WO2010019184A1 - Patterning method to create a mask - Google Patents

Patterning method to create a mask Download PDF

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Publication number
WO2010019184A1
WO2010019184A1 PCT/US2009/004216 US2009004216W WO2010019184A1 WO 2010019184 A1 WO2010019184 A1 WO 2010019184A1 US 2009004216 W US2009004216 W US 2009004216W WO 2010019184 A1 WO2010019184 A1 WO 2010019184A1
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WO
WIPO (PCT)
Prior art keywords
mask
channel
mask material
channels
substrate
Prior art date
Application number
PCT/US2009/004216
Other languages
French (fr)
Inventor
Christopher Barrie Rider
Christopher Lee Bower
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Eastman Kodak Company
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Publication date
Application filed by Eastman Kodak Company filed Critical Eastman Kodak Company
Publication of WO2010019184A1 publication Critical patent/WO2010019184A1/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
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/027—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34
    • H01L21/0271—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers
    • H01L21/0272—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers for lift-off processes
    • 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
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
    • H01L21/321—After treatment
    • H01L21/3213—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer
    • H01L21/32139—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer using masks
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
    • H10K71/20—Changing the shape of the active layer in the devices, e.g. patterning
    • H10K71/221—Changing the shape of the active layer in the devices, e.g. patterning by lift-off techniques

Definitions

  • the invention relates to a patterning method and in particular to a method of patterning thin layers deposited on a surface in the manufacture of, in particular, electronic, optical and optoelectronic devices.
  • the invention also relates to devices manufactured by the method and to patterning layers and substrates on which devices can be manufactured.
  • the present invention solves the problem of how to pattern a wide range of thin layers with improved resolution, better alignment, high feature density and high quality using a wide range of deposition techniques.
  • Our invention improves upon the lift-off techniques described in the prior art, by allowing for the patterning of features with finer resolutions than traditional printing technologies, in combination with providing a means of self-alignment both between multiple thin-layers and between in-plane features.
  • a method of forming a patterned mask on a surface comprising the following steps: providing the surface with at least one channel and depositing a flowable mask material adjacent to the at least one channel, such that the material is directed into the at least one channel by the action of capillary forces.
  • the invention provides a method of creating micro-patterned devices or microstructures by patterning thin films which are deposited onto a substrate.
  • a channel or channels is created upon the substrate, the channel width being of fine enough resolution such that a flowable mask material can be drawn along the channel by capillary forces.
  • the word "flowable" is used here in the sense that the mask material may be either in a flowable state at the time of deposition or may be rendered flowable by any convenient process after deposition.
  • the channels form the negative image of the desired pattern and may be at a finer resolution than that obtainable by standard printing methods.
  • the thin layer or layers which are to be patterned are then deposited over the substrate and the channels; the mask material is then removed along with the thin layer or layers on top of the mask.
  • the mask material can be removed by dissolving in a suitable solvent, or in some cases can be peeled out of the channels. In this manner the desired pattern is created in the thin layer or layers.
  • multiple thin layers can be patterned in a single step.
  • the layers can be deposited sequentially using either liquid based techniques or vapour deposition over the mask material. Subsequent removal of the mask material allows for the simultaneous removal of multiple layers, resulting in a self-aligned vertical layer stack which is difficult to achieve by any other method.
  • the method of the invention is self-aligning. It is insensitive to substrate distortion and very accurately aligns, for example, the gate electrode of a TFT to the semiconductor channel region between the source and drain electrodes with no overlap. This reduces parasitic capacitance and improves device speed.
  • a further advantage of this method is that when liquid layers are to be patterned, the liquids used for the thin layers do not have to be formulated to allow deposition by inkjet or other printing techniques, they can simply be coated as a uniform layer by any standard thin-film liquid coating technique such as spin, bar or air-knife coating, which generally have a much larger formulation window.
  • Coating the thin layers in this manner, or by use of vapour deposition also means that the thickness uniformity of the layers is improved, since there is no change in thickness at the edge of the patterned region. For example, if a surface energy mask is used to create a patterned liquid coating there are often variations in the thickness of the patterned liquid at the interface between the contrasting surface energy regions.
  • the invention also allows the pre-patteming step to be simplified and thus further reduces the cost and time to manufacture electronic devices. There is no requirement for, for example, the formation of banks or areas of surface energy contrast.
  • embossing alone is enough to prepare the substrate for patterning.
  • Embossing is a low cost technique and may be done roll- to-roll so that incremental costs in preparing the substrate for deposition are minimised versus some of the other methods.
  • Embossing is also possible down to features sizes of 1 OOnm and thus enables very high resolution features to be made. Therefore this approach enables high resolution patterns to be made.
  • Figures Ia to Id shows the steps involved in simultaneous patterning of one or more thin layers
  • Figures 2a to 2d show the steps involved in patterning a thin layer on a substrate with 'V grooves in which the mask can be mechanically peeled out;
  • Figures 3a to 3d show the steps involved in patterning two thin layers on a substrate with 'V grooves in which the mask is washed off;
  • Figures 4a to 4d show the steps involved in patterning a thin layer on a substrate with 'V grooves in which the mask is washed off; and Figures 5a to 5d show the steps involved in patterning a thin layer on a substrate with 'V grooves in which the mask is created on top of the layer to be patterned then mechanically peeled out.
  • the present invention provides an improved method for patterning thin layers on a surface which may be used in the manufacture of electronic and optoelectronic devices.
  • the surface may be either side of a planar substrate, or may be a surface on a three dimensional object.
  • a surface is pre-patterned with the inverse of the desired pattern in the form of open, capillary channels, which are sufficiently narrow so as to promote capillary wicking of a flowable mask material when the mask material is deposited adjacent to or in the channels.
  • the channels may be created by a number of different means such as laser patterning or ablation or printing, but in the preferred embodiment, the channels are created by high resolution embossing of the substrate. The use of embossing is advantageous since it may be done at low cost, in a roll-to-roll manner, and it is possible to create features as small as 1 OOnm which is well below that of standard printing techniques.
  • the channels may be formed by printing suitable material by inkjet, flexographic printing, screen-printing, gravure printing or some other patterned deposition technique.
  • a channel is in general any elongate surface topology which promotes the flow of liquid along it by capillary forces.
  • the cross-sectional geometry of channels may be either square, rectangular, hemi-cylindrical, curved or more preferably 'V shaped to promote efficient capillary wicking of the mask material along the channels. Other channel geometries are possible, such as step edges.
  • ⁇ a is less than (90° - ⁇ /2) wicking will occur as described in "Flow of simple liquids down narrow V grooves", Mann et al., Phys. Rev.E.
  • Figure Ia shows a substrate 11 on which channels 12 with square cross-section have been created.
  • a flowable mask material is deposited into or adjacent to the channels by any convenient method such as inkjet printing, flexographic printing, gravure printing, lithographic printing, screen printing, electrophotographic printing or any other patterned deposition method for solid or liquid materials.
  • the flowable mask material by thin film coating methods such as blade coating, bar coating, air knife coating or dip coating provided that the mask material has sufficient time to fill the capillary channels and withdraw from the non-pattern regions of the substrate.
  • This process may be facilitated by the use of deposition regions adjacent to the channels, where the flowable mask material is deposited, which act as reservoirs to hold the mask materials prior to filling the channels.
  • the channels may be treated to modify the surface properties prior to the entry of the flowable mask material.
  • the flowable mask material is drawn into the channels by capillary action.
  • the movement of flowable material into the channel stops when either the pressure in the flowable material body is everywhere the same, or when the flowable material solidifies.
  • Figure Ib shows the substrate after the channels have been filled with the flowable mask material 13.
  • the mask material may be treated after filling the channels so that it solidifies. This may be achieved by using polymeric material dissolved in a suitable solvent which evaporates to leave a layer of the polymer within the channels.
  • the mask material may be a monomer and a cross-linking agent such as PDMS which cures at an increased rate when the temperature is elevated. In this embodiment there is no solvent loss and therefore no shrinkage of the mask material occurs when it is cured within the channels.
  • mask material is deposited in a deposition region, but does not flow into the channel region. Energy is applied to the mask material such that the material becomes flowable.
  • phase change inks which contain temperature sensitive polymers such as polynipam which can change viscosity by several orders of magnitude when the temperature is increased beyond a certain critical temperature.
  • Another material that displays this property would be a material that melts above a certain temperature, such as, for example, solders and waxes or low melting point solids such as alkanes with a chain length greater than 16 carbon atoms. Once the viscosity has dropped, the material may flow and is able to be directed into the channel by capillary wicking from the deposition area. After the material has flowed down the channel, the viscosity again returns to its normal ambient state as the material cools.
  • patterned deposition methods such as offset lithographic printing or flexographic printing may be used to achieve coarse positioning of a mask material on the surface of a patterned substrate. Fine positioning is achieved by capillary wicking of the original printed deposit along the mask channel after a change in material viscosity is achieved.
  • the mask material is not treated to solidify it after filling the channels, but instead remains as a liquid mask.
  • Suitable materials for this embodiment are high boiling point liquids that have boiling points greater than 100° C or more preferably greater than the maximum deposition temperature of the technique that is used to apply subsequent thin layers over the mask.
  • Liquids such as silicone oils, ionic liquids, alkanes with less than 16 carbon atoms and siloxanes are all suitable mask materials.
  • the present invention offers a method for making patterns of any flowable mask material, including liquids containing dispersions of solid particles.
  • the liquid may contain at least one of: a polymer, a monomer, a high molecular weight molecule, a solid particle, an emulsion, a high boiling point liquid.
  • the use of a polymeric material that is subsequently cross-linked within the channels is preferred since this minimises the amount of shrinkage of the mask, and helps to maintain a higher fill ratio of the channels.
  • the thin layers which are to be patterned can be coated on top of the masked substrate. This may be done using any suitable vapour deposition method such as for example sputter- coating, vacuum evaporation, ALD or CVD. Alternatively the thin layers to be patterned may be coated using a liquid deposition method such as spin coating, dip coating, meter bar coating or air knife coating or any other suitable thin film liquid coating technique. These methods have the advantage of having much broader formulation windows for a given material compared to printing techniques which generally have specific requirements for viscosity, rheological profile and surface tension. One or more layers may be coated.
  • Figure Ic shows the substrate after deposition of two thin layers 14, 15 which are to be patterned.
  • the mask material is then removed either mechanically by peeling it out of the channels or may be removed by dissolving it in a suitable solvent. Removal of the mask material also removes the one or more thin layers which were above the mask material, to leave the desired pattern 16 in the thin layers remaining on the substrate, as shown in figure Id.
  • the substrate may be immersed in a suitable solvent which dissolves the mask but not the thin layers. An ultrasonic bath may be used to aid removal of the mask material. Since the channels 12 are formed on the substrate before deposition of the thin films to be patterned, the method is insensitive to substrate distortions during the patterning and deposition processes and therefore has the advantage of being able to create "self- aligned" features in the final pattern.
  • V shaped grooves with a pitch of approximately 500 micrometers pitch in polycarbonate (3M optical lighting film, SOLF TM) were used as the substrate material.
  • the substrate 21 had grooves 22 with 90 degree angle as shown in figure 2a.
  • the flowable mask material was Polydimethlyl siloxane (PDMS) monomer mixed 10: 1 with a crosslinking agent (Sylgard 184). A few micro-litres was deposited into the channels at one end of the substrate using a micro-pipette. The mask material was subsequently driven along the channels by capillary forces and filled the channels 23 as shown schematically in figure 2b. The sample was heated to approximately 60° Celsius and left for 1 hour to allow the PDMS to cross-link and become solid.
  • PDMS Polydimethlyl siloxane
  • a thin layer of aluminium 24 approximately lOOnm thick was deposited on top of the substrate and masked channels by vacuum evaporation using an Edwards minilab, as shown in figure 2c.
  • the mask material and aluminium on top of it was removed from non-adjacent channels by mechanically peeling out the PDMS from every other channel 25 as shown in figure 2d.
  • Example 2 The same masking process as described in example 1 was repeated, but this time approximately lOOnm of titanium dioxide was deposited over the top of the masked substrate by using a low temperature atmospheric atomic-layer deposition (ALD) process. This could also have been achieved by using a conventional vacuum-based ALD process. The mask material and the titania layer on top of it were removed from non-adjacent channels by mechanically peeling out the PDMS from every other channel 25 as shown in figure 2d.
  • ALD atmospheric atomic-layer deposition
  • V shaped grooves 32 with a pitch of approximately 300 micrometers in polycarbonate (3M optical lighting film, SOLF TM) were used as the substrate material.
  • the flowable mask material was PVA (GH 17, Gosen) at 0.3% w/w in solvent mixture of 2: 1 Isopropanol to deionised water.
  • a few micro-litres was deposited into the channels at one end of the substrate 31 using a micro-pipette.
  • the mask material was subsequently driven along the channels by capillary forces and filled the channels.
  • the sample was heated to approximately 6O 0 C to drive off the solvent and leave a thin coating of PVA within the channels 33 as shown schematically in figure 3b.
  • the channels and PVA were then overcoated with a first layer of approximately 50nm of ZnO 35 deposited by an atmospheric ALD process, followed by a second layer of approximately 30nm of vacuum deposited silver 34.
  • the mask and the two layers on top of the mask were removed by submerging the sample in deionised water and placing it in a sonic bath for 10 minutes.
  • the ZnO and Ag layers remained on the tops of the peaks 37 where no PVA was present, but were removed from the base 36 of the channels along with the PVA.
  • V shaped grooves 42 with a pitch of approximately 300 micrometers in polycarbonate (3M optical lighting film, SOLFTM) were used as the substrate material.
  • the flowable mask material 43 was a long chain alkane wax, eicosane, (C 2O H 44 , Aldrich Chemicals).
  • the wax has a low melting point of around 35° C but a boiling point of around 220° C.
  • a small quantity of the wax was deposited onto the channels at one end of the sample. Upon heating the sample to 90° C, the eicosane melted and became flowable It was then driven along the channels by capillary forces as shown in figure 4b.
  • the sample was then overcoated with a layer of titania 44 approximately 50nm thick using an atmospheric ALD process at 100° C.
  • the eicosane was a liquid in the base of the channels.
  • the eicosane mask and the titania layer on top of it were subsequently removed by submerging the sample in decane and placing in a sonic bath for 10 minutes.
  • the result was thin layer of titania on the peaks 46 of the channels and removal of titania from the base 45 of the channels as shown in figure 4d.
  • Example 6 As in the previous examples, V shaped grooves 52 with a pitch of approximately 300 micrometers in polycarbonate (3M optical lighting film, SOLFTM) were used as the substrate 51 material. A thin layer of silver 53 approximately 50nm thick was deposited on top of the substrate by vacuum evaporation using an Edwards MinilabTM, as shown in figure 5b.
  • the flowable mask material was polydimethlyl siloxane (PDMS) monomer mixed 10:1 with a crosslinking agent (SyI gard 184). A few micro-litres were deposited into every other channel at one end of the substrate using a micro-pipette. The mask material was subsequently driven along the channels by capillary forces and filled the channels 54 as shown schematically in figure 5c.
  • PDMS polydimethlyl siloxane
  • the sample was heated to approximately 60° Celsius and left for 1 hour to allow the PDMS to cross-link and become solid.
  • the entire sample was then placed into a solution of 1 Og/litre potassium dichromate & 1 Og/litre sulphuric acid etchant for a few seconds, which removed the silver from the substrate where it was not covered with the mask.
  • the sample was then dried then the mask material was removed from non-adjacent channels by mechanically peeling out the PDMS from every other channel 55, to leave patterned lines of silver 56 as shown in figure 5d.

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Abstract

A method of creating micro patterned devices by patterning thin films which are deposited on a substrate. A channel or channels is created on the substrate, the width being of fine enough resolution such that a flowable mask material can be drawn along the channel by capillary forces.

Description

PATTERNING METHOD TO CREATE A MASK
FIELD OF THE INVENTION
The invention relates to a patterning method and in particular to a method of patterning thin layers deposited on a surface in the manufacture of, in particular, electronic, optical and optoelectronic devices. The invention also relates to devices manufactured by the method and to patterning layers and substrates on which devices can be manufactured.
BACKGROUND OF THE INVENTION
When fabricating electrical devices such as TFTs or optoelectronic devices it is often desirable to pattern thin layers, or multiple thin layers at high resolution, with precise alignment between features within these layers. Despite the huge cost of factories to manufacture TFTs on glass and the complexity of the TFT manufacturing process, the technology is now well-established for active matrix liquid crystal displays and is based largely on photolithographic techniques for depositing patterns of the various materials into multilayer structures. In addition to being expensive, these photolithographic techniques are also time consuming and often involve multiple steps. The use of printing technologies, such as inkjet, offers a lower cost alternative that has fewer steps than lithographic patterning. However, the resolution of printing technologies is often not sufficient to pattern the very fine features required for devices such as TFTs.
The use of a mask layer or lift-off layer to pattern thin layers created by vapour deposition techniques such as evaporation has been described in EPOl 93820. A removable mask of the inverse of the desired pattern is created by inkjet printing or screen printing. The layer to be patterned is then vacuum deposited on top of the mask. The mask is subsequently removed to leave the desired pattern in the vapour deposited layer. US7332369 describes an extension of this method in which an inkjet printed lift-off mask is used to pattern both vapour deposited and solution deposited layers, to create OFET and OLEDs. In this method it is possible to improve the resolution of the patterned layer beyond that of the method used to print the mask, since the patterned layer is defined by the gap between the printed regions. However this gap width is dependent upon the spreading properties of the printed mask and may not be well defined. In WO2001/017041 there is described a further variation on this method for patterning semiconductor layers in which a 'destructive agent' is printed onto the substrate by inkjet or screen printing which changes the physical properties of subsequently deposited thin layers, for instance changing the conductivity of dissolving portions of the thin layer.
PROBLEM TO BE SOLVED BY THE INVENTION
The present invention solves the problem of how to pattern a wide range of thin layers with improved resolution, better alignment, high feature density and high quality using a wide range of deposition techniques. Our invention improves upon the lift-off techniques described in the prior art, by allowing for the patterning of features with finer resolutions than traditional printing technologies, in combination with providing a means of self-alignment both between multiple thin-layers and between in-plane features.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of forming a patterned mask on a surface, the method comprising the following steps: providing the surface with at least one channel and depositing a flowable mask material adjacent to the at least one channel, such that the material is directed into the at least one channel by the action of capillary forces.
The invention provides a method of creating micro-patterned devices or microstructures by patterning thin films which are deposited onto a substrate. A channel or channels is created upon the substrate, the channel width being of fine enough resolution such that a flowable mask material can be drawn along the channel by capillary forces. The word "flowable" is used here in the sense that the mask material may be either in a flowable state at the time of deposition or may be rendered flowable by any convenient process after deposition. The channels form the negative image of the desired pattern and may be at a finer resolution than that obtainable by standard printing methods. The thin layer or layers which are to be patterned are then deposited over the substrate and the channels; the mask material is then removed along with the thin layer or layers on top of the mask. The mask material can be removed by dissolving in a suitable solvent, or in some cases can be peeled out of the channels. In this manner the desired pattern is created in the thin layer or layers.
ADVANTAGEOUS EFFECT OF THE INVENTION
By use of the present invention, multiple thin layers can be patterned in a single step. The layers can be deposited sequentially using either liquid based techniques or vapour deposition over the mask material. Subsequent removal of the mask material allows for the simultaneous removal of multiple layers, resulting in a self-aligned vertical layer stack which is difficult to achieve by any other method.
The method of the invention is self-aligning. It is insensitive to substrate distortion and very accurately aligns, for example, the gate electrode of a TFT to the semiconductor channel region between the source and drain electrodes with no overlap. This reduces parasitic capacitance and improves device speed.
A further advantage of this method is that when liquid layers are to be patterned, the liquids used for the thin layers do not have to be formulated to allow deposition by inkjet or other printing techniques, they can simply be coated as a uniform layer by any standard thin-film liquid coating technique such as spin, bar or air-knife coating, which generally have a much larger formulation window.
Coating the thin layers in this manner, or by use of vapour deposition, also means that the thickness uniformity of the layers is improved, since there is no change in thickness at the edge of the patterned region. For example, if a surface energy mask is used to create a patterned liquid coating there are often variations in the thickness of the patterned liquid at the interface between the contrasting surface energy regions.
The invention also allows the pre-patteming step to be simplified and thus further reduces the cost and time to manufacture electronic devices. There is no requirement for, for example, the formation of banks or areas of surface energy contrast.
In a preferred embodiment embossing alone is enough to prepare the substrate for patterning. Embossing is a low cost technique and may be done roll- to-roll so that incremental costs in preparing the substrate for deposition are minimised versus some of the other methods. Embossing is also possible down to features sizes of 1 OOnm and thus enables very high resolution features to be made. Therefore this approach enables high resolution patterns to be made.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example with reference to the following drawings in which:
Figures Ia to Id shows the steps involved in simultaneous patterning of one or more thin layers;
Figures 2a to 2d show the steps involved in patterning a thin layer on a substrate with 'V grooves in which the mask can be mechanically peeled out;
Figures 3a to 3d show the steps involved in patterning two thin layers on a substrate with 'V grooves in which the mask is washed off;
Figures 4a to 4d show the steps involved in patterning a thin layer on a substrate with 'V grooves in which the mask is washed off; and Figures 5a to 5d show the steps involved in patterning a thin layer on a substrate with 'V grooves in which the mask is created on top of the layer to be patterned then mechanically peeled out. DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an improved method for patterning thin layers on a surface which may be used in the manufacture of electronic and optoelectronic devices. The surface may be either side of a planar substrate, or may be a surface on a three dimensional object.
A surface is pre-patterned with the inverse of the desired pattern in the form of open, capillary channels, which are sufficiently narrow so as to promote capillary wicking of a flowable mask material when the mask material is deposited adjacent to or in the channels. The channels may be created by a number of different means such as laser patterning or ablation or printing, but in the preferred embodiment, the channels are created by high resolution embossing of the substrate. The use of embossing is advantageous since it may be done at low cost, in a roll-to-roll manner, and it is possible to create features as small as 1 OOnm which is well below that of standard printing techniques. In another embodiment the channels may be formed by printing suitable material by inkjet, flexographic printing, screen-printing, gravure printing or some other patterned deposition technique.
A channel is in general any elongate surface topology which promotes the flow of liquid along it by capillary forces. The cross-sectional geometry of channels may be either square, rectangular, hemi-cylindrical, curved or more preferably 'V shaped to promote efficient capillary wicking of the mask material along the channels. Other channel geometries are possible, such as step edges. The greater the channel angle, the slower the rate of wicking will be. When the advancing contact angle, θa, is less than (90° - β/2) wicking will occur as described in "Flow of simple liquids down narrow V grooves", Mann et al., Phys. Rev.E. 52, p3967, 2005, where β is the angle between the two sides of the 'V groove. Preferably, θa should be set somewhat below this value to facilitate rapid wicking along the channel and thus minimise evaporation losses from the liquid which may change its flow characteristics as it wicks. Figure Ia shows a substrate 11 on which channels 12 with square cross-section have been created. A flowable mask material is deposited into or adjacent to the channels by any convenient method such as inkjet printing, flexographic printing, gravure printing, lithographic printing, screen printing, electrophotographic printing or any other patterned deposition method for solid or liquid materials. It is also possible to deposit the flowable mask material by thin film coating methods such as blade coating, bar coating, air knife coating or dip coating provided that the mask material has sufficient time to fill the capillary channels and withdraw from the non-pattern regions of the substrate. This process may be facilitated by the use of deposition regions adjacent to the channels, where the flowable mask material is deposited, which act as reservoirs to hold the mask materials prior to filling the channels. The channels may be treated to modify the surface properties prior to the entry of the flowable mask material.
The flowable mask material is drawn into the channels by capillary action. The movement of flowable material into the channel stops when either the pressure in the flowable material body is everywhere the same, or when the flowable material solidifies. Figure Ib shows the substrate after the channels have been filled with the flowable mask material 13.
The mask material may be treated after filling the channels so that it solidifies. This may be achieved by using polymeric material dissolved in a suitable solvent which evaporates to leave a layer of the polymer within the channels. Alternatively the mask material may be a monomer and a cross-linking agent such as PDMS which cures at an increased rate when the temperature is elevated. In this embodiment there is no solvent loss and therefore no shrinkage of the mask material occurs when it is cured within the channels. In another embodiment, mask material is deposited in a deposition region, but does not flow into the channel region. Energy is applied to the mask material such that the material becomes flowable. Materials that display this property would include phase change inks, which contain temperature sensitive polymers such as polynipam which can change viscosity by several orders of magnitude when the temperature is increased beyond a certain critical temperature. Another material that displays this property would be a material that melts above a certain temperature, such as, for example, solders and waxes or low melting point solids such as alkanes with a chain length greater than 16 carbon atoms. Once the viscosity has dropped, the material may flow and is able to be directed into the channel by capillary wicking from the deposition area. After the material has flowed down the channel, the viscosity again returns to its normal ambient state as the material cools. The benefit of this approach is that very low-cost patterned deposition methods such as offset lithographic printing or flexographic printing may be used to achieve coarse positioning of a mask material on the surface of a patterned substrate. Fine positioning is achieved by capillary wicking of the original printed deposit along the mask channel after a change in material viscosity is achieved.
In an alternative embodiment, the mask material is not treated to solidify it after filling the channels, but instead remains as a liquid mask. Suitable materials for this embodiment are high boiling point liquids that have boiling points greater than 100° C or more preferably greater than the maximum deposition temperature of the technique that is used to apply subsequent thin layers over the mask. Liquids such as silicone oils, ionic liquids, alkanes with less than 16 carbon atoms and siloxanes are all suitable mask materials. The present invention offers a method for making patterns of any flowable mask material, including liquids containing dispersions of solid particles. The liquid may contain at least one of: a polymer, a monomer, a high molecular weight molecule, a solid particle, an emulsion, a high boiling point liquid. The use of a polymeric material that is subsequently cross-linked within the channels is preferred since this minimises the amount of shrinkage of the mask, and helps to maintain a higher fill ratio of the channels.
Once the channels have been filled with mask material, the thin layers which are to be patterned can be coated on top of the masked substrate. This may be done using any suitable vapour deposition method such as for example sputter- coating, vacuum evaporation, ALD or CVD. Alternatively the thin layers to be patterned may be coated using a liquid deposition method such as spin coating, dip coating, meter bar coating or air knife coating or any other suitable thin film liquid coating technique. These methods have the advantage of having much broader formulation windows for a given material compared to printing techniques which generally have specific requirements for viscosity, rheological profile and surface tension. One or more layers may be coated. Use of these methods ensures that a uniform thin film is obtained over the entire sample, thus avoiding thickness variations that often occur at the edges of printed features. Figure Ic shows the substrate after deposition of two thin layers 14, 15 which are to be patterned. The mask material is then removed either mechanically by peeling it out of the channels or may be removed by dissolving it in a suitable solvent. Removal of the mask material also removes the one or more thin layers which were above the mask material, to leave the desired pattern 16 in the thin layers remaining on the substrate, as shown in figure Id. To employ the solvent method, the substrate may be immersed in a suitable solvent which dissolves the mask but not the thin layers. An ultrasonic bath may be used to aid removal of the mask material. Since the channels 12 are formed on the substrate before deposition of the thin films to be patterned, the method is insensitive to substrate distortions during the patterning and deposition processes and therefore has the advantage of being able to create "self- aligned" features in the final pattern.
Example 1
In this example, V shaped grooves with a pitch of approximately 500 micrometers pitch in polycarbonate (3M optical lighting film, SOLF ™) were used as the substrate material. The substrate 21 had grooves 22 with 90 degree angle as shown in figure 2a. In this example the flowable mask material was Polydimethlyl siloxane (PDMS) monomer mixed 10: 1 with a crosslinking agent (Sylgard 184). A few micro-litres was deposited into the channels at one end of the substrate using a micro-pipette. The mask material was subsequently driven along the channels by capillary forces and filled the channels 23 as shown schematically in figure 2b. The sample was heated to approximately 60° Celsius and left for 1 hour to allow the PDMS to cross-link and become solid.
A thin layer of aluminium 24 approximately lOOnm thick was deposited on top of the substrate and masked channels by vacuum evaporation using an Edwards minilab, as shown in figure 2c. In this example the mask material and aluminium on top of it was removed from non-adjacent channels by mechanically peeling out the PDMS from every other channel 25 as shown in figure 2d.
Example 2 The same masking process as described in example 1 was repeated, but this time approximately lOOnm of titanium dioxide was deposited over the top of the masked substrate by using a low temperature atmospheric atomic-layer deposition (ALD) process. This could also have been achieved by using a conventional vacuum-based ALD process. The mask material and the titania layer on top of it were removed from non-adjacent channels by mechanically peeling out the PDMS from every other channel 25 as shown in figure 2d.
Example 3
The same masking process as described in example 1 above was repeated, but this time a first layer of approximately lOOnm of aluminium was deposited by vacuum evaporation, followed by approximately lOOnm of titanium dioxide deposited over the top of lOOnm of aluminium by using a low temperature ALD process. In this manner the PDMS mask was covered with two thin layers. The PDMS and layers on top were subsequently mechanically peeled out of every alternate groove in the substrate to leave a multilayer pattern on the substrate.
Example 4
As in the previous examples, V shaped grooves 32 with a pitch of approximately 300 micrometers in polycarbonate (3M optical lighting film, SOLF ™) were used as the substrate material. In this example the flowable mask material was PVA (GH 17, Gosen) at 0.3% w/w in solvent mixture of 2: 1 Isopropanol to deionised water. A few micro-litres was deposited into the channels at one end of the substrate 31 using a micro-pipette. The mask material was subsequently driven along the channels by capillary forces and filled the channels. The sample was heated to approximately 6O0C to drive off the solvent and leave a thin coating of PVA within the channels 33 as shown schematically in figure 3b. The channels and PVA were then overcoated with a first layer of approximately 50nm of ZnO 35 deposited by an atmospheric ALD process, followed by a second layer of approximately 30nm of vacuum deposited silver 34. The mask and the two layers on top of the mask were removed by submerging the sample in deionised water and placing it in a sonic bath for 10 minutes. The ZnO and Ag layers remained on the tops of the peaks 37 where no PVA was present, but were removed from the base 36 of the channels along with the PVA.
Example 5
As in the previous examples, V shaped grooves 42 with a pitch of approximately 300 micrometers in polycarbonate (3M optical lighting film, SOLF™) were used as the substrate material. In this example the flowable mask material 43 was a long chain alkane wax, eicosane, (C2OH44, Aldrich Chemicals). The wax has a low melting point of around 35° C but a boiling point of around 220° C. A small quantity of the wax was deposited onto the channels at one end of the sample. Upon heating the sample to 90° C, the eicosane melted and became flowable It was then driven along the channels by capillary forces as shown in figure 4b. The sample was then overcoated with a layer of titania 44 approximately 50nm thick using an atmospheric ALD process at 100° C. At this temperature during the deposition process the eicosane was a liquid in the base of the channels. The eicosane mask and the titania layer on top of it were subsequently removed by submerging the sample in decane and placing in a sonic bath for 10 minutes. The result was thin layer of titania on the peaks 46 of the channels and removal of titania from the base 45 of the channels as shown in figure 4d.
Example 6 As in the previous examples, V shaped grooves 52 with a pitch of approximately 300 micrometers in polycarbonate (3M optical lighting film, SOLF™) were used as the substrate 51 material. A thin layer of silver 53 approximately 50nm thick was deposited on top of the substrate by vacuum evaporation using an Edwards Minilab™, as shown in figure 5b. The flowable mask material was polydimethlyl siloxane (PDMS) monomer mixed 10:1 with a crosslinking agent (SyI gard 184). A few micro-litres were deposited into every other channel at one end of the substrate using a micro-pipette. The mask material was subsequently driven along the channels by capillary forces and filled the channels 54 as shown schematically in figure 5c. The sample was heated to approximately 60° Celsius and left for 1 hour to allow the PDMS to cross-link and become solid. The entire sample was then placed into a solution of 1 Og/litre potassium dichromate & 1 Og/litre sulphuric acid etchant for a few seconds, which removed the silver from the substrate where it was not covered with the mask. The sample was then dried then the mask material was removed from non-adjacent channels by mechanically peeling out the PDMS from every other channel 55, to leave patterned lines of silver 56 as shown in figure 5d.

Claims

CLAIMS:
1. A method of forming a patterned mask on a surface, the method comprising the following steps: a) providing the surface with at least one channel b) depositing a flowable mask material adjacent to the at least one channel, such that the material is directed into the at least one channel by the action of capillary forces.
2. A method as claimed in claim 1 , wherein the mask material is thereafter treated to solidify it .
3. A method as claimed in any preceding claim wherein the mask material is deposited in or adjacent to the at least one channel by a printing method.
4. A method as claimed in any preceding claim wherein prior to depositing the mask material, the at least one channel is treated to modify its surface properties.
5. A method as claimed in any preceding claim wherein the mask material is made flowable after being deposited on the surface.
6. A method as claimed in any preceding claim wherein the mask material contains at least one of: a polymer, a monomer, a high molecular weight molecule, a solid particle, an emulsion, a high boiling point liquid.
7. A patterning substrate comprising a surface with at least one channel arranged to form a desired mask pattern, such that when a flowable mask material is deposited adjacent to the at least one channel, the material is directed into the at least one channel by the action of capillary forces to form the patterned mask.
8. A patterning substrate as claimed in claim 7 including a mask material in the least one channel.
PCT/US2009/004216 2008-08-15 2009-07-21 Patterning method to create a mask WO2010019184A1 (en)

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Citations (4)

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JP2002141351A (en) * 2000-10-31 2002-05-17 Japan Science & Technology Corp Circuit board and method of forming metal wiring
EP1780815A2 (en) * 2005-10-31 2007-05-02 Fuji Electric Holdings Co., Ltd. Organic thin film transistor and manufacturing method thereof
US20070096080A1 (en) * 2003-07-02 2007-05-03 Cain Paul A Rectifying diodes
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JP2002141351A (en) * 2000-10-31 2002-05-17 Japan Science & Technology Corp Circuit board and method of forming metal wiring
US7332369B2 (en) * 2002-08-06 2008-02-19 Merck Patent Gmbh Organic electronic devices
US20070096080A1 (en) * 2003-07-02 2007-05-03 Cain Paul A Rectifying diodes
EP1780815A2 (en) * 2005-10-31 2007-05-02 Fuji Electric Holdings Co., Ltd. Organic thin film transistor and manufacturing method thereof

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Title
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