Polishing composition and polishing method

Abstract

Provided is a polishing composition that contains a cellulose derivative, said polishing composition exhibiting improved polishing properties and being capable of improving the wettability of a polished silicon wafer surface. The polishing composition contains abrasive grains, the cellulose derivative, a basic compound, and water. The zeta potential of the polishing composition is -24.0 mV or greater.

Description

[Technical Field]

[0001] The present invention relates to a silicon wafer polishing composition and a method for polishing silicon wafers using the polishing composition. This application claims priority to Japanese Patent Application No. 2020-044714, filed on March 13, 2020, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] The surface of a silicon wafer used as a component of a semiconductor device or the like is generally finished to a high-quality mirror surface through a lapping step (rough polishing step) and a polishing step (precise polishing step). The polishing step typically includes a pre-polishing step (preliminary polishing step) and a finish polishing step (final polishing step). Patent Document 1, for example, is an example of a technical document relating to a polishing composition for silicon wafers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent No. 5196819 Summary of the Invention [Problem to be solved by the invention]

[0004] Silicon wafers are required to have high-quality surfaces. Therefore, in such applications, polishing compositions containing abrasive grains and water, as well as a water-soluble polymer, are preferably used for purposes such as protecting the surface of the object to be polished and improving wettability. Maintaining the polished surface wet with water (with a water film attached) can prevent foreign matter in the air from directly adhering to the polished silicon wafer surface, thereby reducing surface defects caused by such foreign matter. Surfaces with such wettability tend to be easily cleaned, and cleaning can easily produce a higher-quality surface. For example, Patent Document 1 proposes a polishing composition containing hydroxyethyl cellulose as a water-soluble polymer.

[0005] However, in compositions containing cellulose derivatives as water-soluble polymers, polishing processability tends to decrease due to the protective effect of the cellulose derivatives, and it is not easy to achieve both polishing processability and wettability of the polished surface. Furthermore, conventional compositions containing cellulose derivatives do not necessarily provide sufficient wettability.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polishing composition containing a cellulose derivative, which can improve polishing processability and improve the wettability of the silicon wafer surface after polishing. Another object of the present invention is to provide a method for polishing silicon wafers using such a polishing composition. [Means for solving the problem]

[0007] According to the present specification, a silicon wafer polishing composition is provided. This polishing composition contains abrasive grains, a cellulose derivative, a basic compound, and water. The polishing composition is characterized by having a zeta potential of -24.0 mV or higher. A polishing composition having such a configuration improves the polishing rate and improves wettability after polishing.

[0008] In some preferred embodiments, the cellulose derivative has a weight average molecular weight (Mw) of 80×10 4By using such a cellulose derivative, the above-mentioned zeta potential can be preferably realized, and the effects of the technology disclosed herein can be preferably exhibited.

[0009] In some preferred embodiments, the content of the cellulose derivative is 0.1 to 20 parts by weight relative to 100 parts by weight of the abrasive grains. By setting the content of the cellulose derivative within a predetermined range relative to the content of the abrasive grains, the polishing rate is improved and wettability also tends to be improved.

[0010] In some preferred embodiments, the content of the basic compound is 0.001 wt % or more and less than 0.1 wt %. This configuration makes it easier to adjust the zeta potential of the polishing composition to a suitable range, and can suitably achieve an improvement in the polishing rate.

[0011] In some preferred embodiments, the pH of the polishing composition is 8.0 or more and 12.0 or less. In a polishing composition having the above pH, the effect of improving processability by having the above zeta potential is preferably exhibited.

[0012] In some preferred embodiments, silica particles are used as the abrasive particles. The effects of the technology disclosed herein are preferably realized in a composition containing silica particles as abrasive particles. Furthermore, the use of silica particles can prevent contamination of silicon wafers by components derived from the abrasive particles. As the silica particles, for example, colloidal silica is preferred.

[0013] In some preferred embodiments, the average primary particle diameter of the silica particles is 5 nm or more and 100 nm or less. By using silica particles having an average primary particle diameter of a predetermined value or more, the polishing rate is likely to be improved. Furthermore, by using silica particles having an average primary particle diameter of a predetermined value or less, a high-quality polished surface is likely to be obtained.

[0014] The polishing composition disclosed herein is preferably used for polishing a silicon surface. The polishing composition disclosed herein can improve the polishing rate and wettability when polishing a silicon wafer, which is a polishing object having a silicon surface.

[0015] The polishing composition disclosed herein is preferably used for polishing silicon wafers that have been subjected to lapping, for example, and is particularly preferably used for finish polishing of silicon wafers.

[0016] The present specification also provides a method for polishing silicon wafers using any of the polishing compositions disclosed herein. The polishing method includes a preliminary polishing step and a finish polishing step. The finish polishing step is characterized in that a substrate to be polished is polished using a polishing composition containing abrasive grains, a cellulose derivative, a basic compound, and water, and having a zeta potential of -24.0 mV or higher. According to this polishing method, the finish polishing step improves the polishing rate while improving the wettability of the wafer surface after polishing, resulting in a higher-quality silicon wafer surface. DETAILED DESCRIPTION OF THE INVENTION

[0017] Preferred embodiments of the present invention will be described below. It should be noted that matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field.

[0018] <Characteristics of the polishing composition> The polishing composition disclosed herein is characterized by a zeta potential of -24.0 mV or higher. Here, the zeta potential of the polishing composition refers to the zeta potential of the polishing composition measured using a zeta potential measuring device. More specifically, it refers to the zeta potential measured for the particles contained in the polishing composition. A polishing composition having a zeta potential of -24.0 mV or higher can achieve both improved polishing processability and improved wettability of the polished surface after polishing. In implementing the technology disclosed herein, it is not necessary to clarify the mechanism by which the zeta potential of the polishing composition contributes to improved polishing processability and wettability after polishing. However, the following is considered. With regard to polishing processability, an increase in the zeta potential of a polishing composition with a negative zeta potential means that the electrostatic repulsion of particles, including abrasive grains, in the polishing composition is reduced. As a result, the particles, including abrasive grains, are more likely to mechanically interact with the object to be polished, improving processability. In particular, when the surface of the silicon wafer to be polished has a negative charge, similar to the particles in the polishing composition, the effect is thought to be significantly exhibited. Furthermore, regarding the improvement of wettability, when the particles in the polishing composition are easily acted on the surface of the silicon wafer to be polished as described above, these particles act on the silicon wafer surface in a form containing abrasive grains or cellulose derivatives, contributing to the improvement of the hydrophilicity of the surface and improving wettability. However, the effect of the technology disclosed herein should not be interpreted as being limited to the above mechanism alone.

[0019] The zeta potential of the polishing composition is preferably -22.0 mV or more, more preferably -21.0 mV or more, even more preferably -20.0 mV or more, and may be -19.0 mV or more, from the viewpoint of improving the polishing rate. The upper limit of the zeta potential is not particularly set, and is usually less than 0.0 mV. From the viewpoint of the dispersibility of the polishing composition and the surface quality of the polished surface, it is suitably -5.0 mV or less, preferably -10.0 mV or less, and may be, for example, -15.0 mV or less. The zeta potential of the polishing composition can be set by the type and content of abrasive grains, the type, molecular weight, and content of cellulose derivatives, the presence or absence of addition of other additives (water-soluble polymers other than cellulose derivatives or basic compounds), the type and content thereof, pH, etc.

[0020] The zeta potential of the polishing composition can be measured using a known or commonly used zeta potential measuring device, specifically, by the method described in the examples below.

[0021] <Abrasive grain> The material and properties of the abrasive grains contained in the polishing composition disclosed herein are not particularly limited and can be appropriately selected depending on the intended use and mode of use of the polishing composition. Examples of abrasive grains include inorganic particles, organic particles, and organic-inorganic composite particles. Specific examples of inorganic particles include oxide particles such as silica particles, alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, and red iron oxide particles; nitride particles such as silicon nitride particles and boron nitride particles; carbide particles such as silicon carbide particles and boron carbide particles; diamond particles; and carbonates such as calcium carbonate and barium carbonate. Specific examples of organic particles include polymethyl methacrylate (PMMA) particles, poly(meth)acrylic acid particles (here, (meth)acrylic acid refers collectively to acrylic acid and methacrylic acid), and polyacrylonitrile particles. These abrasive grains may be used alone or in combination of two or more types.

[0022] The abrasive grains are preferably inorganic particles, and among these, particles made of metal or semi-metal oxides are preferred, with silica particles being particularly preferred. In polishing compositions that can be used for polishing (e.g., finish polishing) objects having a silicon surface, such as silicon wafers, it is particularly useful to employ silica particles as the abrasive grains. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which the abrasive grains are essentially made of silica particles. Here, "substantially" means that 95% by weight or more (preferably 98% by weight or more, more preferably 99% by weight or more, and even 100% by weight) of the particles constituting the abrasive grains are silica particles.

[0023] Specific examples of silica particles include colloidal silica, fumed silica, precipitated silica, etc. Silica particles can be used alone or in combination of two or more types. Colloidal silica is particularly preferred because it is easy to obtain a polished surface with excellent surface quality after polishing. As colloidal silica, for example, colloidal silica produced by an ion exchange method using water glass (sodium silicate) as a raw material, or alkoxide method colloidal silica (colloidal silica produced by the hydrolysis and condensation reaction of alkoxysilane) can be preferably used. Colloidal silica can be used alone or in combination of two or more types.

[0024] The true specific gravity (true density) of the abrasive grain constituent material (e.g., silica constituting silica particles) is preferably 1.5 or more, more preferably 1.6 or more, and even more preferably 1.7 or more. An increase in the true specific gravity of the abrasive grain constituent material tends to increase the physical polishing ability. There is no particular upper limit for the true specific gravity of the abrasive grain, but it is typically 2.3 or less, for example, 2.2 or less. The true specific gravity of the abrasive grain (e.g., silica particles) can be measured by a liquid displacement method using ethanol as the displacement liquid.

[0025] The average primary particle diameter of the abrasive grains (typically silica particles) is not particularly limited, but from the viewpoint of polishing efficiency, etc., it is preferably 5 nm or more, more preferably 10 nm or more. From the viewpoint of obtaining a higher polishing effect, the average primary particle diameter is preferably 15 nm or more, more preferably 20 nm or more (e.g., more than 20 nm). Furthermore, from the viewpoint of suppressing local stress applied by the abrasive grains to the surface of the object to be polished, the average primary particle diameter of the abrasive grains is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 40 nm or less. The technology disclosed herein can also be preferably implemented in an embodiment using abrasive grains having an average primary particle diameter of 35 nm or less (typically less than 35 nm, more preferably 32 nm or less, e.g., less than 30 nm), because a higher-quality surface (e.g., a surface with a low haze level) can be easily obtained.

[0026] In this specification, the average primary particle size is calculated from the specific surface area (BET value) measured by the BET method as follows: average primary particle size (nm) = 6000 / (true density (g / cm 3 )×BET value(m 2 / g)). For example, in the case of silica particles, the average primary particle size (nm) = 2727 / BET value (m 2 The average primary particle diameter can be calculated from the specific surface area (particle diameter / g). The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritics, product name "Flow Sorb II 2300".

[0027] The average secondary particle diameter of the abrasive grains is not particularly limited and can be appropriately selected, for example, from a range of about 15 nm to 300 nm. From the viewpoint of improving polishing efficiency, the average secondary particle diameter is preferably 30 nm or more, and more preferably 35 nm or more. In some embodiments, the average secondary particle diameter may be, for example, 40 nm or more, 45 nm or more, preferably 50 nm or more, and even 60 nm or more, or even 65 nm or more (e.g., 70 nm or more). Furthermore, the average secondary particle diameter is usually advantageously 250 nm or less, preferably 200 nm or less, and more preferably 150 nm or less. In some embodiments, the average secondary particle diameter may be 120 nm or less, or 100 nm or less.

[0028] In this specification, the average secondary particle size refers to the particle size (volume average particle size) measured by dynamic light scattering. The average secondary particle size of the abrasive grains can be measured by dynamic light scattering using, for example, "Nanotrac (registered trademark) UPA-UT151" manufactured by Nikkiso Co., Ltd.

[0029] The shape (external shape) of the abrasive grains may be spherical or non-spherical. Specific examples of non-spherical particles include peanut-shaped (i.e., peanut shell-shaped), cocoon-shaped, confetti-shaped, and rugby ball-shaped. For example, abrasive grains in which most of the particles are peanut-shaped or cocoon-shaped can be preferably used.

[0030] Although not particularly limited, the average value of the ratio of the major axis to the minor axis of the abrasive grains (average aspect ratio) is, in principle, 1.0 or more, preferably 1.05 or more, and more preferably 1.1 or more. By increasing the average aspect ratio, higher polishing efficiency can be achieved. Furthermore, from the viewpoint of reducing scratches, etc., the average aspect ratio of the abrasive grains is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.5 or less.

[0031] The shape (outer shape) and average aspect ratio of abrasive grains can be determined, for example, by observation using an electron microscope. A specific procedure for determining the average aspect ratio involves, for example, using a scanning electron microscope (SEM), drawing the smallest rectangle circumscribing each particle image for a predetermined number (e.g., 200) of silica particles whose individual particle shapes can be recognized. Then, for each rectangle drawn for each particle image, the long side length (long diameter value) is divided by the short side length (short diameter value) to calculate the long diameter / short diameter ratio (aspect ratio). The average aspect ratio can be determined by arithmetically averaging the aspect ratios of the predetermined number of particles.

[0032] <Cellulose derivatives> The polishing composition disclosed herein contains a cellulose derivative. The cellulose derivative is a polymer containing β-glucose units as the main repeating unit. Specific examples of the cellulose derivative include hydroxyethyl cellulose (HEC), hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, and carboxymethyl cellulose. Among these, HEC is preferred. One type of cellulose derivative may be used alone, or two or more types may be used in combination.

[0033] The Mw of the cellulose derivative used in the polishing composition disclosed herein is not limited to a specific range, and any suitable value can be adopted within the range in which the zeta potential of the polishing composition is equal to or greater than a predetermined value. The Mw of the cellulose derivative is, for example, 30×10 4 Can be more than 50 x 10 4 From the viewpoint of improving the polishing rate, the Mw of the cellulose derivative is preferably 80×10 4 greater than 100×10 4 greater than 120×10 4 more preferably 140×10 4 Larger than, say, 150×10 4It may be greater than 100. Cellulose derivatives tend to be easily adsorbed to abrasive grains (preferably silica particles), and in such cases, it is thought that the larger the Mw of a cellulose derivative, the greater the effect of reducing the electrostatic repulsion of the abrasive grains. However, the technology disclosed herein is not limited to this interpretation. The upper limit of the Mw of the cellulose derivative is set to 300 × 10 from the viewpoint of dispersibility, etc. 4 It can be 250 x 10 4 The following is appropriate: 200 x 10 4 It may be the following:

[0034] The relationship between the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the cellulose derivative is not particularly limited. For example, the molecular weight distribution (Mw / Mn) of the cellulose derivative is 4.0 or more, and may be greater than 5.0. The Mw / Mn may be 8.0 or more (e.g., 9.0 or more). A cellulose derivative having an Mw / Mn of a predetermined value or more can exhibit the effects of low molecular weight materials and high molecular weight materials in a well-balanced manner. From the viewpoint of preventing the generation of aggregates in the polishing composition and performance stability, the Mw / Mn may be 20 or less, suitably 15 or less, or may be 12 or less.

[0035] In this specification, the Mw and Mn of the cellulose derivatives are values ​​(water-based, polyethylene oxide equivalent) based on gel permeation chromatography (GPC). The GPC measurement device used may be a Tosoh HLC-8320GPC model. The measurement conditions are as follows: [GPC measurement conditions] Sample concentration: 0.1% by weight Column: TSKgel GMPW XL Detector: differential refractometer Eluent: 100mM sodium nitrate aqueous solution Flow rate: 1.0mL / min Measurement temperature: 40℃ Sample injection volume: 200 μL Standard sample: Polyethylene oxide

[0036] Although not particularly limited, the content of the cellulose derivative in the polishing composition can be, for example, 0.01 parts by weight or more, and may be 0.05 parts by weight or more per 100 parts by weight of abrasive grains in the polishing composition.From the viewpoint of better utilizing the use effect of the cellulose derivative, the content is preferably 0.1 parts by weight or more, more preferably 1 part by weight or more, and even more preferably 2 parts by weight or more.In addition, from the viewpoint of the filterability of the polishing composition, the content of the cellulose derivative per 100 parts by weight of abrasive grains is usually 50 parts by weight or less, for example, 30 parts by weight or less is appropriate, preferably 20 parts by weight or less, and may be 10 parts by weight or less, 8 parts by weight or less, or 6 parts by weight or less (for example, 4 parts by weight or less).

[0037] <Basic compounds> The polishing composition disclosed herein contains a basic compound. The basic compound can be appropriately selected from various basic compounds that dissolve in water and increase the pH of the aqueous solution. For example, nitrogen-containing organic or inorganic basic compounds, phosphorus-containing basic compounds, alkali metal hydroxides, alkaline earth metal hydroxides, various carbonates and hydrogen carbonates, etc. can be used. Examples of nitrogen-containing basic compounds include quaternary ammonium compounds, ammonia, amines (preferably water-soluble amines), etc. Examples of phosphorus-containing basic compounds include quaternary phosphonium compounds. Such basic compounds can be used alone or in combination of two or more.

[0038] Specific examples of alkali metal hydroxides include potassium hydroxide and sodium hydroxide. Specific examples of carbonates or bicarbonates include ammonium bicarbonate, ammonium carbonate, potassium bicarbonate, potassium carbonate, sodium bicarbonate, and sodium carbonate. Specific examples of amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N-(β-aminoethyl)ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, anhydrous piperazine, piperazine hexahydrate, 1-(2-aminoethyl)piperazine, N-methylpiperazine, guanidine, and azoles such as imidazole and triazole. Specific examples of quaternary phosphonium compounds include quaternary phosphonium hydroxides such as tetramethylphosphonium hydroxide and tetraethylphosphonium hydroxide.

[0039] As the quaternary ammonium compound, a quaternary ammonium salt (typically a strong base) such as a tetraalkylammonium salt or a hydroxyalkyltrialkylammonium salt can be used. The anion component in such a quaternary ammonium salt is, for example, OH - , F - , Cl - , Br - , I - , ClO4 - , BH4 - Examples of the quaternary ammonium compounds include those in which the anion is OH. - Specific examples of quaternary ammonium hydroxides include tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, and tetrahexylammonium hydroxide; hydroxyalkyltrialkylammonium hydroxides such as 2-hydroxyethyltrimethylammonium hydroxide (also known as choline); and the like.

[0040] The basic compound in the technology disclosed herein is preferably at least one basic compound selected from alkali metal hydroxides, quaternary ammonium hydroxides, and ammonia. Of these, quaternary ammonium hydroxides and ammonia are more preferred, and ammonia is particularly preferred. The technology disclosed herein can be preferably implemented in an embodiment in which the basic compound contained in the polishing composition essentially consists of ammonia. In this embodiment, the content of basic compounds other than ammonia (e.g., quaternary ammonium hydroxide) is 1 / 10 or less (e.g., 1 / 30 or less) of the ammonia content by weight, and can be less than 0.003 wt % (even less than 0.001 wt %) in the polishing composition. In such an embodiment, the zeta potential of the polishing composition can be easily adjusted to a predetermined value or higher, and the effects of the technology disclosed herein can be suitably exhibited.

[0041] Although not particularly limited, the content of the basic compound in the polishing composition can be, for example, 0.01 parts by weight or more, or may be 0.05 parts by weight or more, per 100 parts by weight of abrasive grains in the polishing composition.From the viewpoint of better utilizing the effect of the basic compound, the content is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, and even more preferably 1.0 parts by weight or more.In addition, the content of the basic compound per 100 parts by weight of abrasive grains can be 30 parts by weight or less, suitably less than 10 parts by weight, preferably 5 parts by weight or less, and may be 3 parts by weight or less.By setting the content of the basic compound to be within a predetermined range relative to the amount of abrasive grains, the zeta potential of the polishing composition can be easily set to a predetermined value or more, and the removal rate can be better improved.

[0042] Although not particularly limited, the content of the basic compound in the polishing composition can also be determined by the relationship between the content of abrasive grains contained in the polishing composition and the specific surface area. Specifically, the ratio of the specific surface area of ​​abrasive grains × the content of abrasive grains / the content of basic compound can be, for example, 1000 or more, and may be 1500 or more. From the viewpoint of better utilizing the effect of the basic compound, the above value is preferably 1750 or more, for example, 2000 or more. Furthermore, the ratio of the specific surface area of ​​abrasive grains × the content of abrasive grains / the content of basic compound can be 15000 or less, and is suitably less than 12000, preferably 11000 or less, and may be 10000 or less (e.g., 8000 or less). By setting the content of the basic compound to be within a predetermined range relative to the amount of abrasive grains, the zeta potential of the polishing composition can be easily adjusted to a predetermined value or more, and the removal rate can be further improved. Here, the specific surface area of ​​the abrasive grains refers to the specific surface area (BET value) measured by the BET method.

[0043] <Optional polymer> The polishing composition disclosed herein may contain, as an optional component, a water-soluble polymer other than a cellulose derivative (hereinafter also referred to as an optional polymer), provided that the effects of the present invention are not significantly impaired. Examples of such optional polymers include starch derivatives, polyvinyl alcohol-based polymers, N-vinyl polymers, and N-(meth)acryloyl polymers. Examples of starch derivatives include pregelatinized starch, pullulan, carboxymethyl starch, and cyclodextrin. A polyvinyl alcohol-based polymer refers to a polymer containing vinyl alcohol units (hereinafter also referred to as "VA units") as repeating units. A polyvinyl alcohol-based polymer may contain only VA units as repeating units, or may contain VA units and repeating units other than VA units (hereinafter also referred to as "non-VA units"). Furthermore, the polyvinyl alcohol-based polymer may be unmodified polyvinyl alcohol (unmodified PVA) or modified polyvinyl alcohol (modified PVA). The N-vinyl polymer may be a homopolymer or copolymer of an N-vinyl monomer. Specific examples of N-vinyl polymers include homopolymers of N-vinylpyrrolidone (VP) and copolymers with a copolymerization ratio of VP of 70% by weight or more. N-(meth)acryloyl polymers can be homopolymers or copolymers of N-(meth)acryloyl monomers. Specific examples of N-(meth)acryloyl polymers include homopolymers of N-isopropylacrylamide (NIPAM), copolymers with a copolymerization ratio of NIPAM of 70% by weight or more, homopolymers of N-acryloylmorpholine (ACMO), and copolymers with a copolymerization ratio of ACMO of 70% by weight or more. The optional polymer is preferably nonionic. The content of the optional polymer is typically less than 100 parts by weight, suitably less than 50 parts by weight, or even less than 30 parts by weight, 10 parts by weight, 5 parts by weight, or even less than 1 part by weight per 100 parts by weight of the cellulose derivative. The technology disclosed herein can be suitably implemented in an embodiment that substantially does not contain such optional polymers.

[0044] <Surfactant> The polishing composition disclosed herein can optionally contain a surfactant. By incorporating a surfactant into the polishing composition, haze on the surface of the object to be polished after polishing can be more effectively reduced. Any of anionic, cationic, nonionic, and amphoteric surfactants can be used as the surfactant. Typically, anionic or nonionic surfactants are preferred. Nonionic surfactants are more preferred from the viewpoints of low foaming and ease of pH adjustment. Examples of nonionic surfactants include oxyalkylene polymers such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; polyoxyalkylene derivatives (e.g., polyoxyalkylene adducts) such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkylamines, polyoxyethylene fatty acid esters, polyoxyethylene glyceryl ether fatty acid esters, and polyoxyethylene sorbitan fatty acid esters; and copolymers of multiple oxyalkylenes (e.g., diblock copolymers, triblock copolymers, random copolymers, and alternating copolymers). The surfactant preferably includes a surfactant containing a polyoxyalkylene structure. The surfactants can be used alone or in combination of two or more.

[0045] Specific examples of nonionic surfactants containing a polyoxyalkylene structure include block copolymers of ethylene oxide (EO) and propylene oxide (PO) (diblock copolymers, PEO (polyethylene oxide)-PPO (polypropylene oxide)-PEO type triblock copolymers, PPO-PEO-PPO type triblock copolymers, etc.), random copolymers of EO and PO, polyoxyethylene glycol, polyoxyethylene propyl ether, polyoxyethylene butyl ether, polyoxyethylene pentyl ether, polyoxyethylene hexyl ether, polyoxyethylene octyl ether, polyoxyethylene-2-ethylhexyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene isodecyl ether, polyoxyethylene tridecyl ether, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene isostearyl ether ... 2-ethylhexyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene isodecyl ether, polyoxyethylene tridecyl ether, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene isostearyl ether, polyoxyethylene propyl ether, polyoxyethylene butyl ether, polyoxyethylene pentyl ether, polyoxyethylene Examples of the hydroxypropyl methylcellulose include polyoxyethylene oleyl ether, polyoxyethylene phenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene styrenated phenyl ether, polyoxyethylene laurylamine, polyoxyethylene stearylamine, polyoxyethylene oleylamine, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene distearate, polyoxyethylene monooleate, polyoxyethylene dioleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopaltimate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan tetraoleate, polyoxyethylene castor oil, and polyoxyethylene hydrogenated castor oil.Among these, preferred surfactants include block copolymers of EO and PO (particularly PEO-PPO-PEO type triblock copolymers), random copolymers of EO and PO, and polyoxyethylene alkyl ethers (for example, polyoxyethylene decyl ether).

[0046] The molecular weight of surfactants is typically 1 x 10 4 The molecular weight is preferably less than 7,000 from the viewpoint of the filterability of the polishing composition and the cleanability of the polished object, and is preferably less than 4,000, more preferably less than 3,500, from the viewpoint of reducing haze. The molecular weight of the surfactant is preferably 200 or more from the viewpoint of surface activity, and is preferably 250 or more (e.g., 300 or more) from the viewpoint of haze reduction. The preferred range of the molecular weight of the surfactant may vary depending on the type of surfactant. For example, when a polyoxyethylene alkyl ether is used as the surfactant, the molecular weight is preferably 1,500 or less, and may be 1,000 or less (e.g., 500 or less). When a PEO-PPO-PEO triblock copolymer is used as the surfactant, the molecular weight may be, for example, 500 or more, 1,000 or more, or even 2,000 or more (e.g., 2,500 or more). The molecular weight of the surfactant may be the weight-average molecular weight (Mw) (water-based, polyethylene oxide equivalent) determined by GPC or the molecular weight calculated from the chemical formula.

[0047] When the polishing composition disclosed herein contains a surfactant, its content is not particularly limited as long as it does not significantly impair the effects of the present invention. Generally, from the viewpoint of cleaning properties, the content of surfactant per 100 parts by weight of abrasive grains is suitably 20 parts by weight or less, preferably 15 parts by weight or less, and more preferably 10 parts by weight or less (e.g., 6 parts by weight or less). The content can be, for example, 5 parts by weight or less, 4 parts by weight or less, or 3 parts by weight or less per 100 parts by weight of abrasive grains. From the viewpoint of better demonstrating the effects of the surfactant, the content of surfactant per 100 parts by weight of abrasive grains is suitably 0.001 parts by weight or more, preferably 0.005 parts by weight or more, and may be 0.01 parts by weight or more, or even 0.05 parts by weight or more. In some preferred embodiments, the content of surfactant per 100 parts by weight of abrasive grains may be 0.1 parts by weight or more from the viewpoint of reducing haze. The polishing composition disclosed herein may also be preferably implemented in an embodiment that is substantially free of surfactant.

[0048] <Water> The polishing composition disclosed herein typically contains water. Ion-exchanged water (deionized water), pure water, ultrapure water, distilled water, etc. can be preferably used as the water. To minimize the inhibition of the functions of other components contained in the polishing composition, the water used preferably has a total transition metal ion content of, for example, 100 ppb or less. For example, the purity of the water can be increased by removing impurity ions using an ion exchange resin, removing foreign matter using a filter, distillation, or other procedures.

[0049] <Other ingredients> The polishing composition disclosed herein may further contain, as necessary, known additives that can be used in polishing compositions (typically, silicon wafer polishing compositions), such as chelating agents, organic acids, organic acid salts, inorganic acids, inorganic acid salts, preservatives, and antifungal agents, within the range that does not significantly impair the effects of the present invention. The polishing composition disclosed herein can be suitably implemented in an embodiment that is substantially free of chelating agents.

[0050] The polishing composition disclosed herein is preferably substantially free of an oxidizing agent. If an oxidizing agent is contained in the polishing composition, when the polishing composition is applied to a polishing target (silicon wafer), the surface of the polishing target may be oxidized to form an oxide film, which may result in a decrease in the polishing rate. Specific examples of oxidizing agents include hydrogen peroxide (H2O2), sodium persulfate, ammonium persulfate, and sodium dichloroisocyanurate. The phrase "the polishing composition is substantially free of an oxidizing agent" means that the polishing composition does not contain an oxidizing agent, at least intentionally.

[0051] <ph> The pH of the polishing composition disclosed herein is typically 8.0 or higher, preferably 8.5 or higher, more preferably 9.0 or higher, even more preferably 9.5 or higher, for example, 10.0 or higher. Increasing the pH of the polishing composition tends to improve polishing efficiency. Furthermore, particles, including abrasive grains, in the polishing composition disclosed herein tend to exhibit greater electrostatic repulsion as the pH increases, and the surface of the silicon wafer to be polished also tends to be more negatively charged. According to the technology disclosed herein, by increasing the zeta potential of the polishing composition within the above pH range, the particles contained in the polishing composition can be made to act favorably on the silicon wafer surface. On the other hand, from the viewpoint of preventing dissolution of abrasive grains (e.g., silica grains) and suppressing a decrease in the mechanical polishing action of the abrasive grains, the pH of the polishing composition is preferably 12.0 or lower, preferably 11.8 or lower, more preferably 11.5 or lower, and even more preferably 11.0 or lower.

[0052] In the technology disclosed herein, the pH of a composition can be determined by using a pH meter (for example, a glass electrode hydrogen ion concentration indicator (model number F-23) manufactured by HORIBA, Ltd.) and performing three-point calibration using standard buffer solutions (phthalate pH buffer solution, pH: 4.01 (25°C), neutral phosphate pH buffer solution, pH: 6.86 (25°C), and carbonate pH buffer solution, pH: 10.01 (25°C)), then placing the glass electrode in the composition to be measured and measuring the value after 2 minutes or more have passed and the value has stabilized.

[0053] <Polishing liquid> The polishing composition disclosed herein is typically supplied to an object to be polished in the form of a polishing liquid containing the polishing composition and used to polish the object to be polished. The polishing liquid can be prepared, for example, by diluting any of the polishing compositions disclosed herein (typically with water). Alternatively, the polishing composition can be used as a polishing liquid as is. That is, the concept of a polishing composition in the technology disclosed herein encompasses both a polishing liquid (working slurry) that is supplied to an object to be polished and used to polish the object to be polished, and a concentrated liquid (i.e., undiluted polishing liquid) that is diluted and used as a polishing liquid. Another example of a polishing liquid containing the polishing composition disclosed herein is a polishing liquid obtained by adjusting the pH of the composition.

[0054] The content of abrasive grains in the polishing composition is not particularly limited, but is typically 0.01% by weight or more, preferably 0.05% by weight or more. The content may be, for example, 0.10% by weight or more, 0.20% by weight or more, 0.30% by weight or more, or 0.40% by weight or more. Increasing the content of abrasive grains can achieve a higher polishing rate. The content is suitably 10% by weight or less, preferably 7% by weight or less, more preferably 5% by weight or less, and even more preferably 2% by weight or less, for example, 1% by weight or less, or even 0.5% by weight or less. This can achieve a surface with lower haze. The above abrasive grain content can be preferably adopted in an embodiment in which the polishing composition is used in the form of a polishing liquid.

[0055] The concentration of the cellulose derivative in the polishing composition is not particularly limited, and can be, for example, 0.0001 wt% or more. From the viewpoint of favorably exhibiting the effects of using the cellulose derivative, 0.0005 wt% or more is appropriate. From the viewpoint of improving the polishing rate and improving the wettability of the polishing surface, the concentration of the cellulose derivative is preferably 0.001 wt% or more, more preferably 0.002 wt% or more, and may be, for example, 0.004 wt% or more, or 0.008 wt% or more. Furthermore, from the viewpoint of polishing efficiency, the concentration of the cellulose derivative is usually preferably 0.2 wt% or less, more preferably 0.1 wt% or less, and may be 0.05 wt% or less (for example, 0.03 wt% or less). The above-mentioned cellulose derivative concentration can be preferably adopted in an embodiment in which the polishing composition is used in the form of a polishing liquid.

[0056] When the polishing composition disclosed herein contains a basic compound, the concentration of the basic compound in the polishing composition is not particularly limited. From the viewpoint of improving the polishing rate, the concentration is usually suitably 0.0005 wt % or more, preferably 0.001 wt % or more, and more preferably 0.005 wt % or more. Furthermore, from the viewpoint of reducing haze, the concentration is suitably less than 0.1 wt %, preferably less than 0.05 wt %, and more preferably less than 0.03 wt % (e.g., less than 0.025 wt %). By setting the content of the basic compound within a predetermined range, the zeta potential of the polishing composition can be easily adjusted to a predetermined value or more, and the polishing rate can be further improved. The above basic compound concentration can be preferably adopted in an embodiment in which the polishing composition is used in the form of a polishing liquid.

[0057] <Concentrate> The polishing composition disclosed herein may be in a concentrated form (i.e., in the form of a concentrated polishing liquid, which can also be understood as a stock polishing liquid) before being supplied to the object to be polished. Such a concentrated polishing composition is advantageous from the viewpoints of convenience and cost reduction during production, distribution, storage, etc. The concentration ratio is not particularly limited and can be, for example, about 2 to 100 times in volume terms, and is usually about 5 to 50 times (e.g., about 10 to 40 times). Such a concentrate can be diluted at a desired time to prepare a polishing liquid (working slurry), which can then be supplied to the object to be polished. The dilution can be carried out, for example, by adding water to the concentrate and mixing the mixture.

[0058] <Preparation of Polishing Composition> The polishing composition used in the technology disclosed herein may be a single-component type or a multi-component type such as a two-component type. For example, the polishing composition may be configured so that a polishing liquid is prepared by mixing a part A containing at least abrasive grains among the components of the polishing composition with a part B containing at least a portion of the remaining components, and then mixing and diluting these at an appropriate timing as needed.

[0059] The method for preparing the polishing composition is not particularly limited. For example, the components constituting the polishing composition may be mixed using a well-known mixing device such as a blade mixer, an ultrasonic disperser, or a homomixer. The manner in which these components are mixed is not particularly limited. For example, all the components may be mixed at once, or may be mixed in an appropriately set order.

[0060] <Application> The polishing composition of the technology disclosed herein can be particularly preferably used for polishing a surface made of silicon (typically, polishing a silicon wafer). A typical example of the silicon wafer referred to here is a silicon single crystal wafer, for example, a silicon single crystal wafer obtained by slicing a silicon single crystal ingot.

[0061] The polishing composition disclosed herein can be preferably applied to a polishing step of an object to be polished (e.g., a silicon wafer). Before the polishing step with the polishing composition disclosed herein, the object to be polished may be subjected to a general treatment that can be applied to an object to be polished in a step upstream of the polishing step, such as lapping or etching.

[0062] The polishing composition disclosed herein can be preferably used, for example, in polishing an object to be polished (e.g., a silicon wafer) that has been prepared in an upstream process to have a surface roughness of 0.01 nm to 100 nm. The surface roughness Ra of the object to be polished can be measured, for example, using a laser scanning surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement System Inc. Use in final polishing (finish polishing) or the polishing immediately before is effective, and use in final polishing is particularly preferred. Here, final polishing refers to the final polishing step in the manufacturing process of the object (i.e., a step in which no further polishing is performed after that step).

[0063] <Polishing> The polishing composition disclosed herein can be used for polishing an object to be polished, for example, in an embodiment including the following steps: Hereinafter, a preferred embodiment of a method for polishing an object to be polished (e.g., a silicon wafer) using the polishing composition disclosed herein will be described. That is, a polishing liquid containing any of the polishing compositions disclosed herein is prepared. The preparation of the polishing liquid may include adjusting the concentration (e.g., diluting) of the polishing composition, adjusting the pH, or the like to prepare the polishing liquid. Alternatively, the polishing composition may be used as is as the polishing liquid.

[0064] Next, the polishing liquid is supplied to the object to be polished, and polishing is carried out by a conventional method. For example, when performing finish polishing of a silicon wafer, typically, a silicon wafer that has undergone a lapping process is set in a general polishing device, and the polishing liquid is supplied to the surface of the silicon wafer to be polished through the polishing pad of the polishing device. Typically, while continuously supplying the polishing liquid, the polishing pad is pressed against the surface of the silicon wafer to be polished, and the two are moved relatively (for example, rotated). Polishing of the object to be polished is completed through this polishing process.

[0065] The polishing pad used in the polishing step is not particularly limited. For example, a polishing pad of a foamed polyurethane type, a nonwoven fabric type, a suede type, or the like can be used. Each polishing pad may contain abrasive grains or may not contain abrasive grains. Usually, a polishing pad that does not contain abrasive grains is preferably used.

[0066] The object to be polished using the polishing composition disclosed herein is typically cleaned. Cleaning can be performed using an appropriate cleaning solution. The cleaning solution used is not particularly limited, and examples include SC-1 cleaning solution (a mixture of ammonium hydroxide (NH4OH), hydrogen peroxide (HO2), and water (HO)) and SC-2 cleaning solution (a mixture of HCl, HO2, and HO), which are commonly used in the semiconductor field. The temperature of the cleaning solution can be, for example, in the range from room temperature (typically about 15°C to 25°C) to about 90°C. From the viewpoint of improving the cleaning effect, a cleaning solution of about 50°C to 85°C can be preferably used. [Example]

[0067] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "%" is based on weight.

[0068] <Preparation of Polishing Composition> (Examples 1 to 3 and Comparative Example 1) Abrasive grains, a cellulose derivative, a basic compound, and deionized water (DIW) were mixed to prepare a polishing composition concentrate according to each example. Colloidal silica with an average primary particle size of 35 nm was used as the abrasive grains, hydroxyethyl cellulose (HEC) with the Mw shown in Table 1 was used as the cellulose derivative, and ammonia was used as the basic compound. The resulting polishing composition concentrate was diluted 20 times by volume with deionized water (DIW) to obtain a polishing composition with an abrasive grain concentration of 0.46%, a cellulose derivative concentration of 0.012%, and a basic compound concentration of 0.01%.

[0069] <Zeta potential measurement> The zeta potential of each polishing composition was measured under the following conditions using a zeta potential measuring device. The measuring device used was a "Zetasizer nano ZSP" manufactured by Malvern. The measurement results are shown in the corresponding columns in Table 1. [Zeta potential measurement conditions] Dispersion medium: Water Measurement temperature: 25℃ Model: Smoluchowski

[0070] <Polishing rate> (Silicon wafer polishing) The object to be polished was a silicon wafer with a diameter of 200 mm (conductivity type: P type, crystal orientation: <100> , COP (Crystal Originated Particle: Crystal defect)-free) was prepared, immersed in an HF aqueous solution (HF concentration: 2%) for 30 seconds to remove the oxide film, and polished under the following conditions using the polishing composition of each example as a polishing liquid.

[0071] [Polishing conditions] Polishing equipment: Single-wafer polishing equipment manufactured by Okamoto Machine Tools Manufacturing Co., Ltd., model "PNX-322" Polishing load: 15kPa Rotation speed of the surface plate: 30 rpm Head (carrier) rotation speed: 30 rpm Polishing pad: Fujibo Ehime polishing pad, product name "POLYPAS27NX" Polishing liquid supply rate: 0.4L / min (flowing) Polishing liquid temperature: 20℃ Polishing time: 600 seconds

[0072] (Silicon wafer cleaning) After polishing, the silicon wafer was removed from the polishing machine and immersed in a cleaning solution of NH4OH (29%): HO2 (31%): deionized water = 1:1:12 (volume ratio) for 5 minutes for cleaning (SC-1 cleaning). After that, the wafer was immersed in deionized water with the ultrasonic oscillator running and dried using a spin dryer.

[0073] (evaluation) The weight of the silicon wafer was measured before and after polishing, and the polishing rate [nm / min] was calculated from the weight difference.

[0074] <Water-repellent distance after polishing> Silicon wafers were polished under the following conditions, and the surface of the silicon wafer (the polished surface) was washed for 10 seconds with running water at a flow rate of 7 L / min. After washing, the wafer was left standing with its diagonal line aligned vertically (vertical position), and the water-repellent distance was measured after 3 minutes. Specifically, the length of the section of the diagonal line on the wafer surface that was not wetted with water from the edge of the wafer was measured, and this value was recorded as the water-repellent distance [mm]. The water-repellent distance is an index of the hydrophilicity of the polished surface, and the more hydrophilic the polished surface, the smaller the water-repellent distance tends to be. The maximum water-repellent distance in this evaluation test was the diagonal length of the wafer, or approximately 85 mm. The measurement results are shown in the corresponding columns in Table 1.

[0075] (Silicon wafer polishing) The object to be polished was a 60 mm square silicon wafer (conductivity type: P type, crystal orientation: <100> , COP-free) was prepared and immersed in an HF aqueous solution (HF concentration: 2%) for 30 seconds to remove the oxide film, and polishing was carried out using the polishing composition of each example as a polishing liquid under the following conditions.

[0076] [Polishing conditions] Polishing device: Engis Japan tabletop polishing machine, model "EJ-380IN" Polishing load: 21kPa Rotation speed of the surface plate: 30 rpm Head (carrier) rotation speed: 30 rpm Polishing pad: Fujibo Ehime polishing pad, product name "POLYPAS27NX" Polishing liquid supply rate: 0.6 L / min (flowing) Polishing liquid temperature: 20℃ Polishing time: 4 minutes

[0077] [Table 1]

[0078] As shown in Table 1, in Examples 1 to 3, in which the zeta potential of the polishing composition was -24.0 mV or more, the polishing rate was improved, and further, the water-repellent distance on the polished silicon wafer surface was reduced, improving wettability, compared to Comparative Example 1, in which the zeta potential of the polishing composition was less than -24.0 mV.

[0079] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.< / ph>

Claims

1. A silicon wafer polishing composition comprising: The method includes the steps of: abrasive grains; a cellulose derivative; a basic compound; and water; The cellulose derivative has a weight average molecular weight of 30×10 4 or more, The polishing composition has a zeta potential of −24.0 mV or more and less than 0.0 mV.

2. The weight average molecular weight of the cellulose derivative is 80×10 ４ The polishing composition of claim 1 , wherein the polishing composition has a molecular weight of 1000 or more.

3. 3. The polishing composition according to claim 1, wherein the content of said cellulose derivative is 0.1 to 20 parts by weight per 100 parts by weight of said abrasive grains.

4. 4. The polishing composition according to claim 1, wherein the content of the basic compound is 0.001% by weight or more and less than 0.1% by weight.

5. The polishing composition according to claim 1 , wherein the pH of the polishing composition is 8.0 or more and 12.0 or less.

6. The polishing composition according to claim 1 , wherein the abrasive grains are silica grains.

7. 7. The polishing composition according to claim 6, wherein the average primary particle diameter of the silica particles is 5 nm or more and 100 nm or less.

8. The polishing composition according to claim 1 , which is used for polishing a surface made of silicon.

9. The polishing composition according to claim 1 , which is used for finish polishing of silicon wafers.

10. 1. A method for polishing a silicon wafer, comprising: It includes a preliminary polishing step and a finish polishing step, In the finish polishing step, The method includes the steps of: abrasive grains; a cellulose derivative; a basic compound; and water; The cellulose derivative has a weight average molecular weight of 30×10 4 or more, A polishing method comprising polishing a substrate to be polished using a polishing composition having a zeta potential of −24.0 mV or more and less than 0.0 mV.

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