KR20100082765A - Polishing pad and method of use - Google Patents

Abstract

A polishing pad has one or more polishing elements made from a hydrogel material having an intrinsic ability to absorb water. The hydrogel material may or may not have micropores, but has a water absorption capability of 4%-60% by weight, a wet tensile strength greater than 1000 psi, a flexural modulus greater than 2000 psi, and a wet Shore D hardness between 25-80, inclusive. The hydrogel material may be made from one or a combination of the following moeties: urethane, alkylene oxides, esters, ethers, acrylic acids, acrylamides, amides, imides, vinylalcohols, vinylacetates, acrylates, methacrylates, sulfones, urethanes, vinylchlorides, etheretherketones, and/or carbonates.

Description

Polishing Pads and How to Use {POLISHING PAD AND METHOD OF USE}

This invention claims priority to US patent application Ser. No. 11 / 846,304, filed August 28, 2007, which is hereby incorporated by reference in its entirety.

The present invention relates to the field of chemical mechanical planarization (CMP), and more particularly to CMP pads with reduced defects.

In modern integrated circuit (IC) fabrication, a layer of material is applied to embedded structures formed on a semiconductor wafer. Chemical mechanical planarization (CMP) is a polishing process used to remove these layers and polish the surface of the wafer. CMP can be implemented for both oxides and metals and generally involves the use of chemical slurry applied in conjunction with a polishing pad that moves with respect to the wafer (e.g., the pad is primarily rotating with respect to the wafer). do. The resulting smooth and flat surface is necessary to maintain the photolithographic depth of focus for subsequent wafer processing steps and to ensure that metal interconnects are not deformed over the contour step. need. In damascene processing, CMP requires the removal of metals such as tungsten or copper from the top surface of the dielectric to form interconnect structures.

Polishing pads are typically made of urethane from the form of castings filled with microporous elements or from non-woven felt coated with polyurethane. In use, the pad is rotated in contact with the rotating wafer to perform polishing. Typically, two kinds of polishing pads are used, a hard polishing pad and a soft polishing pad. Hard pads are typically used in applications requiring planarization of micro-scale features on the wafer surface, while soft pads are used when planarization is not required. For example, soft pads can be used in a multi-step polishing process in which a wafer is first polished to a hard pad to planarize the surface and then to a soft pad to form a smooth finish. Hard pads typically form surface defects, such as micro-scratches, and are not effective in carrying out the removal of slurry particles. Thus, soft pads are used to polish the surface of the wafer to not only smooth fine scratches but also to enable more efficient removal of particle defects.

In an embodiment of the present invention, one or more polishing members (eg, a single polishing surface or multiple polishing surfaces or members) made of a hydrogel material having an intrinsic ability to absorb water. It provides a polishing pad having a). The hydrogel materials collectively have a water absorption capacity of 4% to 60% by weight, wet tensile strength of greater than 1000 psi, flexural modulus of greater than 2000 psi, and wet between 25-80. It may have a Shore D hardness and may not have micro-porosity. In another embodiment, the hydrogel material collectively has a water absorption capacity of 4% to 60% by weight, microporosity of 1% to 20% by volume, micropores of 20-100 microns, wet tensile strength of greater than 1000 psi, Flexural modulus greater than 2000 psi, and wet Shore D hardness between 25-80. In either case, the hydrogel material is prepared from one of the following moieties or combinations thereof: urethanes, alkylene oxides, esters, ethers, acrylic acid acids, acrylamides, amides, imides, vinylalcohols, vinyl acetates, acrylates, methacrylates, sulfones, Urethanes, vinylchlorides, etheretherketones, and / or carbonates.

According to an embodiment of the present invention, a polishing pad made of a material having an inherent ability to absorb water is provided in the presence of a polishing composition disposed between an upper layer overlying a semiconductor wafer and the polishing pad. Polishing may be performed by rotating the wafer and the polishing pad relative to each other, located near the semiconductor wafer and performing removal of some or all of the top layer (eg, copper) overlying the wafer. Prior to initiating the polishing operation, the polishing pad may be wetted in a solution (eg, water, polishing composition, electrolyte solution such as copper sulfate, etc.). If an electrolyte solution is used, the polishing pad can be connected to an electrical source during the polishing operation.

In some cases, an anodic current is applied to the polishing pad (or its polishing surface) while a cathodic bias is provided by external means, and the semiconductor wafer is pressed against the polishing surface. In other cases, a cathode current is applied to the polishing pad or surface, with a bipolar bias being provided by external means, and the semiconductor wafer is pressed against the polishing surface.

Polishing pads having a polishing surface composed of a material having an inherent ability to absorb water may be subjected to one of injection molding, extrusion, reaction injection molding or sintering. Can be prepared. Surface features may be formed on the polishing surface of the polishing pad during the manufacturing step.

The present invention will be described with reference to the accompanying drawings, but is not limited thereto.
1A illustrates a conventional polishing pad of a conventional type, which may include a polishing surface comprised of a hydrogel material having an inherent ability to absorb water in accordance with one embodiment of the present invention.
1B illustrates a polishing pad having a plurality of polishing members, wherein one or more of the polishing members are made of a hydrogel material having inherent ability to absorb water in accordance with another embodiment of the present invention. .
2 illustrates a method of using a polishing pad formed with a polishing surface made of a hydrogel material having an inherent ability to absorb water in accordance with one embodiment of the present invention.

Described herein are polishing pads with reduced defects, methods of using such pads, and materials useful for making CMP polishing pads with reduced defects. As previously described, CMP involves the process of removing the film from the surface of the wafer by pressing the polishing pad against the wafer and rotating these members relative to each other in the presence of polishing compositions (eg slurry). During the polishing process, a slurry layer is formed between the wafer and the pad to form a hydrodynamic boundary layer. It is important to maintain a uniform fluid layer between the pad and the wafer during the polishing process. If the boundary layer is minimized or completely removed, the pads will come into direct contact with the wafer resulting in the interaction of the two bodies, causing larger defects. In contrast, an interface with significant lubrication will not only enable more uniform polishing but also minimize defects. This is particularly important in the case of copper CMP where the film to be polished is very soft and can be easily scratched by direct wafer-pad contact.

Conventional polishing pads are made of a polymer, typically urethane, having a structure that provides a means for distributing the slurry under the wafer during the polishing process. Such structures include voids or micro-pores, which prevent the introduction of bubbles formed during the casting process or by adding hollow micro members as disclosed in US Pat. No. 5,578,362. Included throughout. US Pat. No. 6,896,593 discloses the use of supercritical CO ₂ to form pores during the molding process.

Once the pad is formed, the top surface can be further processed by mechanical or laser means to add grooves. For example, US Pat. No. 5,489,233 discloses a surface having a solid plastic sheet without the inherent ability to absorb or transport the slurry, and a flow channel for transporting the slurry across the wafer and enabling polishing. Discuss the use of textures or patterns. Surface tissue is mechanically formed on the pad through machining.

During the polishing process, the pads can be conditioned to form microstructures using fine, diamond coated discs, which form microgroove channels to further enhance slurry distribution under the wafer. . During the wafer polishing process, the pads also undergo plastic deformation, which reduces the slurry distribution, resulting in poor material removal and removal uniformity. The conditioning process removes plastic strained layers and restores polishing performance.

In conventional pads, the material itself does not have micropores, grooves and microgrooves that actively participate in slurry distribution and the inherent ability to absorb significant water or polishing solutions. Slurry distribution capacity is important for defects as well as for material removal uniformity. If the slurry distribution between the pad and the wafer is poor, there is a possibility that the slurry under the wafer will cause direct pad-wafer contact in an insufficient slurry-poor region resulting in a defect.

In one embodiment, the present invention provides a polymer polishing pad having inherent ability to absorb a polishing solution or water to provide a very low defect polishing surface. Such polishing pads can be prepared from a hydrogel material having the ability to absorb polishing solutions or water in the range of 5-60% by weight. The water adsorption capacity is controlled during the material synthesis process. Pad materials with an inherent ability to absorb water or polishing solutions will provide a lubricious surface during the polishing process and will minimize the possibility of direct pad-wafer contact, further eliminating or minimizing defects, particularly scratch defects. . Methods for preparing hydrophilic urethane formulations are described in US Pat. No. 5,859,166; 5,763,682; 5,424,338; 5,334,691; 5,120,816; 5,118,779; And 4,008,189, each of which is incorporated herein by reference.

Pad material properties play an important role in defects caused on the wafer surface. Hard pads are typically associated with larger defects, substantially scratch defects, while soft pads are typically associated with fewer defects. One important aspect of a soft pad is that the pad surface can be locally conformed to prevent "hard contact" between the wafer and the pad surface. Another aspect of local surface conformality is the pad-water interface's ability to maintain an aqueous interface. The aqueous interface provides the necessary lubricity between the water and the pad to eliminate or minimize the possibility of causing scratches. Water absorbent polymer materials provide a very stable polishing interface to minimize the possibility of defects.

US Pat. No. 5,763,682 describes that many conventional isocyanate-based foams are non-hydrophilic (ie, relatively hydrophobic). Conventional urethane-based foams exhibit aversion to aqueous fluids, and thus such foams are unable to absorb or collect significant amounts of aqueous fluids. Thus, conventional polyurethane foam can be considered inadequate to provide a polishing interface with great lubricity.

Since urethanes are made by the reaction of isocyanates with polyols, the hydrophilic aspect of the final polymer chain can be controlled by the choice of polyols. U.S. Patent US 5,859,166; 5,763,682; 5,424,338; 5,334,691; 5,120,816; 5,118,779; And 4,008,189 disclose methods of improving the hydrophilicity of urethane components. Hydrophilic polyurethanes can be prepared by adding ethylene oxide units and alkylene oxide units to the polyol molecule.

The total hydroxyl content of the polyols is also an important factor in the hydrophilicity of the polyurethanes. In the technical field of the present invention, it is known that the polyhydric alcohol-alkylene oxide adduct reactant used must contain a certain proportion of ethylene oxide in the molecule in order to obtain sufficient hydrophilicity in the foam. . See US Pat. No. 3,457,203, which is incorporated herein by reference. Early hydrophilic polyurethane foams were prepared from this adduct, a product of a mixture of polyhydric alcohols and mixtures of higher alkylene oxides such as ethylene oxide and propylene oxide. However, when wet, these components showed deterioration in mechanical properties.

US Pat. No. 4,008,189 discloses compositions that can minimize such degradation in physical properties using a polyol mixture consisting of three oxyalkylated polyether polyol reactants. The first of these is a trihydroxy alcohol nucleus, a polyoxyethylene chain segment attached to the nucleus through one end thereof, and a polyoxyethylene chain segment through one end thereof. It features polyoxypropylene chain segments to be attached. Such polyols can be prepared by methods well known in the art, in which the triol initiator condenses sequentially in the presence of an alkaline catalyst such as KOH, first with ethylene oxide and then with propylene oxide. have.

Such compositions are expected to be particularly suitable for polishing applications as they allow for a high lubricity polishing interface. Moreover, although thermoplastic formulations can be used, cross-linked polymer networks are expected to provide the best properties. Lubrizol Corp's Tecophilic ^® Extrusion Molding formulation is one of this class of materials. Such materials are adjusted to absorb between 20% and 100% by weight of water. The absorbency of water is associated with the loss of mechanical properties, so the higher the weight percentage of water absorbed, the greater the loss of mechanical strength. Thus, although water absorption as high as 100% by weight can be used, it would be advantageous to use an agent that absorbs approximately 5-20% by weight of water.

1A is a cross-sectional view of a conventional polishing pad 100, such as an IC 1000 pad provided by Rohm and Haas. The polishing pad 100 includes microelements 102 embedded in the polymer matrix 104, which may be polyurethane. The surface of the pad includes grooves 106 for the transport of the slurry during the polishing process. Such commercially useful polishing pads may include a number of surface modifications to affect slurry distribution across the surface of the pad.

1B shows SemiQuest, Inc. Shows a cross-sectional view of the polishing pad 108, which is prepared by US Patent Application US 11 / 697,622, filed Apr. 6, 2007, which is assigned to the applicant of the present invention and incorporated herein by reference. The pad 108 consists of a polishing member 110, which is supported on a compressible under-foam 112 disposed below the guide plate 114. The polishing action is provided by a polishing member made of a rigid polymer material, while slurry distribution is performed by open spaces between the polishing members. The open space is filled with open cell foam.

In embodiments of the present invention, the polishing surfaces 104 and / or 110 of all or one of the pads described above may be made of hydrophilic polymer material. For example, such a polishing surface may be formed of a hydrogel material capable of absorbing water or polishing solution in the range of 4-60% by weight. Such hydrogel material may be one or a combination of the following moieties: urethane, alkylene oxides, esters, ethers, acrylic acids , Acrylamides, amides, imides, vinyl alcohols, vinyl acetate, vinyl acetates, acrylates, methacrylates, sulfones, urethanes (urethanes), vinyl chlorides, etheretherketones, and / or carbonates. The imide is a functional group consisting of a primary amine or ammonia, bound to one dicarboxylic acid or two carboxylic acid groups, typically ammonia or primary amine, and Prepared directly from the acid (s) or acid anhydrides thereof.

In certain embodiments of the invention, the polishing surface of the pad does not have micro-porosity, and collectively wet tensile strength greater than 1000 psi, flexural modulus greater than 2000 psi ), And / or hydrogels having wet Shore D hardness between 25-80. In other cases, the hydrogel material may collectively comprise about 1% by volume to 20% by volume of micropores, between about 20-100 microns of micropores, wet tensile strength greater than 1000 psi, flexural modulus greater than 2000 psi, and It can have a wet Shore D hardness between 25-80.

During a polishing operation, a polishing pad made of a hydrogel material according to the present invention is a semiconductor wafer (eg, a wafer having one or more thin films, oxides and / or metal layers disposed thereon) in the presence of a polishing compound. The two surfaces are rotated relative to each other to effect the removal of some or all of the top layer disposed on the surface of the wafer substrate. 2 illustrates this arrangement. The polishing pad 200 is attached to a turntable 202 and placed in proximity to the wafer 204 on the platen 206. Slurry or other polishing compound 208 is introduced between the polishing pad and the wafer and the pad and / or wafer rotate relative to each other.

In some cases, the polishing pad may be wetted with water or polishing solution prior to use in the polishing operation. For example, the pad may be wetted for a period of time (eg, 10 minutes or more) to form a stable polishing surface prior to processing the wafer.

Moreover, the polishing pad constructed in accordance with the present invention can be soaked in the electrolyte solution to form the conductive matrix and the surface. One example of such an electrolyte solution is copper sulfate. Such pads may be attached to an external electrical source during polishing operations. Such a connection may be anodic, and a bipolar or cathodic bias may be applied by external means. In this way, a polishing pad saturated with an electrolyte solution (such as copper sulphate), subjected to an anodic current while a negative bias is provided by external means, fills the structure formed into the underlying film to affect removal of the conductive layer. An upper conductive layer (such as copper) may be pressed against the deposited semiconductor wafer. Alternatively, a polishing pad constructed in accordance with the present invention and saturated with an electrolyte solution (such as copper sulfate) may be subjected to a bipolar current while a bipolar bias is applied by external means. The pad may be pressed against the semiconductor wafer on which the top conductive layer (such as copper) is deposited to fill the structure formed into the underlying film to affect the deposition of the conductive layer.

Polishing pads composed of hydrogel materials in accordance with the present invention can be prepared using injection molding, extrusion, reaction injection molding or sintering. Surface features may be formed on such pads during the manufacturing process. Such features can assist in slurry distribution during polishing operations.

As such, polishing pads having reduced defects, methods of using and manufacturing such pads, and materials useful for making such pads have been described. Although described with reference to certain illustrative embodiments, the present invention should not be limited thereby, and should only be determined in connection with the following claims.

Claims (27)

As a polishing pad,
One or more polishing members,
The polishing member is made of a hydrogel polymer that has a unique ability to absorb water and does not have fine pores,
The hydrogel material collectively has a water absorption capacity of 4% to 60% by weight, wet tensile strength greater than 1000 psi, flexural modulus greater than 2000 psi, and wet Shore D hardness between 25-80,
Polishing pads.
The method of claim 1,
The hydrogel material has the following moieties:
Urethanes, alkylene oxides, esters, ethers, acrylic acids, acrylamides, amides, imides, vinyl alcohols ), Vinyl acetates, acrylates, methacrylates, sulfones, urethanes, vinyl chlorides, etheretherketones, and / or carbonates carbonates)
Made of one or a combination thereof,
Polishing pads.
As a wafer polishing method,
Placing a polishing pad made of a material having an inherent ability to absorb water, in the presence of a polishing composition disposed between the polishing pad and an upper layer overlying the semiconductor wafer, and
Rotating the wafer and the polishing pad relative to each other to effect removal of some or all of the top layer overlying the wafer,
Wafer Polishing Method.
The method of claim 3,
Further comprising soaking the polishing pad in solution prior to initiating a polishing operation,
Wafer Polishing Method.
The method of claim 4, wherein
Wherein the solution comprises water,
Wafer Polishing Method.
The method of claim 4, wherein
Wherein the solution comprises a polishing composition,
Wafer Polishing Method.
The method of claim 4, wherein
The soaking step lasts more than 10 minutes,
Wafer Polishing Method.
The method of claim 4, wherein
The solution is an electrolyte solution,
Wafer Polishing Method.
The method of claim 8,
The electrolyte solution is copper sulfate,
Wafer Polishing Method.
10. The method of claim 9,
During the polishing operation, the polishing pad is connected to an electrical source,
Wafer Polishing Method.
The method of claim 10,
The electrical connection to the pad is anodic,
Wafer Polishing Method.
The method of claim 10,
The electrical connection to the pad is cathodic,
Wafer Polishing Method.
As a polishing pad,
One or more polishing members,
The polishing member is made of a hydrogel material,
The hydrogel material collectively has a water absorption capacity of 4% to 60% by weight, microporosity of 1% by volume to 20% by volume, micropores of 20-100 microns, wet tensile strength of greater than 1000 psi, greater than 2000 psi Having flexural modulus, and wet Shore D hardness between 25-80,
Polishing pads.
The method of claim 13,
The hydrogel material has the following moieties:
Urethanes, alkylene oxides, esters, ethers, acrylic acids, acrylamides, amides, imides, vinyl alcohols ), Vinyl acetates, acrylates, methacrylates, sulfones, urethanes, vinyl chlorides, etheretherketones, and / or carbonates carbonates)
Made of one or a combination thereof,
Polishing pads.
As a wafer polishing method,
Soaking a polishing pad in an electrolyte solution having a polishing surface made of a material having an inherent ability to absorb water,
Positioning the polishing surface of the polishing pad near the semiconductor wafer in the presence of a polishing composition disposed between the polishing pad and an upper layer overlying the semiconductor wafer, and
Rotating the wafer and the polishing pad relative to each other to effect removal of some or all of the top layer overlying the wafer,
Wafer Polishing Method.
16. The method of claim 15,
The electrolyte solution is copper sulfate,
Wafer Polishing Method.
16. The method of claim 15,
Wherein the polishing surface is attached to an electrical source during the polishing operation,
Wafer Polishing Method.
The method of claim 17,
Wherein the electrical connection to the polishing surface is anodic
Wafer Polishing Method.
The method of claim 17,
The electrical connection to the polishing surface is cathodic
Wafer Polishing Method.
16. The method of claim 15,
Applying a bipolar current to the polishing surface while providing a negative bias by external means, and pressing the semiconductor wafer against the polishing surface,
Wafer Polishing Method.
The method of claim 20,
The electrolyte solution is copper sulfate,
Wafer Polishing Method.
The method of claim 20,
The top layer is copper,
Wafer Polishing Method.
16. The method of claim 15,
Applying a bipolar current to the polishing surface while being provided by a bipolar bias by external means, and pressing the semiconductor wafer against the polishing surface,
Wafer Polishing Method.
The method of claim 23, wherein
The electrolyte solution is copper sulfate,
Wafer Polishing Method.
The method of claim 23, wherein
The top layer is copper,
Wafer Polishing Method.
Manufacturing a polishing pad having a polishing surface made of a material having an inherent ability to absorb water using one of injection molding, extrusion, reaction injection molding, or sintering,
Way. The method of claim 26,
Further comprising forming a surface feature on the polishing surface of the polishing pad during the manufacturing step,
Way.

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