Polishing composition and polishing method

Abstract

To provide a polishing composition that can improve the wettability of a polished silicon wafer surface and reduce haze.SOLUTION: A silicon wafer polishing composition includes abrasive grains, a cellulose derivative, a surfactant, a basic compound, and water, and the cellulose derivative has a weight-average molecular weight of greater than 120×104, and the surfactant has a molecular weight of less than 4,000.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polishing composition for silicon wafers and a method for polishing silicon wafers using the polishing composition. This application claims priority based on Japanese Patent Application No. 2020-044716, filed on March 13, 2020, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] The surface of a silicon wafer, which is used as a component of a semiconductor product, is generally finished to a high-quality mirror surface through a lapping process (rough polishing process) and a polishing process (precise polishing process). The polishing process typically includes a pre-polishing process (preliminary polishing process) and a finish polishing process (final polishing process). 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] 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] 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 that can achieve both reduced haze and improved wettability on the polished silicon wafer surface. 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 this specification, a silicon wafer polishing composition is provided, which contains abrasive grains, a cellulose derivative, a surfactant, a basic compound, and water. The cellulose derivative has a weight-average molecular weight of 120×10 4 and the molecular weight of the surfactant is less than 4000. A polishing composition having such a configuration can reduce haze on the polished silicon wafer surface and improve wettability at the same time.

[0008] The polishing composition disclosed herein can contain a nonionic surfactant as the surfactant. With this configuration, it is possible to effectively reduce haze on the polished silicon wafer surface while improving wettability.

[0009] The polishing composition disclosed herein can contain a surfactant having a polyoxyalkylene structure as the surfactant. With this configuration, the haze reduction effect is more suitably exhibited.

[0010] The pH of the polishing composition disclosed herein can be 8.0 or more and 12.0 or less. In such a configuration, the effects of the technology disclosed herein (reduced haze and improved wettability) can be preferably achieved. By setting the pH within a predetermined range, the polishing efficiency of silicon wafers also tends to improve.

[0011] In the polishing composition disclosed herein, the content of the surfactant per 100 parts by weight of the abrasive grains can be set to 0.005 parts by weight or more and 15 parts by weight or less, which more suitably achieves the haze reduction effect.

[0012] In the polishing composition disclosed herein, the content of the cellulose derivative per 100 parts by weight of the abrasive grains can be set to 0.1 parts by weight or more and 20 parts by weight or less. With this configuration, the wettability can be more suitably improved.

[0013] Silica particles can be preferably used as the abrasive grains contained in the polishing composition disclosed herein. The technology disclosed herein can be suitably implemented in the form of a polishing composition containing silica particles as abrasive grains. Furthermore, by using silica particles, contamination of silicon wafers by components derived from the abrasive grains can be prevented. As the silica particles, for example, colloidal silica is preferred.

[0014] The average primary particle diameter of the silica particles can be 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, it is easy to obtain an improvement in polishing efficiency. Furthermore, by using silica particles having an average primary particle diameter of a predetermined value or less, it is easy to obtain a high-quality polished surface.

[0015] The polishing composition disclosed herein can be used for finish polishing of silicon wafers. By using the polishing composition for finish polishing, it is possible to more suitably achieve both improved wettability and reduced haze on the surface of the polished silicon wafer.

[0016] According to this specification, a method for polishing a silicon wafer is provided. The polishing method includes a preliminary polishing step and a final polishing step. The final polishing step includes polishing a silicon wafer using a polishing agent containing abrasive grains, a cellulose derivative, a surfactant, a basic compound, and water, wherein the cellulose derivative has a weight average molecular weight of 120×10 4 and the molecular weight of the surfactant is less than 4,000. According to the polishing method having such a configuration, 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] <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.

[0019] 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.

[0020] 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.

[0021] 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. Increasing 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, e.g., 2.2 or less, 2.0 or less, or 1.9 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.

[0022] 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., greater 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 45 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 43 nm or less (typically less than 43 nm, more preferably 40 nm or less, e.g., less than 38 nm), because a higher-quality surface (e.g., a surface with a low haze level) can be easily obtained.

[0023] In some preferred embodiments, silica particles having an average primary particle size of 30 nm or less are used as abrasive grains. This more effectively reduces haze on the polished silicon wafer surface. The average primary particle size is preferably 29 nm or less, and may be 28 nm or less. By using such small-diameter silica particles, the silicon wafer surface can be uniformly processed.

[0024] 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."

[0025] 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.

[0026] In some preferred embodiments, silica particles having an average secondary particle diameter of 60 nm or less are used as abrasive grains. This more effectively reduces haze on the polished silicon wafer surface. 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 such small-diameter silica particles, the silicon wafer surface can be uniformly processed.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] <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 in which a specific surfactant is used. 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 150×10 4 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:

[0032] 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.

[0033] 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.

[0034] 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, 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 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, even more preferably 2 parts by weight or more, and may be 3 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, preferably 20 parts by weight or less, may be 10 parts by weight or less, may be 8 parts by weight or less, or may be 6 parts by weight or less (for example, 5 parts by weight or less).

[0035] <Surfactant> The polishing composition disclosed herein contains a surfactant having a molecular weight of less than 4000. By incorporating a surfactant having a molecular weight of less than 4000 into the polishing composition, haze on the surface of the object to be polished after polishing can be effectively reduced. Specifically, surfactants with limited molecular weights are thought to be easily adsorbed to the surface of the object to be polished (silicon wafer) and effectively contribute to reducing haze on the polished surface without impairing good wettability. However, the technology disclosed herein is not limited to this interpretation. From the viewpoint of haze reduction, the molecular weight of the surfactant is preferably less than 3700, more preferably less than 3500, and even more preferably less than 3300. From the viewpoint of surface activity, etc., the molecular weight of the surfactant is usually appropriate to be 200 or more, and from the viewpoint of haze reduction effect, etc., it is preferably 250 or more (e.g., 300 or more). 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, its molecular weight is preferably 1500 or less, and may be 1000 or less (e.g., 500 or less). Furthermore, for example, when a PEO-PPO-PEO triblock copolymer is used as the surfactant, the molecular weight thereof may be, for example, 500 or more, 1000 or more, 1500 or more, 2000 or more, or even 2500 or more.

[0036] 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

[0037] The surfactant contained in the polishing composition disclosed herein may be any of anionic, cationic, nonionic, and amphoteric surfactants. Generally, 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., polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkylamines, polyoxyethylene fatty acid esters, polyoxyethylene glyceryl ether fatty acid esters, and polyoxyethylene sorbitan fatty acid esters) (e.g., polyoxyalkylene adducts); 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 may be used alone or in combination.

[0038] 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).

[0039] The content of the surfactant in the polishing composition disclosed herein is not particularly limited. From the viewpoint of better exerting the effect of the surfactant, the content of the surfactant per 100 parts by weight of the 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, from the viewpoint of reducing haze, the content of the surfactant per 100 parts by weight of the abrasive grains is 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, even more preferably 1 part by weight or more, and may even be 2 parts by weight or more. From the viewpoint of cleaning properties, etc., the content of the surfactant per 100 parts by weight of the abrasive grains is suitably 20 parts by weight or less, preferably 15 parts by weight or less, more preferably 10 parts by weight or less.

[0040] <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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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 using 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.

[0045] <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.

[0046] <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.

[0047] <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.

[0048] 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.

[0049] <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 abrasive grains (e.g., silica particles) 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 11.0 or lower, more preferably 10.8 or lower, even more preferably 10.6 or lower, for example, 10.3 or lower.

[0050] 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.

[0051] <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.

[0052] 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.

[0053] 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 wettability, 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.

[0054] The concentration of surfactant in the polishing composition is not particularly limited, and can be, for example, 0.00001 wt% or more. 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. In addition, the concentration of the surfactant can be 0.5 wt% or less, and from the viewpoint of polishing efficiency and cleaning ability, 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 the embodiment in which the polishing composition is used in the form of a polishing liquid.

[0055] The concentration of the basic compound in the polishing composition is not particularly limited. From the viewpoint of improving polishing efficiency, the concentration is usually set to 0.0005% by weight or more, preferably 0.001% by weight or more. From the viewpoint of reducing haze, the concentration is set to less than 0.1% by weight, preferably less than 0.05% by weight, and more preferably less than 0.03% by weight (for example, less than 0.025% by weight).

[0056] <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.

[0057] <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.

[0058] 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.

[0059] <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.

[0060] 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.

[0061] 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).

[0062] <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.

[0063] 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.

[0064] 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.

[0065] 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]

[0066] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "%" is by weight unless otherwise specified.

[0067] <Preparation of Polishing Composition> Example 1 A polishing composition concentrate according to this example was prepared by mixing abrasive grains, a cellulose derivative, a surfactant, a basic compound, and deionized water (DIW). As the abrasive grains, colloidal silica having an average primary particle diameter of 42 nm was used, and as the cellulose derivative, Mw of 210 × 10 4 Hydroxyethyl cellulose (HEC) with a molecular weight of 3100 was used as the surfactant, PEO-PPO-PEO block copolymer (EO:PO = 160:30 (molar ratio)) with a molecular weight of 3100 was used as the surfactant, and ammonia was used as the basic compound. The obtained polishing composition concentrate was diluted 20 times by volume with deionized water (DIW) to obtain a polishing composition with an abrasive concentration of 0.46%, a cellulose derivative concentration of 0.018%, a surfactant concentration of 0.024%, and a basic compound concentration of 0.01%.

[0068] Example 2 As a surfactant, polyoxyethylene decyl ether (C10PEO5, ethylene oxide addition mole number 5) having a molecular weight of 378 was used. The concentration of the surfactant was 0.012%. In other respects, the polishing composition of this example was prepared in the same manner as in Example 1.

[0069] Example 3 Polyoxyethylene octyl ether (C8PEO6, ethylene oxide addition mole number 6) with a molecular weight of 394 was used as the surfactant. The surfactant concentration was 0.012%. In addition, a cellulose derivative with a Mw of 130 × 10 4 The polishing composition of this example was prepared in the same manner as in Example 1 except for the above.

[0070] Example 4 As the abrasive grains, colloidal silica having an average primary particle diameter of 27 nm was used. The abrasive grain concentration was 0.34%. In other respects, the polishing composition of this example was prepared in the same manner as in Example 1.

[0071] (Comparative Example 1) A polishing composition according to this example was prepared in the same manner as in Example 1, except that no surfactant was used.

[0072] (Comparative Example 2) As the water-soluble polymer, polyvinyl alcohol (PVA) having a molecular weight of 5900 was used at a concentration of 0.012%. In other respects, the polishing composition of this example was prepared in the same manner as in Example 1.

[0073] (Comparative Example 3) As the cellulose derivative, instead of the HEC with Mw of 210×10 4 , an HEC with Mw of 59×10 4 was used, and a polishing composition according to this example was prepared in the same manner as in Example 1 except for this.

[0074] <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% by weight Column: Asahipak GF-7MHQ, Asahipak GF-310HQ (7.5 mm I.D.×300 mm×2 pieces) Eluent: 0.7% aqueous sodium chloride solution Flow rate: 1.0 mL / min Detector: Differential refractometer Column temperature: 40°C Sample injection volume: 100 μL Standard sample: Pullulan·glucose

[0075] <Polishing of Silicon Wafer> As the object to be polished, a silicon wafer with a diameter of 200 mm (conductivity type: P-type, crystal orientation: <100>, free of COP (Crystal Originated Particle: crystal defect)) that was pre-polished under the following polishing condition 1 was prepared. The pre-polishing was performed using a polishing liquid containing 1.0% of silica particles (colloidal silica with an average primary particle diameter of 42 nm) and 0.068% of potassium hydroxide in deionized water.

[0076] [Polishing Condition 1] Polishing device: Single wafer polishing device "PNX-322" manufactured by Okamoto Machinery Works, Ltd. Polishing load: 15 kPa Rotational speed of the platen: 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

[0077] 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.

[0078] [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 solution temperature: 20℃ Plate cooling water temperature: 20℃ Polishing time: 4 minutes

[0079] 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.

[0080] <Haze measurement> After cleaning, the surface of the silicon wafer was inspected using a wafer inspection device manufactured by KLA Tencor, 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. A haze ratio of less than 100% can be said to have a haze reduction effect. A smaller haze ratio indicates a higher haze reduction effect. The "Haze [%]" column in Table 1 indicates the above-mentioned haze ratio.

[0081] <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.

[0082] (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.

[0083] [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 solution temperature: 20℃ Polishing time: 4 minutes

[0084] [Table 1]

[0085] As shown in Table 1, Mw is 120 × 10 4 The polishing compositions of Examples 1 to 4, which contain a cellulose derivative having a molecular weight of 120×10 or more and a surfactant having a molecular weight of less than 4,000, were confirmed to have a haze-reducing effect and a wettability-improving effect on the polished silicon wafer surface. On the other hand, in Comparative Examples 1 and 2, which did not use a surfactant having a molecular weight of less than 4,000, no haze-reducing effect was obtained. In addition, the cellulose derivative contained a surfactant having a molecular weight of 120×10 4 In Comparative Example 3, in which only the following materials were used, the water-repellent distance after polishing was large, and compared with Examples 1 to 4, the wettability was low. From the above results, it is found that the abrasive grains, the cellulose derivative, the surfactant, the basic compound, and water are contained in the abrasive grains, and the weight average molecular weight of the cellulose derivative is 120×10 4 and the molecular weight of the surfactant is less than 4,000, it is possible to achieve both reduced haze and improved wettability on the polished silicon wafer surface.

[0086] 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 abrasive includes an abrasive grain, a cellulose derivative, a surfactant, a basic compound, and water, The weight average molecular weight of the cellulose derivative is 120×10 ４ is larger than A polishing composition wherein the surfactant has a molecular weight of less than 4,000.

2. The polishing composition according to claim 1 , wherein the surfactant is a nonionic surfactant.

3. The polishing composition according to claim 2 , wherein the surfactant comprises a surfactant having a polyoxyalkylene structure.

4. The polishing composition according to claim 1 , having a pH of 8.0 or more and 12.0 or less.

5. 5. The polishing composition according to claim 1, wherein the content of the surfactant is 0.005 parts by weight or more and 15 parts by weight or less relative to 100 parts by weight of the abrasive grains.

6. 6. The polishing composition according to claim 1, wherein the content of the cellulose derivative is 0.1 parts by weight or more and 20 parts by weight or less per 100 parts by weight of the abrasive grains.

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

8. 8. The polishing composition according to claim 7, wherein the silica particles have an average primary particle size of 5 nm or more and 100 nm or less.

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 abrasive grains include a cellulose derivative, a surfactant, a basic compound, and water, and the cellulose derivative has a weight average molecular weight of 120×10 ４ and the molecular weight of the surfactant is less than 4,000.

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