to the back side of the wafer after the grinding operation.
18. The method of any one of claims 1 to 17, further comprising the additional step e) of releasing the shape memory polymer film from the top side of the wafer by exposing said film to a temperature above its transition temperature (Ttrans)-
19. An assembly, comprising a wafer and a shape memory film, wherein the assembly is obtained by a method of any one of claims 1 to 17.
20. An assembly, comprising a wafer and a shape memory polymer film as used in any one of claims 1 to 17, wherein the wafer has a plurality of grooves on the top side of the wafer and the shape memory polymer film is attached to the top side of the wafer.
21. Use of a shape memory polymer film as a fixing device for a wafer having a plurality of grooves on one side of the wafer.
22. Use of a shape memory polymer film as a fixing device in dicing before grinding (DBG) processes.
PCT/US2012/044955 2011-07-01 2012-06-29 Method for handling a wafer WO2013006442A2 (en)

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CN104891426A (en) * 2015-04-07 2015-09-09 哈尔滨工业大学 Preparation method for micropattern film with selective stimulation recovery function
US9607896B2 (en) 2011-07-01 2017-03-28 Henkel IP & Holding GmbH Use of repellent material to protect fabrication regions in semi conductor assembly

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WO2013006442A3 (en) 2013-05-10

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