Polishing composition and method for polishing silicon wafers

Abstract

The present invention provides a polishing composition capable of reducing minute defects of a semiconductor wafer after polishing. The polishing composition comprises a polishing grain, an alkaline compound, a wetting agent, and a nonionic surfactant, the surface tension γ ud of the polishing composition is 64 mN / m or less, the surface tension γ d of water diluted 20 times is 20 mN / m or more, the ratio γ ud of the surface tension γ d of the polishing composition to the surface tension γ ud of the water diluted 20 times is 1.10 or more and 1.40 or less. Here, the surface tension γ ud and the ratio γ d are values measured at 25°C.

Description

Technical Field

[0001] This invention relates to a grinding composition and a grinding method for silicon wafers. Background Technology

[0002] Semiconductor wafer polishing using CMP (Chemical Mechanical Polishing) achieves high-precision smoothing and planarization through multi-stage polishing. The final fine polishing process aims to reduce minute defects.

[0003] In the polishing of semiconductor wafers, especially in the fine polishing process of silicon wafers, the polishing compositions generally contain water-soluble polymers such as hydroxyethyl cellulose, as described in Japanese Patent Application Publication Nos. 2001-15461, 2010-34509, and 2011-61089. These water-soluble polymers hydrophilize the surface of the semiconductor wafer, inhibiting damage to the semiconductor wafer caused by abrasive particle adhesion, excessive chemical etching, and abrasive particle aggregation. Therefore, it is known that this reduces minute defects.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2012-216723

[0007] Patent Document 2: Japanese Patent Application Publication No. 2009-147267

[0008] Patent Document 3: International Publication No. 2013 / 137212 Summary of the Invention

[0009] In recent years, with the miniaturization of semiconductor device design rules, stricter management is required for even minute defects on the surface of semiconductor wafers. The current requirements for surface quality, even after polishing using the aforementioned techniques, are insufficient and require further improvement.

[0010] The purpose of this invention is to provide a polishing composition that can reduce minute defects in a polished semiconductor wafer.

[0011] One embodiment of the grinding composition of the present invention comprises abrasive grains, an alkaline compound, a wetting agent, and a nonionic surfactant, with a surface tension γ. ud The surface tension γ when diluted with water to a factor of 20 is below 64 mN / m. d Relative to the above surface tension γ ud The ratio of γ d / γud The value is between 1.10 and 1.40. Specifically, the surface tension γ mentioned above... ud and γ d Let the value be the one measured at 25℃.

[0012] According to the present invention, minute defects in the polished semiconductor wafer can be reduced.

[0013] Brief description of the attached diagram

[0014] [ Figure 1 ]: Figure 1 A scatter plot showing the relationship between the γd / γud of the polishing composition and the number of minute defects (relative value) of the polished wafer.

[0015] Implementation of the invention

[0016] The inventors of this invention conducted various studies to solve the above-mentioned problems. As a result, they discovered that by reducing the surface tension γ of the grinding composition... ud and the surface tension γ when the grinding composition is diluted 20 times with water. d Relative to surface tension γ ud The ratio of γ d / γ ud By adjusting to specific ranges, the balance between the protective effect of the abrasive particles and the wafer surface and their affinity with water is improved, thereby reducing micro-defects.

[0017] This invention is based on this insight. The following is a detailed description of a grinding composition according to one embodiment of the invention.

[0018] One embodiment of the grinding composition of the present invention comprises abrasive grains, an alkaline compound, a wetting agent, and a nonionic surfactant, with a surface tension γ. ud The surface tension γ when diluted with water to a factor of 20 is below 64 mN / m. d Relative to surface tension γ ud The ratio of γ d / γ ud The value is between 1.10 and 1.40. Specifically, the surface tension γ mentioned above... ud and γ d Let the value be the one measured at 25℃.

[0019] The abrasive particles can be made of materials commonly used in this field, such as colloidal silica, fuming silica, colloidal alumina, fuming alumina, and cerium oxide, with colloidal silica or fuming silica being preferred. The particle size of the abrasive particles is not particularly limited; for example, abrasive particles with an average secondary particle size of 30–100 nm can be used. The lower limit of the average secondary particle size of the abrasive particles is preferably 40 nm, more preferably 50 nm. The upper limit of the average secondary particle size of the abrasive particles is preferably 90 nm.

[0020] The content of abrasive particles is not particularly limited, for example, it is 0.10 to 20.0% by weight of the total grinding composition (stock solution). The lower limit of the content of abrasive particles 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 abrasive particles is preferably 18.0% by weight, more preferably 15.0% by weight, and more preferably 12.0% by weight.

[0021] The grinding composition is used, for example, diluted 5 to 100 times during grinding. The grinding composition of this embodiment is preferably diluted to a concentration of 100 to 8000 ppm (wt ppm; hereinafter the same) for use. The lower limit of the dilution ratio is preferably 10 times, more preferably 15 times. The upper limit of the dilution ratio is preferably 80 times, more preferably 60 times, and more preferably 50 times.

[0022] Basic compounds react efficiently with wafer surfaces, contributing to the polishing characteristics of chemical mechanical polishing (CMP). Examples of basic compounds include ammonia, ammonium compounds, amine compounds, and inorganic basic compounds.

[0023] Ammonium compounds include, for example, ammonium salts and quaternary ammonium hydroxides. Specifically, examples include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), and tetrabutylammonium hydroxide (TBAH).

[0024] Amine compounds include, for example, primary amines, secondary amines, tertiary amines, heterocyclic amines, and their salts. Specifically, 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.

[0025] Inorganic alkali compounds include, for example, alkali metal hydroxides, alkali metal salts, alkaline earth metal hydroxides, and alkaline earth metal salts. Specifically, inorganic alkali compounds include potassium hydroxide, sodium hydroxide, potassium bicarbonate, potassium carbonate, sodium bicarbonate, and sodium carbonate.

[0026] The aforementioned alkaline compounds can be used alone or in combination of two or more. Among the aforementioned alkaline compounds, alkali metal hydroxides, alkali metal salts, ammonia, ammonium salts, and quaternary ammonium hydroxides are particularly preferred.

[0027] The content of alkaline compounds (the total amount when two or more are present) is not particularly limited, and is, for example, 0.01 to 1.50% by weight of the total grinding composition (stock solution). The lower limit of the content of alkaline compounds is preferably 0.05% by weight, more preferably 0.10% by weight. The upper limit of the content of alkaline compounds is preferably 1.20% by weight, more preferably 1.00% by weight, and even more preferably 0.80% by weight.

[0028] Wetting agents are substances effective in maintaining the hydrophilicity of the wafer surface. If the hydrophilicity of the wafer surface decreases, foreign matter can easily adhere to the wafer and remain there without being cleaned off. If foreign matter remains on the wafer, there is a risk of reduced surface precision.

[0029] Wetting agents include, for example, cellulose derivatives, vinyl polymers, and polysaccharides. Examples of cellulose derivatives include hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methylcellulose. Examples of vinyl polymers include polyvinyl alcohol, modified polyvinyl alcohol, polyvinylpyrrolidone, poly-N-vinylformamide, copolymers of polyvinyl alcohol and polyvinylpyrrolidone, and copolymers of modified polyvinyl alcohol and polyvinylpyrrolidone. Examples of polysaccharides include starch, cyclodextrin, trehalose, and pullulan. Other wetting agents include, for example, polyacrylamide and polymethyl methacrylate.

[0030] Modified polyvinyl alcohol is, for example, a vinyl alcohol-based resin having a 1,2-diol structural unit represented by the general formula (1). That is, in addition to having the structural unit of polyvinyl alcohol, the modified polyvinyl alcohol also has a 1,2-diol structural unit represented by formula (1). The amount of 1,2-diol structural unit modification in the polymer is not particularly limited, for example, 1 to 20 mol%.

[0031] [Chemistry 1]

[0032]

[0033] Among them, R 1 R 2 and R 3 Each can independently represent a hydrogen atom or an organic group, X represents a single bond or a bonded chain, and R... 4 R 5 and R b Each can be used to independently represent a hydrogen atom or an organic group.

[0034] Among modified polyvinyl alcohols having 1,2-diol structural units, a structure in which R1 to R6 of the 1,2-diol structural unit represented by general formula (1) are all hydrogen atoms and X is a single bond is particularly preferred. That is, a structure containing structural units of the following formula (2) is particularly preferred.

[0035] [Chemistry 2]

[0036]

[0037] From the perspective of providing high wettability to the wafer surface and being easily washable without leaving residue on the wafer, cellulose derivatives and modified polyvinyl alcohols are preferred wetting agents. Furthermore, hydroxyethyl cellulose is particularly preferred among cellulose derivatives. Modified polyvinyl alcohols having the aforementioned 1,2-diol structural units are preferred.

[0038] The content of the wetting agent (the total amount when there are two or more types) is not particularly limited, for example, it is 0.01 to 1.20% by weight of the total grinding composition (stock solution). The lower limit of the wetting agent content is preferably 0.05% by weight, more preferably 0.10% by weight. The upper limit of the wetting agent content is preferably 0.90% by weight, more preferably 0.60% by weight.

[0039] Nonionic surfactants are effective in reducing minute defects. Examples of nonionic surfactants include ethylenediamine tetraethylene oxide polypropylene oxide (Poloxamine), epoxy alkane polymer monomers, copolymers of various epoxy alkane (e.g., diblock, triblock, random, and alternating copolymers), polyoxyalkylene alkyl ethers, polyoxyalkylene glycerol ethers, polyoxyalkylene alkylbenzene ethers, polyoxyalkylene alkylamines, polyoxyalkylene alkylamides, polyoxyalkylene fatty acid esters, polyoxyalkylene ethylsorbitan fatty acid esters, polyoxyalkylene castor oil, and polyoxyalkylene methyl glucosides.

[0040] Examples of epoxy alkyl polymer monomers include polyethylene glycol and polypropylene glycol. Examples of copolymers of various epoxy alkyl groups include polyoxyethylene polyoxypropylene ether, trimethylolpropane tris(polyoxyethylene polyoxypropylene) ether, and polyoxyethylene polyoxypropylene butyl ether. Examples of polyoxyalkylene alkyl ethers include polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, and polyoxyethylene stearyl ether. Examples of polyoxyalkylene glycerol ethers include polyoxyethylene glycerol ether and polyoxypropylene glycerol ether. Examples of polyoxyalkylene alkylphenyl ethers include polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, and polyoxyethylene p-isopropylphenylphenyl ether. Examples of polyoxyalkylene alkylamines include polyoxyethylene laurylamine and polyoxyethylene oleylamine. 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 monolauric acid polyoxyethylene sorbitan and monopalmitic acid polyoxyethylene sorbitan. Examples of polyoxyalkylene castor oil include polyoxyethylene castor oil and polyoxyethylene hydrogenated castor oil. Examples of polyoxyalkylene methyl glucosides include polyoxyethylene methyl glucoside and polyoxypropylene methyl glucoside.

[0041] The content of nonionic surfactants (the total amount when two or more types are present) is not particularly limited, and is, for example, 0.1 to 1000 ppm of the total content of the grinding composition (stock solution). The lower limit of the nonionic surfactant content 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 nonionic surfactant content is preferably 800 ppm, more preferably 600 ppm.

[0042] The grinding composition of this embodiment may further include a pH adjuster. The pH of the grinding composition of this embodiment is preferably 8.0 to 12.0.

[0043] The remaining portion of the grinding composition in this embodiment is mainly water. In addition to the above, the grinding composition of this embodiment may also be formulated with any formulation agents generally known in the field of grinding compositions, such as organic acids, inorganic acids, preservatives, defoamers, and chelating agents.

[0044] The surface tension γ of the grinding composition in this embodiment ud The surface tension γ is below 64 mN / m and is obtained by diluting it with water to a factor of 20. d Relative to surface tension γ ud The ratio of γ d / γ ud It is between 1.10 and 1.40. Among them, the surface tension γ... d and γ ud Let the value be the one measured at 25℃.

[0045] That is, the surface tension γ of the original solution of the grinding composition in this embodiment before dilution. ud To achieve a surface tension below 64 mN / m, the stock solution is diluted 20 times; in other words, the stock solution is mixed with water at a weight ratio of 1:19. Let the surface tension at this point be γ. d γ d / γ ud It is between 1.10 and 1.40. This reduces minor defects.

[0046] By reducing the surface tension of the polishing composition, the wetting and affinity of the wetting agent and nonionic surfactant to the surface of the abrasive particles are improved. This results in the following effects: enhanced protection of the abrasive particle surface by the wetting agent and nonionic surfactant, reducing the likelihood of damage caused by the abrasive particles during wafer polishing; less foreign matter residue; and easier removal of foreign matter. Furthermore, similarly to the protection of the abrasive particle surface, the protection of the wafer surface by the wetting agent and nonionic surfactant is also improved.

[0047] On the other hand, if the surface tension of the grinding composition is too low, it will not readily bind with water when diluted with water, resulting in unstable grinding performance. By using γ... ud and γ d / γ ud By adjusting to specific ranges, the balance between the protective effect of the abrasive particles and the wafer surface and their affinity with water is improved, thereby reducing micro-defects.

[0048] γ ud and γ d The surface tension can be adjusted by the type and content of abrasive particles, alkaline compounds, wetting agents, and nonionic surfactants. Among these, the type and content of wetting agents and nonionic surfactants have the greatest impact, especially the type and content of nonionic surfactants. Although the effect varies depending on the type, there is a trend that higher wetting agent content leads to lower surface tension. Furthermore, although the effect varies even for the same type, there is a trend that higher wetting agent content leads to lower surface tension. In addition to the above, preservatives or defoamers also affect surface tension.

[0049] Furthermore, even if the two grinding compositions have γ ud For the same degree, γ d / γ udHowever, the situation can vary. Specifically, the degree of increase in surface tension after dilution can differ depending on the composition of the grinding composition. The increase in surface tension after dilution primarily depends on the type and concentration of the wetting agent and the nonionic surfactant.

[0050] γ ud The upper limit is preferably 62 mN / m, more preferably 60 mN / m, more preferably 58 mN / m, and even more preferably 56 mN / m. ud There is no particular limitation on the lower limit, but it is preferably 40mN / m, more preferably 45mN / m, and even more preferably 50mN / m.

[0051] γ d / γ ud The upper limit is preferably 1.35, more preferably 1.30, and even more preferably 1.25. γ d / γ ud The lower limit is preferably 1.15.

[0052] The grinding composition of this embodiment is prepared by appropriately mixing abrasive particles, an alkaline compound, a wetting agent, a nonionic surfactant, etc., and then adding water. Alternatively, the grinding composition of this embodiment is prepared by sequentially mixing abrasive particles, an alkaline compound, a wetting agent, a nonionic surfactant, etc., in water. As a method for mixing these components, methods commonly used in the technical field of grinding compositions, such as homogenizers and ultrasonic equipment, are used.

[0053] The polishing composition described above, after being diluted with water to an appropriate concentration, is used for polishing semiconductor wafers. The water used for dilution may be, for example, ion-exchanged water, pure water, ultrapure water, or distilled water.

[0054] The polishing composition of this embodiment is preferably used for polishing silicon wafers (bare wafers), especially for fine polishing. A method for polishing a silicon wafer according to an embodiment of the present invention includes polishing the silicon wafer using the above-described polishing composition. Example

[0055] The present invention will now be described in more detail through examples. However, the present invention is not limited to these examples.

[0056] The grinding compositions of Examples 1 to 15 and Comparative Examples 1 to 12 shown in Table 1 were prepared.

[0057] [Table 1]

[0058]

[0059] The remainder of the grinding composition in Table 1 is water. The abrasive particles used are colloidal silica with average secondary particle sizes of 50 nm and 70 nm. HEC-1, HEC-2, and HEC-3, listed under "Type" of wetting agent, are hydroxyethyl cellulose with weight average molecular weights (Mw) of 800,000, 500,000, and 250,000, respectively. The modified PVA (polyvinyl alcohol) is a butene glycol-vinyl alcohol polymer with a degree of polymerization of 450 and a degree of saponification of 98 mol% or more (fully saponified). The S1 to S7 entries under "Type" of nonionic surfactants are shown in Table 2.

[0060] [Table 2]

[0061]

[0062] Surface tension γ of these grinding compositions before dilution ud and the surface tension γ when diluted 20 times d Measurements were performed. Surface tension was measured using a fully automated contact angle meter (Drop MasterDM 500, manufactured by Kyowa Interface Science Co., Ltd.). At 25°C, surface tension was measured five times for each abrasive composition, and the average value was set as the surface tension value (γ). ud or γ d ).

[0063] Regarding the surface tension value, the specific gravity of the grinding composition is also taken into account during the analysis. The specific gravity of the grinding composition is determined as follows: First, weigh the empty, dried specific gravity bottle W1 using an electronic balance. Fill the empty specific gravity bottle with pure water and cap it, wipe off the pure water adhering to the surface, and weigh the total weight W2. Discard the pure water, fill the specific gravity bottle with the grinding composition and cap it, wipe off the grinding composition adhering to the surface, and weigh the total weight W3. Calculate the specific gravity of the grinding composition using the following formula.

[0064] The specific gravity of the grinding composition = (W3-W1) / (W2-W1)

[0065] Surface tension was measured using the pendant drop method. Analysis was performed using the Young-Laplace curve fitting method.

[0066] Using the polishing compositions of these embodiments and comparative examples, a 12-inch silicon wafer was polished. The silicon wafer was P-type with a resistivity of 0.1 Ωcm or more and less than 100 Ωcm. The polishing surface was set as... <100> The grinding apparatus used was an SPP800S single-sided grinding apparatus manufactured by Okamoto Machine Tools Co., Ltd. A chamois pad was used as the grinding pad. The grinding composition was diluted according to the dilution ratio listed in the "Dilution Ratio" column of Table 1 and fed at a rate of 1 L / min. The rotation speed of the pressure plate was set to 50 rpm, the rotation speed of the carrier was set to 49 rpm, and the grinding load surface pressure was set to 100 g / cm². 2 Grinding was performed for 3 minutes. In addition, before grinding with the grinding compositions of the examples and comparative examples, pre-grinding was performed for 2 minutes using the grinding slurry Nanopure (registered trademark) NP7050S (manufactured by Nitta Dupont Co., Ltd.).

[0067] Minor defects in the polished silicon wafers were measured using a wafer surface inspection device (MAGICS M5640, manufactured by Lasertec Corporation). The results are shown in the "Defects" column of Table 1. The values ​​in the same column are relative values ​​when Comparative Example 1 is set to 100.

[0068] The wettability of the polished silicon wafers was evaluated. Specifically, the surface of the polished silicon wafers was washed with running water for 15 seconds, and then the wafers were held vertically upright. Five seconds after the initial standing period, the wettability of each wafer was evaluated. Wafers with a water-repellent portion less than 5 mm from the outer periphery were rated "○", those between 6 and 10 mm were rated "Δ", and those greater than 11 mm were rated "×". The results are shown in the "Wafer Wettability" column of Table 1.

[0069] As shown in Table 1, γ ud Below 64mN / m and γ d / γ ud The polishing compositions of Examples 1 to 15, with a P-value of 1.10 or higher and 1.40 or lower, have a microdefect rate of 50% or less compared to the polishing composition of Comparative Example 1. Furthermore, they also exhibit excellent wettability properties on the wafer.

[0070] Figure 1 To represent the γ of the grinding composition d / γ ud A scatter plot showing the relationship between the number (relative value) of minute defects on the polished wafer and the total number of defects. Hollow markers indicate that the wetting agent is hydroxyethyl cellulose (HEC-1, HEC-2, or HEC-3), and solid markers indicate that the wetting agent is modified polyvinyl alcohol. Figure 1It is known that, when the wetting agent is any of hydroxyethyl cellulose or modified polyvinyl alcohol, by using γ d / γ ud Setting it to 1.10 or higher and 1.40 or lower can reduce minor defects.

[0071] The embodiments of the present invention have been described above. These embodiments are merely examples for implementing the present invention. Therefore, the present invention is not limited to the above embodiments, and can be implemented by appropriate modifications without departing from its spirit.

Claims

1. A grinding composition comprising: Abrasive particles, alkaline compounds, wetting agents, and Nonionic surfactants The surface tension γ of the stock solution of the grinding composition ud Below 64 mN / m The surface tension γ of the grinding composition stock solution was diluted with water to 20 times its weight. d Relative to the surface tension γ ud The ratio of γ d / γ ud A value between 1.10 and 1.

40. in, The surface tension γ d and γ ud Let the value be the one measured at 25℃.

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

3. The grinding composition according to claim 1 or 2, wherein, The alkaline compound is selected from one or more of alkali metal hydroxides, alkali metal salts, ammonia, ammonium salts, and quaternary ammonium hydroxides.

4. The grinding composition according to claim 1 or 2, which is used after being diluted 5 to 100 times.

5. The polishing composition according to claim 1 or 2, used for polishing silicon wafers.

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

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