Composition for polishing

Abstract

SOLUTION: To provide a polishing composition including a colloidal silica containing colloidal silica particles, a pH adjusting agent, and a chelating agent.EFFECT: A polishing composition is easy to be removed in cleaning after polishing. Surface polishing with the polishing composition enables a substrate having a surface with a high flatness, low defects and a low surface roughness to be prepared with low cost and high productivity. Thus, it is possible to provide a substrate having high surface quality suitable as a substrate for mask blanks such as a glass substrate containing SiO2 as a main component, particularly, as a substrate for mask blanks used in EUVL.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a polishing composition suitable for surface polishing of mask blank substrates such as glass substrates mainly composed of SiO2, in particular, for surface polishing of mask blank substrates for EUV lithography. [Background technology]

[0002] In recent years, EUV lithography (hereinafter abbreviated as "EUVL"), an exposure technology using EUV (Extreme Ultra Violet, hereinafter abbreviated as "EUV") light, has been attracting attention in order to realize the formation of finer patterns than conventional photolithography using ultraviolet light. EUV light is light in the wavelength band of the soft X-ray region or vacuum ultraviolet region with a wavelength of about 0.2 to 100 nm, and a reflective mask is used as a transfer mask for EUVL. The substrate for the mask blank used in such a reflective mask is required to have a surface with extremely reduced surface roughness, flatness, and number of micro defects.

[0003] The surface quality of such mask blank substrates is greatly affected by the properties of the abrasive used in the final stage of the polishing process (hereinafter referred to as final polishing). Colloidal silica dispersions have been widely used as abrasives for final polishing of mask blank substrates, but in order to achieve the extremely reduced surface roughness and number of micro-defects required for the surface of mask blank substrates for EUVL, it is necessary to use colloidal silica dispersions with colloidal silica particles smaller in diameter than those conventionally used.

[0004] For example, Japanese Patent Laid-Open Publication No. 2006-35413 (Patent Document 1) describes a method for polishing the surface of a glass substrate mainly composed of SiO2 for use as a reflective mask for EUVL to a surface that has extremely small surface roughness and is smooth and has high surface precision, using a slurry that contains fine colloidal silica particles with an average primary particle diameter of 5 nm or more and less than 20 nm, water, and acid and has a pH adjusted to a range of 0.5 to 4.

[0005] Moreover, WO 2013 / 146990 (Patent Document 2) describes a method for reducing roughness in the high spatial frequency region of a glass substrate surface by catalyst-referred etching (CARE). CARE is a method for reducing surface roughness by removing convex portions on the substrate surface using active species generated from molecules in a processing solution adsorbed to a catalyst. WO 2013 / 146990 reports that CARE makes the irregularities (surface roughness) constituting the main surface very uniform while maintaining very high smoothness, and furthermore, the surface of the glass substrate has a higher proportion of concave portions than convex portions relative to a reference surface, so that the defect size of the main surface tends to be smaller. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2006-35413 A [Patent Document 2] International Publication No. 2013 / 146990 Summary of the Invention [Problem to be solved by the invention]

[0007] As described in JP 2006-35413 A, if fine colloidal silica particles having an average primary particle size of 5 nm or more and less than 20 nm are used, it is possible to reduce the surface roughness to a certain extent, but even if the average primary particle size is within the above range, if association-type colloidal silica particles having a high degree of association are used, it is difficult to obtain the surface roughness required for the surface of a mask blank substrate for EUVL. Furthermore, colloidal silica particles having a small average primary particle size are more likely to adhere to the surface of a glass substrate mainly composed of SiO2 than those having a large average primary particle size, and are difficult to remove by physical removal methods such as ultrasonic cleaning and scrubbing cleaning.

[0008] Furthermore, under acidic polishing conditions with a pH of 0.5 to 4, the absolute value of the zeta potential of the glass substrate surface becomes small, and colloidal silica particles and micro-foreign substances present in the slurry tend to adhere strongly to the glass substrate surface mainly composed of SiO2 during polishing, making it even more difficult to remove them in the cleaning process. Therefore, in this case, cleaning with high etching properties that deteriorate the surface roughness is required to remove colloidal silica particles and micro-foreign substances, and as a result, it is very difficult to achieve both the surface roughness and the reduction of micro-defects required for the surface of the mask blanks substrate for EUVL. In fact, the glass substrate described in JP 2006-35413 A does not have a sufficiently reduced surface roughness, and the surface roughness RMS is at least about 0.09 nm, which is not sufficient for the surface quality of the mask blanks substrate for EUVL.

[0009] On the other hand, the CARE described in WO 2013 / 146990 is a chemical polishing method, which has a lower processing efficiency and takes a long time compared to polishing using abrasive grains. In fact, in Example 5 of WO 2013 / 146990, the processing time of CARE is 50 minutes. In addition, it requires an apparatus that applies a polishing mechanism completely different from the apparatus used for polishing using abrasive grains, which is a general-purpose method, and furthermore, it uses very expensive Pt as a catalyst. Therefore, CARE has low productivity and is inferior in economics.

[0010] The present invention has been made in consideration of the above circumstances, and aims to provide a polishing composition that is suitable for surface polishing of substrates such as glass substrates mainly composed of SiO2, in particular for surface polishing of substrates for mask blanks for EUVL, and that can productively produce substrates having surfaces that are highly flat, have few defects, and have small surface roughness. [Means for solving the problem]

[0011] As a result of intensive research to achieve the above-mentioned object, the inventors have found that by using a polishing composition containing colloidal silica including colloidal silica particles, a pH adjuster, and a chelating agent, in particular a polishing composition in which, for colloidal silica particles present in the polishing composition, the maximum value of the autocorrelation function G2(f) calculated from a predetermined formula is 1.40 or more in a frequency f range of 0.001 MHz or more and 1 MHz or less, for polishing a substrate surface, a substrate having a highly flat, low defect, and small surface roughness surface can be produced inexpensively and with good productivity, and further that it is particularly effective to use this polishing composition for final polishing of the substrate surface, thereby completing the present invention.

[0012] Therefore, the present invention provides the following polishing composition. 1 A polishing composition comprising colloidal silica including colloidal silica particles (excluding colloidal silica particles carrying an anionic functional group), a pH adjuster, and a chelating agent, The translational motion of colloidal silica particles present in the polishing composition is measured by laser using a dynamic light scattering method, and the time dependency of the scattered light intensity I(t) is calculated based on the following formula (1):

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[0013] The polishing composition of the present invention is easily removable by cleaning after polishing, and by surface polishing with the polishing composition of the present invention, a substrate having a highly flat surface with few defects and small surface roughness can be produced inexpensively and with good productivity, and a substrate having high surface quality that is suitable as a substrate for mask blanks such as a glass substrate mainly composed of SiO2, in particular as a substrate for mask blanks for EUVL, can be provided. [Brief description of the drawings]

[0014] [Figure 1] 2 is a graph showing values ​​of the autocorrelation function G2(f) of colloidal silica particles in the polishing compositions of Examples 1 to 4 and Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention will be described in detail below. The polishing composition of the present invention contains colloidal silica (colloidal silica dispersion) containing colloidal silica particles, a pH adjuster, and a chelating agent. Colloidal silica is an aqueous dispersion containing colloidal silica particles (colloidal silica particles). The synthesis method of colloidal silica particles is not particularly limited, but from the viewpoint of reducing metal contamination, it is preferable to use high-purity colloidal silica particles produced by hydrolyzing organic silicate compounds such as alkoxysilane. As the colloidal silica, commercially available products can be used. Examples of commercially available products include GP series, PL series, and BS series manufactured by Fuso Chemical Co., Ltd.

[0016] The average primary particle diameter DA1 of the colloidal silica particles is preferably 5 nm or more, and is preferably 50 nm or less, particularly preferably 30 nm or less, from the viewpoint of compatibility between ease of removal of colloidal silica particles in the polishing composition remaining on the substrate surface after polishing, reduction of surface roughness and concave defects, and polishing efficiency. The average primary particle diameter DA1 of the colloidal silica particles can be calculated from the specific surface area (e.g., BET specific surface area) measured by gas adsorption method. In this case, the specific surface area can be measured by using colloidal silica before being made into the polishing composition, and the colloidal silica particles in a dry state.

[0017] The degree of association P=DA2 / DA1, calculated by dividing the average secondary particle diameter DA2 of the colloidal silica particles contained in the colloidal silica (this average secondary particle diameter is the average secondary particle diameter of the colloidal silica particles in the state of an aqueous dispersion containing the colloidal silica particles before being made into a polishing composition) by the average primary particle diameter DA1, is preferably 1.8 or less, particularly 1.3 or less. Note that the average secondary particle diameter DA2 of the colloidal silica particles means the average particle diameter of secondary particles formed by association of primary particles of the colloidal silica particles (for example, secondary particles are formed by association of primary particles during the synthesis of the primary particles of the colloidal silica particles), so the degree of association P will not be lower than 1. Theoretically, the degree of association P is 1 or more, but the practical lower limit is generally 1.1 or more.

[0018] The degree of association P reflects the shape of colloidal silica particles, and the degree of association P usually depends on the synthesis conditions of colloidal silica particles. In general, the closer the degree of association P of colloidal silica particles is to 1, the closer the particle shape is to a perfect sphere, which is advantageous in achieving the surface roughness and reduction of concave defects required for the substrate surface. On the other hand, since the proportion of particles having anisotropic shape increases, the non-uniformity of the surface shape of the substrate after polishing increases, in order to suppress the deterioration of surface roughness and the occurrence of concave defects, it is preferable that the degree of association P is 1.8 or less. The average secondary particle diameter DA2 of colloidal silica particles can be measured by dynamic light scattering. In this case, the measurement by dynamic light scattering can be performed using an aqueous dispersion containing colloidal silica particles before being made into a polishing composition (in a state in which the colloidal silica particles are dispersed in water).

[0019] In order to suppress a deterioration in productivity due to a decrease in polishing efficiency and an increase in the load in the cleaning step due to an increase in colloidal silica particles adhering to the substrate surface after polishing, the polishing composition of the present invention preferably has a concentration of colloidal silica particles of 10 mass % or more, and more preferably 40 mass % or less, and particularly preferably 30 mass % or less.

[0020] The pH adjuster is not particularly limited, and may be, for example, an alkali metal hydroxide, an alkaline earth metal hydroxide, a basic salt, an amine, or ammonia. Specific examples include potassium hydroxide, sodium hydroxide, calcium hydroxide, sodium borate, monoethanolamine, diethanolamine, triethanolamine, and ethylenediamine. Among these, diethanolamine and triethanolamine are preferred, which can be mixed uniformly with water at any ratio and form a chelate complex with metal ions. The pH adjuster may be used alone or in combination. In addition, from the viewpoint of adjusting the pH of the polishing composition to a desired range while suppressing the thickening of the polishing composition, the concentration of the pH adjuster in the polishing composition is preferably 0.1% by mass or more, 10% by mass or less, and particularly 5% by mass or less.

[0021] The pH of the polishing composition of the present invention is preferably 8 or more, more preferably 8.5 or more, in order to obtain good dispersion stability of the colloidal silica particles in the polishing composition and to suppress deterioration of cleanability caused by the colloidal silica particles or minute foreign matter present in the polishing composition being easily strongly adhered to the substrate surface during polishing due to the absolute value of the zeta potential of the substrate surface becoming smaller. On the other hand, in order to suppress the deterioration of the surface roughness of the substrate, which makes it difficult to obtain the surface roughness required for the surface of the substrate for EUVL mask blanks, the pH of the polishing composition is preferably 10.5 or less, more preferably 10 or less.

[0022] The chelating agent is not particularly limited, but may be aldonic acids, aminocarboxylic acids, hydroxycarboxylic acids, phosphonic acids, and salts thereof, etc. Specific examples include gluconic acid, glucoheptonic acid, nitrilotriacetic acid, and hydroxyethylethylenediaminetriacetic acid. ,workman Examples of suitable carboxylic acids include ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, citric acid, malic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilotris(methylenephosphonic acid), 2-phosphonobutane-1,2,4-tricarboxylic acid, pyrophosphoric acid, and salts thereof. Among these, preferred are hydroxycarboxylic acids such as citric acid and malic acid, nitrilotriacetic acid, and hydroxyethylethylenediaminetriacetic acid. ,workman Aminocarboxylic acids such as ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid are preferred, and citric acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid are more preferred, which form stable chelate complexes with metal ions that are difficult to completely remove from the polishing environment. The chelating agents may be used alone or in combination.

[0023] The presence of metal ions in the polishing composition significantly inhibits the dispersion of colloidal silica particles, promoting the generation of coarse particles that cause adhesion of colloidal silica particles to the substrate surface and polishing scratches. The polishing composition contains a chelating agent, which can suppress the effects of metal ions. In addition, from the viewpoint of ensuring the dispersion stability of colloidal silica particles while sufficiently suppressing the effects of metal ions, the concentration of the chelating agent in the polishing composition is preferably 0.1% by mass or more, 10% by mass or less, particularly 5% by mass or less, and especially 1% by mass or less.

[0024] By adding a pH adjuster and a chelating agent to colloidal silica, a change occurs in the electric double layer surrounding the surface of the colloidal silica particles in the colloidal silica, and the surface properties of the colloidal silica particles become completely different from those of the colloidal silica particles in colloidal silica to which no pH adjuster or chelating agent has been added.

[0025] The polishing composition of the present invention can be calculated by the following formula (1) based on I(t), which represents the time dependency (time fluctuation) of the scattered light intensity obtained by measuring the translational motion of colloidal silica particles present in the polishing composition with a laser by a dynamic light scattering method:

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[0026] If the maximum value of the autocorrelation function G2(f) in the frequency f range of 0.001 MHz to 1 MHz is less than 1.40, it may be difficult to remove the colloidal silica particles remaining on the substrate surface after polishing by ultrasonic cleaning. G2(f) obtained by variable transformation of G2(τ) to frequency f=1 / τ is useful in grasping the characteristics of the translational motion of the colloidal silica particles in the polishing composition from the viewpoint of frequency. This can be said to be an index showing the degree to which the colloidal silica particles are present together in the polishing composition. By adjusting the concentration of each component of the polishing composition so that the maximum value of G2(f) in the range of 1 kHz (0.001 MHz) to 1 MHz, which is the frequency band used in ultrasonic cleaning of substrates, is 1.4 or more, it becomes easy to remove the colloidal silica particles attached to the substrate surface after polishing by ultrasonic cleaning, even if the colloidal silica particles have a small average primary particle diameter.

[0027] The zeta potential of the colloidal silica particles present in the polishing composition of the present invention (the zeta potential of the colloidal silica particles in the polishing composition) is preferably -5 mV or less, more preferably -10 mV or less, from the viewpoint of preventing the progression of aggregation and gelation during polishing due to the low dispersion stability of the colloidal silica particles. If the zeta potential exceeds 0 mV, in the case of a negatively charged substrate such as a glass substrate, the colloidal silica particles in the polishing composition are strongly adhered to the surface, making it difficult to remove by washing. The same tendency occurs even if the zeta potential is in the range of more than -5 mV and 0 mV or less. In addition, the lower the zeta potential, the higher the dispersion stability of the colloidal silica particles, but if the dispersion stability is high, the colloidal silica particles in the polishing composition may be adhered to the substrate surface alone (in the state of primary particles), resulting in deterioration of washability. From the viewpoint of suppressing this, the zeta potential of the colloidal silica particles present in the polishing composition is preferably -40 mV or more, more preferably -35 mV or more.

[0028] The polydispersity index of the colloidal silica particles present in the polishing composition of the present invention (the polydispersity index of the colloidal silica particles when present in the polishing composition) is preferably 0.3 or less, particularly 0.2 or less, from the viewpoint of suppressing the deterioration of surface roughness and the increase of concave defects due to the non-uniformity of the particle diameter of the secondary particles resulting in the non-uniformity of the surface shape of the polished substrate. The polydispersity index is an index showing the uniformity of the particle diameter of the secondary particles, and can be measured by a dynamic light scattering method. Theoretically, the polydispersity index is 0 or more, but the practical lower limit is generally 0.01 or more.

[0029] The polishing composition of the present invention can be suitably used as an abrasive for polishing substrates such as glass substrates mainly composed of SiO2, particularly for final polishing (finish polishing). As a substrate for mask blanks used in lithography technology for drawing fine patterns using EUV light, a glass substrate mainly composed of SiO2 is generally used, but surface polishing using the polishing composition of the present invention can form a surface with high flatness, low defects, and small surface roughness, particularly in surface polishing of a glass substrate mainly composed of SiO2. The glass substrate mainly composed of SiO2 is not particularly limited, but includes a synthetic quartz glass substrate composed of SiO2 and a titania-doped synthetic quartz glass substrate (for example, a titania-doped synthetic quartz glass substrate in which synthetic quartz glass is doped with titania at a concentration of 5 to 10% by mass). In particular, since it is necessary to use a substrate with a small thermal expansion coefficient in the exposure process with EUVL, a titania-doped synthetic quartz glass substrate is suitable as a substrate for mask blanks for EUVL.

[0030] The substrate is cut to a predetermined size according to the material, further processed as necessary, and surface polished. For example, in the case of a glass substrate such as a glass substrate mainly composed of SiO2, for example, a glass ingot of the material is molded, annealed, sliced, chamfered, and lapped to obtain a raw substrate. The raw substrate can be polished, for example, by a rough polishing process, a flatness measuring process for measuring the flatness of the surface of the roughly polished substrate, a partial polishing process, and a final polishing process. In the final polishing process for determining the surface quality, it is particularly effective to use the polishing composition of the present invention. In addition, as polishing using an abrasive, batch-type double-sided polishing is common, but polishing using the polishing composition of the present invention may be batch-type polishing or sheet-type polishing, and may be double-sided polishing or single-sided polishing.

[0031] A glass substrate mainly composed of SiO2 polished with the polishing composition of the present invention can be suitably used for semiconductor-related electronic materials, and is particularly suitable as a mask blank substrate with low defects (for example, 5 or less defects of 34 nm or more on a 132 mm × 132 mm main surface) required for mask blank substrates for EUVL, which is considered to be the most advanced process in the field of lithography technology. EXAMPLES

[0032] EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0033] [Example 1] Triethanolamine as a pH adjuster and citric acid as a chelating agent were added to colloidal silica containing colloidal silica particles having an average primary particle diameter DA1 of 14 nm, an average secondary particle diameter DA2 of 18 nm, and a degree of association P=DA2 / DA1 of 1.3, to prepare a polishing composition having a colloidal silica particle concentration of 20 mass%, a pH adjuster concentration of 0.3 mass%, and a chelating agent concentration of 0.1 mass%.

[0034] The translational motion of colloidal silica particles present in the polishing composition is measured by laser using a dynamic light scattering method, and the time dependence of the scattered light intensity I(t) is calculated based on the following formula (1):

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[0035] The polishing composition thus obtained was used to perform final polishing (finish polishing) of the main surfaces (both sides) of four titania-doped synthetic quartz glass substrates (152 mm × 152 mm, thickness 6.35 mm) using a soft suede polishing cloth at a polishing pressure of 100 gf / cm. 2 (approximately 9.81 kPa), the polishing time was 30 minutes, and the polishing stock removal was an amount sufficient to remove scratches introduced during the rough polishing process (0.1 μm or more).

[0036] After polishing, the substrate was washed and dried, and the surface roughness (RMS) of the polished surface was measured using an atomic force microscope (Oxford Instruments), which was 56 pm on average. The flatness (TIR) ​​of the polished surface was measured using a photomask flatness measuring instrument (TROPEL), which was 19 nm on average. Furthermore, a defect inspection of the polished surface was performed using a laser confocal optical system high-sensitivity defect inspection device (Lasertec Corporation), which found an average of 1.5 defects of 34 nm or more. When the shape of these defects was observed with an atomic force microscope, the average number of concave defects was 0.75 and the average number of convex defects was 0.75.

[0037] [Example 2] A polishing composition was prepared in the same manner as in Example 1, except that the pH adjuster concentration was 3.0 mass% and the chelating agent concentration was 1.0 mass%. The autocorrelation function G2(f) was determined in the same manner as in Example 1. The results are shown in FIG. 1. In the frequency f range of 0.001 MHz or more and 1 MHz or less, the maximum value of the autocorrelation function G2(f) was 1.50. In addition, the zeta potential of the colloidal silica particles present in the polishing composition was -30 mV, the polydispersity index was 0.04, and the pH of the polishing composition was 8.5.

[0038] Using the obtained polishing composition, the final polishing (finish polishing) of the titania-doped synthetic quartz glass substrate was carried out in the same manner as in Example 1. After polishing, the surface roughness (RMS) and flatness (TIR) ​​of the polished surface were measured in the same manner as in Example 1, and the surface roughness was 55 pm on average, and the flatness was 20 nm on average. In addition, the defect inspection of the polished surface was carried out in the same manner as in Example 1, and the number of defects of 34 nm or more was 3.50 on average. When the shape of the defects was observed with an atomic force microscope, the number of concave defects was 0.50 on average, and the number of convex defects was 3.0 on average.

[0039] [Example 3] A polishing composition was prepared in the same manner as in Example 2, except that the pH adjuster was diethanolamine. The autocorrelation function G2(f) was determined in the same manner as in Example 1. The results are shown in FIG. 1. The maximum value of the autocorrelation function G2(f) in the frequency f range of 0.001 MHz or more and 1 MHz or less was 1.46. The zeta potential of the colloidal silica particles present in the polishing composition was -29 mV, the polydispersity index was 0.03, and the pH of the polishing composition was 9.4.

[0040] Using the obtained polishing composition, the final polishing (finish polishing) of the titania-doped synthetic quartz glass substrate was carried out in the same manner as in Example 1. After polishing, the surface roughness (RMS) and flatness (TIR) ​​of the polished surface were measured in the same manner as in Example 1, and the surface roughness was 58 pm on average, and the flatness was 22 nm on average. In addition, the defect inspection of the polished surface was carried out in the same manner as in Example 1, and the number of defects of 34 nm or more was 3.00 on average. When the shape of the defects was observed with an atomic force microscope, the number of concave defects was 0.75 on average, and the number of convex defects was 2.25 on average.

[0041] [Example 4] A polishing composition was prepared in the same manner as in Example 2, except that the chelating agent was diethylenetriaminepentaacetic acid. The autocorrelation function G2(f) was determined in the same manner as in Example 1. The results are shown in FIG. 1. The maximum value of the autocorrelation function G2(f) in the frequency f range of 0.001 MHz or more and 1 MHz or less was 1.46. The zeta potential of the colloidal silica particles present in the polishing composition was -19 mV, the polydispersity index was 0.03, and the pH of the polishing composition was 8.4.

[0042] Using the obtained polishing composition, the final polishing (finish polishing) of the titania-doped synthetic quartz glass substrate was carried out in the same manner as in Example 1. After polishing, the surface roughness (RMS) and flatness (TIR) ​​of the polished surface were measured in the same manner as in Example 1, and the surface roughness was 55 pm on average, and the flatness was 21 nm on average. In addition, the defect inspection of the polished surface was carried out in the same manner as in Example 1, and the number of defects of 34 nm or more was 4.0 on average. When the shape of these defects was observed with an atomic force microscope, the number of concave defects was 0.50 on average, and the number of convex defects was 3.50 on average.

[0043] [Comparative Example 1] A polishing composition was prepared with a colloidal silica particle concentration of 20 mass % without adding any pH adjuster or chelating agent, using only colloidal silica containing colloidal silica particles with an average primary particle diameter DA1 of 14 nm, an average secondary particle diameter DA2 of 18 nm, and an association degree P=DA2 / DA1 of 1.3. The autocorrelation function G2(f) was calculated in the same manner as in Example 1. The results are shown in FIG. 1. The maximum value of the autocorrelation function G2(f) in the frequency f range of 0.001 MHz or more and 1 MHz or less was 1.35. The zeta potential of the colloidal silica particles present in the polishing composition was -44 mV, the polydispersity index was 0.32, and the pH of the polishing composition was 7.7.

[0044] Using the obtained polishing composition, the final polishing (finish polishing) of the titania-doped synthetic quartz glass substrate was carried out in the same manner as in Example 1. After polishing, the surface roughness (RMS) and flatness (TIR) ​​of the polished surface were measured in the same manner as in Example 1, and the surface roughness was 65 pm on average, and the flatness was 25 nm on average. In addition, the defect inspection of the polished surface was carried out in the same manner as in Example 1, and the number of defects of 34 nm or more was 299.00 on average. When the shape of these defects was observed with an atomic force microscope, the number of concave defects was 1.25 on average, and the number of convex defects was 297.75 on average.

Claims

1. A polishing composition comprising colloidal silica including colloidal silica particles (excluding colloidal silica particles carrying an anionic functional group), a pH adjuster, and a chelating agent, The translational motion of colloidal silica particles present in the polishing composition is measured by laser using a dynamic light scattering method, and the time dependency of the scattered light intensity I(t) is calculated based on the following formula (1): [0010] (In the formula, T is the measurement time of the scattered light intensity, I(t) is the scattered light intensity at any time t, and I(t+τ) is the scattered light intensity after a predetermined time τ has elapsed from the arbitrary time t.) G calculated by 2 A polishing composition characterized in that the maximum value of the autocorrelation function G2(f) obtained by variable transformation of (τ) to a frequency f = 1 / τ is 1.40 or more in the frequency f range of 0.001 MHz or more and 1 MHz or less.

2. 2. The polishing composition according to claim 1, wherein the zeta potential of colloidal silica particles present in the polishing composition is −40 mV or more and −5 mV or less.

3. 3. The polishing composition according to claim 1, wherein the colloidal silica particles have an average primary particle diameter DA1 of 5 nm or more and 50 nm or less, calculated from a specific surface area measured by a gas adsorption method.

4. 4. The polishing composition according to claim 3, wherein the degree of association P=DA2 / DA1, calculated by dividing the average secondary particle diameter DA2 of the colloidal silica particles contained in the colloidal silica measured by a dynamic light scattering method by the average primary particle diameter DA1, is 1.8 or less.

5. 5. The polishing composition according to claim 1, wherein the colloidal silica particles present in the polishing composition have a polydispersity index of 0.3 or less.

6. 6. The polishing composition according to claim 1, wherein the concentration of colloidal silica particles in the polishing composition is 10% by mass or more and 40% by mass or less.

7. 7. The polishing composition according to claim 1, wherein a concentration of the pH adjuster in the polishing composition is 0.1% by mass or more and 10% by mass or less.

8. 8. The polishing composition according to claim 1, having a pH of 8 or more and 10.5 or less.

9. 9. The polishing composition according to claim 1, wherein the concentration of the chelating agent in the polishing composition is 0.1% by mass or more and 10% by mass or less.

10. SiO 2 10. The polishing composition according to claim 1, which is used for polishing a glass substrate and comprises as a main component.

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