Polishing composition and method for polishing silicon wafer

Abstract

To provide a polishing composition capable of reducing microdefects in a semiconductor wafer after polishing.SOLUTION: A polishing composition contains abrasive grains, a basic compound, a wetting agent, and a nonionic surfactant, and the surface tension γud is 64 mN / m or less, and the ratio γd / γud to the surface tension γud when diluted 20 times with water is 1.10 to 1.40. However, the surface tension γud and ratio γd are values measured at 25°C.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a polishing composition and a method for polishing a silicon wafer. [Background technology]

[0002] Polishing semiconductor wafers using CMP involves multiple steps of polishing to achieve highly accurate smoothing and flattening. The main purpose of the final polishing process is to reduce micro-defects.

[0003] Polishing compositions used in the polishing of semiconductor wafers, particularly in the finish polishing process of silicon wafers, generally contain water-soluble polymers such as hydroxyethyl cellulose as described in, for example, JP 2001-15461 A, JP 2010-34509 A, and JP 2011-61089 A. The water-soluble polymers have the role of making the surface of the semiconductor wafer hydrophilic, and suppress damage to the semiconductor wafer caused by adhesion of abrasive grains to the surface, excessive chemical etching, aggregation of abrasive grains, etc. It is known that this can reduce micro-defects. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-216723 A [Patent Document 2] JP 2009-147267 A [Patent Document 3] International Publication No. 2013 / 137212 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, as design rules for semiconductor devices have become finer, stricter control of micro-defects on the surface of semiconductor wafers is required. The above-mentioned techniques are still insufficient to meet the recent demands for surface quality after polishing, and further improvements are required.

[0006] An object of the present invention is to provide a polishing composition capable of reducing microdefects in polished semiconductor wafers. [Means for solving the problem]

[0007] The polishing composition according to one embodiment of the present invention includes an abrasive grain, a basic compound, a wetting agent, and a nonionic surfactant, and has a surface tension of γ ud is 64 mN / m or less, and the surface tension γ d The surface tension γ ud Ratio to γ d / γ ud is 1.10 or more and 1.40 or less. However, the surface tension γ ud and γ d is the value measured at 25°C. Effect of the Invention

[0008] According to the present invention, it is possible to reduce micro-defects in polished semiconductor wafers. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a scatter plot showing the relationship between γd / γud of a polishing composition and the number (relative value) of microdefects on a polished wafer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present inventors have carried out various studies in order to solve the above problems. As a result, ud and the surface tension γ when this polishing composition was diluted 20 times with water. d Surface tension γud Ratio to γ d / γ ud It has been found that by adjusting each of these within a prescribed range, the balance between the protective effect on the abrasive grains and the wafer surface and the compatibility with water can be improved, thereby reducing micro-defects.

[0011] The present invention has been completed based on this finding. A polishing composition according to one embodiment of the present invention will be described in detail below.

[0012] The polishing composition according to one embodiment of the present invention includes an abrasive grain, a basic compound, a wetting agent, and a nonionic surfactant, and has a surface tension of γ ud is 64 mN / m or less, and the surface tension γ d Surface tension γ ud Ratio to γ d / γ ud is 1.10 or more and 1.40 or less. However, the surface tension γ ud and γ d is the value measured at 25°C.

[0013] The abrasive grains may be those commonly used in this field, such as colloidal silica, fumed silica, colloidal alumina, fumed alumina, and ceria, with colloidal silica or fumed silica being particularly preferred. The particle size of the abrasive grains is not particularly limited, but those having an average secondary particle diameter of, for example, 30 to 100 nm may be used. The lower limit of the average secondary particle diameter of the abrasive grains is preferably 40 nm, more preferably 50 nm. The upper limit of the average secondary particle diameter of the abrasive grains is preferably 90 nm.

[0014] The content of the abrasive grains is not particularly limited, but is, for example, 0.10 to 20.0% by weight of the entire polishing composition (undiluted solution). The lower limit of the content of the abrasive grains is preferably 1.0% by weight, more preferably 3.0% by weight, and more preferably 5.0% by weight. The upper limit of the content of the abrasive grains is preferably 18.0% by weight, more preferably 15.0% by weight, and more preferably 12.0% by weight.

[0015] The polishing composition is used, for example, diluted 5 to 100 times during polishing. The polishing composition according to the present embodiment is preferably used diluted so that the concentration of abrasive grains is 100 to 8000 ppm (ppm by weight; the same applies below). The lower limit of the dilution ratio is preferably 10 times, and more preferably 15 times. The upper limit of the dilution ratio is preferably 80 times, and more preferably 60 times, and even more preferably 50 times.

[0016] The basic compound reacts efficiently with the wafer surface and contributes to the polishing characteristics of chemical mechanical polishing (CMP). Examples of the basic compound include ammonia, ammonium compounds, amine compounds, inorganic alkali compounds, and the like.

[0017] Examples of the ammonium compound include ammonium salts, quaternary ammonium hydroxides, etc. Specific examples include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrabutylammonium hydroxide (TBAH), etc.

[0018] Examples of the amine compound include primary amines, secondary amines, tertiary amines, heterocyclic amines, and salts thereof. Specific examples include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, hexylamine, cyclohexylamine, ethylenediamine, hexamethylenediamine, diethylenetriamine (DETA), triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, monoethanolamine, diethanolamine, triethanolamine, N-(β-aminoethyl)ethanolamine, anhydrous piperazine, piperazine hexahydrate, 1-(2-aminoethyl)piperazine, N-methylpiperazine, piperazine hydrochloride, and guanidine carbonate.

[0019] Examples of inorganic alkali compounds include hydroxides of alkali metals, salts of alkali metals, hydroxides of alkaline earth metals, salts of alkaline earth metals, etc. Specific examples of inorganic alkali compounds include potassium hydroxide, sodium hydroxide, potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, sodium carbonate, etc.

[0020] The above-mentioned basic compounds may be used alone or in combination of two or more. Among the above-mentioned basic compounds, alkali metal hydroxides, alkali metal salts, ammonia, ammonium salts, and quaternary ammonium hydroxides are particularly preferred.

[0021] The content of the basic compound (when two or more kinds are contained, the total amount) is not particularly limited, but is, for example, 0.01 to 1.50% by weight of the entire polishing composition (undiluted solution). The lower limit of the content of the basic compound is preferably 0.05% by weight, more preferably 0.10% by weight. The upper limit of the content of the basic compound is preferably 1.20% by weight, more preferably 1.00% by weight, and more preferably 0.80% by weight.

[0022] A wetting agent is a substance that is effective in keeping the surface of a wafer hydrophilic. If the hydrophilicity of the wafer surface decreases, foreign matter is more likely to adhere to the wafer and to remain on the wafer without being removed by cleaning. If foreign matter remains on the wafer, the surface precision of the wafer may decrease.

[0023] Examples of the wetting agent include cellulose derivatives, vinyl polymers, and polysaccharides. Examples of the cellulose derivatives include hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose. Examples of the vinyl polymers include polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl pyrrolidone, poly-N-vinyl formamide, copolymers of polyvinyl alcohol and polyvinyl pyrrolidone, and copolymers of modified polyvinyl alcohol and polyvinyl pyrrolidone. Examples of the polysaccharides include starch, cyclodextrin, trehalose, and pullulan. Examples of other wetting agents include polyacrylamide and polymethyl methacrylate.

[0024] The modified polyvinyl alcohol is, for example, a vinyl alcohol resin having a 1,2-diol structural unit represented by the following general formula (1). That is, this modified polyvinyl alcohol has a 1,2-diol structural unit represented by formula (1) in addition to a polyvinyl alcohol structural unit. The modification amount of the 1,2-diol structural unit in the polymer is not particularly limited, but is, for example, 1 to 20 mol %.

[0025] [ka] However, R 1 , R 2 , and R 3 each independently represents a hydrogen atom or an organic group, X represents a single bond or a bonded chain, R 4 , R 5 , and R 6 each independently represents a hydrogen atom or an organic group.

[0026] Among modified polyvinyl alcohols having a 1,2-diol structural unit, R 1 ~R 6 are all hydrogen atoms and X is a single bond. That is, it is particularly preferred that the compound contains a structural unit of the following formula (2). [ka]

[0027] Among the wetting agents, cellulose derivatives and modified polyvinyl alcohol are preferred because they have a high ability to impart wettability to the surface of the wafer and can be easily washed off without remaining on the wafer. Among the cellulose derivatives, hydroxyethyl cellulose is particularly preferred. Among the modified polyvinyl alcohols, modified polyvinyl alcohols having the above-mentioned 1,2-diol structural unit are preferred.

[0028] The content of the wetting agent (when two or more kinds are contained, the total amount) is not particularly limited, but is, for example, 0.01 to 1.20% by weight of the entire polishing composition (undiluted solution). The lower limit of the content of the wetting agent is preferably 0.05% by weight, more preferably 0.10% by weight. The upper limit of the content of the wetting agent is preferably 0.90% by weight, more preferably 0.60% by weight.

[0029] Nonionic surfactants are effective in reducing micro defects. Examples of nonionic surfactants include ethylenediaminetetrapolyoxyethylenepolyoxypropylene (poloxamine), oxyalkylene polymers, copolymers of multiple types of oxyalkylenes (e.g., diblock, triblock, random, and alternating copolymers), polyoxyalkylene alkyl ethers, polyoxyalkylene glyceryl ethers, polyoxyalkylene alkylphenyl ethers, polyoxyalkylene alkylamines, polyoxyalkylene alkylamides, polyoxyalkylene fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyalkylene castor oil, and polyoxyalkylene methyl glucosides.

[0030] Examples of the oxyalkylene polymer monomer include polyethylene glycol and polypropylene glycol. Examples of the copolymer of multiple types of oxyalkylene include polyoxyethylene polyoxypropylene ether, trimethylolpropane tris(polyoxyethylene polyoxypropylene) ether, and polyoxyethylene polyoxypropylene butyl ether. Examples of the polyoxyalkylene alkyl ether include polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, and polyoxyethylene stearyl ether. Examples of the polyoxyalkylene glyceryl ether include polyoxyethylene glyceryl ether and polyoxypropylene glyceryl ether. Examples of the polyoxyalkylene alkyl phenyl ether include polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, and polyoxyethylene paracumyl phenyl ether. Examples of the polyoxyalkylene alkyl amine include polyoxyethylene lauryl amine and polyoxyethylene oleyl amine. Examples of polyoxyalkylene alkylamides include polyoxyethylene oleylamide and polyoxyethylene stearylamide. Examples of polyoxyalkylene fatty acid esters include polyoxyethylene monolaurate and polyoxyethylene monostearate. Examples of polyoxyethylene sorbitan fatty acid esters include polyoxyethylene sorbitan monolaurate and polyoxyethylene sorbitan monopaltimate. Examples of polyoxyalkylene castor oils include polyoxyethylene castor oil and polyoxyethylene hydrogenated castor oil. Examples of polyoxyalkylene methyl glucosides include polyoxyethylene methyl glucoside and polyoxypropylene methyl glucoside.

[0031] The content of the nonionic surfactant (when two or more kinds are contained, the total amount) is not particularly limited, but is, for example, 0.1 to 1000 ppm of the entire polishing composition (undiluted solution). The lower limit of the content of the nonionic surfactant is preferably 5 ppm, more preferably 10 ppm, more preferably 30 ppm, more preferably 50 ppm, and more preferably 80 ppm. The upper limit of the content of the nonionic surfactant is preferably 800 ppm, and more preferably 600 ppm.

[0032] The polishing composition according to this embodiment may further contain a pH adjuster. The pH of the polishing composition according to this embodiment is preferably 8.0 to 12.0.

[0033] The balance of the polishing composition according to the present embodiment is mainly water. In addition to the above, the polishing composition according to the present embodiment may optionally contain additives generally known in the field of polishing compositions, such as organic acids, inorganic acids, preservatives, antifoaming agents, and chelating agents.

[0034] The polishing composition according to the present embodiment has a surface tension γ ud The surface tension γ when diluted 20 times with water is 64 mN / m or less. d Surface tension γ ud Ratio to γ d / γ ud is 1.10 or more and 1.40 or less. However, the surface tension γ d and γ ud is the value measured at 25°C.

[0035] That is, the polishing composition according to the present embodiment has a surface tension γ ud When the stock solution is diluted 20 times, in other words, when the stock solution is mixed with water in a weight ratio of 1:19, the surface tension is γ d As, γ d / γ ud is 1.10 or more and 1.40 or less. This makes it possible to reduce minute defects.

[0036] By lowering the surface tension of the polishing composition, the wettability and compatibility of the wetting agent and the nonionic surfactant with the abrasive grain surface is improved. This enhances the protective effect of the wetting agent and the nonionic surfactant on the abrasive grain surface, and the wafer is less likely to be scratched by the abrasive grain when polished, less likely to leave foreign matter, and more likely to be removed. In addition, the protective effect of the wetting agent and the nonionic surfactant on the wafer surface is enhanced, similar to the protective effect on the abrasive grain surface.

[0037] On the other hand, if the surface tension of the polishing composition is too low, it becomes difficult to mix with water when diluted with water, and the polishing performance becomes unstable. ud and γ d / γ ud By adjusting each of these within a prescribed range, a good balance is achieved between the protective effect for the abrasive grains and the wafer surface and the compatibility with water, making it possible to reduce micro-defects.

[0038] Gamma ud and γ d can be adjusted by the type and content of abrasive grains, the type and content of basic compound, the type and content of wetting agent, and the type and content of nonionic surfactant. Among them, the type and content of wetting agent and the type and content of nonionic surfactant have a large effect, and the type and content of nonionic surfactant has a relatively large effect. Although it varies depending on the type, the higher the content of wetting agent, the lower the surface tension tends to be. Also, although it also varies depending on the type, the higher the content of surface tension agent, the lower the surface tension tends to be. In addition to the above, preservatives and defoamers also affect the surface tension.

[0039] The γ of the two polishing compositions ud Even if γ d / γ ud In other words, the degree of increase in surface tension when diluted may vary depending on the formulation of the polishing composition. The degree of increase in surface tension when diluted mainly depends on the type and concentration of the wetting agent and nonionic surfactant.

[0040] Gammaud The upper limit of γ is preferably 62 mN / m, more preferably 60 mN / m, more preferably 58 mN / m, and even more preferably 56 mN / m. ud The lower limit is not particularly limited, but is preferably 40 mN / m, more preferably 45 mN / m, and even more preferably 50 mN / m.

[0041] Gamma d / γ ud The upper limit of γ is preferably 1.35, more preferably 1.30, and even more preferably 1.25. d / γ ud The lower limit is preferably 1.15.

[0042] The polishing composition according to the present embodiment is prepared by appropriately mixing abrasive grains, a basic compound, a wetting agent, a nonionic surfactant, etc., and adding water. Alternatively, the polishing composition according to the present embodiment is prepared by sequentially mixing abrasive grains, a basic compound, a wetting agent, a nonionic surfactant, etc., with water. As a means for mixing these components, a means commonly used in the technical field of polishing compositions, such as a homogenizer or ultrasonic waves, is used.

[0043] The polishing composition described above is used for polishing semiconductor wafers after being diluted with water to an appropriate concentration. The water used for dilution is, for example, ion-exchanged water, pure water, ultrapure water, distilled water, etc.

[0044] The polishing composition according to the present embodiment can be suitably used for polishing silicon wafers (bare wafers), particularly for finish polishing. A method for polishing silicon wafers according to one embodiment of the present invention includes polishing silicon wafers with the above-mentioned polishing composition. EXAMPLES

[0045] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0046] Polishing compositions of Examples 1 to 15 and Comparative Examples 1 to 12 shown in Table 1 were prepared.

[0047] [Table 1]

[0048] The balance of the polishing composition in Table 1 is water. Colloidal silica with average secondary particle diameters of 50 nm and 70 nm was used as the abrasive grains. HEC-1, HEC-2, and HEC-3 in the "Type" column of wetting agents are hydroxyethyl celluloses with weight average molecular weights Mw of 800,000, 500,000, and 250,000, respectively. The modified PVA is a butenediol vinyl alcohol polymer with a degree of polymerization of 450 and a degree of saponification of 98 mol% or more (complete saponification). S1 to S7 in the "Type" column of nonionic surfactants are as shown in Table 2.

[0049] [Table 2]

[0050] The surface tension γ of these polishing compositions before dilution ud , and the surface tension γ when diluted 20 times d The surface tension was measured using a fully automatic contact angle meter (Drop Master DM 500, manufactured by Kyowa Interface Science Co., Ltd.). Five surface tension measurements were performed for each polishing composition at 25° C., and the average value was taken as the surface tension value (γ ud or gamma d ) was decided.

[0051] The surface tension value was analyzed taking into consideration the specific gravity of the polishing composition. The specific gravity of the polishing composition was calculated as follows. First, the weight W1 of a dry, empty pycnometer was measured using an electronic balance. The empty pycnometer was filled with pure water and the lid was placed on it, the pure water on the surface was wiped off, and the total weight W2 was measured. The pure water was discarded, the pycnometer was filled with the polishing composition and the lid was placed on it, the polishing composition on the surface was wiped off, and the total weight W3 was measured. The specific gravity of the polishing composition was calculated using the following formula. Specific gravity of polishing composition=(W3-W1) / (W2-W1)

[0052] The surface tension was measured by the pendant drop method, and the curve fitting method (Young-Laplace method) was used for analysis.

[0053] Using the polishing compositions of the Examples and Comparative Examples, 12-inch silicon wafers were polished. The silicon wafers used had a P-type conductivity and a resistivity of 0.1 Ωcm or more and less than 100 Ωcm. The polished surface was <100> The polishing machine used was an SPP800S single-sided polishing machine manufactured by Okamoto Machine Tool Works, Ltd. The polishing pad used was a suede pad. The polishing composition was diluted at the ratio shown in the "Dilution ratio" column in Table 1 and supplied at a supply rate of 1 L / min. The rotation speed of the platen was 50 rpm, the rotation speed of the carrier was 49 rpm, and the polishing load surface pressure was 100 gf / cm. 2 Prior to polishing with the polishing compositions of the Examples and Comparative Examples, preliminary polishing was performed for 2 minutes using a polishing slurry Nanopure (registered trademark) NP7050S (manufactured by Nitta DuPont Co., Ltd.).

[0054] Microdefects on the polished silicon wafers were measured using a wafer surface inspection device (MAGICS M5640 manufactured by Lasertec Corporation). The results are shown in the "Defect" column of Table 1. The values ​​in this column are relative values ​​with Comparative Example 1 taken as 100.

[0055] The wettability of the silicon wafers after polishing was evaluated. Specifically, the surfaces of the silicon wafers after polishing were rinsed with running water for 15 seconds, and then the silicon wafers were placed vertically and left to stand. The wettability of each silicon wafer was evaluated 5 seconds after being left to stand. A case in which the distance of the water-repellent part from the outer circumference of the polished surface was 5 mm or less was evaluated as "○", a case in which it was 6-10 mm was evaluated as "△", and a case in which it was 11 mm or more was evaluated as "×". The results are shown in the "Wafer wettability" column in Table 1.

[0056] As shown in Table 1, γ udis 64 mN / m or less, and γ d / γ ud In the polishing compositions of Examples 1 to 15, in which the value was 1.10 or more and 1.40 or less, the number of microdefects was 50% or less compared to the polishing composition of Comparative Example 1. In addition, the properties of imparting wettability to the wafer were also good.

[0057] FIG. 1 shows the γ d / γ ud 1 is a scatter diagram showing the relationship between the number of microdefects (relative value) on the wafer after polishing and the number of microdefects on the wafer after polishing. The open marks indicate that the wetting agent is hydroxyethyl cellulose-based (HEC-1, HEC-2, or HEC-3), and the solid marks indicate that the wetting agent is modified polyvinyl alcohol. From FIG. 1, it can be seen that whether the wetting agent is hydroxyethyl cellulose-based or modified polyvinyl alcohol, γ d / γ ud It can be seen that micro defects can be reduced by setting the value to 1.10 or more and 1.40 or less.

[0058] The above describes the embodiments of the present invention. The above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, and the above-described embodiments can be appropriately modified and carried out without departing from the spirit of the present invention.

Claims

1. Abrasive grains and A basic compound, A wetting agent; and a nonionic surfactant, surface tension γ ｕｄ is 64 mN / m or less, Surface tension γ when diluted 20 times with water ｄ The surface tension γ ｕｄ Ratio to γ ｄ / γ ｕｄ The polishing composition, wherein the polishing coefficient is 1.10 or more and 1.40 or less. However, the surface tension γ ｄ and γ ｕｄ is the value measured at 25°C.

2. The polishing composition according to claim 1, The polishing composition, wherein the wetting agent is one or more selected from the group consisting of cellulose derivatives, polysaccharides, and vinyl polymers.

3. The polishing composition according to claim 1 or 2, The polishing composition, wherein the basic compound is at least one selected from the group consisting of an alkali metal oxide, an alkali metal salt, ammonia, an ammonium salt, and a quaternary ammonium hydroxide.

4. The polishing composition according to any one of claims 1 to 3, A polishing composition that is used after being diluted 5 to 100 times.

5. The polishing composition according to any one of claims 1 to 4, A polishing composition used for polishing silicon wafers.

6. A method for polishing a silicon wafer, comprising polishing a silicon wafer with the polishing composition according to any one of claims 1 to 5.

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