Polishing composition and polishing method

Abstract

Provided is a polishing composition such that the surface of a polished silicon wafer exhibits reduced haze and improved wettability. This polishing composition contains silica particles, a cellulose derivative, a basic compound, and water. The silica particles have an average primary particle size of 30 nm or less, and an average secondary particle size of 60 nm or less. The weight-average molecular weight of the cellulose derivative is greater than 120×104.

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. 2020-044715, 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) prevents 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 silica particles as abrasive grains and hydroxyethyl cellulose as a water-soluble polymer.

[0005] Furthermore, reducing haze is important for achieving a high-quality surface. Therefore, it would be more preferable to reduce haze while improving the wettability of the silicon wafer surface after polishing as described above. However, conventional compositions containing cellulose derivatives such as those described in Patent Document 1 do not necessarily impart sufficient wettability, and there is also room for improvement in terms of haze.

[0006] Therefore, an object of the present invention is to provide a polishing composition and a polishing method that contain silica particles and a cellulose derivative and that can achieve both reduced haze and improved wettability on the polished silicon wafer surface. [Means for solving the problem]

[0007] According to the present specification, a silicon wafer polishing composition is provided. This polishing composition contains silica particles, a cellulose derivative, a basic compound, and water. Here, the silica particles have an average primary particle size of 30 nm or less and an average secondary particle size of 60 nm or less. The cellulose derivative has a weight-average molecular weight (Mw) of 120×10 4The polishing composition having such a configuration can reduce haze on the polished silicon wafer surface and improve wettability at the same time. More specifically, by using silica particles with a relatively small diameter in combination with a cellulose derivative having a relatively high molecular weight, it is possible to reduce haze and improve wettability at the same time.

[0008] In some preferred embodiments, the cellulose derivative has a weight average molecular weight of 150×10 4 By using such a cellulose derivative, a polishing surface with excellent wettability can be realized.

[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 silica particles. By setting the content of the cellulose derivative to a predetermined range relative to the content of the silica particles, the effects of the technology disclosed herein can be preferably achieved.

[0010] In some preferred embodiments, the pH of the polishing composition is 8.0 or more and 12.0 or less. By using a polishing composition having the above pH, it is possible to preferably achieve both reduced haze and improved wettability while exhibiting a predetermined polishing efficiency.

[0011] In some preferred embodiments, the content of the silica particles is 0.01% by weight or more and 10% by weight or less. By setting the content of the silica particles within the predetermined range, it is possible to preferably achieve both polishing efficiency due to the silica particles and haze reduction.

[0012] In some preferred embodiments, the polishing composition further comprises a surfactant. By using relatively small-diameter silica particles and a surfactant in a composition containing a high-molecular-weight cellulose derivative, it is possible to effectively reduce haze on the polished silicon wafer surface while improving wettability.

[0013] In some preferred embodiments, the polishing composition contains a nonionic surfactant as the surfactant. By using relatively small silica particles and a nonionic surfactant in a composition containing a high molecular weight cellulose derivative, the wettability is improved and the haze reduction effect is more suitably achieved.

[0014] In some preferred embodiments, the molecular weight of the surfactant is less than 4000. By using relatively small silica particles and a surfactant with a molecular weight of less than 4000 in a composition containing a high molecular weight cellulose derivative, it is possible to improve wettability and effectively reduce haze on the polished silicon wafer 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. In the finish polishing step, a substrate to be polished is polished using the polishing composition. The polishing composition includes silica particles, a cellulose derivative, a basic compound, and water, and the silica particles have an average primary particle diameter of 30 nm or less and an average secondary particle diameter of 60 nm or less, and the cellulose derivative has a weight-average molecular weight of 120×10 4 According to this polishing method, after the finish polishing step, a high-quality silicon wafer surface having low haze and high wettability can be obtained. 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] <Silica particles> The polishing composition disclosed herein contains silica particles. The silica particles are used as abrasive grains in the polishing composition. A first feature of the polishing composition is that the silica particles contained therein have an average primary particle diameter of 30 nm or less. This reduces haze on the silicon wafer surface after polishing. The average primary particle diameter is preferably less than 30 nm and may be 29 nm or less. By using silica particles with such small diameters, the silicon wafer surface can be uniformly processed. Furthermore, from the viewpoint of polishing efficiency, etc., the average primary particle diameter of the silica particles 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., 25 nm or more).

[0019] 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) The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritics, under the trade name "Flow Sorb II 2300."

[0020] A second feature of the silica particles disclosed herein is that they have an average secondary particle diameter of 60 nm or less. This reduces haze on the surface of the silicon wafer after polishing. The average secondary particle diameter is preferably 55 nm or less, and more preferably 50 nm or less (e.g., less than 50 nm). By using silica particles with such small diameters, the surface of the silicon wafer can be uniformly processed. From the viewpoint of improving polishing efficiency, the average secondary particle diameter of the silica particles is preferably 30 nm or more, more preferably 35 nm or more, and even more preferably 40 nm or more (e.g., more than 40 nm).

[0021] 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 silica particles can be measured by dynamic light scattering using, for example, "Nanotrac (registered trademark) UPA-UT151" manufactured by Nikkiso Co., Ltd.

[0022] The silica particles are not particularly limited as long as they have the above-mentioned average primary particle size and average secondary particle size, and examples thereof include colloidal silica, fumed silica, precipitated silica, etc. The 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. The colloidal silica can be used alone or in combination of two or more types.

[0023] The true specific gravity (true density) of the silica constituting the silica particles is preferably 1.5 or more, more preferably 1.6 or more, and even more preferably 1.7 or more. As the true specific gravity of the silica particle-constituting material increases, the physical polishing ability tends to increase. The upper limit of the true specific gravity of the silica particles is not particularly limited, but is typically 2.3 or less, for example, 2.2 or less, 2.0 or less, or 1.9 or less. The true specific gravity of the silica particles can be measured by a liquid displacement method using ethanol as the displacement liquid.

[0024] The shape (external shape) of the silica particles 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, silica particles in which most of the particles are peanut-shaped or cocoon-shaped can be preferably used.

[0025] Although not particularly limited, the average value of the long diameter / short diameter ratio (average aspect ratio) of silica particles 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 silica particles is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.5 or less.

[0026] The shape (external shape) and average aspect ratio of silica particles can be determined, for example, by electron microscope observation. 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.

[0027] The polishing composition disclosed herein may contain abrasive particles other than silica particles (hereinafter also referred to as "non-silica abrasive particles"), provided that the effects of the present invention are not significantly impaired. Examples of non-silica abrasive particles include inorganic particles, organic particles, and organic-inorganic composite particles. Specific examples of inorganic particles include oxide particles such as 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 particles may be used singly or in combination.

[0028] The technology disclosed herein can be preferably implemented in an embodiment using substantially only silica particles as abrasive grains. In such an embodiment, the effect of using small-diameter silica particles is preferably exhibited. From this viewpoint, the proportion of silica particles in the total amount of abrasive grains is suitably 90% by weight or more, preferably 95% by weight or more, and can be, for example, 98% by weight or more (e.g., 99 to 100% by weight).

[0029] <Cellulose derivatives> The cellulose derivative contained in the polishing composition disclosed herein has a weight average molecular weight (Mw) of 120×10 as measured by the method (gel permeation chromatography (GPC)) described in the Examples below. 4 This makes it possible to reduce haze and improve the wettability of the polished silicon wafer surface in an embodiment using small-diameter silica particles. The Mw of the cellulose derivative is 125×10 4 It may be 135 x 10 4 From the viewpoint of improving wettability, it is preferable that the thickness is larger than 150×104 greater than 180×10 4 greater than 200×10 4 It is believed that the larger the Mw of a cellulose derivative, the better its adsorption to the silicon wafer surface and water, and the greater its contribution to improving wettability. However, the technology disclosed herein is not limited to this interpretation. The upper limit of the Mw of a cellulose derivative is set to 300 × 10 from the viewpoint of dispersibility, etc. 4 It can be 270 x 10 4 The following is appropriate: 250 x 10 4 It may be the following:

[0030] 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, and may be 12 or less. In this specification, the Mn of the cellulose derivative, like the Mw, is measured by the method (GPC) described in the Examples below.

[0031] The cellulose derivative contained in the polishing composition disclosed herein is a polymer containing β-glucose units as the main repeating unit. Specific examples of cellulose derivatives 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.

[0032] Although not particularly limited, the content of cellulose derivative in polishing composition can be, for example, 0.01 weight parts or more, and can be 0.05 weight parts or more per 100 weight parts of silica particles in this polishing composition.From the viewpoint of making the use effect of cellulose derivative more effective, the content is preferably 0.1 weight parts or more, more preferably 1 weight parts or more, and even more preferably 2 weight parts or more, and can be, for example, 3 weight parts or more, 5 weight parts or more, or 8 weight parts or more. Furthermore, the content of the cellulose derivative per 100 parts by weight of silica particles is typically 50 parts by weight or less, for example, 30 parts by weight or less is appropriate, and preferably 20 parts by weight or less, for example, 15 parts by weight or less, 8 parts by weight or less, or 6 parts by weight or less, from the viewpoint of the filterability of the polishing composition, etc.

[0033] <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.

[0034] 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.

[0035] 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.

[0036] 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 a configuration, the effect of the technology disclosed herein (combining haze reduction and wettability improvement) is preferably achieved.

[0037] Although not particularly limited, the content of basic compound in polishing composition can be, for example, 0.01 parts by weight or more, and can be 0.05 parts by weight or more per 100 parts by weight of silica particles in the polishing composition.From the viewpoint of better utilizing the effect of using 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 basic compound per 100 parts by weight of silica particles can be 30 parts by weight or less, suitably less than 10 parts by weight, preferably 5 parts by weight or less, and can be 3 parts by weight or less.

[0038] <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.

[0039] <Surfactant> Some preferred embodiments of the polishing composition 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 reduced more effectively. 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 contains a surfactant containing a polyoxyalkylene structure. The surfactants can be used alone or in combination of two or more.

[0040] 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).

[0041] When the polishing composition disclosed herein contains a surfactant, the molecular weight of the surfactant is typically 1×10 4 The molecular weight is preferably less than 7000 from the viewpoint of the filterability of the polishing composition and the cleanability of the polished object, and is preferably less than 4000, more preferably less than 3500, from the viewpoint of reducing haze. The molecular weight of the surfactant is usually 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 effect. The more preferable 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 1500 or less, and may be 1000 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, 1000 or more, or even 2000 or more (e.g., 2500 or more).

[0042] The molecular weight of the surfactant can be determined by weight-average molecular weight (Mw) determined by GPC or by molecular weight calculated from the chemical formula. When determining the molecular weight of the surfactant by GPC, it is recommended to use a GPC measuring device manufactured by Tosoh Corporation, model number "HLC-8320GPC." 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

[0043] 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 silica particles 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., 8 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 silica particles 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 silica particles may be 0.1 parts by weight or more from the viewpoint of reducing haze. The polishing composition disclosed herein may also be substantially surfactant-free.

[0044] <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.

[0045] <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.

[0046] 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 oxidizing agent is not intentionally added.

[0047] <ph> The pH of the polishing composition disclosed herein is usually 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. As the pH of the polishing composition increases, the polishing efficiency tends to improve. On the other hand, from the viewpoint of preventing dissolution of silica particles and suppressing a decrease in the mechanical polishing action of the silica particles, the pH of the polishing composition is suitably 12.0 or lower, preferably 11.0 or lower, more preferably 10.8 or lower, even more preferably 10.6 or lower, for example, 10.3 or lower.

[0048] 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.

[0049] <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.

[0050] The content of silica particles 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, 0.15% by weight or more, 0.20% by weight or more, or 0.30% by weight or more. By increasing the content of silica particles, higher polishing efficiency can be achieved. 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 allows for a surface with lower haze. The above silica particle content can be preferably adopted in an embodiment in which the polishing composition is used in the form of a polishing liquid.

[0051] 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 effect of using the cellulose derivative, 0.0005 wt% or more is appropriate. From the viewpoint of 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, 0.005 wt% or more, 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.

[0052] The concentration of the basic compound in the polishing composition disclosed herein is not particularly limited. From the viewpoint of polishing efficiency, etc., the concentration is usually appropriate to be 0.0005 wt% or more, preferably 0.001 wt% or more. Also, from the viewpoint of haze reduction, etc., the concentration is appropriate to be less than 0.1 wt%, preferably less than 0.05 wt%, more preferably less than 0.03 wt% (for example, less than 0.025 wt%). 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.

[0053] When the polishing composition disclosed herein contains a surfactant, the concentration of the surfactant in the polishing composition is not particularly limited. The concentration of the surfactant can be 0.00001 wt% or more, and from the viewpoint of reducing haze, the concentration is suitably 0.0001 wt% or more, preferably 0.0005 wt% or more, and more preferably 0.001 wt% or more. The concentration of the surfactant can be 0.5 wt% or less, and from the viewpoint of polishing efficiency, cleanability, etc., the concentration is suitably 0.25 wt% or less, preferably 0.1 wt% or less, and more preferably 0.05 wt% or less. The above surfactant concentration can be preferably adopted in an embodiment in which the polishing composition is used in the form of a polishing liquid.

[0054] <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.

[0055] <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 silica particles and a part B containing at least a part of the remaining components of the polishing composition, and then mixing and diluting them at an appropriate timing as needed.

[0056] 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.

[0057] <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.

[0058] 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.

[0059] 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).

[0060] <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.

[0061] 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.

[0062] 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.

[0063] 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]

[0064] 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.

[0065] <Preparation of Polishing Composition> Example 1 A polishing composition concentrate according to this example was prepared by mixing silica particles, a cellulose derivative, a basic compound, and deionized water (DIW). As the silica particles, colloidal silica having an average primary particle diameter of 27 nm and an average secondary particle diameter of 46 nm was used. As the cellulose derivative, Mw of 210 × 10 4 Hydroxyethyl cellulose (HEC) was used, 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 a silica particle concentration of 0.17%, a cellulose derivative concentration of 0.018%, and a basic compound concentration of 0.01%.

[0066] Example 2 A polishing composition according to this example was prepared in the same manner as in Example 1, except that the concentration of silica particles in the polishing composition was set to 0.34%.

[0067] Example 3 As a cellulose derivative, Mw is 130 × 10 4 A polishing composition according to this example was prepared in the same manner as in Example 1, except that HEC was used.

[0068] (Example 4) A polishing composition according to this example was prepared in the same manner as in Example 2, except that a surfactant was further added. The surfactant concentration in the polishing composition was 0.024%. As the surfactant, a PEO-PPO-PEO type triblock polymer with a molecular weight of 3,100 (EO:PO = 160:30 (molar ratio)) was used.

[0069] (Example 5) A polishing composition according to this example was prepared in the same manner as in Example 4, except that a polyoxyethylene decyl ether (C10PEO5, number of moles of ethylene oxide added: 5) with a molecular weight of 378 was used as the surfactant, and the surfactant concentration in the polishing composition was 0.012%.

[0070] (Comparative Example 1) A polishing composition according to this example was prepared in the same manner as in Example 1, except that colloidal silica with an average primary particle diameter of 42 nm and an average secondary particle diameter of 66 nm was used as the silica particles, and the silica particle concentration in the polishing composition was 0.46%.

[0071] (Comparative Example 2) As the cellulose derivative, a polishing composition according to this example was prepared in the same manner as in Example 2, except that HEC with Mw of 59×10 4 was used.

[0072] (Measurement of Mw) The Mw of the cellulose derivative used in each example was measured under the following GPC measurement conditions. (GPC Measurement Conditions) Measuring device: HLC-8320GPC (manufactured by Tosoh Corporation) Sample concentration: 0.1 wt% Column: Asahipak GF-7MHQ, Asahipak GF-310HQ (7.5 mm I.D. × 300 mm × 2 pieces) Eluent: 0.7% sodium chloride aqueous solution Flow rate: 1.0mL / min Detector: differential refractometer Column temperature: 40℃ Sample injection volume: 100 μL Standard sample: pullulan and glucose

[0073] <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> Silicon wafers (COP (Crystal Originated Particle: Crystal Defect) Free) were prepared by pre-polishing under the following polishing condition 1. Pre-polishing was performed using a polishing solution containing 1.0% silica particles (colloidal silica with an average primary particle diameter of 42 nm) and 0.068% potassium hydroxide in deionized water.

[0074] [Polishing conditions 1] Polishing equipment: Single-wafer polishing equipment model "PNX-322" manufactured by Okamoto Machine Tools Manufacturing Co., Ltd. Polishing load: 15kPa Rotation speed of the surface plate: 30 rpm Head (carrier) rotation speed: 30 rpm Polishing pad: Nitta Haas Corporation, product name "SUBA800" Pre-polishing liquid supply rate: 0.55L / min Pre-polishing liquid temperature: 20℃ Plate cooling water temperature: 20℃ Polishing time: 2 minutes

[0075] The polishing compositions according to the examples prepared above were used as polishing liquids to polish the pre-polished silicon wafers under the following polishing conditions 2.

[0076] [Polishing conditions 2] Polishing equipment: Single-wafer polishing equipment model "PNX-322" manufactured by Okamoto Machine Tools Manufacturing Co., Ltd. Polishing load: 15kPa Rotation speed of the surface plate: 30 rpm Head (carrier) rotation speed: 30 rpm Polishing pad: Fujimi Incorporated, product name "SURFIN 000FM" Polishing fluid supply rate: 0.4L / min Polishing liquid temperature: 20℃ Plate cooling water temperature: 20℃ Polishing time: 4 minutes

[0077] The polished silicon wafer was removed from the polishing machine and cleaned using a cleaning solution of NH4OH (29%): HO2 (31%): deionized water (DIW) = 1:1:12 (volume ratio) (SC-1 cleaning). Specifically, two cleaning tanks, the first and second, were prepared, and each was filled with the above cleaning solution and maintained at 60°C. The polished silicon wafer was immersed in the first cleaning tank for 5 minutes, then passed through a rinse tank in which it was immersed in ultrapure water and subjected to ultrasonic waves, and then immersed in the second cleaning tank for 5 minutes. After that, it was immersed in ultrapure water and subjected to ultrasonic waves, and then dried using a spin dryer.

[0078] <Haze measurement> After cleaning, the surface of the silicon wafer was inspected using a wafer inspection device manufactured by KLA Tencor Corporation, product name "Surfscan SP2 XP The haze (ppm) was measured in DWO mode using a meter. The results were converted into relative values ​​(haze ratios) with the haze value of Comparative Example 1 set to 100%, and are shown in Table 1. If the haze ratio is less than 100%, it can be said that a significant haze improvement effect can be confirmed, and the smaller the haze ratio value, the greater the haze improvement effect.

[0079] <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.

[0080] (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.

[0081] [Polishing conditions] Polishing device: Engis Japan Co., Ltd. tabletop polishing machine, model "EJ-380IN" Polishing load: 21kPa Rotation speed of the surface plate: 30 rpm Head (carrier) rotation speed: 30 rpm Polishing liquid supply rate: 0.6 L / min (flowing) Polishing liquid temperature: 20℃ Polishing time: 4 minutes

[0082] [Table 1]

[0083] As shown in Table 1, silica particles having an average primary particle size of 30 nm or less and an average secondary particle size of 60 nm or less and a silica particle having an Mw of 120 × 10 4 In Examples 1 to 5, which used polishing compositions containing a cellulose derivative having an average primary particle size of more than 30 nm and an average secondary particle size of more than 60 nm, the haze on the polished silicon wafer surface was reduced compared to Comparative Example 1, which used silica particles having an average primary particle size of more than 30 nm and an average secondary particle size of more than 60 nm. 4 The water-repellent distance was reduced compared to Comparative Example 2, which used the following cellulose derivative. In other words, it can be said that the wettability of the wafer after polishing was improved. From the above results, it is found that the composition contains silica particles, a cellulose derivative, a basic compound, and water, and the average primary particle size of the silica particles is 30 nm or less, the average secondary particle size is 60 nm or less, and the Mw of the cellulose derivative is 120 × 10 4 It can be seen that a polishing composition having a larger .DELTA.A than 1000 can achieve both reduced haze and improved wettability in polishing silicon wafers.

[0084] 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 composition comprises silica particles, a cellulose derivative, a basic compound, and water, The silica particles have an average primary particle size of 30 nm or less and an average secondary particle size of 60 nm or less, The weight average molecular weight of the cellulose derivative is 120×10 ４ is larger than A polishing composition, wherein the content of the cellulose derivative in the polishing composition is 5.29 parts by weight or more per 100 parts by weight of the silica particles.

2. The weight average molecular weight of the cellulose derivative is 150×10 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 the cellulose derivative is 5.29 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the silica particles.

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

5. 5. The polishing composition according to claim 1, wherein the content of the silica particles is 0.01% by weight or more and 10% by weight or less.

6. The polishing composition according to claim 1 , further comprising a surfactant.

7. The polishing composition according to claim 6 , which contains a nonionic surfactant as the surfactant.

8. 8. The polishing composition according to claim 6, wherein the surfactant has a molecular weight of less than 4,000.

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

10. A method for polishing a silicon wafer, comprising a preliminary polishing step and a finish polishing step, in which a substrate to be polished is polished using a polishing composition in the finish polishing step, The polishing composition includes: The composition comprises silica particles, a cellulose derivative, a basic compound, and water, The silica particles have an average primary particle size of 30 nm or less and an average secondary particle size of 60 nm or less, The weight average molecular weight of the cellulose derivative is 120×10 ４ is larger than A polishing method using a polishing composition having a cellulose derivative content of 5.29 parts by weight or more per 100 parts by weight of the silica particles.

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