US20060154579A1

US20060154579A1 - Thermoplastic chemical mechanical polishing pad and method of manufacture

Info

Publication number: US20060154579A1
Application number: US11/033,690
Authority: US
Inventors: Daniel Marks; John Bare; Anthony Clark; Edward Atkinson; Timothy Blotkamp
Original assignee: PsiloQuest
Current assignee: psiloQuest Inc; PsiloQuest
Priority date: 2005-01-12
Filing date: 2005-01-12
Publication date: 2006-07-13
Also published as: US20070015444A1; WO2006076060A1

Abstract

The present invention is directed, in general, to a chemical mechanical polishing pad comprising a closed-cell thermoplastic foam polishing body. The polishing body comprises an ethylene vinyl acetate block copolymer. The ethylene vinyl acetate block copolymer comprises a vinyl acetate content ranging from about 1 to about 18 wt %. The closed-cell thermoplastic foam polishing body also comprises filler particles comprising an average size ranging from about 1 to about 20 microns. Other aspects of the invention comprise a method for manufacturing the above-described chemical mechanical polishing pad and chemical mechanical polishing apparatus comprising the chemical mechanical polishing pad.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention is directed to chemical mechanical polishing pads, and methods of manufacture thereof.

BACKGROUND OF THE INVENTION

Chemical mechanical polishing (CMP) pads have long been used for planarizing microelectronic device surfaces. There are numerous parameters to evaluate polishing performance, including: removal rate, within-wafer polishing non-uniformity, dishing, erosion, defects, polishing pad longevity, and reproducible polishing from substrate-to-substrate and pad-to-pad.
The need for a CMP pad capable of producing a highly planar and low-defect substrate surface is of growing importance as microelectronic device shrink to ever-smaller dimensions. In such situations, the high performance of parameters other than removal rate takes on greater importance.
Accordingly, what is needed is a CMP pad that can provide a highly planar and low-defect microelectronic device substrate surface, while maintaining acceptable removal rates, longevity and reproducibility.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, the present invention provides in one embodiment, a chemical mechanical polishing (CMP) pad comprising a closed-cell thermoplastic foam polishing body. The closed-cell thermoplastic foam polishing body comprises an ethylene vinyl acetate (EVA) block copolymer comprising a vinyl acetate content ranging from about 1 to about 18 wt %. The closed-cell thermoplastic foam polishing body also comprises filler particles comprising an average size ranging from about 1 to about 20 microns.
Another embodiment of the present invention is a method for manufacturing a CMP pad. The method comprises placing the above-described ethylene vinyl acetate block copolymer, filler particles, and a foaming agent, into a container. The method also comprises mixing the ethylene vinyl acetate block copolymer, foaming agent and filler particles together. Closed cells are then formed throughout the ethylene vinyl acetate block copolymer to produce a closed-cell thermoplastic foam polishing body.
Yet another embodiment of the present invention is a CMP apparatus. The CMP apparatus comprises a mechanically driven carrier head and a polishing platen. The carrier head is positionable against the polishing platen to impart a polishing force against the polishing platen. The CMP apparatus further comprises a polishing pad attached to the polishing platen. The polishing pad comprises the above-described closed-cell thermoplastic foam polishing body.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
FIG. 1 presents an cross-sectional view of a portion of an exemplary chemical mechanical polishing pad of the present invention;
FIG. 2 illustrates, by flow diagram, an exemplary method for manufacturing a polishing pad of the present invention; and
FIG. 3 illustrates a cross-sectional view of an exemplary polishing apparatus that includes a polishing pad of the present invention.

DETAILED DESCRIPTION

The CMP pads of the present invention comprise specific combinations of thermoplastic and filler particles that are necessary to make polishing bodies that polish with high planarity and low defect count. While not limiting the scope of invention by theoretical considerations, it is believed that the particular combinations of thermoplastic and filler particles used in the polishing pad of the present invention cooperate to provide a polishing surface that facilitates the removal of unwanted topographies from a microelectronic device substrate surface. In addition, it is believed that particular combinations of thermoplastic and filler particles minimize the production of polishing pad debris produced during polishing. It is thought that debris produced during the use of conventional polishing pads are detrimental to uniform polishing because they contribute to the production of defects in the microelectronic device substrate surface being polished.
FIG. 1 presents a cross-sectional view of a portion of an exemplary CMP pad 100 of the present invention. The CMP pad 100 comprises a closed-cell thermoplastic foam polishing body 110. The closed-cell thermoplastic foam polishing body 110 comprises an ethylene vinyl acetate (EVA) block copolymer 120 and filler particles 130.
A key discovery leading to the present invention was that polishing pads comprising a blend of EVA and polyethylene (PE) are susceptible to thermal breakdown and lost resilience, as indicated by softening, and in some cases melting, during polishing. It is surprising that the use of a polishing body comprising a blend of EVA and PE would so detrimentally affect the polishing body's thermal breakdown and resilience. As part of the present invention, it was found that CMP pads 100 comprising certain EVA block copolymers 120 are much more resistant to thermal and resilience breakdown as compared to blends of EVA and PE.
Numerous experiments conducted as part of the present invention established that it is critical to adjust the vinyl acetate content of the EVA block copolymers 120 within a range that is low enough to impart thermal stability, but high enough to provide a resilient EVA block copolymer 120. As the vinyl acetate content is decreased, the melting point increases. But as the content of vinyl acetate in the EVA block copolymer 120 decreases, so too does the resilience. Specifically, in embodiments of the closed-cell thermoplastic foam polishing body 110, the ethylene vinyl acetate block copolymer 120 comprises a vinyl acetate content ranging from about 1 wt % to about 18 wt %, and more preferably, from about 6 wt % to about 12 wt %.
Advantageous embodiments of the EVA block copolymer 120 have a particular hardness, resilience, melt index, and density that facilitate the preparation of the desired polishing body 110. Preferred embodiments of the EVA block copolymer 120 have a hardness of about 80 to about 100 Shore A (as measured by ASTM D2240). Other preferred embodiments of the EVA block copolymer 120 have a resilience, as characterized by a compression-set, ranging from about 30% to about 50% (ASTM D 395, 10 days at 25° C.). Still other preferred embodiments of the EVA block copolymer 120 have a melt index ranging from about 0.2 to about 25 dg/minute. Yet other preferred embodiments of the EVA block copolymer 120 have a density ranging from about 0.93 to about 0.95 g/cm³.
As well understood by one skilled in the art, the above-described characteristics can be adjusted by changing the vinyl acetate content of the EVA block copolymer 120 within the ranges set forth above, by changing the size of the ethylene and vinyl acetate blocks and by changing the copolymer's 120 molecular weight. One of ordinary skill in the art would be familiar with how these properties of the EVA block copolymer 120 can be adjusted
In some cases, the EVA block copolymer 120 is foamed to different extents to provide the closed-cell thermoplastic foam polishing body 110 with a range of hardness conducive to polishing certain types of materials. The extent of foaming can be characterized in terms of the density of the closed-cell thermoplastic foam polishing body 110 produced. A polishing body 110 having a density ranging from about 0.1 to about 0.4 gm/cm³results in a hardness ranging from about 20 to about 75 Shore A. For example, to polish a metal layer of tungsten it is preferably for the polishing body 110 to have a density of about 0.13 gm/cm³(about 8 lb/ft³), because the polishing body 110 has a hardness ranging from about 20 to about 40 Shore A. As another example, it is preferable to polish a metal layer of copper with a polishing body 110 having a density of about 0.29 gm/cm³(about 18 lb/ft³) because the polishing body 110 has a hardness ranging from about 35 to about 75 Shore A. Still another example is polishing a barrier layer of tantalum or tantalum nitride with a polishing body 110 having a density of about 0.38 gm/cm³(about 24 lb/ft³) because the polishing body 110 has a hardness ranging from about 35 to about 75 Shore A. Of course, to tune the relative rates of polishing of individual or multiple layers of these or different metal layers, or metal layers and barrier layers, a polishing body 110 of different density values than recited above can be used.
As noted above, the vinyl acetate content of the EVA block copolymer 120 represents a balance between thermostability and resilience. In some cases, for instance, it is desirable for the EVA block copolymer 120 to have a certain resilience that is conducive to uniform and repeatable CMP. Resilience here is characterized by the EVA block copolymer's 120 compression-set (ASTM D 395, 10 days at 25° C.). A compression-set equals 100 percent minus the percentage return of the copolymer to its original size along the original dimension that the force was applied. Preferred embodiments of the EVA block copolymer 120 have a compression set ranging from about 30% to about 50%. Preferred embodiments of the closed-cell thermoplastic foam polishing body 110 produced by foaming such EVA block copolymers 120 have a compression set ranging from about 2% to about 15% (ASTM D 395, 10 days at 25° C.).
To avoid distortion or melting during the elevated temperatures and pressures attained during CMP, it is advantageous for the EVA block copolymer 120 to have a particular range of thermostability. Thermostability can be characterized in terms of the EVA block copolymer's 120 melting point or melt index as measured using ASTM D1238. Some preferred embodiments of the EVA block copolymer 120 have a melt point ranging from about 85 to about 105° C., and more preferably, about 88 to 100° C. Other preferred embodiments of the EVA block copolymer 120 have a melt index ranging from about 0.2 to about 25 dg/minute, and more preferably from about 0.2 to about 6 dg/minute. The closed-cell thermoplastic foam polishing body 110 produced by foaming these embodiments of the EVA block copolymer 120 has substantially the same melting point or melt index as the EVA block copolymer 120. In some instances by cross-linking the EVA block copolymer as discussed below, the melting point of the polishing body 110 is higher than that of the commercially provided EVA block copolymer.
Non-limiting examples of commercially available EVA block copolymers 120 suitable for use in the present invention include copolymers available under the trademark ELVAX™ (trademark of E.I.du Pont de Nemours & Company, Wilmington, Del.), or under the trademark AIRFLEX™ (Air Products & Chemicals, Inc., Allentown, Pa.) or under the trademark Ultrathene® (Equistar Chemicals, LP, Houston, Tex.) or under the trademark Escorene (ExxonMobil Chemical, Houston, Tex.) or other suitable supplier.
Non-limiting examples of preferred EVA block copolymers include ELVAX 460, which has a vinyl acetate content of 18 wt %, a melting point of 88° C., a compression set of 50%, a density of 0.941 g/cm³, and Shore A hardness of 90; ELVAX 550, which has a vinyl acetate content of 15 wt %, a melting point of 93° C., a compression set of 54%, a density of 0.935 g/cm³, and Shore A hardness of 92; ELVAX 660, which has a vinyl acetate content of 12 wt %, a melting point of 96° C., a compression set of 39%, density of 0.933 g/cm³, and Shore A hardness of 95; ELVAX 670, which has a vinyl acetate content of 12 wt %, a melting point of 96° C., a compression set of 53%, a density of 0.933 g/cm³, and Shore A hardness of 96; ELVAX 750, which has a vinyl acetate content of 9 wt %, a melting point of 100° C., a compression set of 46%, a density of 0.930 g/cm³, and Shore A hardness of 95; ELVAX 760, which has a vinyl acetate content of 9 wt %, a melting point of 100° C., a compression set of 33%, a density of 0.930 g/cm³, and Shore A hardness of 97.
Another key discovery leading to the present invention is the realization that it is critical for the closed-cell thermoplastic foam polishing body 110 to comprise filler particles 130. While not limiting the scope of the invention by theory, it is believed that filler particles 130 of a particular size advantageously provide the surface 135 of the polishing body 110 with a plurality of projections 140 that facilitates the uniform polishing of a microelectronic device substrate. It is further believed that there is a cooperative interaction between the CMP pad projections 140 and slurry particles that facilitate uniform polishing. Moreover, because the filler particles 130 are distributed throughout the polishing body 110, new projections are presented to the surface 135 as the polishing body 110 is removed during polishing. In addition it is thought that the projections 140 force the slurry particles into close and turbulent contact with the substrate during polishing, thereby facilitating the removal of unwanted topography from the substrate surface.
To facilitate the above functions, it is beneficial for the size of the filler particles 130 to be about 10 to about 1000 times larger than the slurry particles that are used in conjunction with the CMP pad 100. Typically, CMP slurry particles range from about 0.03 microns to about 0.2 microns in diameter.
In addition, it is preferred that the fillet particles 130 comprise a hardness ranging from about 6 to about 8 mohs. In some preferred embodiments, the filler particles 130 comprise inorganic oxides such as silica, alumina, ceria, titania, or zirconia. It is desirable for the filler particle 130 content in the closed-cell thermoplastic foam polishing body 110 to range from about 3 to about 20 wt %. In some preferred embodiments, the filler particle 130 content ranges from about 10 to about 20 wt %, and even more preferably, about 15 wt %.
In some preferred embodiments of the closed-cell thermoplastic foam polishing body 110 the EVA block copolymer 120 is cross-linked. While not limiting the scope of the invention by theory, it is believed that a polishing body 110 comprising a cross-linked EVA block copolymer 120 advantageously makes the polishing body 110 less prone to deformation during polishing as compared to a polishing body 110 comprised of non-cross-linked EVA block copolymers 120. In addition, cross-linking is thought to beneficially increase the chemical resistant to degradation to slurry chemistries. Furthermore, because cross-linking increases the effective molecular weight, it is thought that the cross-linked EVA block copolymer 120 advantageously has an increased tear resistance, increased tensile strength, decreased tensile elongation and decreased dimensional thermal stability. Additional, it is thought that the cross-linked EVA block copolymer 120 has a distribution of melting points that is on average higher than the non-cross-linked EVA block copolymer 120
As well known to those skilled in the art the extent of cross-linking can be characterized in terms of a gel fraction, the fraction of the EVA block copolymer 120 that cannot be extracted by a solvent, in accordance with ASTM D 2765. Preferred embodiments of the polishing body 110 have a gel fraction ranging from about 60% to about 95%.
Embodiments of the closed-cell thermoplastic foam polishing body 110 can comprise additional components. In some cases, for example, the closed-cell thermoplastic foam polishing body 110 can comprise a colorant, such as about 4.5 wt % of titania, the titania particles having a size of about 0.29 microns. The closed-cell thermoplastic foam polishing body 110 can also comprise trace amounts (e.g., about 1 to 2 wt %) of a foaming agent, a cross-linking agent, reaction products of the cross-linking or foaming agent, or catalysts to activate the cross-linking agent or foaming agent.
In certain preferred embodiments of the present invention, an interior of the closed-cell thermoplastic foam polishing body 110 comprise cells 150 having an average size 155 ranging from about 50 to about 300 microns, and more preferably, from about 100 to about 200 microns. The term cell 150 as used herein, refers to any volume defined by a membrane within the EVA block copolymer 120 occupied by air, or other gases from a foaming agent. Of course, as well known to those skilled in the art, the foaming gases inside the cells can out-gas after the manufacture of the closed-cell thermoplastic polishing body, and be substantially replaced by air. Cell size 155 can be determined using standardized protocols, developed and published by the American Society for Testing and Materials (West Conshohocken, Pa.), such as ASTM D3576, incorporated herein by reference.
Some preferred embodiments of the CMP pad 100 comprise concave cells 160 at the surface 135 having an average diameter 165 that is substantially the same as the average size 155 as the cells 150. The concave cells 160 are formed from cells 150 upon exposing the closed cell thermoplastic foam 110, as further discussed below. In certain preferred embodiments, the cells 150 are substantially spheroidal. However, the cells 150 and concave cells 160 can also comprise irregular shapes.
In some embodiments, the CMP pad 100 further comprises an optional backing 170 coupled to the polishing body 110. Coupling can be direct, for example by thermally bonding the backing 170 to the polishing body 110, or indirect, for example using a conventional adhesive 175, or a combination of direct or indirect coupling. In some instances, a stiff backing 170 advantageously limits the compressibility and elongation of the closed-cell thermoplastic foam 120 during polishing, which in turn, beneficially reduces erosion and dishing effects during CMP. In certain preferred embodiments, the backing 170 comprises a high-density thermoplastic (i.e., greater than about 0.98 gm/cc), and more preferably, a polyethylene, such as condensed high-density polyethylene. Preferably, the high-density thermoplastic is not foamed. Of course, other high-density polymers can be advantageously used as the backing 170.
In some instances, it is advantageous to characterize embodiments of the CMP pads 100 in terms of their performance parameters with respect to polishing. CMP can be done on a microelectronic device substrate or any of the various insulating or conducting layers, lines, vias, or other structures comprising a microelectronic device. The term microelectronic device substrate as used herein refers to any material comprising the various insulating or conducting layer, lines, vias or other structures that a microelectronic device can comprise. For instance, the microelectronic device can comprise a semiconductor device on a silicon wafer, and the metal layers, barrier layers or dielectric films above the silicon substrate.
Any one or a combination of performance parameters, including non-uniformity, dishing and erosion, defect count, removal rates, and longevity can be used to characterize the CMP pad 100. For instance, non-uniformity can be quantified by measuring the within-wafer-non-uniformity (WIWNU) provided by the CMP pad 100. The term WIWNU as used herein, refers to the non-uniformity of tungsten removal across a microelectronic device substrate surface, such as a semiconductor wafer. Contour plots of the tungsten surface after polishing are preferably measured electrically by determining sheet resistance at numerous points distributed across the wafer. The average post-polishing depths of tungsten removed across the semiconductor wafer, the standard deviation of the depth removed and the percent standard deviation of the depth removed, i.e., the WIWNU, are calculated from the measurements of sheet resistance.
Non-uniformity was measured under standardized conditions comprising a standard commercial four-point probe resistance measurement tool (such as a ResMap Model No. 168 from Creative Design Engineering, Inc., Cupertino, Calif.), measuring twenty-five points across the diameter of the substrate with a five-millimeter exclusion on the edge of the substrate. The microelectronic device substrate polished by the CMP pad 100 was a test silicon wafer manufactured by SVM Microelectronics. The test wafer comprised a silicon base wafer comprising successively coated layers of 600 nm of thermally grown silicon dioxide, 25 nm of PVD titanium, 40 nm of PVD titanium nitride, and top layer of 800 nm of CVD tungsten. Similar test wafers from other manufacturers could be used for measuring removal rate and WIWNU.
As well known to those skilled in the art, dishing occurs when a metal line on a microelectronic device substrate recedes below the level of an adjacent dielectric region on the substrate. Erosion occurs when the dielectric insulators separating conductive features recede below the level of the field oxide. Dishing and erosion were measured by conventional stylus profiling. For the purposes of the present invention, both dishing and erosion were measured by determining the total indicated run-out (TIR). TIR is defined as the difference in height from the highest and lowest point on the microelectronic device substrates polished by the CMP pad 100.
The microelectronic device substrate polished by the CMP pad 100 was a test silicon wafer manufactured by SVM Microelectronics. The test wafer comprised a silicon base wafer coated with successive layers comprising 500 nm of thermally grown silicon dioxide, patterned with a Sematech 854 test pattern and etched through the silicon dioxide to stop on the silicon, followed by 25 nm of PVD titanium, 40 nm of PVD titanium nitride, and a top layer of 800 nm of CVD tungsten. Similar test wafers from other manufacturers could be used for measuring dishing and erosion or TIR.
The term defect count as used herein refers to defects as assessed using a Surfscan® SP-1 (KLA-Tencor, San Jose, Calif.) with a threshold of 0.2 microns. The defect count is the cumulative counts of all light scattering events from a polished substrate, regardless of the cause. The defect count was observed after polishing a tungsten covered 200 mm wafer substrate with the CMP pad 100 on a rotational polishing apparatus (such as a Model No. 472 CMP polisher from IPEC (NOVELLUS), CHANDLER, Ariz.), using a down force of about 5-7 psi (340-480 hPa), a backside pressure of about 1.5-2.5 psi (100-170 hPa), a table speed of about 85 rpm, a carrier speed of about 80 rpm, and a slurry flow rate of about 120 ml/min (using a typical tungsten polishing slurry, such as Cabot Semi-Sperse® W2000).
Of course, a CMP pad 100 capable of polishing a substrate surface at an acceptable removal rate and having acceptable longevity remains important because these properties facilitate faster microelectronic device fabrication and hence greater manufacturing throughput. For the purposes of the present invention, an acceptable removal rate is defined as the removal of at least about 200 nanometers of tungsten from a microelectronic device surface per minute by the CMP pad 100.
The removal rate is characterized under standardized test conditions comprising a conventional rotational polishing apparatus (such as a Model No. 472 CMP polisher from IPEC (NOVELLUS), CHANDLER, Ariz.) with a downforce of 5-7 psi (340-480 hPa), backside pressure of about 1.5-2.5 psi (100-170 hPa), a table rotation speed of about 80 rpm, a carrier head rotation speed of about 85 rpm, and a slurry flow rate of 120 ml/min (using a typical tungsten polishing slurry, such as Cabot Semi-Sperse® W2000). The resulting removal rate is measured by using a standard commercial 4-point probe resistance measurement tool (such as a ResMap Model No. 168 from Creative Design Engineering, Inc., Cupertino, Calif.), measuring twenty-five points across the diameter of the substrate with five-millimeter exclusion on the edge of the substrate.
The microelectronic device substrate polished by the CMP pad 100 was a test silicon wafer manufactured by SVM Microelectronics. The test wafer comprised a silicon base wafer with successively coated layers of 250 nm of thermally grown silicon dioxide, 25 nm of PVD titanium, 40 nm of PVD titanium nitride, and top layer of 800 nm of CVD tungsten. Similar test wafers from other manufacturers could be used for measuring removal rate and WIWNU.
For the purposes of the present invention, longevity is defined as the number of microelectronic device substrates that can be polished by the CMP pad 100 within acceptable ranges of polishing parameters (e.g., a removal rate of at least about 200 nm/min, WIWNU of ≦8% and defect count of less than about 100). An acceptable longevity is defined as at least 1000 substrates being polished for 1 minute each, or a total polishing lifetime of 1000 min, under standardized test conditions.
The CMP pad's 100 tungsten polishing properties were assessed using a commercial polisher (such as a Model No. 472 CMP polisher from IPEC (NOVELLUS), CHANDLER, AZ). Unless otherwise noted, the removal rate of tungsten during polishing was assessed using a down force of about 5-7 psi (340-480 hPa), a backside pressure of about 1.5-2.5 psi (100-170 hPa), a table speed of about 85 rpm, a carrier speed of about 80 rpm, and a commercially available slurry (Cabot, Rohm & Haas, Fujimi) at a slurry flow rate of about 120 ml/min.
Yet another embodiment of the present invention is a method for manufacturing a polishing pad. Turning to the exemplary flow diagram depicted in FIG. 2, the method 200 comprises placing into a container: an EVA block copolymer in step 210, filler particles in step 220, and a foaming agent in step 230.
The EVA block copolymer can comprise any of the embodiments described above. Copolymerisation products of ethylene with vinyl acetate and can be produced by any conventional process well know to those skilled in the art, including bulk continuous polymerization or solution polymerisation. As noted above, the EVA block copolymer comprises a vinyl acetate content ranging from about 1 wt % to about 18 wt %.
As also noted above, the filler particles comprise an average size ranging from about 1 micron to about 20 microns, and can comprise any of the embodiments described above.
In some cases the foaming agent comprise a heat-activated foaming agent, such as azodicarbonamide, preferably combined with a catalyst such as zinc oxide. In some preferred embodiments, for example, azodicarbonamide and zinc oxide are heat activated at a temperature ranging from about 149 to about 165° C. In other cases the foaming agent comprises a blowing agent, such as nitrogen or fluorocarbon gas. In still other embodiments, the foaming agent comprises a combination of heat-activated foaming agent and blowing agent.
The method for preparing the polishing pad comprises a step 240 of mixing together the EVA block copolymer, filler particles and foaming agent. Any pair or all three of the EVA block co-polymer, filler particles and foaming agent can be mixed together before or after being placed in the container.
After performing steps 210 through 240, in certain preferred embodiments, the EVA block co-polymer is cross-linked in step 250. In some cases cross-linking is carried out after the mixing step 240 and at substantially the same time that the closed cells are being formed as further discussed below. It is desirable for cross-linking to be done on the EVA block co-polymer when heated to a molten state so that EVA block co-polymer has a substantially amorphous structure. For example, in some preferred embodiments, heating the EVA block co-polymer to a molten state and heat activating a foaming agent are carried out at the same time.
Preferred cross-linking agents used in step 250 are organic peroxide, and more preferably dialkyl peroxides, such as dicumyl peroxide or a,a′-bis(t-butylperoxy) diisopropylbenzene, commercially available as Di-Cup® and Vul-Cup®, respectively (Geo Specialty Chemicals, Cleveland, Ohio). In some preferred embodiments the cross-linking agent is heat activated at about 149 to about 165° C. Of course, other conventional cross-linking agents well known to those skilled in the art could be used. One skilled in the art would be familiar with the amounts of cross-linking agent and procedures to prepare the cross-linked EVA block copolymers. Preferably, the cross-linked EVA block copolymer has a gel fraction ranging from about 60% to about 95%.
Closed cells are formed, in step 260, throughout the EVA block copolymer to produce a closed-cell thermoplastic foam polishing body. Any conventional foaming process well known to those of ordinary skill in the art can be used to form the closed cells. For instance, a heat-activated foaming agent can be decomposed in step 262 by heating with a catalyst to produce foaming gases such as carbon monoxide and nitrogen gas. Alternatively, in step 264, a blowing agent, such as carbon dioxide or nitrogen gas, can be introduced into the thermoplastic polishing body, preferably under pressure in a closed container. In still other instances, forming the closed-cell thermoplastic foam polishing body comprises both steps 262 and 264.
In some preferred embodiments, forming the closed-cell thermoplastic foam polishing body is at least partially carried out while the container is open, in step 270. In some cases, for example, EVA block copolymer, filler particles, foaming agent, and optional cross-linking agent, are added to the container in steps 210 to 240, the container is closed, and then container is heated to a temperature ranging from about 149 to about 165° C. The increased pressure inside the container substantially suppresses the formation of cells. After a suitable period to allow cross linking of the EVA block copolymer and heat activation of the foaming agent as per step 262, the container is opened. The reduced pressure associated with opening the container in step 270 allows gases from the foaming agent to expand, resulting in the formation of closed cells to their final dimensions.
Surprisingly, thermoplastic foam polishing bodies whose closed-cells that are at least partially formed in an open container, particularly when using a heat activated foaming agent, have superior polishing parameters as compared to thermoplastic foam polishing bodies made in a closed container. While not limiting the scope of the present invention by theory, it is thought that superior polishing parameters of such a polishing body are due to the formation of closed cells having uniform dimensions. The advantageous use of an open container is surprising because it is expected that the use of a closed container would provide batches of closed-cell thermoplastic foam polishing bodies having more uniform properties.
It is still within the scope of the present invention, however, for closed-cell formation to be carried out entirely in closed containers, in step 275. As an example, in some embodiments the EVA block copolymer, filler particles, foaming agent, and optional cross-linking agent, are added to the container in steps 210 to 240 and the closed container is heated to a temperature ranging from about 149 to about 165° C. After a time sufficient to allow cross linking of the EVA block copolymer and heat activation of the blowing agent, the contents of the container are transferred to a second container having a larger volume than the first container and subject to continued heating at the above-cited temperature range. The extended period of heating and lower pressure in the second container, as a result of the larger volume of the second container as compared to the first container, allow gases from the blowing agent to expand resulting in formation of closed cells in step 275. One skilled in the art would understand that step 275 could further include heating to other temperature ranges, or the use of a plurality of containers to facilitate the formation of the closed-cells.
In certain optional embodiments, the method for preparing the CMP pad 200 can further comprise, in step 280, exposing cells within the closed-cell thermoplastic foam polishing body to form a surface comprising concave cells. The surface of concave cells can be formed by skiving the closed-cell thermoplastic foam substrate. The term skiving as used herein is defined as any process to a cut away a thin layer of the surface of the substrate so as to expose concave cells within the substrate. Skiving can be achieved using any conventional technique and device well known to one of ordinary skill in the art. In some cases exposing comprises fixing the thermoplastic foam substrate on a planar surface and cutting away a thin layer of the closed-cell thermoplastic foam to provide a thermoplastic foam polishing body ranging in thickness from about 1000 microns to about 3000 microns.
In other optional embodiments, the method for preparing the polishing pad also comprises, in step 290, coupling the thermoplastic foam substrate to a stiff backing, such as high-density thermoplastics as described above. In certain preferred embodiments, coupling 290 is direct by thermal welding to the thermoplastic backing and thermoplastic foam substrate together. In other embodiments, coupling is indirect via chemical bonding using a conventional adhesive, such as epoxy or other materials well known to those skilled in the art.
Yet another embodiment of the present invention is a CMP apparatus. As illustrated in FIG. 3, the exemplary apparatus 300 comprises a mechanically driven carrier head 310 and a polishing platen 320. The carrier head 310 is positionable against the polishing platen 320 to impart a polishing force against the polishing platen 320. The CMP apparatus 300 further includes a CMP pad 330 attached to the polishing platen 320.
The CMP pad 330 comprises a closed-cell thermoplastic foam polishing body 335. The closed-cell thermoplastic foam polishing body 335 comprises an ethylene vinyl acetate block copolymer 340, which in turn, comprises vinyl acetate ranging from about 1 wt % to about 18 wt % and filler particles 345 comprising an average size ranging from about 1 micron to about 20 microns. The CMP pad 330 can comprise any of the above-described embodiments, such as presented in FIGS. 1 and 2. Optional embodiments of the CMP pad 330 can further comprise an backing 350 that is coupled to the closed-cell thermoplastic foam polishing body 335, as discussed above, via a conventional adhesive 355 or by thermal welding.
Additional optional embodiments of the CMP apparatus 300 further comprise a conventional carrier ring 360 and adhesive 365 to securely couple the microelectronic device substrate 370 to the carrier head 310.
Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the scope of the invention.

Claims

1. A chemical mechanical polishing pad comprising:

a closed-cell thermoplastic foam polishing body comprising:

an ethylene vinyl acetate block copolymer comprising a vinyl acetate content ranging from about 1 to about 18 wt %; and

filler particles comprising an average size ranging from about 1 to about 20 microns, and

wherein an interior of said closed-cell thermoplastic foam polishing body comprise cells having an average size ranging from about 50 to about 300 microns.

2. The chemical mechanical polishing pad as recited in claim 1, wherein a polishing surface of said closed-cell thermoplastic foam polishing body comprise projections raised above said polishing surface by no more than said average size.

3. The chemical mechanical polishing pad as recited in claim 1, wherein a polishing surface of said closed-cell thermoplastic comprises concave cells having said average diameter.

4. The chemical mechanical polishing pad as recited in claim 1, wherein said ethylene vinyl acetate block copolymer has a vinyl acetate content ranging from about 6 to about 12 wt %.

5. The chemical mechanical polishing pad as recited in claim 1, wherein said ethylene vinyl acetate block copolymer has a melt index ranging from 0.2 to about 25 dg/min (ASTM D1238).

6. The chemical mechanical polishing pad as recited in claim 1, wherein said closed-cell thermoplastic foam polishing body has a hardness ranging from about 20 to about 75 Shore A.

7. The chemical mechanical polishing pad as recited in claim 1, wherein said closed-cell thermoplastic foam polishing body has a gel fraction ranging from about 60 to about 90 percent.

8. The chemical mechanical polishing pad as recited in claim 1, wherein said thermoplastic foam polishing body has a density ranging from about 0.1 to about 0.4 g/cm³.

9. The chemical mechanical polishing pad as recited in claim 1, wherein said closed-cell thermoplastic foam polishing body comprise said filler particle ranging from about 3 to about 20 wt %.

10. The chemical mechanical polishing pad as recited in claim 1, wherein said closed-cell thermoplastic foam polishing body comprise said filler particles ranging from about 10 to about 20 wt %.

11. The chemical mechanical polishing pad as recited in claim 1, wherein said filler particles have a hardness ranging from about 6 to about 8 mohs.

12. The chemical mechanical polishing pad as recited in claim 1, wherein said closed-cell thermoplastic foam polishing body has a tungsten removal rate of least about 200 nm/min, a non-uniformity (WIWNU) of about 8% or less and longevity of at least about 1000 polishing minutes per pad.

13. The chemical mechanical polishing pad as recited in claim 1, wherein said closed-cell thermoplastic foam polishing body has a dishing parameter of less than 100 nm on a 100 micron line and an erosion parameter of less than 300 nm on an array of 1 micron lines and spaces at 50% pattern density.

14. The chemical mechanical polishing pad as recited in claim 1, wherein said closed-cell thermoplastic foam polishing body has a defect count of less than about 50 counts per 200 mm substrate.

15-20. (canceled)

21. A chemical mechanical polishing apparatus comprising:

a mechanically driven carrier head; a polishing platen, said carrier head being positionable against said polishing platen to impart a polishing force against said polishing platen; and

a polishing pad attached to said polishing platen, said polishing pad comprising:

a closed-cell thermoplastic foam polishing body comprising:—

22. The chemical mechanical polishing pad as recited in claim 1, wherein said average size ranges from about 100 to about 200 microns.