Preparation Method of Vertically Micro-Porous Polyurethane Polishing Pad

Abstract

The present invention relates to a preparation method of a vertical microporous polyurethane polishing pad, which comprises the following steps: coating a polyurethane casting solution on the surface of a substrate, and then immersing it in a coagulating solution to cause phase inversion of the polyurethane casting solution on the surface of the substrate to solidify into a film. While forming the film, regular vertical micropores are formed in the direction perpendicular to the film surface. Subsequently, washing with water and drying are carried out to obtain the vertical microporous polyurethane polishing pad. The polyurethane casting solution comprises the following materials in parts by weight: 100 parts of polyurethane resin, 2-5 parts of surfactant, and 30-80 parts of solvent. The polyurethane resin comprises the following materials synthesized by 100% by weight: 20-30% of polyester polyol, 5-9% of MDI, 2-6% of polyethylene oxide, 0.02-0.03% of end-capping agent, and the balance is solvent. The polyurethane polishing pad of the present invention has a relatively high porosity, hardness, and mechanical properties. At the same time, the vertical micropores inside the polyurethane are evenly distributed and regular in shape, and its surface has a relatively low surface roughness.

Description

Technical Field

[0001] The present invention relates to the technical field of polishing pads for chemical mechanical polishing, and particularly to a preparation method of a vertical microporous polyurethane polishing pad. Background Art

[0002] Chemical mechanical polishing (CMP) is used to achieve planarization by combining chemical reactions and mechanical abrasion. The polishing pad is one of the important consumables that determine the polishing rate and planarization ability in CMP. It has a fiber board structure with many follicular pores on its surface. During the CMP process, it has functions such as storing and transporting the polishing liquid, removing processing residues, transmitting mechanical loads, and maintaining the polishing environment. The polishing pad used for CMP must have good chemical stability (corrosion resistance), hydrophilicity, and mechanical properties. Polishing pads can generally be divided into two types: hard and soft. Hard polishing pads can better ensure the flatness of the workpiece surface; soft polishing pads can obtain a polished surface with a very small machining affected layer and surface roughness value. According to the material and structure, they can be divided into polyurethane polishing pads, non-woven fabric polishing pads, non-woven fabric polishing pads with a villous structure, and two-layer composite polishing pads.

[0003] The main component of the polyurethane polishing pad is foamed and cured polyurethane. Its surface consists of many closed unit structures of hollow sphere micropores. These micropores play roles such as collecting machining removal products, transporting the polishing liquid, and ensuring chemical corrosion during CMP, which helps to improve the polishing efficiency and polishing uniformity; the larger the pore size, the stronger its transportation ability, but too large a pore size will affect the rigidity and density of the polishing pad. The most widely used such polishing pad is the IC1000 type polishing pad of the American company Rodel, and this type of polishing pad is mostly used for rough polishing of silicon wafers. The raw material of the non-woven fabric polishing pad is polymer cotton-like fibers. The most widely used such polishing pad is SubalⅥ of the American company Rodel, and this type of polishing pad is mostly used for fine polishing of silicon wafers. The non-woven fabric polishing pad with a villous structure has a non-woven fabric as the substrate, a polymer layer in the middle, and a porous villous structure on the surface layer. The most widely used such polishing pad is the Politex polishing pad of the American company Rodel, and this type of polishing pad is mostly used for fine polishing of silicon wafers. The two-layer composite polishing pad takes into account the requirements of flatness and uniformity, and adopts an upper-hard and lower-soft two-layer composite structure, such as the IC1000 / SubalⅥ composite structure polishing pad (there is an adhesive layer between the two layers). The upper layer uses the harder IC1000 to withstand the mechanical and chemical effects during CMP, improve the material removal rate to obtain a higher flatness, and the lower layer uses the softer SubalⅥ to improve the compressibility of the polishing process, which helps to improve the contact uniformity between the polishing pad surface and the workpiece and ensure uniform material removal.

[0004] At present, the polyurethane polishing pads used for rough polishing of silicon wafers still adopt imported materials. Domestic polyurethane polishing pads have defects such as irregular polyurethane foam structure, high surface roughness, low hardness, and low strength, making it difficult for them to gain a foothold in the integrated circuit manufacturing. Summary of the Invention

[0005] In order to solve the defects of the existing polishing pads, such as irregular polyurethane foam structure, high surface roughness, low hardness, and low strength, a vertical microporous polyurethane polishing pad and its preparation method are provided. The polyurethane polishing pad of the present invention has a relatively high porosity, hardness, and mechanical properties. At the same time, the vertical micropores inside the polyurethane are evenly distributed and regular in shape, and its surface has a relatively low surface roughness.

[0006] In order to achieve the above objectives, the present invention is realized through the following technical solutions:

[0007] The preparation method of the vertical microporous polyurethane polishing pad includes the following steps:

[0008] Coat the polyurethane casting solution on the surface of the substrate, and then immerse it in the coagulating solution to cause phase inversion of the polyurethane casting solution on the surface of the substrate to solidify into a film. At the same time of film formation, regular vertical micropores are formed inside the film perpendicular to the film surface. Subsequently, wash with water and dry to obtain the vertical microporous polyurethane polishing pad;

[0009] The polyurethane casting solution includes the following materials in parts by weight: 100 parts of polyurethane resin, 2 - 5 parts of surfactant, and 30 - 80 parts of solvent;

[0010] Among them, the polyurethane resin is synthesized from the following materials in 100% by weight: 20 - 30% of polyester polyol, 5 - 9% of MDI, 2 - 6% of polyethylene oxide, 0.02 - 0.03% of end-capping agent, and the balance is solvent.

[0011] Further, the polyester polyol is condensed from bisphenol A-type compound and adipic acid in a molar ratio of 1:(1 - 2). Among them, the bisphenol A-type compound is one or more of propylene glycol tetra-isopropanol ether, bisphenol A propoxy compound, and bisphenol A ethoxy compound, and their structures are as follows:

[0012]

[0013] Still further, the conditions for the synthesis process of the polyester polyol are: add 0.08% of polymerization inhibitor (such as methylhydroquinone) and 0.05% of organotin catalyst based on the total mass of the added materials. Under nitrogen protection, first react at 150 - 170 °C for 1 - 2 h to drain water, and then raise the temperature to 200 - 230 °C to continue the reaction until the acid value of the reaction system reaches 5 - 15 mgKOH / g and the hydroxyl value reaches 40 - 60 mgKOH / g.

[0014] Further, the synthesis conditions of the polyurethane resin are as follows: graft the polyester polyol with polyethylene oxide and a part of the solvent at 180 - 200 °C for 2 - 5 h, then cool down to 75 - 80 °C, add MDI and react until the viscosity of the system reaches 150,000 - 250,000 cps, and then cool down to 60 - 70 °C and add a capping agent for capping reaction for 0.5 - 3 h to obtain the polyurethane resin.

[0015] Further, the capping agent is methanol; the solvent is DMF.

[0016] Further, the surfactant is sodium dioctyl sulfosuccinate.

[0017] Further, the coagulating liquid is a mixture of ethanol and water, and the volume percentage of ethanol in the coagulating liquid is at least 5%.

[0018] Beneficial technical effects: In the present invention, by designing the polyester polyol to have both a rigid chain and a flexible chain, and controlling a certain amount of carboxyl groups and hydroxyl groups in the polyester polyol, the remaining carboxyl groups in the polyester polyol will continue to graft with polyethylene oxide subsequently, and the remaining hydroxyl groups in the polyester polyol will condense with MDI to obtain a polyurethane resin with an aromatic polyurethane - long - chain polyether structure. The molecular structure is reasonably designed, having both a certain amount of rigid molecular chains and a certain amount of flexible molecular chains, so that the polyurethane resin has good strength and toughness; in addition, the grafted polyethylene oxide plays a chain - extending role to increase the flexibility of the molecular chain on the one hand, and on the other hand, enables the polyurethane to maintain a regular vertical microporous structure during the film - forming stage of solidification, reducing the problem of the decline in mechanical properties caused by the generation of irregular sponge - like pores and intramolecular crystallites. Subsequently, an anionic surfactant is added when preparing the polyurethane casting solution, which enables fine - tuning of the length, pore shape, etc. of the formed vertical micropores during the film - forming stage of polyurethane solidification. At the same time, the fine - tuning effect of the vertical micropores also includes the role of ethanol added to the coagulating liquid. When a mixed solution of ethanol and water is used as the coagulating liquid for polyurethane film - forming during solidification, ethanol can control the problem of excessive pore diameter of the vertical micropores. The polyurethane polishing pad of the present invention has a high porosity, hardness, and mechanical properties. At the same time, the vertical micropores inside the polyurethane are evenly distributed and regular in shape, and its surface has a low surface roughness. Description of the Drawings

[0019] Figure 1 It is a microscope image of the vertical - micropore polyurethane polishing pad of Example 1. In the figure, the thickness of the polyurethane layer is 0.7 mm, the pore depth is 0.035 - 0.68 mm, and the maximum pore diameter does not exceed 0.275 mm. Detailed Embodiments

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0021] Unless otherwise specifically stated, the numerical values set forth in these embodiments do not limit the scope of the present invention. Well-known techniques and methods in the relevant art may not be discussed in detail, but in appropriate cases, such techniques and methods should be regarded as part of the specification. In all examples shown and discussed herein, any specific values should be construed as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments may have different values.

[0022] The experimental methods without specific conditions in the following embodiments are generally determined according to national standards; if there are no corresponding national standards, they are carried out according to general international standards or the standard requirements proposed by relevant enterprises. Unless otherwise specified, all parts are by weight, and all percentages are by weight percentage.

[0023] Example 1

[0024] (1) Preparation of polyester polyol: Bisphenol A ethoxy compound and adipic acid with a molar ratio of 1.1:1 are added to a reaction kettle, and then 0.08% of methylhydroquinone polymerization inhibitor and 0.05% of organotin catalyst based on the total mass of the materials are added. Under nitrogen protection, first carry out atmospheric esterification reaction at 160 °C for 1.5 h while draining water, then evacuate the vacuum, and raise the temperature to 220 °C for polycondensation until the acid value of the reaction system reaches 8.5 mgKOH / g and the hydroxyl group reaches 56 mgKOH / g.

[0025] (2) Preparation of polyurethane resin: It includes 30 wt% of the above polyester polyol, 7 wt% of MDI, 5 wt% of polyethylene oxide, 0.02 wt% of methanol capping agent, and the balance is DMF;

[0026] Polyethylene oxide and half of the weight of DMF are added to the polyester polyol obtained above, and grafting reaction is carried out at 200 °C for 4 h; then the temperature is lowered to 80 °C, MDI and the remaining DMF are added and reacted until the viscosity of the system reaches 150000 cps, then the temperature is lowered to 70 °C, and a methanol capping agent is added for capping reaction for 1 h, and stirring is continued at this temperature for 1 h to obtain the polyurethane resin.

[0027] (3) Preparation of polyurethane casting solution: 100 parts of the polyurethane resin synthesized in step (2), 3 parts of sodium diisooctyl sulfosuccinate, and 60 parts of DMF are stirred and mixed evenly, and then degassed for standby.

[0028] (4) Preparation method of vertical microporous polyurethane polishing pad: Prepare a coagulating liquid, which is a mixture of ethanol and water, and the volume percentage content of ethanol is 5%.

[0029] The polyurethane casting solution in the above step (3) is coated on the surface of the fabric, and the coating thickness is at least 0.5 mm. Then, the whole is immersed in the coagulating liquid to cause phase inversion of the polyurethane casting solution on the fabric surface and solidify into a film. At the same time of film formation, regular vertical micropores are formed in the direction perpendicular to the film surface. Subsequently, it is washed with water and dried to obtain the vertical microporous polyurethane polishing pad.

[0030] Example 2

[0031] (1) Preparation of polyester polyol: Add bisphenol A propoxy compound and adipic acid with a molar ratio of 1.2:1 into a reaction kettle, then add 0.08% of methylhydroquinone polymerization inhibitor and 0.05% of organotin catalyst based on the total mass of the materials. Under nitrogen protection, first carry out an atmospheric esterification reaction at 160 °C for 1.5 h while draining water, then evacuate, and raise the temperature to 220 °C for polycondensation until the acid value of the reaction system reaches 8.5 mgKOH / g and the hydroxyl value reaches 56 mgKOH / g.

[0032] (2) Preparation of polyurethane resin: including 25 wt% of the above polyester polyol, 8 wt% of MDI, 6 wt% of polyethylene oxide, 0.02 wt% of methanol capping agent, and the balance is DMF;

[0033] Add polyethylene oxide and half of the weight of DMF to the polyester polyol obtained above, and carry out a grafting reaction at 200 °C for 4 h; then cool down to 80 °C, add MDI and the remaining DMF, and react until the viscosity of the system reaches 150000 cps. Then cool down to 70 °C and add the methanol capping agent for a capping reaction for 1 h, and continue to stir at this temperature for 1 h to obtain the polyurethane resin.

[0034] (3) Preparation of polyurethane casting solution: 100 parts of the polyurethane resin synthesized in step (2), 2 parts of sodium diisooctyl sulfosuccinate, and 60 parts of DMF are stirred and mixed evenly, and then degassed for standby.

[0035] (4) Preparation method of vertical microporous polyurethane polishing pad: Prepare a coagulating liquid, which is a mixture of ethanol and water, and the volume percentage content of ethanol is 5%.

[0036] Coat the polyurethane casting solution obtained in step (3) above on the fabric surface with a coating thickness of at least 0.5 mm, and then immerse the whole in the coagulation bath to cause phase inversion of the polyurethane casting solution on the fabric surface and solidify it into a film. Regularly arranged vertical micropores are formed inside perpendicular to the film surface during film formation. Subsequently, wash with water and dry to obtain a vertical micropore polyurethane polishing pad.

[0037] Example 3

[0038] (1) Preparation of polyester polyol: Add bisphenol A tetraisopropyl ether and adipic acid with a molar ratio of 1:1 to the reaction kettle, then add 0.08% of methylhydroquinone polymerization inhibitor and 0.05% of organotin catalyst based on the total mass of the materials. Under nitrogen protection, first carry out atmospheric esterification reaction at 160 °C for 2 h while draining water, then evacuate and raise the temperature to 220 °C for polycondensation until the acid value of the reaction system reaches 8.5 mg KOH / g and the hydroxyl value reaches 56 mg KOH / g.

[0039] (2) Preparation of polyurethane resin: It includes 20 wt% of the above polyester polyol, 9 wt% of MDI, 4 wt% of polyethylene oxide, 0.03 wt% of methanol capping agent, and the balance is DMF;

[0040] Add polyethylene oxide and half of the weight of DMF to the polyester polyol obtained above, and carry out graft reaction at 200 °C for 4 h; then cool down to 80 °C, add MDI and the remaining DMF and react until the viscosity of the system reaches 150000 cps, then cool down to 70 °C and add methanol capping agent for capping reaction for 1 h, and continue to stir at this temperature for 1 h to obtain polyurethane resin.

[0041] (3) Preparation of polyurethane casting solution: Stir and mix 100 parts of the polyurethane resin synthesized in step (2), 5 parts of sodium diisooctyl sulfosuccinate and 70 parts of DMF evenly and then defoam for standby.

[0042] (4) Preparation method of vertical micropore polyurethane polishing pad: Prepare a coagulation bath, which is a mixture of ethanol and water, and the volume percentage content of ethanol is 5%;

[0043] Coat the polyurethane casting solution obtained in step (3) above on the fabric surface with a coating thickness of at least 0.5 mm, and then immerse the whole in the coagulation bath to cause phase inversion of the polyurethane casting solution on the fabric surface and solidify it into a film. Regularly arranged vertical micropores are formed inside perpendicular to the film surface during film formation. Subsequently, wash with water and dry to obtain a vertical micropore polyurethane polishing pad.

[0044] Comparative Example 1

[0045] The preparation method of the polyurethane polishing pad in this comparative example is the same as that in Example 1, except that in the synthesis of the polyurethane resin in step (2), polyethylene oxide is not added, and the polyester diol used in the synthesis is PTMG2000 (tetrahydrofuran homopolyether); in step (4), the coagulating liquid is water containing 20% by volume of DMF.

[0046] Perform performance tests on the polyurethane polishing pads of the above examples and comparative examples, including Shore hardness, porosity, surface roughness, rebound rate, and tensile strength.

[0047] Among them, for the test method of porosity, the approximate porosity can be calculated by observing the number and size of pores on the surface of a certain area of the polishing pad under a microscope.

[0048] Among them, the rebound rate (%) = (thickness after compression and rebound / original thickness) × 100. During the measurement process, apply a uniform pressure of 10 kg to the measured surface for 2 min, then remove the pressure and measure its thickness, which is the thickness after compression and rebound.

[0049] The results are shown in Table 1.

[0050] Table 1 Performance of Polyurethane Polishing Pads in Comparative Examples and Examples

[0051] IC1000 Example 1 Comparative Example 1 Example 2 Example 3 PU layer thickness mm 1.2 0.7 0.7 0.7 0.7 Surface porosity % ＜60 ＞70 ＜60 ＞70 ＞70 Tensile strength MPa 47 48 35 45 46 Rebound rate % 80 86 70 84 82 Surface roughness μm 6.2 7.0 12.3 7.2 7.5 Hardness shore D 67.8 75.5 60.4 73.9 74.6

[0052] The compressibility of the polishing pad determines the degree of fit between the polishing pad and the workpiece surface during the polishing process, and has a certain influence on the material removal rate and the degree of surface flattening. During the CMP process, the polishing pad is repeatedly compressed - rebounded - recompressed under the action of changing polishing pressure, etc., which is a dynamic process. When an external force presses on the polyurethane layer and causes it to be compressed, due to the uniform distribution of vertically ordered and regularly shaped vertical micropores in the polyurethane, it shows isotropy in the axial direction, that is, it shows elastic recovery performance after being compressed. At the same time, the pressure also acts on the molecular skeleton of the polyurethane. Since the polyurethane molecular skeleton of the present invention has approximately equal amounts of rigid chains and flexible chains, the rigid chains enable it to maintain a certain mechanical strength under repeated pressure to achieve elastic recovery, while the flexible chains enable it to have flexibility under repeated pressure to be compressed. It is observed that the sizes of the vertical micropores in the polyurethane layer of Comparative Example 1 are uneven and the arrangement is irregular, and the irregular vertical micropores do not perform the function of axial isotropy, and the flexible chains account for the vast majority in the polyurethane molecular structure, which makes its rebound rate lower after being compressed. The imported IC1000 polyurethane polishing pad has a foaming structure similar to a sponge, with regular circular pores, so the rebound rate is better. The polyurethane polishing pad of the present invention has the same effect as the imported product.

[0053] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention should cover within the protection scope of the present invention any equivalent substitution or change made according to the technical solution and inventive concept of the present invention.

Claims

1. Preparation method of vertical microporous polyurethane polishing pad, characterized in that, It includes the following steps: Coat the polyurethane casting solution on the surface of the substrate, and then immerse it in the coagulation liquid to cause phase inversion and solidification of the polyurethane casting solution on the surface of the substrate into a film. Regularly arranged vertical micropores are formed perpendicular to the film surface during film formation. Subsequently, wash with water and dry to obtain a vertical micropore polyurethane polishing pad. The polyurethane casting solution includes the following materials in parts by weight: 100 parts of polyurethane resin, 2 - 5 parts of surfactant, and 30 - 80 parts of solvent. Among them, the polyurethane resin is synthesized from the following materials in 100% by weight: 20 - 30% of polyester polyol, 5 - 9% of MDI, 2 - 6% of polyethylene oxide, 0.02 - 0.03% of end-capping agent, and the balance is solvent. The polyester polyol is condensed from bisphenol A-type compound and adipic acid in a molar ratio of 1:(1 - 2). The synthesis conditions of the polyurethane resin are as follows: Graft react the polyester polyol, polyethylene oxide, and a part of the solvent at 180 - 200 °C for 2 - 5 h, then cool down to 75 - 80 °C, add MDI and react until the viscosity of the system reaches 150000 - 250000 cps, and then cool down to 60 - 70 °C and add the end-capping agent for end-capping reaction for 0.5 - 3 h to obtain the polyurethane resin.

2. The preparation method of the vertical microporous polyurethane polishing pad according to claim 1, characterized in that, The bisphenol A-type compound is one or more of propylenediol tetra-isopropanol ether, bisphenol A propoxy compound, and bisphenol A ethoxy compound.

3. The preparation method of the vertical microporous polyurethane polishing pad according to claim 2, characterized in that, The conditions for the synthesis process of the polyester polyol are as follows: Add 0.08% of polymerization inhibitor and 0.05% of organotin catalyst based on the total mass of the added materials. Under nitrogen protection, first react at 150 - 170 °C for 1 - 2 h to drain water, and then raise the temperature to 200 - 230 °C and continue to react until the acid value of the reaction system reaches 5 - 15 mgKOH / g and the hydroxyl value reaches 40 - 60 mgKOH / g.

4. The preparation method of the vertical microporous polyurethane polishing pad according to any one of claims 1-3, characterized in that, The end-capping agent is methanol; the solvent is DMF.

5. The preparation method of the vertical microporous polyurethane polishing pad according to any one of claims 1-3, characterized in that, The surfactant is sodium diisooctyl sulfosuccinate.

6. The preparation method of the vertical microporous polyurethane polishing pad according to any one of claims 1-3, characterized in that The coagulation liquid is a mixture of ethanol and water, and the volume percentage of ethanol in the coagulation liquid is at least 5%.

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