Polishing composition and method for polishing silicon wafer

Abstract

A polishing composition is provided that can reduce micro-defects on a semiconductor wafer after polishing. A polishing composition includes: an abrasive; a basic compound; a wetting agent; and a non-ionic surfactant, where the surface tension Yud is not higher than 64 mN / rn, and the ratio of the surface tension after dilution with water by a factor of 20, Yd, to the surface tension Yud, denoted by Yd / Yud, is not lower than 1.10 and not higher than 1.40. Here, the surface tensions Yud and Yd are measurements at 25 °C.

Description

Polishing composition and method for polishing silicon wafers

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

[0002] CMP polishing of semiconductor wafers involves multiple steps of polishing to achieve high-precision smoothing and flattening. The main purpose of the final polishing step 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 a water-soluble polymer 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 polymer serves to hydrophilize the surface of the semiconductor wafer and suppresses damage to the semiconductor wafer due to adhesion of abrasive grains to the surface, excessive chemical etching, agglomeration of abrasive grains, etc. It is known that this can reduce micro-defects.

[0004] JP 2012-216723 A JP 2009-147267 A International Publication No. 2013 / 137212

[0005] In recent years, as design rules for semiconductor devices have become increasingly finer, stricter control of micro-defects on the surfaces 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.

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

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

[0009] FIG. 1 shows the γ ｄ / γ ｕｄ 1 is a scatter plot showing the relationship between the number of micro defects (relative value) on the polished wafer and the number of micro defects on the polished wafer.

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

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

[0012] A polishing composition according to one embodiment of the present invention comprises abrasive grains, a basic compound, a wetting agent, and a nonionic surfactant, and has a surface tension 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, provided that the surface tension γ ｕｄ and γ ｄ is a value measured at 25°C.

[0013] The abrasive grains can 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 with an average secondary particle diameter of 30 to 100 nm can be used, for example. The lower limit of the average secondary particle diameter of the abrasive grains is preferably 40 nm, and 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 wt % of the total polishing composition (undiluted solution). The lower limit of the content of the abrasive grains is preferably 1.0 wt %, more preferably 3.0 wt %, and more preferably 5.0 wt %. The upper limit of the content of the abrasive grains is preferably 18.0 wt %, more preferably 15.0 wt %, and even more preferably 12.0 wt %.

[0015] The polishing composition is diluted, for example, 5 to 100 times before use during polishing. The polishing composition according to this embodiment is preferably diluted to an abrasive concentration of 100 to 8000 ppm (ppm by weight; the same applies hereinafter). 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 even more preferably 50 times.

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

[0017] The ammonium compound is, for example, an ammonium salt, a quaternary ammonium hydroxide, 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 alkali metal hydroxides, alkali metal salts, alkaline earth metal hydroxides, alkaline earth metal salts, etc. Specific examples of inorganic alkali compounds include potassium hydroxide, sodium hydroxide, potassium bicarbonate, potassium carbonate, sodium bicarbonate, sodium carbonate, etc.

[0020] The basic compounds may be used alone or in combination of two or more. Among the 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 types are contained, the total amount) is not particularly limited, but is, for example, 0.01 to 1.50 wt % of the entire polishing composition (undiluted solution). The lower limit of the content of the basic compound is preferably 0.05 wt %, more preferably 0.10 wt %. The upper limit of the content of the basic compound is preferably 1.20 wt %, more preferably 1.00 wt %, and even more preferably 0.80 wt %.

[0022] Wetting agents are substances that are effective in maintaining the hydrophilicity of the wafer surface. When the hydrophilicity of the wafer surface decreases, foreign matter is more likely to adhere to the wafer and remain on the wafer without being removed by cleaning. If foreign matter remains on the wafer, the wafer's surface precision may be reduced.

[0023] Examples of wetting agents include cellulose derivatives, vinyl polymers, and polysaccharides. Examples of cellulose derivatives include hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose. Examples of 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 polysaccharides include starch, cyclodextrin, trehalose, and pullulan. 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): In other words, this modified polyvinyl alcohol has, in addition to the structural unit of polyvinyl alcohol, a 1,2-diol structural unit represented by formula (1). 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] 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 ６are all hydrogen atoms and X is a single bond. That is, a compound containing a structural unit of the following formula (2) is particularly preferred.

[0027] Among wetting agents, cellulose derivatives and modified polyvinyl alcohol are preferred because they have a high ability to impart wettability to the wafer surface and can be easily washed off without remaining on the wafer. Among cellulose derivatives, hydroxyethyl cellulose is particularly preferred. Among 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 types are contained, the total amount) is not particularly limited, but is, for example, 0.01 to 1.20 wt % of the entire polishing composition (undiluted solution). The lower limit of the content of the wetting agent is preferably 0.05 wt %, more preferably 0.10 wt %. The upper limit of the content of the wetting agent is preferably 0.90 wt %, more preferably 0.60 wt %.

[0029] Nonionic surfactants are effective in reducing microdefects. 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 oxyalkylene polymer monomers include polyethylene glycol and polypropylene glycol. Examples of copolymers of multiple types of oxyalkylenes 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 glyceryl ethers include polyoxyethylene glyceryl ether and polyoxypropylene glyceryl ether. Examples of polyoxyalkylene alkyl phenyl ethers include polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, and polyoxyethylene paracumylphenyl 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 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 types 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, even more preferably 50 ppm, and even more preferably 80 ppm. The upper limit of the content of the nonionic surfactant is preferably 800 ppm, 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 this embodiment is mainly water. In addition to the above, the polishing composition according to this embodiment can 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 is 64 mN / m or less, and the surface tension γ when diluted 20 times with water ｄ The surface tension γ ｕｄ Ratio to γ ｄ / γ ｕｄ is 1.10 or more and 1.40 or less, provided that the surface tension γ ｄ and γ ｕｄ is a value measured at 25°C.

[0035] That is, the polishing composition according to this embodiment has a surface tension γ ｕｄ When this 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 micro defects.

[0036] By lowering the surface tension of the polishing composition, the wettability and compatibility of the wetting agent and nonionic surfactant with the abrasive grain surface are improved. This enhances the protective effect of the wetting agent and nonionic surfactant on the abrasive grain surface, resulting in effects such as less scratches caused by the abrasive grains when polishing a wafer, less residue of foreign matter, and easier removal of foreign matter. Furthermore, similar to the protective effect on the abrasive grain surface, the protective effect of the wetting agent and nonionic surfactant on the wafer surface is also enhanced.

[0037] On the other hand, if the surface tension of the polishing composition is too low, it will not mix well with water when diluted with water, and the polishing performance will become unstable. ｕｄ and γ ｄ / γ ｕｄ By adjusting each of these values ​​to fall within a predetermined range, the balance between the protective effect on the abrasive grains and wafer surface and the compatibility with water can be improved, thereby reducing 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 these, the type and content of wetting agent and the type and content of nonionic surfactant have a large effect, with the type and content of nonionic surfactant having a particularly large effect. While 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 antifoaming agents also affect surface tension.

[0039] The γ values ​​of the two polishing compositions ｕｄ Even if γ ｄ / γ ｕｄ The degree of increase in surface tension upon dilution may vary depending on the formulation of the polishing composition. The degree of increase in surface tension upon dilution mainly depends on the type and concentration of the wetting agent and nonionic surfactant.

[0040] gamma ｕｄThe upper limit of γ is preferably 62 mN / m, more preferably 60 mN / m, even more preferably 58 mN / m, and even more preferably 56 mN / m. ｕｄ The lower limit of 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 this 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 this embodiment can be prepared by sequentially mixing the abrasive grains, the basic compound, the wetting agent, the nonionic surfactant, etc., with water. These components can be mixed using a homogenizer, ultrasonic waves, or other means commonly used in the technical field of polishing compositions.

[0043] The polishing composition described above is diluted with water to an appropriate concentration and then used for polishing semiconductor wafers. The water used for dilution may be, for example, ion-exchanged water, pure water, ultrapure water, distilled water, or the like.

[0044] The polishing composition according to this 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 a silicon wafer with the polishing composition.

[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]

[0048] The remainder of the polishing composition in Table 1 is water. Colloidal silica with average secondary particle sizes of 50 nm and 70 nm was used as 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 (completely saponified). S1 to S7 in the "Type" column of nonionic surfactants are as shown in Table 2.

[0049]

[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 γ ｄ )

[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 determined as follows. First, the weight W1 of a dry, empty pycnometer is measured using an electronic balance. The empty pycnometer is filled with pure water and the lid is placed on it, the pure water on the surface is wiped off, and the total weight W2 is measured. The pure water is discarded, and the pycnometer is filled with the polishing composition and the lid is placed on it, the polishing composition on the surface is wiped off, and the total weight W3 is measured. The specific gravity of the polishing composition is determined by 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 analysis was performed by the curve fitting method (Young-Laplace method).

[0053] Using the polishing compositions of these Examples and Comparative Examples, 12-inch silicon wafers were polished. The conductivity type of the silicon wafers used was P-type, with a resistivity of 0.1 Ωcm or more and less than 100 Ωcm. The polished surface was the <100> plane. The polishing apparatus used was an SPP800S single-sided polishing apparatus manufactured by Okamoto Machine Tools 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 platen rotation speed was 50 rpm, the carrier rotation speed was 49 rpm, and the polishing load surface pressure was 100 gf / cm. ２ Before polishing with the polishing compositions of Examples and Comparative Examples, preliminary polishing was carried out 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 numerical values ​​in this column are relative values ​​when Comparative Example 1 is set to 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 left standing vertically. The wettability of each silicon wafer was evaluated 5 seconds after being left standing. A case in which the distance of the water-repellent portion from the outer periphery 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 ｕｄ is 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 with the polishing composition of Comparative Example 1. In addition, the wettability imparting property to the wafer was also good.

[0057] FIG. 1 shows the γ ｄ / γ ｕｄ1 is a scatter diagram showing the relationship between the number of micro-defects (relative value) on the wafer after polishing and the number of micro-defects on the wafer after polishing. Open marks indicate that the wetting agent is a hydroxyethyl cellulose-based agent (HEC-1, HEC-2, or HEC-3), and solid marks indicate that the wetting agent is a modified polyvinyl alcohol. From FIG. 1, it can be seen that whether the wetting agent is a hydroxyethyl cellulose-based agent or a modified polyvinyl alcohol, γ ｄ / γ ｕｄ It can be seen that by setting the value of the saturation coefficient to 1.10 or more and 1.40 or less, it is possible to reduce the number of micro-defects.

[0058] The embodiments of the present invention have been described above. 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. A polishing composition comprising an abrasive grain, a basic compound, a wetting agent, and a nonionic surfactant, having a surface tension γ ｕｄ of 64 mN / m or less, and a ratio γ ｄ of the surface tension γ ｕｄ to the surface tension γ ｄ / γ ｕｄ of 1.10 or more and 1.40 or less when diluted 20-fold with water. However, the surface tensions γ ｄ and γ ｕｄ are values measured at 25°C.

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

3. The polishing composition according to claim 1 or 2, wherein the basic compound is at least one selected from the group consisting of oxides of alkali metals, salts of alkali metals, ammonia, ammonium salts, and quaternary ammonium hydroxides.

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

5. The polishing composition according to any one of claims 1 to 4, which is used for polishing a silicon wafer.

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.