KR100499601B1 - Improved Polishing Pads And Methods Relating Thereto - Google Patents

Abstract

The polishing pad of the present invention has a polishing surface made of a hydrophilic material. The polishing surface has a topography produced by thermoforming. This topography consists of large and small forms that promote the flow of polishing fluid and promote smoothing and flattening.

Description

Improved Polishing Pads And Methods Relating Thereto}

The present invention generally relates to a polishing pad useful for the manufacture of semiconductor devices and the like. More specifically, the polishing pad of the present invention comprises an advantageous hydrophilic material with innovative surface topography that generally improves predictability and polishing performance.

Fabrication of integrated circuits generally requires polishing one or more substrates such as silicon, silicon dioxide, tungsten or aluminum. Such polishing is usually performed using a polishing pad together with the polishing fluid.

The semiconductor industry requires precise grinding of narrow tolerances, but it is very common for unwanted “pad to pad” deviations in polishing performance. Thus, there is a need in the semiconductor industry for polishing pads that are more predictable in high precision polishing operations.

Summary of the Invention

The present invention relates to thermoformed (or embossed) polishing pads with innovative polishing surfaces formed from innovative hydrophilic materials. The pad of the present invention has (i) a density of greater than 0.5 g / cm 3, (ii) a critical surface tension of at least 34 mN / m, (iii) a tensile modulus of 0.02 to 5 gigapascals, and (iv) at 30 ° C. The tensile modulus of elasticity to the tensile modulus at 60 ℃ of 1.0 to 2.5, (v) hardness of 25 to 80 Shore D, (vi) yield stress of about 2.1 to 41.4 megapascals (300 to 6000 psi) And (vii) a tensile strength of 7 to 105 megapascals (1000 to 15,000 psi) and (viii) a hydrophilic material having an elongation at break of 500% or less. In a preferred embodiment, the abrasive layer comprises a plurality of soft domains and hard domains.

The abrasive of the present invention does not include felt-based polishing pads prepared by incorporating a polymer into a fiber substrate as described in US Pat. No. 4,927,432 to Budinger et al.

The abrasive surface has the topography produced by the thermoforming method. This topography consists of large and small surface features that facilitate the flow of the polishing fluid and promote smoothing and planarization.

The present invention relates to a polishing pad having an innovative abrasive surface made from an innovative hydrophilic abrasive. More particularly, the invention relates to improved polishing pads useful for polishing substrates, particularly substrates used in the manufacture of semiconductor devices and the like. The compositions and methods of the present invention may also be useful in other industries and may be applied to many materials including, but not limited to, silicon, silicon dioxide, metals, dielectrics, ceramics, glass, and the like. The term "polishing" (and any form thereof) as used throughout this specification should be understood to include "flattening" (and any corresponding form).

The present invention recognizes (1) the detrimental effects on precision polishing caused by damage occurring when expressing surface features into conventional pads, and (2) how damage occurs during the manufacture of polishing pads. And (3) teach a method of making pads with less damage, and (4) have a higher predictability of pad performance due to greater surface reproducibility compared to conventional pads made by cutting or skewing. It is innovative in that it teaches a manufacturing method and (5) teaches a novel method of incorporating a surface form into the pad during manufacture of the pad. None of these features of the present invention have ever been recognized in the art and have not made a truly significant contribution to precision polishing technology.

The polishing pad of the present invention includes highly reproducible and advantageous surface topography that minimizes surface damage such as indentation and protrusion, which often occurs during pad manufacture.

Pad making methods, such as cutting and cutting, cause damage that tends to vary from pad to pad. Conventional pad manufacturing methods include a method of manufacturing a pad by cutting a slice of a polymer cake. When this cake is cut by a blade, directional surface damage, including indentations and protrusions, usually remains on the pad surface. This damage usually varies from pad to pad as the blade dulls.

Another step in pad fabrication is to incorporate channels or other shapes into the pad surface to facilitate the flow of the polishing fluid. Conventional pads are generally machined or cut these surface shapes into the pad. This also generally tends to leave damage on the pad surface and in the cut area. Other factors, such as temperature, humidity, and line speed variations, also contribute to pad surface characteristics. This variation leads to performance variation per pad and has difficulty in delineating the optimum polishing parameters.

The pads of the present invention are manufactured with little or no crushing of the abrasive surface, machining or similar forms. Unwanted directional patterns, such as directional patterns caused by cutting, are generally removed. The surface form or part thereof is applied onto the pad (or into the pad) without breaking the polishing surface. This eliminates the problems associated with the prior art.

According to the invention the surface morphology incorporated after the manufacture of the pad is at least partly produced by thermoforming. Thermoforming is any method of heating the surface of a pad and permanently deforming it by some means, such as pressure or stress. Thermoforming reduces the degree of damage compared to conventional pads. Thermoforming also provides a surface form that is more reproducible than cutting or machining the surface due to the consistency of the thermoforming die. Thus, the pad of the present invention is more predictable in performance and allows contouring of optimal polishing parameters.

In one embodiment, the surface form is incorporated into the surface of the polishing pad by heating the pad surface until the pad surface softens and then shaping the pad surface using a die and pressure. Such surface forms preferably comprise one or more indentations whose average depth and / or width are greater than about 0.05 mm, preferably greater than about 0.1 mm. This surface shape facilitates the flow of polishing fluid to improve polishing performance.

In another embodiment, the pad is extruded to produce a sheet of material. The material may be made of an abrasive belt by making a bond at both ends of the sheet, or in other embodiments the sheet may be cut to produce pads of any shape or size. In another embodiment of the present invention, a compression molding method is used. At this time, the flexible polymer is placed on a die and pressed to spread the polymer throughout the mold, and then solidified and released from the mold.

In another embodiment, the pad material is extruded onto a second solid or semisolid material such that the extruded material solidifies and adheres to the second material. The second material can reinforce the pad so that the solidified extruded material does not have to bear on its own. Alternatively or in addition to this, the second material may provide structural fastness to the pad, improving performance and life and / or adding flexibility in manufacturing.

In a preferred embodiment of the present invention, the surface form is embossed with a cooling roller used to remove or greatly reduce the plastic flow after embossing. This results in highly reproducible embossed indentations, so that the pad-to-pad variations typically found in pads manufactured by many conventional methods are generally reduced. This reproducibility is also the result of the embossing die surface being kept substantially the same for each pad produced by it. This is ultimately achieved with more predictable pad performance. Predictability of performance is an important aspect of precision polishing pads. Pad consistency allows for more accurate standard work processes, resulting in more productive polishing. Moreover, the use of rollers to form the surface allows the pads to be made into continuous sheets.

For optimal polishing performance, smaller surface shapes (less than 50 μ) are required in addition to the surface shapes that have previously been cut or machined into pads. These small dimension shapes are usually incorporated prior to the first use of the pad and periodically incorporated during pad use. This is called "conditioning". If conditioning is performed prior to use of the pad, it is referred to as "preliminary conditioning" and if it is in use, it is called "reconditioning". Small dimensional surface shapes during the use of the pad may experience unwanted plastic flow and may be damaged by debris. Smaller dimensions are reproduced by conditioning. It has been surprisingly found that in the case of the polishing pad of the present invention, reconditioning during use is generally less necessary than conventional polishing pads. This is another proof that the pad of the present invention is generally superior to conventional pads.

The pad of the present invention can be conditioned using a wear material. Small dimension surface shapes can be created by moving the abrasive surface and the abrasive surface against each other. In one embodiment, the wear material is a rotating structure in which a plurality of hard particles are embedded in the surface (preferably permanently fixed), and the shape may be circular, square, rectangular, oval or any geometric shape. Due to the movement of the hard particles moving against the pad surface, the pad surface may experience plastic flow, fragmentation or both (at the point of contact with the particles). The wear surface does not have to rotate against the pad surface and can move against the pad in one of several ways, including vibration, linear motion, irregular orbits, rolling, and the like.

The plastic flow, fragmentation, or both generated as described above (due to the abrasion surface) produces a small dimensional surface morphology on the outer surface of the pad. The small dimension surface shape may include an indentation and a protrusion adjacent at least one of the indentations. In one embodiment the protrusions account for at least 0.1% of the surface area of the pad polishing surface, the indentation having an average depth of less than 50 microns, more preferably less than 10 microns, and the average height of the protrusions less than 50 microns, more preferably 10 Is less than a micron. Such surface deformation, preferably with abrasion surface, will cause minimal wear removal of the polishing surface, but only furrows into the pads while keeping a significant amount (if any) of the pad material away from the polishing surface. However, even less desirable, it can be acceptable as long as the wear removal of the pad material produces a small dimensional surface shape.

Preferred wear surfaces for conditioning are preferably metal discs, preferably embedded with diamonds between 1 micron and 0.5 mm in size. The pressure between the conditioning disk and the polishing pad during conditioning is preferably between about 0.69 and 172.3 kilopascals (0.1 to about 25 lb / in ² ). The rotational speed of the disk is preferably 1 to 1000 revolutions per minute.

Preferred conditioning disks are 10.16 cm (4 in), 100 grit diamond disks (e.g. REST Disk (manufactured by RE Science, Inc.)). Optimal conditioning has a downward pressure of approximately 6.9 kilopascals (10 lb / in ² ), platen speed of 75 rpm, sweep profile of bell type, pre-use conditioning sweeps of 15, and The reconditioning sweep number was 15.

In some cases conditioning can be carried out in the presence of a conditioning fluid, preferably a water based fluid containing wear particles.

According to the present invention, small dimension shapes may arise in the course of thermoforming using all or part of the innovative thermoforming dies. The difference in affinity for the pad material allows the pad to be selectively released from the die to obtain the desired small dimension surface morphology.

According to the present invention, thermoforming dies differ in affinity for pad materials. The small affinity portion can be released with little or no destruction of the pad surface. The high affinity portion prevents the pad from releasing from the die, which may result in plastic flow or chipping of the surface at this site. This process produces the desired small dimension of the surface. Affinity differences can result from differences in materials, differences in die coatings, or differences in the physical shape of the dies.

In one embodiment the thermoformed die consists of two or more materials having different affinity for the pad material. The part of the pad surface close to the high affinity site upon release ruptures, leading to the desired surface morphology. In another embodiment, the die surface is coated to create low and high affinity regions. In another embodiment, the die is shaped to grab the pad material at a particular location, such that the pad protrusion snaps into the die, creating a small dimension of the surface shape. In another embodiment, this grabbing effect is created by protrusion material as opposed to protrusion shape.

Formation of the surface morphology during pad manufacture reduces or eliminates the need for preconditioning. In addition, this generation of surface morphology allows better control and reliable replication of small dimensions compared to surface deformation using wear means.

Any prepolymer chemistry may be used according to the invention, including polymer systems other than urethane, provided that the final product has (i) a density of greater than 0.5 g / cm 3, more preferably greater than 0.7 g / cm 3, Even more preferably greater than about 0.9 g / cm 3, (ii) a critical surface tension of at least 34 mN / m, (iii) a tensile modulus of 0.02 to 5 gigapascals, and (iv) a tensile modulus at 30 ° C. versus 60 The tensile modulus at 1.0 ° C. is 1.0-2.5, (v) hardness is 25-80 Shore D, (vi) yield stress is about 2.1-41.4 megapascals (300-6000 psi), and (vii) tensile strength is About 7 to 105 megapascals (1000 to 15,000 psi) and (viii) have an elongation at break of 500% or less. This property is possible for many materials useful for extrusion and similar methods, such materials include polycarbonate, polysulfone, nylon, ethylene copolymers, polyethers, polyesters, polyether-polyester copolymers, acrylics Polymers, polymethyl methacrylates, polyvinyl chlorides, polycarbonates, polyethylene copolymers, polyethylene imines, polyurethanes, polyether imides, polyketones, and the like, and photochemically reactive derivatives thereof.

In a preferred embodiment, the pad material is sufficiently hydrophilic such that the critical surface tension is at least 34 mN / m, more preferably at least 37 mN / m, most preferably at least 40 mN / m. Critical surface tension defines the wettability of a solid surface by pointing to the lowest surface tension of a liquid that exhibits a contact angle of more than zero degrees to the solid. Thus, polymers with higher critical surface tensions are more easily wettable and therefore more hydrophilic. The critical surface tension of a typical polymer is as follows.

Polymer Critical Surface Tension (mN / m)

Polytetrafluoroethylene 19

Polydimethylsiloxane 24

Silicone rubber 24

Polybutadiene 31

Polyethylene 31

Polystyrene 33

Polypropylene 34

Polyester 39-42

Polyacrylamide 35-40

Polyvinyl Alcohol 37

Polymethyl Methacrylate 39

Polyvinyl Chloride 39

Polysulfone 41

Nylon 6 42

Polyurethane 45

Polycarbonate 45

In one embodiment the pad matrix is at least

1.acrylated urethane,

2. acrylated epoxy,

3. ethylenically unsaturated organic compounds having carboxy, benzyl or amide functionality,

4. aminoplast derivatives with pendant unsaturated carbonyl groups,

5. isocyanurate derivatives with at least one pendant acrylate group,

6. vinyl ether,

7. urethane,

8. polyacrylamide,

9. ethylene / ester copolymers or acid derivatives thereof,

10. polyvinyl alcohol,

11.polymethyl methacrylate,

12. polysulfone,

13. polyamide,

14. polycarbonate,

15. polyvinyl chloride,

16. epoxy,

17. Copolymers of the above or

18. It is derived from combinations thereof.

Preferred pad materials include urethane, carbonate, amide, sulfone, vinyl chloride, acrylate, methacrylate, vinyl alcohol, ester or acrylamide moieties. The pad material may be porous or nonporous. In one embodiment the matrix is nonporous and in another embodiment the matrix is nonporous and without fiber reinforcement. The pad material may also include wear material.

In a preferred embodiment, the abrasive material comprises (1) a number of hard domains that withstand plastic flow during polishing and (2) a number of less hard domains that are less resistant to plastic flow during polishing. This complex property provides a dual mechanism that has been found to be particularly advantageous in polishing silicon dioxide, dielectric materials and metals.

This rigid phase size is preferably less than 100 microns in any dimension (height, width or length), more preferably less than 50 microns, even more preferably less than 25 microns and most preferably less than 10 microns. Likewise the non-solid phase is preferably less than 100 microns, more preferably less than 50 microns, even more preferably less than 25 microns, most preferably less than 10 microns. Preferred dual phase materials include polyurethane polymers having soft segments (providing a hard phase) and hard segments (providing a hard phase). These domains are prepared as materials resulting from phase separation due to incompatibility between two (hard and soft) polymer segments.

Other polymers with hard and soft segments may also be suitable, for example ethylene copolymers, copolyesters, block copolymers, polysulfone copolymers and acrylic copolymers. The hard and soft domains in the pad material are also (1) hard and soft segments present along the polymer backbone, (2) crystalline and amorphous regions in the pad material, and (3) hard and soft polymers into alloys. Or by (4) combining the polymer with an organic or inorganic filler.

The abrasive material of the present invention does not include felt-based polishing pads made by incorporating a polymer onto a fiber substrate as described in US Pat. No. 4,972,432 to Budinger et al.

The pad of the present invention is preferably used in combination with a polishing fluid (which may include wear particles). During polishing, the polishing fluid is located between the polishing surface of the pad and the workpiece to be polished. As the relative position between the pad and the substrate changes, the surface shape allows the polishing fluid to flow better along the interface between the pad and the substrate to be polished and promotes smoothing and flattening. By improving the flow of polishing fluid and the interaction between the pad and the substrate, polishing performance can generally be more efficient and effective.

The pad of the invention is preferably attached to the platen in use so as to be close enough to the workpiece to be polished. Surface non-uniformity is removed from the workpiece at a speed that depends on many parameters, including the pad pressure (or vice versa) applied to the workpiece surface, the speed at which the pad and the workpiece move relative to each other, and the composition of the polishing fluid. Generally the pressure between the workpiece and the abrasive layer is greater than 0.1 kg / m 2.

The polishing fluid is preferably water based and wear particles may or may not be necessary depending on the composition of the polishing layer. For example, an abrasive layer comprising wear particles may not require wear particles in the polishing fluid.

The following examples show the use of polishing pads with embossed polishing surfaces.

<Example 1>

This example shows an example of using a low-embossed pad to polish a soft metal such as aluminum.

Thermoplastic polyurethane (MP-1880, J. P. Stevens) with a hardness of 85 Shore A was extruded into 25 mil sheets at high temperature. The sheet was then embossed in a hexagonal pattern at elevated temperature so that the sheet surface consisted of a raised hexagonal face. Each hexagonal surface contains finer grooves to facilitate slurry flow across the surface. The hexagons are approximately 5 mm in diameter and are separated by 0.5 mm channels. The embossed polyurethane sheet was laminated with a pressure-sensitive adhesive, cut into circles, and used as a polishing pad. The resulting pad was used for aluminum CMP polishing using a Westech 372U polisher. Using typical polishing conditions such as down pressure, carrier and platen rates, aluminum and oxide removal rates were 2280 A / min and 70 A / min, respectively, and the selectivity of Al: Ox was 32: 1.

<Example 2>

This example shows an example in which an oxide inner layer dielectric is polished using an embossed high hardness pad.

A thermoplastic polyurethane (Texin 470D, manufactured by Miles Inc.) with a hardness of 70 Sho D was extruded into a 50 mil sheet at high temperature. This sheet was then embossed at elevated temperature using a pattern similar to that described in Example 1. The embossed polyurethane sheet was laminated with a pressure sensitive adhesive, cut into circles and made available as a polishing pad. The resulting pads were used in combination with an ILD1300 slurry (Rodel Inc.) to heat Thermal Oxide CMP polishing using a Westtec 372U polisher. Using typical polishing conditions such as down pressure, carrier and platen speed, the oxide removal rates were greater than 2000 A / min, respectively, and the overall nonuniformity of the wafer was less than 10%.

The foregoing description and examples should not be understood as limiting in any way. The scope of the invention is only determined by the claims.

This application claims the benefit for US Provisional Application No. 60 / 054,906, filed August 6, 1997.

Background of the Invention

Claims (18)

(i) a density greater than 0.5 g / cm 3, (ii) a critical surface tension of at least 34 mN / m, (iii) a tensile modulus of 0.02 to 5 gigapascals, and (iv) a tensile modulus at 30 ° C. versus 60 The tensile modulus of elasticity at 1.0 ° C. is 1.0 to 2.5, (v) hardness is 25 to 80 Shore D, (vi) yield stress is about 2.1 to 41.4 megapascals (300 to 6000 psi), and (vii) Tensile strength is 7-105 megapascals (1000-15,000 psi), (viii) elongation at break is 500% or less, urethane, carbonate, amide, ester, ether, acrylate, methacrylate, acrylic acid, methacryl A surface morphology comprising at least one moiety selected from the group consisting of acids, sulfones, acrylamides, halides and hydroxides, and also expressed by thermoforming methods, which have at least one dimension greater than 0.01 mm and To facilitate the flow of semiconductor devices or Polishing pad comprising a hydrophilic material having a polishing surface in which a plurality of semiconductor device precursors facilitate chemical mechanical polishing). The polishing pad of claim 1, wherein the hydrophilic material further comprises a plurality of hard domains and a plurality of soft domains having an average size of less than 100 μ. 3. The polishing of claim 2 wherein said hard domains and soft domains are produced by phase separation when said hydrophilic material is produced and said hydrophilic material comprises a polymer having a plurality of hard segments and a plurality of soft segments. Pad. The polishing pad of claim 1, wherein said hydrophilic material consists essentially of two-phase polyurethane. The polishing pad of claim 1, wherein the hydrophilic material further comprises wear particles. The method of claim 1 wherein the hydrophilic material is essentially polymethyl methacrylate, polyvinyl chloride, polysulfone, nylon, polycarbonate, polyurethane, ethylene copolymer, polyether imide, polyethylene imine, polyketone And a material selected from the group consisting of combinations thereof. The polishing pad according to claim 1, which is molded as a sheet by an extrusion method. 8. The polishing pad of claim 7, wherein the sheet has a starting end and a ending end, wherein both ends are joined to form a continuous belt. 8. The polishing pad of claim 7, wherein the sheet is cut to form a pad of any size or shape. The polishing pad of claim 1 produced by compression molding. 2. The polishing pad of claim 1 wherein said thermoforming method is an embossing method. 12. The polishing pad of claim 11 wherein said surface is softened by an increase in temperature such that the surface is embossed due to the pressure applied by the embossing roller cooled to a temperature that maintains the embossing pattern on the abrasive material. The die-forming die of claim 1, wherein the thermoforming die is used to express a surface morphology comprising small dimension shapes having a height, width, or depth of 25 μ or less, wherein the thermoforming die has a low affinity portion and a high affinity portion for pad material. A polishing pad having a portion to selectively release portions of the pad to express a small dimensional surface shape in whole or in part. The method of claim 1, wherein the thermoforming die is used to express a surface morphology comprising small dimension shapes having a height, width, or depth of 25 μ or less, wherein the thermoforming die is capable of releasing material release when surrounded by pad material. An abrasive pad with an obtrusive shaped protrusion to selectively release portions of the pad to form small or large surface shapes over or in part. The method of claim 1, wherein the thermoforming die is used to express a surface morphology comprising small dimension shapes having a height, width, or depth of 25 μ or less, wherein the thermoforming die is made of a material having a higher affinity for pad material. And wherein the protrusions are provided to selectively release portions of the pad to express a small dimension of the surface shape in whole or in part. (a) (i) density is greater than 0.5 g / cm 3, (ii) critical surface tension is at least 34 mN / m, (iii) tensile modulus is from 0.02 to 5 gigapascals, and (iv) tensile at 30 ° C. The elastic modulus to tensile modulus at 60 ° C. is 1.0 to 2.5, (v) hardness is 25 to 80 Shore D, (vi) yield stress is about 2.1 to 41.4 megapascals (300 to 6000 psi), (vii) tensile strength of 7 to 105 megapascals (1000 to 15,000 psi), (viii) elongation at break of 500% or less, urethane, carbonate, amide, ester, ether, acrylate, methacrylate, acrylic acid A surface morphology comprising a hydrophilic material comprising at least one residue selected from the group consisting of methacrylic acid, sulfone, acrylamide, halides and hydroxides, and also expressed by thermoforming methods to facilitate polishing of the workpiece. For polishing comprising a polishing surface having a Providing a pad, (b) bringing the workpiece into close contact with the pad, (c) introducing a polishing fluid between the workpiece and the pad, and (d) causing a relative motion between the pad and the workpiece, the method of chemical mechanical polishing of a semiconductor device or a semiconductor device precursor. (a) thermoforming a small dimensional surface morphology on a hydrophilic polishing surface that is inherently incapable of absorbing or transporting polishing fluids; (b) A method of polishing a substrate comprising polishing the workpiece with the polishing surface by making the pressure between the polishing surface and the workpiece greater than 0.1 kg / m 2. 18. The method of claim 17, further comprising periodically regenerating the small dimensional surface form by moving a wear medium relative to the polishing surface during polishing of the workpiece.