JP7519865B2 - Polishing Method - Google Patents

Description

This disclosure relates to a method for polishing a silicon substrate and a method for manufacturing a semiconductor substrate.

In recent years, the design rules for semiconductor devices have become increasingly finer due to the increasing demand for higher storage capacity of semiconductor memories. As a result, the depth of focus in the photolithography used in the manufacturing process of semiconductor devices has become shallower, and the demands for reduced defects and smoothness of silicon substrates (bare wafers) have become increasingly strict.

In order to improve the quality of silicon substrates, polishing of silicon substrates is carried out in multiple stages. In particular, the final polishing stage, which is performed, aims to suppress surface roughness (haze) and to suppress surface defects (LPD: Light Point Defects) such as particles, scratches, and pits by improving the wettability (hydrophilicity) of the silicon substrate surface after polishing.

The allowable size of surface defects on silicon substrate surfaces is becoming smaller every year, and these defects are usually measured by irradiating the substrate surface with laser light and detecting the scattered light. Therefore, in order to measure smaller defects, it is necessary to reduce the surface roughness (haze) of the silicon substrate and improve the signal-to-noise ratio when measuring defects.

As polishing compositions used for finish polishing, polishing compositions for chemical mechanical polishing using colloidal silica and an alkaline compound are known (Patent Documents 1 to 3).

Patent Document 1 reports a polishing composition containing a water-soluble polymer compound such as hydroxyethyl cellulose or polyethylene oxide as a polishing composition intended to improve the haze level.
Patent Document 2 reports a polishing composition containing a water-soluble polymer compound having a nitrogen-containing group, such as polyvinylpyrrolidone and poly-N-vinylformamide, as a polishing composition intended to reduce the number of surface defects (LPDs).
Patent Document 3 reports a polishing liquid containing a water-soluble polymeric compound having a nitrogen-containing group, such as polyethyleneimine, as a polishing liquid composition that aims to simultaneously achieve a high polishing rate and prevent surface roughening of the substrate surface after polishing.

JP 2004-128089 A JP 2008-53415 A JP 2007-19093 A

In order to reduce surface defects, colloidal silica with smaller particle size is used in the polishing liquid used in the finish polishing, but the polishing speed tends to be slower, and there is a problem in improving the polishing speed.
However, in polishing using the polishing compositions of Patent Documents 1 to 3, the polishing rate is not sufficient.

This disclosure provides a method for polishing silicon substrates and a method for manufacturing semiconductor substrates that can improve the polishing speed.

In one aspect, the present disclosure relates to a polishing method that includes a step of polishing a silicon substrate to be polished using a polishing liquid composition containing silica particles (component A) and an amino group-containing water-soluble polymer (component B), and the polishing is performed under the conditions that the zeta potential of component A is 0 mV or more, the zeta potential of the silicon substrate to be polished is positive, and the sum of the absolute values of the zeta potentials of component A and the silicon substrate to be polished is 28 mV or less.

In one aspect, the present disclosure relates to a method for manufacturing a semiconductor substrate, comprising the steps of polishing a silicon substrate to be polished using the polishing method of the present disclosure, and cleaning the polished silicon substrate.

The present disclosure provides a method for polishing silicon substrates and a method for manufacturing semiconductor substrates that can improve the polishing speed.

This disclosure is based on the finding that a silicon substrate can be polished at high speed by using a polishing composition containing silica particles and an amino group-containing water-soluble polymer under conditions where the zeta potential of the silica particles is 0 mV or more, the zeta potential of the silicon substrate to be polished is positive, and the sum of the absolute values of the zeta potentials of component A and the silicon substrate to be polished is a predetermined value or less.

That is, in one aspect, the present disclosure relates to a polishing method (hereinafter also referred to as the "polishing method of the present disclosure") that includes a step of polishing a silicon substrate to be polished using a polishing liquid composition containing silica particles (component A) and an amino group-containing water-soluble polymer (component B), and that is performed under conditions in which the zeta potential of component A is 0 mV or more, the zeta potential of the silicon substrate to be polished is positive, and the sum of the absolute values of the zeta potentials of component A and the silicon substrate to be polished is 28 mV or less.

According to the present disclosure, in one or more embodiments, the polishing speed can be improved.

Although the details of the mechanism by which the effects of the present disclosure are exerted are not clear, it is presumed as follows.
When the zeta potential of the silica particles (component A) which are polishing particles and the zeta potential of the silicon substrate to be polished have the same sign, a repulsive force acts between the silica particles (component A) and the silicon substrate to be polished, and the force and/or the number of contacts of the silica particles (component A) with the silicon substrate to be polished are reduced, and as a result, the polishing speed is reduced.Therefore, if the repulsive force acting between the silica particles (component A) and the silicon substrate to be polished is reduced, that is, if the sum of the absolute values of the zeta potential of the silica particles (component A) and the zeta potential of the silicon substrate to be polished is reduced, the polishing speed is improved.
The zeta potential of the silica particles and the zeta potential of the silicon substrate to be polished are generally both negative, but in the present disclosure, an amino group-containing water-soluble polymer compound (component B) is adsorbed onto the silica particles (component A) or the silicon substrate to be polished, changing the zeta potential of the silica particles (component A) to 0 mV or more, changing the zeta potential of the silicon substrate to be polished to positive, and reducing the sum of the absolute values of the zeta potentials of the silica particles (component A) and the silicon substrate to be polished, which is believed to make it possible to improve the polishing rate.
However, the present disclosure need not be construed as being limited to these mechanisms.

[Polishing process]
The polishing method of the present disclosure includes a step of polishing a silicon substrate to be polished (hereinafter also referred to as the "polishing step of the present disclosure") using a polishing liquid composition containing silica particles (component A) and an amino group-containing water-soluble polymer (component B) (hereinafter also referred to as the "polishing liquid composition of the present disclosure").
Polishing in the polishing step of the present disclosure is performed under conditions where the zeta potential of component A is 0 mV or more, the zeta potential of the silicon substrate to be polished is positive, and the sum of the absolute values of the zeta potentials of component A and the silicon substrate to be polished is 28 mV or less.

The zeta potential of component A is usually negative, and in the polishing process of the present disclosure, component B is adsorbed to component A, so that the zeta potential of component A becomes 0 mV or positive. In the polishing process of the present disclosure, the zeta potential of component A in the polishing liquid composition of the present disclosure is preferably 0 mV or more, more preferably +2 mV or more, and even more preferably +3 mV or more, from the viewpoint of easily adjusting the zeta potential of the silica particles and silicon substrate by component B, and is preferably +20 mV or less, more preferably +18 mV or less, even more preferably +15 mV or less, even more preferably +10 mV or less, and even more preferably +7 mV or less, in order to improve the polishing rate.

The zeta potential of the silicon substrate to be polished is usually negative, but in the polishing process of the present disclosure, the zeta potential of the silicon substrate to be polished becomes positive by adsorbing component B to the silicon substrate to be polished. In the polishing process of the present disclosure, the zeta potential of the silicon substrate to be polished is preferably greater than 0 mV, more preferably +1 mV or more, even more preferably +2 mV or more, and even more preferably +3 mV or more, from the viewpoint of easily adjusting the zeta potential of the silica particles and silicon substrate by component B, and is preferably +10 mV or less, more preferably +9 mV or less, and even more preferably +8 mV or less, from the viewpoint of improving the polishing rate.

In the polishing process of the present disclosure, the sum of the absolute value of the zeta potential of the silica particles (component A) and the absolute value of the zeta potential of the silicon substrate to be polished is preferably more than 0 mV, more preferably 2 mV or more, even more preferably 5 mV or more, and even more preferably 8 mV or more, from the viewpoint of easily adjusting the zeta potential of the silica particles and the silicon substrate by component B, and is 28 mV or less, preferably 24 mV or less, more preferably 20 mV or less, even more preferably 18 mV or less, even more preferably 15 mV or less, and even more preferably 12 mV or less, from the viewpoint of improving the polishing rate.

In the polishing process of the polishing method of the present disclosure, for example, the silicon substrate to be polished can be pressed against a platen to which a polishing pad is attached, and the silicon substrate to be polished can be polished at a polishing pressure of 3 to 20 kPa. In this disclosure, the polishing pressure refers to the pressure of the platen applied to the surface of the silicon substrate to be polished during polishing.

In the polishing step of the polishing method of the present disclosure, for example, the silicon substrate to be polished can be pressed against a platen to which a polishing pad is attached, and the silicon substrate to be polished can be polished with a polishing liquid composition and a polishing pad surface temperature of 15°C to 40°C. From the viewpoint of achieving both an improvement in the polishing rate and surface quality such as a reduction in surface roughness (haze), the temperature of the polishing liquid composition and the polishing pad surface temperature are preferably 15°C or higher or 20°C or higher, and preferably 40°C or lower or 30°C or lower.

[Silicon substrate to be polished]
The polishing method of the present disclosure is a method for polishing a silicon substrate, and can be used, for example, in a polishing step of polishing a silicon substrate to be polished in a manufacturing method of a semiconductor substrate, or in a polishing step of polishing a silicon substrate to be polished in a polishing method of a silicon substrate. In one or more embodiments, the silicon substrate to be polished using the polishing liquid composition of the present disclosure can be a silicon substrate, etc., and in one or more embodiments, a single crystal silicon substrate, a polysilicon substrate, a substrate having a polysilicon film, a SiN substrate, etc. can be used. From the viewpoint of exerting the effect of the polishing liquid composition of the present disclosure, a single crystal silicon substrate or a polysilicon substrate is preferred, and a single crystal silicon substrate is more preferred.

[Silica particles (component A)]
The polishing composition of the present disclosure contains silica particles (hereinafter also referred to as "component A") as an abrasive. Examples of component A include colloidal silica, fumed silica, pulverized silica, and silica obtained by surface modification thereof. From the viewpoint of achieving both improved polishing rate and storage stability, and from the viewpoint of improving surface quality such as reducing surface roughness (haze), surface defects, and scratches, colloidal silica is preferred. Component A may be one type or a combination of two or more types.

From the viewpoint of ease of use, the use form of component A is preferably a slurry. When component A contained in the polishing liquid composition of the present disclosure is colloidal silica, from the viewpoint of preventing contamination of silicon substrates by alkali metals, alkaline earth metals, etc., the colloidal silica is preferably obtained from a hydrolyzate of an alkoxysilane. Silica particles obtained from a hydrolyzate of an alkoxysilane can be produced by a conventionally known method.

From the viewpoint of maintaining the polishing rate, the average primary particle diameter of component A is preferably 10 nm or more, more preferably 20 nm or more, and from the viewpoint of improving storage stability and improving surface quality such as reducing surface roughness (haze), surface defects and scratches, it is preferably 50 nm or less, more preferably 45 nm or less, even more preferably 40 nm or less, and even more preferably 30 nm or less. From the same viewpoint, the average primary particle diameter of component A is preferably 10 nm or more and 50 nm or less, more preferably 20 nm or more and 45 nm or less, even more preferably 20 nm or more and 40 nm or less, and preferably 20 nm or more and 30 nm or less.
In the present disclosure, the average primary particle size of component A is calculated using the specific surface area S ( ^m2 /g) calculated by the nitrogen adsorption method (BET method). The average primary particle size value is a value measured by the method described in the Examples.

From the viewpoint of maintaining the polishing rate, the average secondary particle diameter of component A is preferably 20 nm or more, more preferably 30 nm or more, and even more preferably 40 nm or more, and from the viewpoint of improving storage stability and improving surface quality such as reducing surface roughness (haze), surface defects, and scratches, it is preferably 100 nm or less, more preferably 90 nm or less, even more preferably 80 nm or less, even more preferably 70 nm or less, and even more preferably 60 nm or less. From the same viewpoint, the average secondary particle diameter of component A is preferably 20 nm or more and 100 nm or less, more preferably 30 nm or more and 90 nm or less, even more preferably 30 nm or more and 80 nm or less, even more preferably 30 nm or more and 70 nm or less, and even more preferably 40 nm or more and 60 nm or less.
In the present disclosure, the average secondary particle size is a value measured by a dynamic light scattering (DLS) method, and is a value measured by the method described in the Examples.

From the viewpoint of improving storage stability and surface quality, the degree of association of component A is preferably 3 or less, more preferably 2.5 or less, and even more preferably 2.3 or less, and from the viewpoint of achieving both an improvement in polishing rate and storage stability and improving surface quality, the degree of association is preferably 1.1 or more, more preferably 1.5 or more, and even more preferably 1.8 or more.

In the present disclosure, the degree of association of component A is a coefficient representing the shape of the silica particles and is calculated by the following formula.
Degree of association = average secondary particle size / average primary particle size

Methods for adjusting the degree of association of component A can be, for example, those described in JP-A-6-254383, JP-A-11-214338, JP-A-11-60232, JP-A-2005-060217, JP-A-2005-060219, etc.

The shape of component A is preferably spherical and/or cocoon-shaped from the viewpoints of achieving both improved polishing speed and storage stability, and of improving surface quality.

The content of component A in the polishing composition of the present disclosure is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, and even more preferably 0.07 mass% or more, calculated as _SiO2 , from the viewpoint of improving the polishing rate, and from the viewpoint of improving storage stability, reducing surface roughness, and reducing residues on the silicon substrate surface, it is preferably 2.5 mass% or less, more preferably 1 mass% or less, and even more preferably 0.8 mass% or less. Therefore, the content of component A in the polishing composition of the present disclosure is preferably 0.01 mass% or more and 2.5 mass% or less, more preferably 0.05 mass% or more and 1 mass% or less, and even more preferably 0.07 mass% or more and 0.8 mass% or less. When component A is a combination of two or more types, the content of component A refers to the total content thereof.
Furthermore, when the silicon substrate to be polished is a single crystal silicon substrate, the content of component A in the polishing liquid composition of the present disclosure is more preferably 0.5 mass% or less, more preferably 0.3 mass% or less, and even more preferably 0.2 mass% or less, from the viewpoint of improving storage stability, reducing surface roughness, and reducing residues on the silicon substrate surface. Therefore, the content of component A in the polishing liquid composition of the present disclosure is more preferably 0.07 mass% or more and 0.5 mass% or less, even more preferably 0.07 mass% or more and 0.3 mass% or less, and even more preferably 0.07 mass% or more and 0.2 mass% or less.
Furthermore, when the silicon substrate to be polished is a polysilicon substrate, the content of component A in the polishing liquid composition of the present disclosure is more preferably 0.1 mass% or more, more preferably 0.2 mass% or more, and even more preferably 0.3 mass% or more from the viewpoint of improving the polishing rate. Therefore, the content of component A in the polishing liquid composition of the present disclosure is more preferably 0.1 mass% or more and 0.8 mass% or less, even more preferably 0.2 mass% or more and 0.8 mass% or less, and even more preferably 0.3 mass% or more and 0.8 mass% or less.

[Amino group-containing water-soluble polymer (component B)]
The polishing liquid composition of the present disclosure contains an amino group-containing water-soluble polymer (hereinafter also referred to as "component B"). It is believed that component B can adjust the zeta potential of the silica particles (component A) and the silicon substrate to be polished, reduce the electrostatic repulsion between the silica particles (component A) and the silicon substrate to be polished, and suppress the aggregation of the silica particles. In the present disclosure, "water-soluble" means that the solubility in water (20°C) is 0.5 g/100 mL or more, preferably 2 g/100 mL or more.

Component B preferably contains a structural unit derived from allylamine from the viewpoint of reducing the sum of the absolute values of the zeta potentials of the silica particles and the silicon substrate to be polished and improving the polishing rate. In one or more embodiments, the amino group-containing water-soluble polymer having a structural unit derived from allylamine has a pKa of preferably 7.7 or more, more preferably 7.8 or more, from the viewpoint of reducing the sum of the absolute values of the zeta potentials of the silica particles and the silicon substrate to be polished and improving the polishing rate, and from the same viewpoint, preferably 9.2 or less, more preferably 8.5 or less, even more preferably 8.3 or less, even more preferably 8.1 or less, and even more preferably 8 or less.

In one or more embodiments, at least a part of the amino groups in the allylamine-derived structural unit preferably has a steric shielding group from the viewpoint of reducing the sum of the absolute values of the zeta potential of the silica particles and the silicon substrate to be polished and improving the polishing rate. In the present disclosure, the steric shielding group refers to a three-dimensional (bulky) substituent that can shield the nitrogen atom of the amino group of component B to suppress cationization, i.e., lower the pKa. From the same viewpoint, the amino group having a steric shielding group is preferably a secondary amino group or a tertiary amino group containing a hydrocarbon group having 3 to 11 carbon atoms and having a hydroxyl group. The number of carbon atoms of the hydrocarbon group is preferably 3 or more from the viewpoint of improving the shielding property of the amino group (suppressing the cationization of the nitrogen atom of the amino group) and improving the polishing rate, and from the viewpoint of improving water solubility and availability, it is preferably 11 or less, more preferably 7 or less, even more preferably 5 or less, and even more preferably 4 or less.

In one or more embodiments, the amino group having a steric shielding group is a modified group of an amino group by a glycidol derivative, and in one or more embodiments, it is a group formed by reacting an amino group in an allylamine-derived structural unit with a glycidol derivative. At least a part of the amino groups of component B1 are modified by a glycidol derivative to become an amino group having a steric shielding group. The equivalent of the glycidol derivative relative to the number of amino groups (1 equivalent) in the allylamine-derived structural unit (hereinafter also referred to as the "glycidol modification rate") is preferably 0 or more, more preferably 0.5 or more, even more preferably 0.6 or more, even more preferably 0.7 or more, even more preferably 0.8 or more, even more preferably 0.9 or more, and from the same viewpoint, it is preferably 1.1 or less, and more preferably 1 or less.

In the present disclosure, the glycidol modification rate is a value measured by the method described in the Examples using ¹³ C-NMR, however, the glycidol modification rate can also be measured by the following method (1) or (2).
(1) It can be calculated from the amino group equivalent of the allylamine polymer and the number of moles of the glycidol derivative used as the reaction raw material.
(2) The nitrogen content N (mass %) of the reaction product of a glycidol derivative and an allylamine polymer is measured, and the nitrogen content N can be calculated from the following formula.
Glycidol modification rate = A/B
Here, A=(100−N×molecular weight of allylamine monomer/14)/molecular weight of glycidol derivative, and B=N/14.

Examples of the glycidol derivative include glycidol and alkyl glycidyl ether, and glycidol is preferred from the viewpoints of availability and improving the polishing rate. From the viewpoint of availability, the alkyl group of the alkyl glycidyl ether is preferably an alkyl group having 1 to 8 carbon atoms, and examples of the alkyl group include methyl, ethyl, propyl, butyl, and 2-ethylhexyl groups. Examples of the alkyl glycidyl ether include methyl glycidyl ether and 2-ethylhexyl glycidyl ether.

In terms of availability and improving the polishing rate, in one or more embodiments, component B may be a polyallylamine in which at least some of the amino groups have a steric shielding group, and in one or more embodiments, a reaction product of polyallylamine and a glycidol derivative may be used. In terms of reducing the total absolute value of the zeta potential of the silica particles and the silicon substrate to be polished and improving the polishing rate, and in terms of availability, component B is preferably a reaction product of polyallylamine and a glycidol derivative, in which the equivalent of the glycidol derivative relative to the number of amino groups (1 equivalent) of polyallylamine is 0.5 or more and 1.1 or less.

In one or more embodiments, an example of Component B is a compound containing a structural unit represented by the following formula (I) (glycidol-modified polyallylamine).

In formula (I), R ¹ and R ² are each a hydrogen atom or a sterically shielding group. Examples of the sterically shielding group include modifying groups derived from glycidol derivatives, and in one or more embodiments, examples include 1-molar or 2-molar adducts of glycidol, and in one or more embodiments, examples include -CH ₂ CH(OH)CH ₂ (OH), -CH ₂ CH(OH)CH ₂ O-CH ₂ CH(OH)CH ₂ (OH), etc.

From the viewpoint of improving the polishing rate, the weight average molecular weight of component B is preferably 800 or more, more preferably 1,000 or more, even more preferably 1,500 or more, and even more preferably 2,000 or more, and from the viewpoint of reducing surface roughness and surface defects, it is preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less, even more preferably 20,000 or less, even more preferably 15,000 or less, even more preferably 12,000 or less, even more preferably 10,000 or less, and even more preferably 8,000 or less. The weight average molecular weight of component B in this disclosure can be measured, for example, by the method described in the Examples.

The content of component B in the polishing composition of the present disclosure is preferably 10 ppm by mass or more, more preferably 20 ppm by mass or more, and even more preferably 30 ppm by mass or more, from the viewpoint of improving the polishing rate, and is preferably 200 ppm by mass or less, more preferably 150 ppm by mass or less, and even more preferably 120 ppm by mass or less, from the viewpoint of reducing surface roughness and surface defects. In this disclosure, 1% by mass is 10,000 ppm by mass (the same applies below).

The ratio of the content of component B to the content of component A in the polishing liquid composition of the present disclosure (mass ratio B/A) is preferably 0.008 or more, more preferably 0.016 or more, and even more preferably 0.025 or more, from the viewpoint of reducing the total absolute value of the zeta potential of the silica particles and the silicon substrate to be polished, and from the same viewpoint, is preferably 0.16 or less, more preferably 0.12 or less, and even more preferably 0.09 or less.

[water]
In one or more embodiments, the polishing liquid composition of the present disclosure may contain water. Examples of water include ion-exchanged water and ultrapure water. The content of water in the polishing liquid composition of the present disclosure may be, for example, the remainder of component A, component B, and any optional components described below.

[Nitrogen-containing basic compound (component C)]
In one or more embodiments, the polishing liquid composition of the present disclosure preferably further contains a nitrogen-containing basic compound (hereinafter also referred to as “component C”) from the viewpoint of adjusting the pH. is preferably a water-soluble nitrogen-containing basic compound from the viewpoint of achieving both an improvement in the polishing rate and storage stability, and from the viewpoint of improving the surface quality. In the present disclosure, the term "water-soluble nitrogen-containing basic compound" refers to a compound having a solubility of 0.5 g/100 mL or more, preferably 2 g/100 mL or more, in water (20° C.). It refers to a nitrogen-containing compound that exhibits basicity when dissolved. In one or more embodiments, component C does not include an amino group-containing water-soluble polymer (component B). Component C is one or a combination of two or more kinds.

In one or more embodiments, component C may be at least one selected from an amine compound and an ammonium compound. Examples of component C include ammonia, ammonium hydroxide, ammonium carbonate, ammonium hydrogen carbonate, dimethylamine, trimethylamine, diethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, N-methylethanolamine, N-methyl-N,N-diethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-dibutylethanolamine, N-(β-aminoethyl)ethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, ethylenediamine, hexamethylenediamine, piperazine hexahydrate, anhydrous piperazine, 1-(2-aminoethyl)piperazine, N-methylpiperazine, diethylenetriamine, tetramethylammonium hydroxide, and hydroxylamine. Among these, from the viewpoint of achieving both improved polishing speed and storage stability, ammonia or a mixture of ammonia and hydroxyamine is preferred as component C, and ammonia is more preferred.

When the polishing liquid composition of the present disclosure contains component C, the content of component C in the polishing liquid composition of the present disclosure is preferably 5 ppm by mass or more, more preferably 10 ppm by mass or more, and even more preferably 20 ppm by mass or more from the viewpoint of improving the polishing rate, and is preferably 500 ppm by mass or less, more preferably 300 ppm by mass or less, and even more preferably 150 ppm by mass or less from the viewpoint of improving storage stability, improving surface quality, and suppressing corrosion of the silicon substrate. From the same viewpoint, the content of component C in the polishing liquid composition of the present disclosure is preferably 5 ppm by mass or more and 500 ppm by mass or less, more preferably 10 ppm by mass or more and 300 ppm by mass or less, and even more preferably 20 ppm by mass or more and 150 ppm by mass or less. When component C is a combination of two or more types, the content of component C refers to the total content thereof.

When the polishing liquid composition of the present disclosure contains component C, the ratio C/A (mass ratio C/A) of the content of component C to the content of component A in the polishing liquid composition of the present disclosure is preferably 0.002 or more, more preferably 0.01 or more, and even more preferably 0.015 or more from the viewpoint of improving the polishing rate, and is preferably 1 or less, more preferably 0.5 or less, even more preferably 0.1 or less, and even more preferably 0.05 or less from the viewpoint of improving storage stability, improving surface quality, and suppressing corrosion of the silicon substrate. From the same viewpoint, the mass ratio C/A in the polishing liquid composition of the present disclosure is preferably 0.002 or more and 1 or less, more preferably 0.01 or more and 0.5 or less, even more preferably 0.01 or more and 0.1 or less, and even more preferably 0.015 or more and 0.05 or less.

[Other ingredients]
The polishing liquid composition of the present disclosure may further contain other components within a range that reduces the sum of the absolute values of the zeta potential of the silica particles and the silicon substrate to be polished. In one or more embodiments, the other components include a water-soluble polymer other than component B, a pH adjuster other than component C, a preservative, an alcohol, a chelating agent, an oxidizing agent, and the like.

[pH]
The pH of the polishing liquid composition of the present disclosure is preferably more than 8.5, more preferably 9 or more, even more preferably 9.5 or more, and even more preferably 10 or more, from the viewpoint of improving the polishing rate and storage stability, and is preferably 14 or less, more preferably 13 or less, even more preferably 12.5 or less, even more preferably 12 or less, even more preferably 11.5 or less, and even more preferably 11 or less. From the same viewpoint, the pH of the polishing liquid composition of the present disclosure is preferably more than 8.5 to 14 or less, more preferably 9 to 13 or less, even more preferably 9.5 to 12.5 or less, even more preferably 9.5 to 12 or less, even more preferably 9.5 to 11.5 or less, and even more preferably 10 to 11 or less. The pH of the polishing liquid composition of the present disclosure can be adjusted using component C or a known pH adjuster. In the present disclosure, the above pH is a value measured by the method described in the Examples.

[pH-pKa]
From the viewpoints of improving the polishing rate and improving storage stability, the pH of the polishing liquid composition of the present disclosure is preferably higher than the pKa of component B. From the same viewpoints, the difference between the pH and the pKa (pH-pKa) is preferably more than 0, more preferably 0.5 or more, even more preferably 1 or more, even more preferably 1.5 or more, and even more preferably 2 or more, and from the viewpoint of improving the surface quality, it is preferably 5.3 or less, more preferably 4 or less, even more preferably 3.5 or less, and even more preferably 3 or less.

The polishing liquid composition of the present disclosure can be produced, for example, by blending component A and component B, and, if desired, water, component C, and other components by a known method. That is, the polishing liquid composition of the present disclosure can be produced, for example, by blending at least component A and component B. Therefore, in another aspect, the present disclosure relates to a method for producing a polishing liquid composition, which includes a step of blending at least component A and component B. In the present disclosure, "blending" includes mixing component A, component B, and, if necessary, water, component C, and other components simultaneously or in any order. The blending can be performed using, for example, a stirrer such as a homomixer, homogenizer, ultrasonic disperser, wet ball mill, or bead mill. The preferred blending amount of each component in the method for producing a polishing liquid composition of the present disclosure can be the same as the preferred content of each component in the polishing liquid composition of the present disclosure described above.

In this disclosure, "the content of each component in the polishing composition" refers to the content of each component at the time of use, i.e., at the time when the polishing composition is first used for polishing.

The polishing liquid composition of the present disclosure may be produced as a concentrate from the viewpoint of storage and transportation, and may be diluted at the time of use. The dilution ratio is preferably 2 times or more, more preferably 10 times or more, even more preferably 30 times or more, and even more preferably 50 times or more from the viewpoint of production and transportation costs, and is preferably 180 times or less, more preferably 140 times or less, even more preferably 100 times or less, and even more preferably 70 times or less from the viewpoint of storage stability. The polishing liquid composition concentrate of the present disclosure can be used by diluting with water so that the content of each component at the time of use is the above-mentioned content (i.e., the content at the time of use). In the present disclosure, the "time of use" of the polishing liquid composition concentrate refers to the state in which the polishing liquid composition concentrate is diluted.

[Method of manufacturing semiconductor substrate]
In another aspect, the present disclosure relates to a method for manufacturing a semiconductor substrate (hereinafter also referred to as the "semiconductor substrate manufacturing method of the present disclosure"), which includes a step of polishing a silicon substrate to be polished using the polishing method of the present disclosure (hereinafter also referred to as the "polishing step") and a step of cleaning the polished silicon substrate (hereinafter also referred to as the "cleaning step"). According to the semiconductor substrate manufacturing method of the present disclosure, the polishing rate can be improved by using the polishing method of the present disclosure, so that high-quality semiconductor substrates can be manufactured at high yield, high productivity, and low cost.

The polishing step in the semiconductor substrate manufacturing method of the present disclosure can include, for example, a lapping (rough polishing) step of planarizing a single crystal silicon substrate obtained by slicing a single crystal silicon ingot into a thin disk, and a finish polishing step of etching the lapped single crystal silicon substrate and then mirror-finishing the surface of the single crystal silicon substrate. The polishing liquid composition of the present disclosure is more preferably used in the finish polishing step from the viewpoint of achieving both improved polishing rate and improved surface quality.

The polishing step in the semiconductor substrate manufacturing method of the present disclosure can include, for example, a step of removing irregularities in the polysilicon film and planarizing a substrate in which a polysilicon film is formed by chemical vapor deposition (CVD) on a silicon substrate having a silicon dioxide film and a silicon nitride film, and a step of simultaneously polishing and planarizing the silicon dioxide film and silicon nitride film directly below and the polysilicon film. From the viewpoint of achieving both improved polishing rate and improved surface quality, the polishing liquid composition of the present disclosure is more preferably used in the step of removing irregularities in the polysilicon film and planarizing the substrate.

In one or more embodiments, the semiconductor substrate manufacturing method of the present disclosure may include a dilution step of diluting a concentrate of the polishing liquid composition of the present disclosure prior to the polishing step. The diluting medium may be, for example, water.

In the polishing step in the semiconductor substrate manufacturing method of the present disclosure, polishing can be performed under the same conditions (zeta potential of the silica particles and the silicon substrate to be polished, polishing pressure, polishing liquid composition and surface temperature of the polishing pad, etc.) as in the polishing step in the polishing method of the present disclosure described above.

In the cleaning step of the semiconductor substrate manufacturing method of the present disclosure, it is preferable to perform inorganic cleaning from the viewpoint of reducing residues on the silicon substrate surface. Examples of cleaning agents used in inorganic cleaning include inorganic cleaning agents containing at least one selected from hydrogen peroxide, ammonia, hydrochloric acid, sulfuric acid, hydrofluoric acid, and ozone water.

In one or more embodiments, the semiconductor substrate manufacturing method of the present disclosure may further include, after the cleaning step, a step of rinsing the cleaned silicon substrate with water and drying it.

The present disclosure will be explained in more detail below with reference to examples, but these are merely illustrative and the present disclosure is not limited to these examples.

1. Preparation of polishing composition (concentrate of polishing composition)
A concentrate (60 times) of the polishing composition was obtained by mixing and stirring silica particles (component A) shown in Tables 1 and 2, a water-soluble polymer (component B or non-component B) shown in Tables 1 and 2, ammonia (component C), and ultrapure water. The pH of the concentrate at 25° C. was 10.6 to 11.0.
(Polishing composition)
The concentrate was diluted 60-fold with ion-exchanged water to obtain polishing compositions of Examples 1 to 4 and Comparative Examples 1 to 3. The content of each component in Tables 1 and 2 is the content of each component (mass % or mass ppm, active content) at the time of use of the diluted polishing composition. The content of ultrapure water is the remainder excluding component A and component B, or non-component B and component C. The pH at 25° C. of each polishing composition (at the time of use) was 10.2 or 10.3.
The pH at 25° C. was measured using a pH meter (Toa Denpa Kogyo Co., Ltd., HM-30G), and was the value measured one minute after immersing the electrodes of the pH meter in the polishing composition or a concentrate thereof.

The following components A, B, non-component B, and C were used in the preparation of each polishing composition.
(Component A)
Colloidal silica [average primary particle size 25 nm, average secondary particle size 49 nm, degree of association 2.0]
(Component B)
Glycidol-modified polyallylamine (modification ratio: 1.0) [manufactured by Nittobo Medical Co., Ltd., weight average molecular weight 6,900]
Polyallylamine [PAA-03, manufactured by Nittobo Medical Co., Ltd., weight average molecular weight 3,000]
(Non-Component B)
Dimethyldiallylammonium chloride-sulfur dioxide copolymer [PAS-A-5, manufactured by Nittobo Medical Co., Ltd., weight average molecular weight 5,000]
Polyethyleneimine [SP-200, weight average molecular weight 10,000, manufactured by Nippon Shokubai Co., Ltd.]
(Component C)
Ammonia [28% by weight ammonia water, Kishida Chemical Co., Ltd., special grade reagent]

2. Measurement methods for various parameters (1) Measurement of average primary particle size of silica particles (component A) The average primary particle size (nm) of component A was calculated by the following formula using the specific surface area S ( ^m2 /g) calculated by the BET (nitrogen adsorption) method.
Average primary particle diameter (nm) = 2727/S

The specific surface area S of component A was measured by carrying out the following [pretreatment], and then weighing out about 0.1 g of a measurement sample to four decimal places into a measurement cell, drying the sample for 30 minutes in an atmosphere at 110°C immediately before measuring the specific surface area, and then measuring the specific surface area S by a nitrogen adsorption method (BET method) using a specific surface area measuring device (Micromeritic automatic specific surface area measuring device "Flowsorb III2305", manufactured by Shimadzu Corporation).
[Preprocessing]
(a) The pH of the slurry of component A is adjusted to 2.5±0.1 with an aqueous solution of nitric acid.
(b) Component A in a slurry state adjusted to pH 2.5±0.1 is placed in a petri dish and dried in a hot air dryer at 150° C. for 1 hour.
(c) After drying, the obtained sample is finely ground in an agate mortar.
(d) The ground sample is suspended in ion-exchanged water at 40° C. and filtered through a membrane filter with a pore size of 1 μm.
(e) The residue on the filter is washed five times with 20 g of ion-exchanged water (40° C.).
(f) The filter with the filtrate attached thereto is placed in a petri dish and dried in an atmosphere at 110° C. for 4 hours.
(g) The dried filtrate (component A) was taken, being careful not to mix in any filter debris, and finely ground in a mortar to obtain a measurement sample.

(2) Average secondary particle diameter of silica particles (component A) The average secondary particle diameter (nm) of component A was measured by adding an abrasive to ion-exchanged water so that the concentration of component A was 0.25% by mass, and then pouring the resulting aqueous dispersion into a Disposable Sizing Cuvette (a 10 mm polystyrene cell) to a height of 10 mm from the bottom, and using a dynamic light scattering method (apparatus name: "Zetasizer Nano ZS", manufactured by Sysmex Corporation).

(3) Measurement of weight-average molecular weight of water-soluble polymer The weight-average molecular weight of the water-soluble polymer (component B, non-component B) was calculated based on peaks in a chromatogram obtained by applying gel permeation chromatography (GPC) under the following conditions.
<Amino group-containing water-soluble polymer (component B), ammonium salt-containing water-soluble polymer, and polyethyleneimine (non-component B)>
Apparatus: HLC-8320 GPC (Tosoh Corporation, detector integrated type)
Column: GS-220HQ + GS-620HQ
Eluent: 0.4M NaCl
Flow rate: 1.0mL/min
Column temperature: 30°C
Detector: Shodex RI SE-61 differential refractive index detector Standard material: monodisperse polyethylene glycol with known molecular weight

(4) Measurement of pKa Using an HM-41K pH meter (Toa DKK Co., Ltd.), an aqueous solution of component B adjusted to 1 M was subjected to potentiometric titration with 0.1 M hydrochloric acid at room temperature. The pKa was calculated from the obtained titration curve.

(5) Glycidol Modification Ratio The glycidol modification ratio was determined by ¹³ C-NMR.
<Measurement conditions>
Sample: 200 mg of glycidol-modified polyallylamine dissolved in 0.6 mL of heavy water. Apparatus used: 400 MHz ¹³ C-NMR (Agilent 400-MR DD2, manufactured by Agilent Technologies, Inc.)
Measurement conditions: ¹³ C-NMR measurement, pulse interval time 5 seconds, tetramethylsilane as standard peak (σ: 0.0 ppm), number of measurement integrations: 5000, range of each peak used for integration:
A: 71.0-72.3 ppm (integral value of the peak of C bound to the secondary hydroxyl group of glycidol reacted with an amino group)
B: 32.0 to 41.0 ppm (integrated value of the peak of the main chain C of allylamine)
<Glycidol modification rate>
The glycidol modification rate (ratio of the amount of glycidol to the amount of amino group equivalent) is calculated by the following formula.
Glycidol modification rate (equivalent ratio) = 2A/B

3. Evaluation of the polishing liquid compositions of Examples 1 and 2 and Comparative Examples 1 and 2 (1) Measurement of zeta potential of silica particles and silicon substrate to be polished Each of the aqueous dispersions shown below was placed in a capillary cell DTS1070, and the zeta potential was measured under the following conditions using a Zetasizer Nano ZS [manufactured by Malvern].
Sample: Refractive index: 1.450 Absorption coefficient: 0.010
Dispersion medium: Viscosity: 0.8872 cP, Refractive index: 1.330, Dielectric constant: 78.5
Temperature: 25°C
(1-1) Preparation of Aqueous Dispersion for Measuring Zeta Potential of Silica Particles The polishing compositions (as used) of Examples 1 and 2 and Comparative Examples 1 and 2 were used as they were as aqueous dispersions for measuring the zeta potential of silica particles.
(1-2) Preparation of Aqueous Dispersion for Measuring Zeta Potential of Single Crystal Silicon Substrate To ion-exchanged water, the water-soluble polymer described in each of Examples 1 and 2 and Comparative Examples 1 and 2 and an aqueous ammonia solution were added, and then 0.1 mass % of fine particles of single crystal silicon substrate pulverized with a bead mill was added, and the mixture was filtered with a syringe filter (manufactured by Sartorius, pore size 1.2 μm) to obtain an aqueous dispersion for measuring the zeta potential of a single crystal silicon substrate.

(2) Polishing Method, etc. Each polishing composition was filtered with a filter (compact cartridge filter "MCP-LX-C10S", manufactured by Advantec Co., Ltd.) immediately before polishing, and finish polishing and cleaning were performed on the following silicon substrates under the following polishing conditions.
<Silicon substrate to be polished>
Single crystal silicon substrate [silicon single-sided mirror substrate with a diameter of 200 mm, conductivity type: P, crystal orientation: 100, resistivity: 0.1 Ω·cm or more and less than 100 Ω·cm]
The single crystal silicon substrate was previously subjected to rough polishing using a commercially available polishing composition (GLANZOX 1302, manufactured by Fujimi Inc.). After rough polishing, the single crystal silicon substrate was subjected to finish polishing and had a haze of 2 to 3 ppm.

<Finish polishing conditions>
Polishing machine: Single-sided 8-inch polishing machine "GRIND-X SPP600s" (manufactured by Okamoto Kogyo)
Polishing pad: Suede pad (manufactured by Toray Co., Ltd., Asker hardness: 64, thickness: 1.37 mm, nap length: 450 μm, opening diameter: 60 μm)
Silicon substrate polishing pressure: 100 g/ ^cm2
Plate rotation speed: 60 rpm
Polishing time: 5 minutes Supply rate of polishing composition: 150 g/min
Temperature of polishing composition: 23°C
Carrier rotation speed: 62 rpm

<Measurement of surface roughness (haze) of silicon substrate>
The value (DWO haze) measured in a dark field wide oblique incidence channel (DWO) using a surface roughness measuring device "Surfscan SP1-DLS" (manufactured by KLA Tencor) was used.

<Cleaning method>
After the finish polishing, the silicon substrate was subjected to ozone cleaning and dilute hydrofluoric acid cleaning as follows. In the ozone cleaning, an aqueous solution containing 20 ppm ozone was sprayed from a nozzle toward the center of the silicon substrate rotating at 600 rpm at a flow rate of 1 L/min for 3 minutes. The temperature of the ozone water was set at room temperature. Next, dilute hydrofluoric acid cleaning was performed. In the dilute hydrofluoric acid cleaning, an aqueous solution containing 0.5 mass % ammonium hydrogen fluoride (special grade, Nacalai Tesque, Inc.) was sprayed from a nozzle toward the center of the silicon substrate rotating at 600 rpm at a flow rate of 1 L/min for 6 seconds. The above ozone cleaning and dilute hydrofluoric acid cleaning were performed as one set, for a total of two sets, and finally spin drying was performed. In the spin drying, the silicon substrate was rotated at 1,500 rpm.

(3) Evaluation of Polishing Rate The weight of each silicon substrate before and after polishing was measured using a precision balance ("BP-210S" manufactured by Sartorius), and the weight difference obtained was divided by the density, area and polishing time of the silicon substrate to determine the single-sided polishing rate per unit time. The results are shown in Table 1. The weight of the silicon substrate after polishing refers to the weight of the silicon substrate after the above-mentioned finish polishing and cleaning were performed.

As shown in Table 1, the polishing liquid compositions of Examples 1 and 2, which were used for polishing under conditions where the zeta potential of component A and the silicon substrate to be polished was positive and the sum of the absolute values of the zeta potential was 28 mV or less, were found to have a superior polishing rate compared to the polishing liquid compositions of Comparative Examples 1 and 2, which were used for polishing under conditions where the zeta potential of component A and the silicon substrate to be polished was positive and the sum of the absolute values of the zeta potential was more than 28 mV.

4. Evaluation of the polishing compositions of Examples 3 and 4 and Comparative Example 3 (1) Measurement of the zeta potential of silica particles and silicon substrate to be polished The zeta potential of silica particles and silicon substrate to be polished was evaluated in the same manner as in 3(1) above using each of the aqueous dispersions shown below. The results are shown in Table 2.
(1-1) Preparation of Aqueous Dispersion for Measuring Zeta Potential of Silica Particles The polishing compositions (as used) of Examples 3 and 4 and Comparative Example 3 were used as they were as aqueous dispersions for measuring the zeta potential of silica particles.
(1-2) Preparation of Aqueous Dispersion for Measuring Zeta Potential of Polysilicon Substrate The water-soluble polymer and the ammonia solution described in each of Examples 3 to 4 and Comparative Example 3 were added to ion-exchanged water, and then 0.1 mass % of fine particles of polysilicon (polycrystalline) substrate pulverized in a bead mill was added, and the mixture was filtered with a syringe filter (manufactured by Sartorius, pore size 1.2 μm) to obtain an aqueous dispersion for measuring the zeta potential of a polysilicon substrate.

(2) Polishing Method Each polishing composition was filtered with a filter (compact cartridge filter "MCP-LX-C10S", manufactured by Advantec Co., Ltd.) immediately before polishing, and the polished silicon substrates described below were polished under the same polishing conditions as in 3(2) above, and then washed by the same washing method as in 3(2) above.
<Silicon substrate to be polished>
Polysilicon substrate [a silicon single-sided mirror substrate having a diameter of 200 mm (conductivity type: P, crystal orientation: 100, resistivity: 0.1 Ω·cm or more and less than 100 Ω·cm) on which a SiO ₂ film of 4400 Å is deposited by plasma CVD, and then a polysilicon film of 8000 Å is deposited by plasma CVD]

(3) Evaluation of the Polishing Rate The polishing rate was evaluated in the same manner as in 3(3) above, using a polysilicon substrate as the silicon substrate to be polished. The results are shown in Table 2.

As shown in Table 2, the polishing liquid compositions of Examples 3 and 4, which were used for polishing under conditions where the zeta potential of component A and the silicon substrate to be polished was positive and the sum of the absolute values of the zeta potential was 28 mV or less, were found to have a superior polishing rate compared to the polishing liquid composition of Comparative Example 3, which was used for polishing under conditions where the zeta potential of component A and the silicon substrate to be polished was positive and the sum of the absolute values of the zeta potential was more than 28 mV.

The polishing method disclosed herein can improve the polishing rate. Therefore, the polishing method disclosed herein is useful as a polishing method used in the manufacturing process of various semiconductor substrates, and is particularly useful as a finish polishing method for silicon substrates.

Claims (15)

The method includes a step of polishing a silicon substrate using a polishing composition containing silica particles (component A) and an amino group-containing water-soluble polymer (component B),
The polishing method is carried out under the conditions that the zeta potential of component A is 0 mV or more, the zeta potential of the silicon substrate to be polished is positive, and the sum of the absolute values of the zeta potentials of component A and the silicon substrate to be polished is 28 mV or less. The polishing method according to claim 1, wherein the zeta potential of component A is 0 mV or more and 20 mV or less. The polishing method according to claim 1 or 2, wherein the zeta potential of the silicon substrate to be polished is greater than 0 mV and less than or equal to 10 mV. The polishing method according to any one of claims 1 to 3, wherein component B contains a structural unit derived from allylamine. The polishing method according to claim 4, wherein the pKa of component B is 7.7 or more and 9.2 or less. The polishing method according to any one of claims 1 to 5, wherein the pH of the polishing composition is greater than the pKa of component B. The polishing method according to any one of claims 1 to 6, wherein the pH of the polishing composition is greater than 8.5 and less than or equal to 14. The polishing method according to any one of claims 1 to 7, wherein the content of component A in the polishing composition is 0.01% by mass or more and 2.5% by mass or less. The polishing method according to any one of claims 1 to 8, wherein the content of component B in the polishing composition is 10 ppm by mass or more and 200 ppm by mass or less. The polishing method according to any one of claims 1 to 9, wherein the ratio B/A of the content of component B to the content of component A in the polishing composition is 0.008 or more and 0.16 or less. The polishing method according to any one of claims 4 to 10, wherein at least a portion of the amino groups in the structural units derived from allylamine have a steric shielding group. The polishing method according to any one of claims 4 to 11, wherein at least a portion of the amino groups in the structural units derived from allylamine are secondary amino groups or tertiary amino groups containing a hydrocarbon group having 3 to 11 carbon atoms and a hydroxyl group. The polishing method according to any one of claims 1 to 12, wherein component B is a reaction product of polyallylamine and a glycidol derivative, and the equivalent of the glycidol derivative relative to the number of amino groups (1 equivalent) of the polyallylamine is 0.5 or more and 1.1 or less. The polishing method according to claim 13, wherein the glycidol derivative is glycidol. A step of polishing a silicon substrate to be polished using the polishing method according to any one of claims 1 to 14;
and cleaning the polished silicon substrate.