Polishing composition

Abstract

To reduce the surface roughness in polishing an Si wafer.SOLUTION: An Si wafer-polishing composition is arranged to target an Si wafer for polishing. The Si wafer-polishing composition comprises silica, a pH adjuster and water, of which pH is 1.0-6.9. In the silica, a silanol group in its surface is substituted with a functional group including an amino group or a carboxy group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polishing composition for Si wafers. [Background technology]

[0002] Ultra-precision processing is an extremely important technology in the manufacturing of semiconductor products. With the recent trend toward miniaturization of LSI devices, the requirements for wafer surface roughness and flatness after precision polishing are becoming increasingly strict. Chemical mechanical polishing (CMP) is used for precision polishing. Various abrasives have been proposed for polishing compounds used in CMP.

[0003] Japanese Patent Application Laid-Open No. 2005-262413 describes the use of colloidal silica, with an average primary particle size of 1 nm or more and less than 40 nm and a zeta potential of -15 to 30 mV, as the abrasive in a polishing composition. This polishing composition can reduce nano-scratches and is suitable for use in polishing precision component substrates such as memory hard disk substrates and semiconductor substrates.

[0004] Japanese Patent Application Laid-Open Publication No. 2017-197590 discloses a polishing composition for polishing an object having an oxide film and a nitride film. This polishing composition has a pH of 2.0 or higher and contains silica exhibiting a positive zeta potential. This polishing composition can improve the polishing rate of an oxide film while suppressing the polishing rate of a nitride film. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-262413 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-197590 Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors have studied the composition of a polishing composition used for polishing Si wafers, and have found that the surface roughness can be reduced by providing a polishing composition with a composition specific to polishing Si wafers.

[0007] An object of the present invention is to provide a polishing composition that can reduce surface roughness when polishing a Si wafer. [Means for solving the problem]

[0008] A polishing composition for Si wafers according to one embodiment of the present invention is used to polish Si wafers. The polishing composition for Si wafers contains silica, a pH adjuster, and water. The pH is 1.0 to 6.9, and silanol groups on the surface of the silica are substituted with functional groups containing amino or carboxy groups. [Effects of the Invention]

[0009] According to the present invention, a polishing composition for Si wafers that can reduce surface roughness during polishing of Si wafers can be obtained. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 shows an example of silica in which the silanol groups on the surface are substituted with functional groups containing amino groups. [Figure 2] FIG. 2 shows an example of silica in which the silanol groups on the surface are substituted with functional groups containing carboxy groups. DETAILED DESCRIPTION OF THE INVENTION

[0011] The inventors have studied the composition of a polishing composition suitable for polishing Si wafers. In their studies, the inventors have attempted to use silica as abrasive grains and to perform surface modification by substituting silanol groups on the silica surface with functional groups. After further studies, the inventors have found that surface roughness can be reduced by making the polishing composition acidic and by configuring it so that the abrasive grains are silica that has been surface-modified with functional groups containing amino or carboxy groups.

[0012] A polishing composition for Si wafers according to one embodiment of the present invention is used to polish Si wafers. The polishing composition for Si wafers contains silica, a pH adjuster, and water. The polishing composition for Si wafers has a pH of 1.0 to 6.9, and silanol groups on the surface of the silica are substituted with functional groups containing amino or carboxy groups. By making the polishing composition acidic and substituting silanol groups on the surface of the silica with functional groups containing amino or carboxy groups, the surface roughness of the Si wafer can be reduced.

[0013] In the polishing composition for Si wafers, the silanol groups on the surface of the silica may be substituted with functional groups containing amino groups, or may be substituted with functional groups containing carboxy groups.

[0014] The mechanism by which the surface roughness of the Si wafer is reduced is not clear, but is considered as follows. By making the polishing composition acidic and substituting the silanol groups on the surface of the silica with functional groups containing amino or carboxy groups, the silanol groups on the surface of the silica are substituted with functional groups that carry a positive charge under acidic conditions. This is thought to make it easier for the zeta potential of the silica to fall within an appropriate range from the viewpoint of reducing surface roughness. As a result, it is thought that the surface roughness of the Si wafer is reduced.

[0015] The present invention also includes an embodiment of a method for polishing a Si wafer and a method for manufacturing a Si wafer including the polishing method. The method for polishing a Si wafer includes a step of polishing the Si wafer with a polishing composition disposed between the Si wafer and a polishing pad. The polishing composition contains abrasive grains, a pH adjuster, and water, and has a pH in the range of 1.0 to 6.9. The abrasive grains have a positive zeta potential under a pH condition of 1.0 to 6.9. The product of the zeta potential of the abrasive grains and the surface zeta potential of the Si wafer (parameter A) is negative (A<0), and the product of the zeta potential of the abrasive grains and the surface zeta potential of the polishing pad (parameter B) is -50 or greater (B≧-50). This polishing method can reduce the surface roughness of the Si wafer.

[0016] In the polishing method, the abrasive grains may be silica, and silanol groups on the surface of the silica may be substituted with functional groups including amino or carboxy groups. This allows the zeta potential of the abrasive grains, the relationship between the zeta potential of the abrasive grains and the Si wafer (A), and the relationship between the abrasive grains and the polishing pad (B) to be set within the above ranges with a simple configuration.

[0017] The polishing pad may be made of polyurethane, which makes it easier to set the relationship (B) between the abrasive grains and the polishing pad within the above range.

[0018] (silica) The silica as abrasive grains contained in the polishing composition of this embodiment may be, for example, colloidal silica. In each silica particle, at least a portion of the silanol groups on the surface are substituted with functional groups containing amino groups or carboxy groups. In other words, the silica is surface-modified with functional groups containing amino groups or carboxy groups. In the polishing composition, the functional groups are fixed to the silica.

[0019] The functional groups substituted with silanol groups on the surface of silica are positively charged under acidic conditions, i.e., pH conditions of 1.0 to 6.9, which is believed to make the abrasive properties, including the zeta potential of silica, in an acidic polishing composition favorable from the viewpoint of polishing performance.

[0020] FIG. 1 is a diagram showing an example of silica in which silanol groups on the surface are substituted with functional groups containing amino groups. In the example shown in FIG. 1, some of the silanol groups on the surface of the silica are substituted with functional groups 10. The functional groups 10 include amino groups 11. The amino groups 11 are functional groups formed by removing hydrogen from ammonia, primary amines, or secondary amines. R1 in FIG. 1 is a bonding chain between Si and the amino groups 20. R1 may be, for example, an alkylene group, a dialkylamino group, or a derivative thereof. For example, the functional group 10 may be a methylamino group, an ethylamino group, a propylamino group, an N-2-(aminoethyl)-3-aminopropyl group, or an N-2-(aminoethyl)-3-aminopropylmethyl group. R2 and R3 are hydrogen or substituents of the amino groups. As an example, the amino groups 11 are -NH3 + may be.

[0021] FIG. 2 is a diagram showing an example of silica in which silanol groups on the surface have been substituted with functional groups containing carboxy groups. In the example shown in FIG. 2, some of the silanol groups on the surface of the silica have been substituted with functional groups 10. The functional groups 10 contain carboxy groups 12. R4 in FIG. 2 is a bonding chain between Si and the carboxy groups 12. R4 may be, for example, an alkylene group such as a propylene group. For example, the functional group 10 may be a formic acid (methanoic acid) group, an acetic acid (ethanoic acid) group, a propionic acid (propanoic acid) group, or a butyric acid (butanoic acid) group.

[0022] The silanol groups on the surface of silica can be replaced with functional groups, for example, by a silane coupling agent. The type of functional group may be one or more. For example, the silica may be subjected to a single-layer treatment by silane coupling treatment, in which the silanol groups are replaced with one type of functional group. Alternatively, the silanol groups may be replaced with functional groups by a multi-layer treatment in which the silane coupling treatment is repeated after the single-layer treatment.

[0023] The content of silica as abrasive grains is not particularly limited, but is, for example, 0.10 to 20 mass% of the total polishing composition. The content of abrasive grains is preferably as low as possible from the viewpoint of reducing polishing scratches and residual foreign matter on the silicon wafer after polishing. On the other hand, if the polishing composition does not contain any abrasive grains, for example, it will be unable to remove the oxide film on the surface of the silicon wafer. The polishing composition is diluted 10 to 45 times before use during polishing. The polishing composition according to this embodiment is preferably diluted to an abrasive grain concentration of 20 to 20,000 ppm (ppm by mass; the same applies hereinafter). The higher the abrasive grain concentration, the more likely microdefects and haze are reduced. The lower limit of the abrasive grain concentration after dilution is preferably 1,000 ppm, more preferably 2,000 ppm. The upper limit of the abrasive grain concentration after dilution is preferably 15,000 ppm, more preferably 10,000 ppm.

[0024] (pH adjuster) The pH of the polishing composition is adjusted to 1.0 to 6.9 by the pH adjuster contained in the polishing composition. The pH of the polishing composition is preferably 1.0 to 6.0, more preferably 1.0 to 5.5. The pH adjuster used is acidic. The pH adjuster is not limited to a specific one, and may be, for example, at least one acid selected from inorganic acids and organic acids.

[0025] The inorganic acid may be at least one acid selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid. Examples of the organic acid include carboxylic acid, ascorbic acid, sulfonic acid, acidic phosphate ester, phosphonic acid, ethylene oxide adduct of alkylamine, polyhydric alcohol partial ester, and carboxylic acid amide.

[0026] Examples of the carboxylic acid include monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, and aromatic carboxylic acids.

[0027] Examples of carboxylic acid amides include ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetate, hydroxyethylethylenediaminetriacetic acid, sodium hydroxyethylethylenediaminetriacetate, diethylenetriaminepentaacetic acid, sodium diethylenetriaminepentaacetate, triethylenetetraminehexaacetic acid, and sodium triethylenetetraminehexaacetate.

[0028] Examples of phosphonic acids include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetrakis(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, and α-methylphosphonosuccinic acid.

[0029] The polishing composition of this embodiment may further contain at least one of the following additives: a water-soluble polymer, a surfactant, and a chelating agent.

[0030] Water-soluble polymers adsorb onto the surface of a workpiece, such as a semiconductor wafer, and modify the surface. This improves polishing uniformity and reduces surface roughness. Examples of water-soluble polymers that can be used include, but are not limited to, celluloses such as hydroxyethyl cellulose (HEC), hydroxyethyl methyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, cellulose acetate, and methyl cellulose; vinyl polymers such as polyvinyl alcohol (PVA), modified PVA (polyvinyl alcohol derivative), and polyvinylpyrrolidone (PVP); glycosides; and other polyhydric alcohols. Polyhydric alcohols are alcohols containing two or more hydroxy groups per molecule. Examples of glycosides include alkylene oxide derivatives of methyl glucoside. Examples of alkylene oxide derivatives of methyl glucoside include polyoxyethylene methyl glucoside and polyoxypropylene methyl glucoside.

[0031] The polishing composition of this embodiment is prepared by appropriately mixing silica, a pH adjuster, and other ingredients and adding water. Alternatively, the polishing composition of this embodiment can be prepared by sequentially mixing the abrasive grains, the pH adjuster, and other ingredients into water. These components can be mixed using a homogenizer, ultrasonic waves, or other means commonly used in the technical field of polishing compositions.

[0032] The polishing composition described above is diluted with water to an appropriate concentration and then used to polish semiconductor wafers. The polishing composition is suitable for polishing Si wafers (silicon substrates). [Example]

[0033] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0034] Slurries containing abrasive grains, pH adjusters, and water were prepared as shown in Table 1. Polishing was performed using these slurries under the following conditions. For each slurry, the pH of the slurry, the zeta potential of the abrasive grains, Si wafer, and polishing pad, parameters A and B, and surface roughness Sa were measured.

[0035] [Table 1]

[0036] (Slurry (polishing composition)) The abrasive grains A, B, C and D in Table 1 are as follows: Abrasive grain A is colloidal silica (product name: Quattron PL-3-C (Fuso Chemical Co., Ltd.)) in which the silanol groups on the surface have been replaced with functional groups containing amino groups (propylamino groups). The propylamino groups that have replaced the silanol groups in Abrasive grain A are functional groups that take on a positive charge in acidic conditions. Abrasive B is colloidal silica (product name: Quattron PL-3 (Fuso Chemical Co., Ltd.)) in which the silanol groups on the surface have not been replaced with functional groups. Abrasive C is colloidal silica (product name: Quattron PL-3-D (Fuso Chemical Co., Ltd.)) in which the silanol groups on the surface have been replaced with functional groups that do not contain either amino or carboxyl groups. The functional groups that have replaced the silanol groups in Abrasive C are negatively charged in acidic conditions. Abrasive D is colloidal silica (product name: Quattron PL-3-P (Fuso Chemical Co., Ltd.)) in which the silanol groups on the surface have been replaced with functional groups containing carboxyl groups (acetate groups). The acetate groups that have replaced the silanol groups in Abrasive D are functional groups that take on a positive charge in acidic conditions.

[0037] (polishing conditions) Polishing equipment: single-sided polishing machine Polishing pad: Polyurethane pad (representative physical properties: hardness 83; JIS-A, compressibility 2.2%, density 0.40 g / cm 3 ) (manufactured by Nitta DuPont Co., Ltd.) Flow rate: 300mL / min Surface pressure: 150 (gf / cm 2 ) Wafer to be polished: 8" silicon wafer

[0038] (zeta potential measurement) The zeta potential of the slurry was measured using a ZETASIZER NANO (manufactured by Malvern) as a measuring device. The zeta potential of the Si wafer and pad was measured using an ELSZ-2 (manufactured by Otsuka Electronics Co., Ltd.) as a measuring device.

[0039] (Parameter calculation) Parameter A: Zeta potential of abrasive grain × Zeta potential of silicon wafer Parameter B: Zeta potential of abrasive grains × Zeta potential of polishing pad

[0040] (Surface roughness Sa measurement conditions) Measuring device: Contour GT-X (manufactured by Bruker) Measurement field of view: 177 μm x 133 μm Sa is calculated as the arithmetic mean height (ISO 25178).

[0041] (Evaluation (Slurry Composition)) The results shown in Table 1 indicate that Examples 1 to 3, which contain silica abrasive grains in which surface silanol groups have been substituted with functional groups containing amino or carboxy groups and have an acidic pH of 1.0 to 6.9, have reduced surface roughness compared to Comparative Examples 1 and 2, which contain silica abrasive grains in which surface silanol groups have not been substituted or have been substituted with functional groups containing neither amino nor carboxy groups and have an acidic pH. Furthermore, Examples 1 to 3 also have reduced surface roughness compared to Comparative Examples 3 and 4, which contain silica abrasive grains in which surface silanol groups have been substituted with functional groups containing amino groups but have an alkaline pH of 7.0 or higher. These results demonstrate that the surface roughness of Si wafers can be reduced by using a slurry containing silica abrasive grains in which surface silanol groups have been substituted with functional groups containing amino or carboxy groups and having an acidic pH. Furthermore, the silanol groups on the surface of abrasive grains A and D have been substituted with functional groups that are positively charged in acidic conditions, while the silanol groups on the surface of abrasive grains C have been substituted with functional groups that are negatively charged in acidic conditions. This indicates that the surface roughness of Si wafers can be reduced by using silica abrasive grains whose surface silanol groups have been substituted with functional groups that are positively charged in acidic conditions in a slurry with an acidic pH.

[0042] (Evaluation (Zeta potential configuration)) Furthermore, in the results shown in Table 1, Examples 1 to 3, in which the surface roughness was reduced, all satisfied the conditions that the abrasive grains had a positive zeta potential, A<0, and B≧−50. In contrast, Comparative Examples 1 to 4, in which the surface roughness was relatively large, did not satisfy one or more of the above three conditions. This indicates that the surface roughness can be reduced when the abrasive grains have a positive zeta potential at a pH of 1.0 to 6.9, the product of the abrasive grains' zeta potential and the surface zeta potential of the Si wafer is negative (A<0), and the product of the abrasive grains' zeta potential and the surface zeta potential of the polishing pad is −50 or greater (B≧−50). It was also found that the above zeta potential conditions are more easily satisfied by using silica abrasive grains in which the surface silanol groups are substituted with functional groups containing amino or carboxy groups and by adjusting the pH to an acidic level.

[0043] 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

[Claim 1] A polishing composition for Si wafers to be polished, comprising: Silica and A pH adjuster; and water, pH is 1.0 to 6.9, A polishing composition for Si wafers, wherein silanol groups on the surface of the silica are substituted with functional groups containing carboxy groups.

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