JP2010182811A - Semiconductor wafer polishing composition and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor wafer polishing composition that hardly causes particle contamination and metal contamination at a plane part of a device wafer etc., when plane and edge parts of the device wafer are polished. <P>SOLUTION: The semiconductor wafer polishing composition contains colloidal silica prepared by adding quaternary ammonium hydroxylate to an active silicic acid solution, which is obtained by hydrolyzing tetra alkoxy silane with an acid catalyst, to make pH in alkali, and growing silica particles through heating. The silica particles have an aspherical shape such that an average diameter in a short-axis direction is 5 to 50 nm and the length in a long-axis direction is 1.2 to 10 times as large as that of the short axis through electron microscope observation, and an average particle diameter calculated by the BET method is 5 to 100 nm. The semiconductor wafer polishing composition contains a pH buffer solution to have buffer operation at 25°C between pH8 to pH11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a polishing process on a silicon wafer or a planar surface and an edge portion of a semiconductor wafer such as a semiconductor device substrate on which a metal film, an oxide film, a nitride film or the like (hereinafter referred to as a metal film) is formed. The present invention relates to a wafer polishing composition to be applied and a method for producing the same.

Electronic components such as ICs, LSIs, or VLSIs that are made of silicon single crystal semiconductor materials as raw materials, have many fine electric circuits on a wafer sliced from a single crystal ingot of silicon or another compound semiconductor into a thin disk shape. It is manufactured on the basis of a small piece-like semiconductor element chip which is divided by writing. The wafer sliced from the ingot is processed into a mirror wafer having a mirror surface finished with a flat surface and an edge surface through processes such as lapping, etching, and polishing (hereinafter also referred to as polishing). In the subsequent device process, a fine electrical circuit is formed on the mirror-finished surface in the subsequent device process. However, from the viewpoint of increasing the speed of LSI, the wiring material is more electrically resistant than conventional aluminum. In low copper, the insulation film between the wiring prevents the diffusion of copper from the silicon oxide film to the low dielectric constant film having a lower dielectric constant and between the copper and the low dielectric constant film into the low dielectric constant film. Therefore, the process has shifted to a wiring formation process having a structure through a barrier film made of tantalum or tantalum nitride. In order to form such a wiring structure and achieve high integration, a polishing process is frequently performed repeatedly for flattening an interlayer insulating film, forming a metal connection part (plug) between upper and lower wirings of a multilayer wiring, and forming a buried wiring. In this flat surface polishing, a semiconductor wafer is placed on a surface plate on which a polishing cloth made of a synthetic resin foam or a suede-like synthetic leather is stretched, and a polishing composition solution is quantitatively supplied while pressing and rotating. However, the method of processing is common.
The edge surface is in a state where the above metal film or the like is irregularly deposited. Until the wafer is divided into semiconductor element chips, the wafer is subjected to a process such as conveyance with the edge portion supported while maintaining the original disk shape. If the outer peripheral side edge of the wafer has an irregular structure at the time of transfer, micro-breakage occurs due to contact with the transfer device, and fine particles are generated. The fine particles generated in the subsequent processes are dissipated and contaminate the surface that has been subjected to precision processing, greatly affecting the product yield and quality. In order to prevent this fine particle contamination, it is necessary to perform mirror polishing of the edge portion of the semiconductor wafer after the formation of the metal film or the like.

  The above-mentioned edge polishing is performed by polishing silica or the like while pressing the edge portion of a semiconductor wafer on a polishing machine in which a polishing cloth made of synthetic resin foam, synthetic leather or nonwoven fabric is attached to the surface of the polishing cloth support. This is achieved by rotating a polishing pad support and / or a wafer while supplying a polishing composition solution containing abrasive grains as a main component. As abrasive grains of the polishing composition used at this time, colloidal silica equivalent to that used for edge polishing of silicon wafers, fumed silica, ceria, alumina, etc. used for planar polishing of device wafers have been proposed. Yes. In particular, colloidal silica and fumed silica are fine particles, and are attracting attention because they can easily obtain a smooth mirror surface. Such a polishing composition is also referred to as a “slurry” and may be described as such below.

  A polishing composition mainly composed of silica abrasive grains is generally a solution containing an alkali component, and the principle of processing is chemical action by the alkali component, specifically, the surface of a silicon oxide film, a metal film or the like. This is a combination of the erosion action and the mechanical polishing action of silica abrasive grains. Specifically, a thin soft erosion layer is formed on the surface of a workpiece such as a wafer by the erosion action of an alkali component. It is presumed that the erosion layer is removed by the mechanical polishing action of fine abrasive grains, and it is considered that the processing proceeds by repeating this process. After the workpiece is polished, a cleaning process is performed to remove silica abrasive grains and alkaline liquid from the processed surface and the edge portion.

In this cleaning process, a problem that metals such as copper, iron, and aluminum remain on the wafer surface has been pointed out. In particular, it is said that the alkali polishing process of the silicon oxide surface is difficult to remove by washing because the metal becomes a metal hydroxide and strongly bonds to the silicon oxide surface. For this reason, improvement of the cleaning method is strongly demanded, and at the same time, high purity of the abrasive is demanded. However, since the cleaning method is complicated and the polishing rate is greatly reduced, the problem has not been solved.
In addition, in the polishing process of silicon wafers, the fact that metal impurities, especially copper, present in the polishing agent diffuse deeply into the wafer, deteriorates the wafer quality, and significantly reduces the characteristics of the semiconductor device. . For this reason, the use of colloidal silica made of alkoxysilane as a raw material, which is relatively expensive and has a low polishing ability, is unavoidable.

Conventionally, various polishing compositions using tetraalkoxysilane as a raw material have been proposed for mirror polishing of semiconductor wafers.
In Patent Document 1, silicate ester (tetraalkoxysilane) is added in the presence of 0.5 to 10% quaternary ammonium hydroxide and 0.01 to 0.001% surfactant as a dispersant. A method for obtaining a silica sol having a particle diameter of about 10 nm by a method of concentrating at 60 to 70 ° C. after decomposition is described.
In Patent Document 2, while maintaining the reaction medium at an alkali concentration of 0.002 to 0.1 mol per liter and a water concentration of 30 mol or more, the reaction medium contains 7 atoms as Si atoms with respect to 1 mol of the alkali. An alkyl silicate (tetraalkoxysilane) in an amount of ˜80 mol is added, the alkyl silicate is hydrolyzed at a temperature below the boiling point of the reaction medium, and the polymerization of silicic acid generated by the hydrolysis is advanced to reduce the particle size. A method for producing colloidal silica having a particle size of 3 to 100 nm is disclosed.
Patent Document 3 describes colloidal silica composed of bowl-shaped silica particles having a major axis / minor axis ratio of 1.4 to 2.2 by hydrolysis of methyl silicate (tetramethoxysilane).
In Patent Document 4, a hydrolyzed solution of an alkyl silicate (tetraalkoxysilane) is used in place of an active silicic acid aqueous solution of the water glass method, and tetraalkylammonium hydroxide is used as an alkali. It is described that colloidal silica containing particles can be obtained.

Although the method of Patent Document 1 can improve the control of the generated silica particle diameter, the particle shape cannot be elongated, and there is a problem that a surfactant exists as an impurity in the final product.
The method of Patent Document 2 is a method of hydrolyzing an alkyl silicate in water, but the generated silica particle diameter can be controlled, but the particle shape cannot be elongated.
The colloidal silica described in Patent Document 3 is preferably high in purity because it uses alkoxysilane as a silica source, and non-spherical silica particles are also obtained. However, ammonia and a large amount of alcohol are required in the reaction system, and these components There are disadvantages such as removal and price.
In any of the methods of Patent Documents 1 to 3, hydrolysis is performed at a relatively low temperature and in a short time due to hydrolysis by an alkali catalyst. Since the colloidal silica obtained in this way has a low particle density, it has a drawback that the polishing rate is lower than that of water glass colloidal silica produced by growing particles of active silicic acid by a build-up method.
Regarding the density of the silica particles, Patent Document 10 has a detailed description.
Since Patent Document 4 uses alkoxysilane as a silica source, high purity is preferable, and non-spherical silica particles are also obtained. However, specific contents for making colloidal silica for polishing using this colloidal silica are described. It has not been.

Many polishing compositions that combine quaternary ammonium and colloidal silica have also been proposed.
In Patent Document 5, colloidal silica is produced by using tetramethylammonium hydroxide instead of sodium hydroxide as an alkali agent used in the particle growth process of colloidal silica, and is substantially free of sodium. Purity colloidal silica is described.
Patent Document 6 discloses a buffer solution having a buffering action between pH 8.7 and 10.6 by adding a combination of weak acid and strong base, weak acid and weak base, or a combination of weak acid and weak base. An adjusted colloidal silicon oxide solution is described, and tetramethylammonium hydroxide is mentioned as a strong base.
Patent Document 7 discloses a polishing composition having a buffering action in which an alkali component and an acid component are added to a colloidal dispersion of silicon oxide fine particles, and quaternary ammonium hydroxide as an alkali component and carbonic acid as an acid component. The ones used are listed.
Patent Document 8 describes a polishing composition containing peanut-shaped colloidal silica and tetramethylammonium hydroxide. Colloidal silica is described as a product of Fuso Chemical Industry Co., Ltd.
Patent Document 9 describes an abrasive for CMP containing a colloidal silica product obtained by reacting quaternary ammonium hydroxide and silicic acid ester (tetraalkoxysilane) and an oxidizing agent. The silicate is also described as TMAH (tetramethylammonium hydroxide) or choline.
The colloidal silica described in Patent Document 5 is a very preferable abrasive because sodium does not exist. However, quaternary ammonium hydroxide alone has a large pH fluctuation during polishing, and a stable polishing rate cannot be obtained.
The colloidal silica described in Patent Document 5 and Patent Document 6 uses water glass as a raw material, and has a larger amount of impurities than those using alkoxysilane as a raw material.
In Patent Document 7, there is a description using fumed silica, which is slightly high in purity, but has a larger amount of impurities than those using alkoxysilane as a raw material.
Since the colloidal silica described in Patent Document 8 is described as a product of Fuso Chemical Industry Co., Ltd., it is a product obtained by hydrolyzing alkoxysilane with an alkali catalyst and has a low polishing power. In addition, quaternary ammonium hydroxide alone has a large pH fluctuation during polishing, and a stable polishing rate cannot be obtained.
The colloidal silica described in Patent Document 9 is a product obtained by hydrolyzing alkoxysilane with an alkali catalyst, and has a low polishing rate. In addition, quaternary ammonium hydroxide alone has a large pH fluctuation during polishing, and a stable polishing rate cannot be obtained.

JP-A 61-209910 JP-A-6-316407 Japanese Patent Application Laid-Open No. 11-60232 JP, 2001-48520, A Claims and Examples JP 2003-89786 A Japanese Patent Laid-Open No. 11-302634 Claims and Examples JP, 2000-80349, A Claims and Examples JP 2005-518668 Gazette JP, 2001-23938, A Claims Japanese Patent Publication No. 3758391

  SUMMARY OF THE INVENTION An object of the present invention is to provide a composition for mirror polishing of the planar and edge portions of a semiconductor wafer, which suppresses the contamination of fine particles and metals generated on the surface of the semiconductor wafer and maintains a high polishing rate while obtaining a good surface state. It is in providing the manufacturing method.

  The inventors of the present invention use colloidal silica obtained by hydrolyzing tetraalkoxysilane with an acid catalyst and obtained by quaternary ammonium hydroxide as a colloidal solution having a buffering action between pH 8-11. Thus, the inventors have found that fine particles and metal contamination generated on the surface of the semiconductor wafer can be suppressed while maintaining a high polishing rate, and the present invention has been completed.

  That is, in the first invention of the present application, quaternary ammonium hydroxide is added to an active silicic acid aqueous solution obtained by hydrolyzing tetraalkoxysilane with an acid catalyst to make the pH alkaline, and the silica particles are grown by heating. The composition for polishing a semiconductor wafer containing the obtained colloidal silica, wherein the silica particles have an average diameter in the minor axis direction of 5 to 50 nm as observed by an electron microscope, and a length in the major axis direction is a minor axis. By having a non-spherical shape that is 1.2 to 10 times, the average particle size calculated by the BET method is 5 to 100 nm, and the semiconductor wafer polishing composition contains a pH buffer solution, A composition for polishing a semiconductor wafer, having a buffering action at 25 ° C. between pH 8-11.

There are many combinations that form a buffer solution having a buffering action between pH 8 and 11, but the buffer solution used in the present application is preferably a combination of a weak acid and a strong base. As the weak acid, a weak acid having a logarithmic value (pKa) of the reciprocal of the acid dissociation constant at 25 ° C. in the range of 8.0 to 12.5 can be used, and carbonic acid, boric acid, phosphoric acid and the like can be used.
Further, the anion constituting the weak acid is a carbonate ion and / or a hydrogen carbonate ion, and the cation of quaternary ammonium hydroxide constituting the strong base is a choline ion, tetramethylammonium ion or tetraethylammonium ion, or these A mixture is preferred.
The semiconductor wafer polishing composition has a conductivity of 25 ° C. per 1% by weight of silica particles by increasing the concentration of the buffer solution and / or having a salt of strong acid and quaternary ammonium hydroxide. It is preferably 15 mS / m or more and 200 mS / m or less.

A second invention of the present application is a method for producing a composition for polishing a semiconductor wafer according to claim 1, wherein the silica concentration is 1 to 8 mol / liter, and the acid concentration is 0.0018 to 0.18 mol / liter. In the first step of preparing an active silicic acid aqueous solution by hydrolyzing tetraalkoxysilane with a composition in a water concentration range of 2 to 30 mol / liter, the active silicic acid prepared in the first step has a silica concentration of 0.2 to 1. Second step of diluting with water so as to be in the range of 5 mol / liter, then adding quaternary ammonium hydroxide so that the pH is 8 to 11, and then heating to grow colloidal particles, second step The colloidal particles produced in the process are concentrated by ultrafiltration to produce a colloidal silica solution having a silica concentration of 20 to 50% by weight. The colloidal silica solution produced in the third process has a pH buffer composition. Fourth step of adding a weak acid with a quaternary ammonium hydroxide, is achieved by the method of manufacturing a more becomes a semiconductor wafer polishing compound.
Further, in the above method for producing a semiconductor wafer polishing composition, it is preferable to perform a step of further growing colloidal particles between the second step and the third step, and to produce colloidal silica having a larger average particle size. Is possible.

  By using the non-spherical colloidal silica particles of the present invention, containing a quaternary ammonium hydroxide, and further using a polishing composition having a pH buffering action in a specific range, the number of adhered fine particles in polishing a semiconductor wafer is It was extremely low, and there were hardly any defects on the polished surface, and it was possible to obtain an excellent effect that a high polishing force could be stably obtained without changing the pH of the circulating liquid.

4 is a TEM photograph of silica particles having an average value of a major axis / minor axis ratio of 10 to 15 obtained in Production Example 1. FIG. 2 is a TEM photograph of silica particles having an average value of a major axis / minor axis ratio of 4 obtained in Production Example 1. FIG. 4 is a TEM photograph of silica particles having an average value of a major axis / minor axis ratio of 4 obtained in Production Example 2. FIG. 4 is a TEM photograph of silica particles having an average value of a major axis / minor axis ratio of 5 obtained in Production Example 3. FIG. 4 is a TEM photograph of silica particles having an average value of a major axis / minor axis ratio of 10 to 15 obtained in Production Example 4. FIG.

Commercially available colloidal silica is usually are stabilized with sodium, 20 to 50% by weight of silica (SiO ₂₎ component contains a sodium component of from 0.07 to 0.22 wt%. As a raw material for stabilizing colloidal silica, sodium hydroxide is generally used. Alkali metal hydroxides such as sodium hydroxide and potassium hydroxide are difficult to purify, and inevitably introduce metal into the product. On the other hand, the quaternary ammonium hydroxide used in the present invention can provide a product in which the amount of metal that causes metal contamination is extremely reduced as compared with an alkali metal hydroxide. In the present invention, the quaternary ammonium hydroxide added to the active silicic acid aqueous solution obtained by hydrolyzing tetraalkoxysilane with an acid catalyst is not particularly limited, but choline, tetramethylammonium hydroxide or tetraethylammonium hydroxide is preferred. By adding quaternary ammonium hydroxide, the composition for polishing a semiconductor wafer is stabilized, and since the impurity content is small, the number of particles adhered to the surface of the polished object is reduced. . That is, the polishing composition of the present invention is colloidal silica stabilized with quaternary ammonium hydroxide, which has very little metal causing metal contamination instead of sodium, so that it is sodium in comparison with commercially available colloidal silica. In addition, it is possible to obtain a polishing composition with less contamination of other metals, and it is possible to reduce contamination of sodium and other metals on the semiconductor wafer surface that occurs during polishing.

Here, “stabilization” will be described. For example, in a state where silica particles are dispersed in pure water, there are silanol groups on the particle surface, and the outside is only water molecules. Since the particles vibrate and move due to Brownian motion, collisions between particles occur, dehydration condensation occurs between silanol groups, particles are connected, and when the connection expands, the viscosity of the colloid increases, eventually It becomes a gel. On the other hand, for example, when the silica particles are dispersed in a dilute aqueous sodium hydroxide solution having a pH of about 9, hydrated sodium cations exist outside the silanol groups on the surface of the particles, and the particles have an anionic charge, outside the hydration phase OH ^- ions are present in close proximity, further there will be water molecules on the outside. When the silica particle surface has such a constrained phase, a repulsive force is generated between the particles, and the collision and connection of the particles do not occur. This is called “stabilization”.

Furthermore, the shape of the silica particles of the present invention observed with an electron microscope has an average diameter in the thickness direction (hereinafter referred to as a short axis) of 5 to 50 nm and a length (hereinafter referred to as a long axis) of 1.2 to The silica particles are 10 times as long as non-spherical silica particles, and the silica particles have an average particle diameter of 5 to 100 nm according to the nitrogen adsorption BET method.
In the polishing process, the shape of the silica particles is an important factor. Briefly describing the polishing process, the workpiece surface is chemically eroded by alkali to form a hydrated thin layer. Next, a process of removing the formed hydrated thin layer by the physical polishing force of the silica particles continuously occurs. The removal rate of this thin layer varies greatly depending on the shape of the silica particles. Increasing the particle size of the silica particles increases the removal rate but tends to cause scratches on the polished surface. Similarly, the non-spherical shape of the silica particles has a higher removal rate than the true spherical shape, but scratches are likely to occur on the polished surface. Therefore, the shape and particle diameter of the silica particles need to be in an appropriate range. Further, the silica particles should not be easily crushed during polishing, or should be agglomerated and gelled.
In order to obtain a good polished surface, the average minor axis of the silica particles by electron microscope observation is preferably 5 to 50 nm. If it is smaller than 5 nm, the polishing rate is low, the particles are likely to aggregate, and the stability of the colloid is lacking. On the other hand, if it is larger than 50 nm, scratches are likely to occur, and the flatness of the polished surface will be lowered. The average value of the major axis / minor axis ratio is preferably 1.2 to 10. If it is less than 1.2, the polishing rate is low, and if it is more than 10, particles are likely to aggregate and the stability of the colloid is lacking. More preferably, it is 1.2-5. The average particle diameter of the silica particles is preferably 5 to 100 nm. As the average particle size of the silica particles of the present invention, the average particle size calculated by the nitrogen adsorption BET method was used.

  In the present invention, it is preferable to maintain the pH of the entire solution in the range of 8 to 11 in order to maintain a stable polishing force during actual polishing. When the pH is less than 8, the polishing rate decreases and falls outside the practical range. On the other hand, when the pH exceeds 11, the etching at the portion other than the polishing portion becomes too strong, and the silica particles start to aggregate, so that the stability of the polishing composition is lowered, and this is also out of the practical range.

  Furthermore, it is preferable that this pH does not change easily due to possible external conditions such as friction, heat, contact with outside air, or mixing with other components. Particularly in edge polishing, the polishing composition is used in a circulating manner. That is, the polishing composition supplied from the slurry tank to the polishing site is used in a manner of returning to the slurry tank. The polishing composition containing only the alkali agent is lowered in pH in a short time during use. This is due to dissolution of the object to be polished and mixing of cleaning water, and fluctuations in the polishing rate caused by fluctuations in pH greatly affect the quality of the object to be polished.

In order to keep the pH of the polishing composition of the present invention constant, a combination of a weak acid having a logarithmic value (pKa) of the reciprocal of the acid dissociation constant at 25 ° C. of 8.0 to 12.5 and quaternary ammonium hydroxide is preferable. The buffer solution composition is good. Also in this case, it is preferable to have a buffering action between pH 8-11.
The anion constituting the weak acid is preferably carbonate ion and / or bicarbonate ion (pKa = 6.35, 10.33), and the cation constituting the strong quaternary ammonium base is choline ion, tetramethylammonium ion or Preferably, it is at least one of tetraethylammonium ions.
When the logarithmic value (pKa) of the reciprocal of the acid dissociation constant at 25 ° C. is less than 8.0, it is not preferable because it is necessary to add a large amount of a strong base to raise the pH. If the logarithmic value (pKa) of the reciprocal of the acid dissociation constant at 25 ° C. is larger than 12.5, it is not preferable because it is difficult to form a buffer solution having a large buffering action that stabilizes the pH in the range of 8-11.

  Examples of weak acids other than carbonic acid include boric acid (pKa = 9.24), phosphoric acid (pKa = 2.15, 7.20, 12.35), and water-soluble organic acids. It doesn't matter.

In the present invention, the polishing process speed can be remarkably improved by increasing the conductivity of the polishing composition solution. The conductivity is a numerical value indicating the ease of passing electricity in the liquid, and is an inverse value of the electrical resistance value per unit length. In the present invention, the numerical value of conductivity per unit length (Siemens) is shown as a numerical value converted to 1% by weight of silica. In the present invention, further preferably equal to preferably against improvement of polishing rate if the conductivity at 25 ° C. is 15mS / m / 1% -SiO ₂ or more, 20mS / m / 1% -SiO 2 or more. Since the addition of salts reduces the stability of the colloid, there is an upper limit on the conductivity. Although an upper limit changes with particle diameters of silica, it is about ₂₀₀ mS / m / 1% -SiO2.
As described above, this processing is an application of the chemical action of alkali, which is its component, specifically, the erosion of a workpiece such as a silicon oxide film or a metal film. That is, a thin soft erosion layer is formed on the surface of a workpiece such as a wafer due to the corrosiveness of alkali. Processing proceeds by removing the thin layer by the mechanical action of fine abrasive grains. The erosion of the metal film is a reaction in which the metal is oxidized, and the metal surface receives electrons from the solution in contact and moves to the solution as metal hydroxide ions. In order for this donation of electrons to proceed quickly, the conductivity of the solution needs to be high.

There are the following two methods for increasing the conductivity. One is a method of increasing the concentration of the buffer solution, and the other is a method of adding salts. In order to increase the concentration of the buffer solution, it is only necessary to increase the concentration without changing the molar ratio of acid to base. The salt used in the method of adding salts is composed of a combination of an acid and a base, but the acid may be either a strong acid or a weak acid, and a mineral acid and an organic acid can be used, or a mixture thereof may be used. . A water-soluble quaternary ammonium hydroxide is used as the base. When adding a combination of a weak acid and a strong base, a strong acid and a weak base, or a combination of a weak acid and a weak base, the pH of the buffer solution may be changed. The above two methods may be used in combination.
The salt of strong acid and quaternary ammonium hydroxide is preferably at least one of quaternary ammonium sulfate, quaternary ammonium nitrate, or quaternary ammonium fluoride. The cation constituting the quaternary ammonium is preferably at least one of choline ion, tetramethylammonium ion or tetraethylammonium ion. As the other quaternary ammonium ions, the aforementioned substances are used.

  A method for producing colloidal silica stabilized with quaternary ammonium hydroxide is described. First, examples of the tetraalkoxysilane used as a raw material include tetramethyl silicate and tetraethyl silicate, but a commercially available silicic acid oligomer having a polymerization degree of 2 to 10 (for example, “ethyl silicate 40” manufactured by Colcoat Co., Ltd.) can also be used. Tetraalkoxysilane is preferably a high-purity product.

  The method described in Patent Document 4 can be applied to the method for producing the active silicic acid aqueous solution used in the present invention. That is, the composition of the silica concentration 1 to 8 mol / liter, the acid concentration 0.0018 to 0.18 mol / liter, and the water concentration 2 to 30 mol / liter. After hydrolysis, an active silicic acid aqueous solution is prepared by diluting with water so that the silica concentration is in the range of 0.2 to 1.5 mol / liter.

  Next, quaternary ammonium hydroxide is added to the aqueous active silicic acid solution to make it alkaline, and then heated to form colloidal particles (seed particle forming step). While maintaining the alkalinity by adding the active silicic acid aqueous solution, the colloidal particles are grown (particle growth step).

  Specifically, conventional operations are performed in the seed particle forming step and the particle growing step. For example, in the seed particle formation step, the silica concentration of the active silicic acid aqueous solution is 2 to 7% by weight, quaternary ammonium hydroxide is added so that the pH is 8 to 10, and the silica particles are heated to 60 to 240 ° C. Seed particles having a minor axis (thickness) of 5 to 20 nm can be formed. Next, in the particle growth step, a build-up method is used, and an aqueous solution of active silicic acid and quaternary ammonium hydroxide are added to a colloid solution of seed particles having a pH of 8 to 11 at 60 to 240 ° C. while maintaining the pH of 8 to 11. Then, the particles are grown to the target particle size. In this way, silica particles can be grown to particles having a minor axis (thickness) of 5 to 50 nm.

  The above production method is generally the same as the production method using alkali metal hydroxide or alkali silicate as an alkali agent, which is a conventional method. That is, instead of an active silicic acid aqueous solution made of sodium silicate, an active silicic acid aqueous solution obtained by hydrolysis of tetraalkoxysilane is used, and an alkali metal hydroxide is substituted in the seed particle forming step and the particle growing step. The difference is that quaternary ammonium hydroxide is used, and in the particle growth process, quaternary ammonium hydroxide is used instead of alkali metal hydroxide.

The quaternary ammonium hydroxide used in the present invention is not particularly limited, but tetramethylammonium hydroxide, tetraethylammonium hydroxide, choline and the like can be used, and a mixture thereof may be used.
In this buffer solution, the anion constituting the weak acid is present in a form having a different valence.
Specifically, in the case of carbonic acid, a combination of carbonate ion and hydrogen carbonate ion (CO ₃ ²⁻ / HCO ₃ ⁻ ), in the case of boric acid, boric acid ion and undissociated boric acid (BO ₃ ⁻ / HBO ₃ ). In the case of phosphoric acid, it is a combination of phosphate ion and monohydrogen phosphate ion (PO ₄ ³⁻ / HPO ₄ ²⁻ ).

Next, silica is concentrated, and evaporative concentration of water may be used, but ultrafiltration is advantageous in terms of energy.
An ultrafiltration membrane with a molecular weight cut-off of 3000-15000 is used. If the membrane is less than 3000, the filtration resistance is too large and the treatment time becomes long and uneconomical. If it exceeds 15000, the degree of purification is low. The material of the membrane includes polysulfone, polyacrylonitrile, sintered metal, ceramic, carbon and the like. Any of them can be used, but polysulfone is easy to use because of its heat resistance and filtration speed. There are spiral, tubular, and hollow fiber types that can be used, but the hollow fiber type is compact and easy to use. In addition, when the ultrafiltration step also serves to wash out and remove the acid catalyst used for the hydrolysis of the tetraalkoxysilane and the alcohol produced by the hydrolysis, if necessary, the pure water can be added even after reaching the target concentration. For example, it is possible to perform washing and removal to increase the removal rate. In this step, it is preferable to concentrate so that the silica concentration is 10 to 50% by weight.

Further, a purification step using an ion exchange resin can be added as needed before or after the ultrafiltration step. For example, it is possible to remove impure metals and alkali metals mixed in the particle growth process by contacting with an H-type strongly acidic cation exchange resin, and contacting the OH-type strongly basic anion exchange resin with an acid catalyst used for hydrolysis. It is possible to further improve the purity by removing the anionic component.
As described above, high-purity colloidal silica stabilized by quaternary ammonium hydroxide, in which the short diameter (thickness) of the silica particles is 5 to 50 nm and the silica concentration is 10 to 50% by weight. Is obtained.

The colloidal silica stabilized by the quaternary ammonium hydroxide of the present invention has excellent properties other than high purity. When the semiconductor wafer is cleaned after polishing and proceeds to the next step, abrasive grains of the abrasive may remain on the cleaned wafer surface. In the case of colloidal silica stabilized with quaternary ammonium hydroxide, this problem is unlikely to occur.
The phenomenon that the silica particles of colloidal silica stabilized with quaternary ammonium are difficult to adhere to the wafer surface has been clarified for the first time by the present inventors. The mechanism can be presumed as follows. First, in the case of colloidal silica stabilized with sodium hydroxide, the silica particles and the wafer are accompanied by a slight evaporation of water during the lapse of a short time while the polishing slurry remains attached to the polished wafer surface. Sodium hydroxide corrodes the surface metal (or metal oxide), and silica and metal hydroxide are bonded. Bonding may be due to fusion between the surface of the silica particles and the metal hydroxide surface, or electrostatic bonding due to the negative charge of silica and the positive charge of the metal hydroxide surface.

  On the other hand, in the case of colloidal silica stabilized with quaternary ammonium, quaternary ammonium ions are present on the surface of the silica particles, and quaternary ammonium ions are also present on the wafer surface. The alkyl group is exposed. The repulsive force between the alkyl groups prevents the silica particles from sticking to the wafer surface. In the field of metal corrosion protection, quaternary ammonium and amines are treated as inhibitors (rust inhibitors). Nitrogen atoms in the molecule are adsorbed on the metal surface, and the alkyl group side faces the liquid phase surface. It is said that it forms a phase and exhibits an anticorrosive action. It is considered that a similar anticorrosive action is also exhibited on the wafer surface.

  Next, the colloidal silica stabilized by the quaternary ammonium hydroxide is added to the fourth acid hydroxide which is a weak acid and a strong base having a logarithmic value (pKa) of the reciprocal of the acid dissociation constant at 25 ° C. of 8.0 to 12.5. A buffer solution combined with ammonium is added and mixed to adjust the pH to 8 to 11 at 25 ° C., and a semiconductor wafer polishing composition having a buffering action between pH 8 and 11 is prepared.

The quaternary ammonium ion is preferably the same as the quaternary ammonium ion used for the production of colloidal silica, and choline ion, tetramethylammonium ion, tetraethylammonium ion, or a mixture thereof can be used. Other quaternary ammonium ions are preferably quaternary ammonium ions composed of an alkyl group having 4 or less carbon atoms or a hydroxyalkyl group having 4 or less carbon atoms, and the alkyl group is a methyl group, an ethyl group, a propyl group, or a butyl group. The hydroxyalkyl group is a hydroxymethyl group, a hydroxyethyl group, a hydroxypropyl group, or a hydroxybutyl group. Specifically, tetrapropylammonium ion, tetrabutylammonium ion, methyltrihydroxyethylammonium ion, triethyl (hydroxyethyl) ammonium ion and the like are preferable.
Further, as other quaternary ammonium ions, benzyltrimethylammonium ions, phenyltrimethylammonium ions, and the like are also preferable.
Since the quaternary ammonium ions have different corrosiveness and polishing performance with respect to the wafer depending on the kind, and also have different abrasive cleaning properties, it is preferable to select and use a combination of a plurality of quaternary ammonium ions.

  In the present invention, the average minor axis of silica particles by electron microscope observation is preferably 5 to 50 nm. However, since electron microscope observation is performed with a limited number of particles, The identification of the particle shape was clarified by the particle size. As a method for measuring the average particle diameter of colloidal silica, there are a BET method and a Sears method in addition to observation with an electron microscope, and both measure specific surface area measured values into average particle diameters. In particular, the BET method is frequently used. In order to convert the measured value of the specific surface area into the particle diameter, the particle is regarded as a true sphere, and therefore the average particle diameter of the BET method does not reflect the essential average particle diameter for non-spherical particles. However, in the case of long and narrow particles as in the present invention, the average particle size of the BET method is in good agreement with the short diameter which is the thickness of the particles. Therefore, in the present invention, the average particle diameter of the BET method is used as a means for clarifying the specification of the particle shape.

  The average particle diameter of colloidal silica silica particles by BET method is 10 nm to 100 nm, preferably 10 nm to 50 nm. The average particle diameter according to the BET method referred to here is an average primary particle diameter calculated from the specific surface area in terms of a true sphere based on the following formula, by measuring the specific surface area of powdered colloidal silica by the nitrogen adsorption BET method.

2720 / specific surface area (m ² / g) = average primary particle diameter (nm) calculated in terms of true sphere

  The manufacturing method of the polishing composition of this invention is demonstrated. The colloidal silica stabilized with the above-mentioned quaternary ammonium hydroxide is prepared as a high concentration colloidal solution so that the silica concentration is 30 to 50% by weight. On the other hand, the buffer solution component is also produced at a high concentration so as to be 20 to 40% by weight. For example, a 29% tetramethylammonium carbonate solution is prepared by neutralizing 25% tetramethylammonium hydroxide with carbon dioxide to pH 10.3. The salt of strong acid and quaternary ammonium hydroxide is produced by neutralizing quaternary ammonium hydroxide with a strong acid. For example, 25% tetramethylammonium hydroxide is neutralized with 98% sulfuric acid to produce a tetramethylammonium sulfate solution at a high concentration. A high-concentration colloidal solution having a silica concentration of 30 to 50% by weight is vigorously stirred, and the above-mentioned high-concentration buffer solution, a high-concentration strong acid, a neutralized solution of quaternary ammonium hydroxide and pure water are added to the semiconductor wafer. A polishing composition is produced.

  The polishing composition of the present invention is preferably an aqueous dispersion having a silica concentration of 20 to 50% by weight based on the entire colloidal solution. The polishing composition is diluted during use to adjust the silica concentration to 2 to 20% by weight. Therefore, the polishing composition of the present invention has a silica concentration of 2 to 50% by weight in the entire range.

  Moreover, the polishing composition of this invention can add the chelating agent which forms copper and a water-insoluble chelate compound. For example, as the chelating agent, known compounds such as azoles such as benzotriazole, quinoline derivatives such as quinolinol and quinaldic acid are preferable.

In order to improve the physical properties of the polishing composition of the present invention, a surfactant, an antifoaming agent, a water-soluble polymer and the like can be added. Moreover, although the polishing composition of the present invention is an aqueous solution, an organic solvent may be added as necessary. For example, the addition of glycerin is effective for preventing freezing during transportation, and the addition of propyl alcohol is effective for improving fluidity.
The surfactant is effective in preventing haze (surface roughness) of the wafer. That is, there is an effect of preventing the polishing liquid from coming into contact with the unpolished surface and etching the wafer surface with an alkali component.
As the surfactant, any of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant can be used. High molecular surfactants and glycols can be used, but anionic surfactants or nonionic surfactants are preferred. As the anionic surfactant, any of sulfonates or fatty acid salts, alkyl ether carboxylates, alkyl ether sulfates, and the like can be used, but sulfonates or fatty acid salts are preferable. As the sulfonate, linear alkylbenzene sulfonic acid and its salt, alpha olefin sulfonic acid and its salt are preferable, and dodecylbenzene sulfonate is most preferable. The fatty acid salt is preferably at least one selected from lauric acid, myristic acid, valmitic acid, stearic acid, and oleic acid. It is convenient to use water-soluble salts such as sodium stearate. As the nonionic surfactant, polyoxyalkylene glycols, fatty acid esters, alkylamine ethylene oxide adducts, glycols or polymer surfactants can be used. Of these, polyoxyethylene alkyl ether and polyethylene glycol are preferable, but polyethylene glycol is most preferable.

The concentration of the surfactant is preferably 0.01 to 10 mmol / Kg. If it is 0.01 mmol / Kg or less, there is no etching prevention effect, and even if it is added at 10 mmol / Kg or more, the effect is not changed and is unnecessary.
Surfactants, especially anionic surfactants, tend to cause a negative phenomenon of foaming depending on how they are used. An antifoaming agent is usually used in combination with this suppression, but a silicone antifoaming agent is extremely effective. Silicone antifoaming agents are available in oil, modified oil, solution, powder, and emulsion types. The modified oil and emulsion types can be used well in colloidal liquids, but the emulsion type is the most effective. High sustainability. Examples of commercially available products include Shin-Etsu Silicone KM grade manufactured by Shin-Etsu Chemical Co., Ltd.
The amount of the antifoaming agent to be used must be determined appropriately depending on the amount of the surfactant, but is generally 1 ppm to 1000 ppm in the polishing composition as an antifoaming active ingredient.

  Moreover, in this invention, the etching prevention effect can be heightened by mix | blending water-soluble polymer. As described above, water-soluble polymers having a molecular weight of 5000 or more and water-soluble polymers having a molecular weight of 100,000 or more are said to function to reduce metal contamination of the wafer and improve flatness. When molecules are used, there is a drawback that only a small amount can be blended so as not to increase the viscosity of the abrasive liquid. It is preferable to use a water-soluble polymer having an average molecular weight of 5000 or less, preferably 500 or more and 3000 or less in an amount of 0.001 to 1 mmol / Kg. Examples of the water-soluble polymer include polyacrylic acid, polymethacrylic acid, polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, maleic acid / vinyl copolymer, xanthan gum, and cellulose derivatives. One or more selected from glycols are preferred. As the cellulose derivative, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose and the like can be used, and hydroxyethyl cellulose is preferable. Polyethylene glycol having a molecular weight of 5000 or less is more preferable.

Next, a method for polishing a semiconductor wafer using the polishing composition of the present invention will be described.
In the case of surface polishing, the polishing surface of the work piece is pressed against a rotatable surface plate having a polishing cloth made of synthetic resin foam or suede-like synthetic leather on the upper or lower surface or one surface, and silicon oxide fine particles are washed with water. While the polishing composition dispersed in is quantitatively supplied, the surface plate and / or the workpiece are rotated to polish the polished surface of the workpiece. The flat polishing processing machine used in the present invention is an apparatus shown in, for example, SH-24 single-side polishing apparatus, 20B double-side polishing apparatus, etc. manufactured by Speed Fam Co., Ltd.

  In the case of edge polishing, generally, a polishing machine in which a polishing cloth made of synthetic resin foam, synthetic leather, nonwoven fabric or the like is attached to the surface of a polishing cloth support is used for an edge portion of a semiconductor wafer or the like as a workpiece. Then, while supplying the polishing composition, the polishing pad support and / or the workpiece are rotated to polish the edge portion. The edge polishing processing machine used in the present invention is, for example, as shown in an EP-200X type edge polishing apparatus manufactured by Speed Fam Co., Ltd. The polishing composition of the present invention comprises a cloth support and a gripping part that grips and rotates the workpiece, and presses the polishing cloth support against an edge portion of the workpiece attached to the gripping part. Rotate the work piece while supplying, and perform mirror polishing of the edge portion of the work piece. That is, polishing is performed while the work piece is pressed against a polishing pad support that is gradually raised or lowered to change its position while the work piece is rotated, and the polishing composition of the present invention is supplied to the work portion. The method for polishing a semiconductor wafer using the polishing composition of the present invention will be described in detail in the following examples. The apparatus is not limited to the above description. For example, in Japanese Patent Laid-Open Nos. 1-71656, 7-314304, 2000-317788, 2002-36079, etc. Any of the devices described can be used.

  Next, the semiconductor wafer polishing composition of the present invention and the polishing method using the same will be specifically described with reference to examples and comparative examples. However, the present invention is not limited to these examples. Absent. Colloidal silica used in Examples and Comparative Examples was produced according to Production Examples 1 to 5 shown below, and additives were produced according to Production Examples 6 and 7.

Production Example 1
<Example of production of tetramethylammonium hydroxide stabilized colloidal silica A>
In advance, 2 g of 35% hydrochloric acid was added to 460 g of deionized water to prepare a diluted hydrochloric acid solution. 960 g of tetramethoxysilane (reagent, converted SiO ₂ concentration: 39 wt%) was collected in a container, and the diluted hydrochloric acid solution was gradually added with stirring. Initially, the two liquids were not separated and mixed, but after a few minutes hydrolysis started and became a transparent uniform liquid with rapid heat generation. Stirring was continued for 30 minutes to complete hydrolysis, and a hydrolyzed solution was obtained. Then, 1160 g of deionized water was added and diluted to suppress polymerization of active silicic acid. In a separate container, 7420 g of deionized water was collected, and the above hydrolyzate was added to make the total amount 10 Kg, and the mixture was aged by stirring for 16 hours. Thus, an active silicic acid aqueous solution having a silica concentration of 3.7% by weight and a pH of 2.8 was obtained.
40 g of a 25% tetramethylammonium hydroxide aqueous solution was added to 2 kg of the active silicic acid aqueous solution having a silica concentration of 3.7% by weight and a pH of 2.8 to adjust the pH to 8.6. Subsequently, the mixture was heated with stirring and kept at 100 ° C. for 1 hour to form colloidal particles, and then allowed to cool to obtain a slightly bluish colloidal silica. This colloidal silica has a pH of 10.1 at 25 ° C., and is observed to be irregularly linked with a minor axis of about 5 to 7 nm and a major axis / minor axis ratio of 5 to 20 when observed with a transmission electron microscope (TEM). It was a non-spherical silica irregularly shaped particle group, and the average value of the major axis / minor axis ratio was 10-15. A TEM photograph of the silica particles is shown in FIG.

Next, the colloidal silica was heated again to 100 ° C., and an aqueous active silicic acid solution was added with stirring to grow particles. 8 Kg of active silicic acid aqueous solution was added over 3 hours, and during the addition, 25% tetramethylammonium hydroxide aqueous solution was added simultaneously to maintain the pH at 9-10. The 25% tetramethylammonium hydroxide aqueous solution used in the simultaneous addition was 84 g. After completion of the addition, the mixture was aged at 100 ° C. for 1 hour and allowed to cool. The obtained colloidal silica is 9.4 kg by evaporation of water, has a pH of 10.0 at 25 ° C., and has a minor axis of about 10 to 14 nm and a major axis / The irregular-shaped particle group of irregularly connected non-spherical silica having a minor axis ratio of 2 to 7 was obtained, and the average value of the major axis / minor axis ratio was 4. A TEM photograph of the silica particles is shown in FIG.
Subsequently, this colloidal silica was subjected to pressure filtration by circulating pumping liquid using a hollow fiber type ultrafiltration membrane (Microsa UF module SIP-1013 manufactured by Asahi Kasei Chemicals Co., Ltd.) having a molecular weight cut off of 6,000 to obtain a silica concentration. The mixture was concentrated to 30% by weight, and about 1200 g of colloidal silica was recovered. The particle size of the colloidal silica obtained by nitrogen adsorption method BET specific surface area measurement was 11 nm. The tetramethylammonium hydroxide stabilized colloidal silica thus obtained will be referred to as colloidal silica A below.

Production Example 2
<Example of production of tetraethylammonium hydroxide stabilized colloidal silica B>
In the same manner as in Production Example 1, 10 kg of an active silicic acid aqueous solution having a silica concentration of 3.7% by weight and a pH of 2.8 was produced.
To 2 kg of active silicic acid aqueous solution, 36 g of 35% tetraethylammonium hydroxide aqueous solution was added with stirring to adjust the pH to 8.6. Subsequently, the mixture was heated with stirring and kept at 100 ° C. for 1 hour to form colloidal particles, and then allowed to cool to obtain a slightly bluish colloidal silica. This colloidal silica has a pH of 10.0 at 25 ° C., and when observed with a transmission electron microscope (TEM), the colloidal silica is randomly connected with a minor axis of about 5 to 7 nm and a major axis / minor axis ratio of 5 to 20. It was a non-spherical silica irregularly shaped particle group, and the average value of the major axis / minor axis ratio was 10-15. The shape of the silica particles was close to the TEM photograph of Production Example 1 shown in FIG.

Next, the colloidal silica was heated again to 100 ° C., and an aqueous active silicic acid solution was added with stirring to grow particles. 8 Kg of active silicic acid aqueous solution was added over 3 hours, and during the addition, 35% tetraethylammonium hydroxide aqueous solution was added simultaneously to maintain the pH at 9-10. The 35% tetraethylammonium hydroxide aqueous solution used in the simultaneous addition was 60 g. After completion of the addition, the mixture was aged at 100 ° C. for 1 hour and allowed to cool. The obtained colloidal silica is 8.8 kg by evaporation of water, has a pH of 9.5 at 25 ° C., and has a minor axis of about 10 to 14 nm and a major axis / The irregular-shaped particle group of irregularly connected non-spherical silica having a minor axis ratio of 2 to 7 was obtained, and the average value of the major axis / minor axis ratio was 4. A TEM photograph of the silica particles is shown in FIG.
Subsequently, this colloidal silica was subjected to pressure filtration by circulating pumping liquid using a hollow fiber type ultrafiltration membrane (Microsa UF module SIP-1013 manufactured by Asahi Kasei Chemicals Co., Ltd.) having a molecular weight cut off of 6,000 to obtain a silica concentration. The mixture was concentrated to 30% by weight, and about 1200 g of colloidal silica was recovered. The particle diameter of the colloidal silica obtained by the nitrogen adsorption method BET specific surface area measurement was 13 nm. The tetraethylammonium hydroxide stabilized colloidal silica thus obtained will be referred to as colloidal silica B below.

Production Example 3
<Example of production of tetramethylammonium hydroxide stabilized colloidal silica C>
A diluted hydrochloric acid solution was prepared in advance by adding 10 g of 35% hydrochloric acid to 2000 g of deionized water. 1070 g of tetraethoxysilane (manufactured by Tama Chemical Co., Ltd., converted SiO ₂ concentration: 29% by weight) was collected in a container, and 380 g of the diluted hydrochloric acid solution was added with stirring. Initially, the two liquids were not separated and mixed, but after about ten minutes, hydrolysis started and the liquid became transparent and uniform with heat generation. Stirring was continued for 30 minutes to complete the hydrolysis to obtain a hydrolyzed solution, which was then diluted by adding 1000 g of deionized water to suppress polymerization of active silicic acid. In a separate container, 5900 g of deionized water was collected, and the above hydrolyzate was added to make a total amount of 8350 g, which was aged by stirring for 16 hours. Thus, an active silicic acid aqueous solution having a silica concentration of 3.7% by weight and a pH of 2.8 was obtained.

  16 g of 25% tetramethylammonium hydroxide aqueous solution was added to 1000 g of the active silicic acid aqueous solution with stirring to adjust the pH to 8.7. Subsequently, the mixture was heated with stirring and kept at 100 ° C. for 1 hour to form colloidal particles, and then allowed to cool to obtain a slightly bluish colloidal silica. This colloidal silica has a pH of 10.1 at 25 ° C., and when observed with a transmission electron microscope (TEM), the colloidal silica is irregularly connected with a minor axis of about 4 to 5 nm and a major axis / minor axis ratio of 5 to 20. It was a non-spherical silica irregularly shaped particle group, and the average value of the major axis / minor axis ratio was 10-15. The shape of the silica particles was close to the TEM photograph of Production Example 1 shown in FIG.

Next, the colloidal silica was heated again to 100 ° C., and an aqueous active silicic acid solution was added with stirring to grow particles. 2000 g of active silicic acid aqueous solution was added over 2 hours, and during the addition, 25% tetramethylammonium hydroxide aqueous solution was added simultaneously to maintain the pH at 9-10. The 25% tetramethylammonium hydroxide aqueous solution used in the simultaneous addition was 14 g. After completion of the addition, the mixture was aged at 100 ° C. for 1 hour and allowed to cool. The obtained colloidal silica is 3260 g by evaporation of water, has a pH of 9.7 at 25 ° C., and has a minor axis of about 7 to 10 nm and a major axis / minor axis as observed by a transmission electron microscope (TEM). It was a group of irregularly shaped non-spherical silica particles having a ratio of 2 to 7 which were irregularly connected, and the average value of the major axis / minor axis ratio was 5. A TEM photograph of the silica particles is shown in FIG.
Subsequently, this colloidal silica was subjected to pressure filtration by circulating pumping liquid using a hollow fiber type ultrafiltration membrane (Microsa UF module SIP-1013 manufactured by Asahi Kasei Chemicals Co., Ltd.) having a molecular weight cut off of 6,000 to obtain a silica concentration. The solution was concentrated to 30% by weight, and about 360 g of colloidal silica was recovered. The particle diameter of the colloidal silica obtained by the nitrogen adsorption method BET specific surface area measurement was 8 nm. The tetramethylammonium hydroxide stabilized colloidal silica thus obtained will be referred to as colloidal silica C below.

Production Example 4
<Example of production of tetraethylammonium hydroxide stabilized colloidal silica D>
In the same manner as in Production Example 3, 8.35 kg of an active silicic acid aqueous solution having a silica concentration of 3.7% by weight and a pH of 2.8 was prepared.
10 g of 35% tetraethylammonium hydroxide aqueous solution was added to 500 g of the active silicic acid aqueous solution with stirring to adjust the pH to 9.0. Subsequently, the mixture was heated with stirring and kept at 100 ° C. for 1 hour to form colloidal particles, and then allowed to cool to obtain a slightly bluish colloidal silica. This colloidal silica has a pH of 10.3 at 25 ° C., and when observed with a transmission electron microscope (TEM), the colloidal silica is randomly connected with a minor axis of about 5 to 7 nm and a major axis / minor axis ratio of 5 to 20. It was a non-spherical silica irregularly shaped particle group, and the average value of the major axis / minor axis ratio was 10-15. The shape of the silica particles was close to the TEM photograph of Production Example 1 shown in FIG.

Next, the colloidal silica was heated again to 100 ° C., and an aqueous active silicic acid solution was added with stirring to grow particles. 6.35 Kg of active silicic acid aqueous solution was added over 6 hours, and during the addition, 35% tetraethylammonium hydroxide aqueous solution was added simultaneously to maintain the pH at 9-10. The 35% tetraethylammonium hydroxide aqueous solution used in the simultaneous addition was 59 g. After completion of the addition, the mixture was aged at 100 ° C. for 1 hour and allowed to cool. The obtained colloidal silica is 5.95 Kg by evaporation of water, has a pH of 10.3 at 25 ° C., has a minor axis of about 25 nm, and a major axis / minor axis as observed by a transmission electron microscope (TEM). The irregularly shaped non-spherical silica particles having a ratio of 1.2 to 3 were formed, and the average value of the major axis / minor axis ratio was 10 to 15. A TEM photograph of the silica particles is shown in FIG.
Subsequently, this colloidal silica was subjected to pressure filtration by circulating pumping liquid using a hollow fiber type ultrafiltration membrane (Microsa UF module SIP-1013 manufactured by Asahi Kasei Chemicals Co., Ltd.) having a molecular weight cut off of 6,000 to obtain a silica concentration. The mixture was concentrated to 30% by weight and about 800 g of colloidal silica was recovered. The particle diameter of this colloidal silica obtained by nitrogen adsorption method BET specific surface area measurement was 21 nm. The tetraethylammonium hydroxide stabilized colloidal silica thus obtained will be referred to as colloidal silica D below.

Production Example 5
<Example of production of tetraethylammonium hydroxide stabilized colloidal silica E>
In the same manner as in Production Example 3, 13.5 kg of an active silicic acid aqueous solution having a silica concentration of 3.7% by weight and a pH of 2.8 was prepared.
To 100 g of the active silicic acid aqueous solution, 2 g of 35% tetraethylammonium hydroxide aqueous solution was added with stirring to adjust the pH to 9.0. Subsequently, the mixture was heated with stirring and kept at 100 ° C. for 1 hour to form colloidal particles, and then allowed to cool to obtain a slightly bluish colloidal silica. This colloidal silica has a pH of 10.3 at 25 ° C., and when observed with a transmission electron microscope (TEM), the colloidal silica is randomly connected with a minor axis of about 5 to 7 nm and a major axis / minor axis ratio of 5 to 20. It was a non-spherical silica irregularly shaped particle group, and the average value of the major axis / minor axis ratio was 10-15. The shape of the silica particles was close to the TEM photograph of Production Example 1 shown in FIG.

Next, the colloidal silica was heated again to 100 ° C., and an aqueous active silicic acid solution was added with stirring to grow particles. 13.4 Kg of active silicic acid aqueous solution was added over 24 hours, and during the addition, 35% tetraethylammonium hydroxide aqueous solution was added simultaneously to maintain the pH at 9-10. The 35% tetraethylammonium hydroxide aqueous solution used in the simultaneous addition was 120 g. After completion of the addition, the mixture was aged at 100 ° C. for 1 hour and allowed to cool. The obtained colloidal silica is 10.1 Kg by evaporation of water, has a pH of 10.3 at 25 ° C., and has a minor axis of about 46 nm and a major axis / minor axis as observed by a transmission electron microscope (TEM). The irregularly shaped non-spherical silica particles having a ratio of 1.2 to 1.8 were formed, and the average value of the major axis / minor axis ratio was 1.5.
Subsequently, this colloidal silica was subjected to pressure filtration by circulating pumping liquid using a hollow fiber type ultrafiltration membrane (Microsa UF module SIP-1013 manufactured by Asahi Kasei Chemicals Co., Ltd.) having a molecular weight cut off of 6,000 to obtain a silica concentration. The mixture was concentrated to 30% by weight and about 800 g of colloidal silica was recovered. The particle diameter of this colloidal silica obtained by nitrogen adsorption method BET specific surface area measurement was 56 nm. The tetraethylammonium hydroxide stabilized colloidal silica thus obtained will be referred to as colloidal silica E below.

Production Example 6
<Production example of additive A>
Carbon dioxide gas was blown into 164 kg of 25% tetramethylammonium hydroxide aqueous solution with vigorous stirring, and neutralized to pH 8.4 to prepare 184.2 kg of 33% tetramethylammonium hydrogen carbonate aqueous solution. To this, 149.1 kg of 25% tetramethylammonium hydroxide aqueous solution was added and mixed to prepare 333.3 kg of a mixed tetramethylammonium solution for buffer composition.

Production Example 7
<Production example of additive B>
To 265 Kg of 25% tetramethylammonium hydroxide aqueous solution, 37.5 Kg of 95% sulfuric acid as a reagent was dropped to neutralize to pH 7 to prepare about 300 Kg of tetramethylammonium sulfate aqueous solution.

Production of Polishing Compositions (C-1 to C-12) Used in the Examples Each of the 17 Kg colloidal silicas A to E produced by the method shown in Production Examples 1 to 5 was produced by the methods shown in Production Examples 6 and 7. Additive A and Additive B were added to the levels shown in Table 1-1 to Table 1-3, and mixed for 24 hours. Thus, a polishing composition having a pH buffering action was produced. The trial polishing compositions were abbreviated as C-1 to C-12, respectively, and their properties were listed in Tables 1-1 to 1-3. And the polishing composition of C-1 to C-12 was used for the Example. In the table, “Na (ppm / SiO ₂ )” represents the sodium concentration per silica. In the table, the conductivity “mS / m / 1% -SiO ₂ ” is a value obtained by measuring the conductivity of each polishing composition using a conductivity meter and dividing the measured value by the silica concentration. Furthermore, TMAHCO ₃ is an abbreviation for tetramethylammonium hydrogen carbonate.

Preparation of polishing compositions (E-1 to E-5) used in comparative examples E-1: Sodium-stabilized colloidal silica composed of commercially available spherical particles (silica doll 40: silica concentration 40.4% by weight, average particle diameter) 1833 nm of sodium (4000 ppm) was added to 3333 g of additive B and mixed for 24 hours. Thus, colloidal silica having a pH buffering action and having a silica concentration of 39% by weight and a pH of 10.4, that is, a polishing composition was prepared. In addition, the electrical conductivity of this polishing composition was 691 mS / m, and the electrical conductivity divided by the silica concentration was 17.7 mS / m / 1% -SiO ₂ .
E-2: Using the colloidal silica A produced in Production Example 1 of the present application, a polishing composition was prepared so as to have the composition shown in Table 2.
E-3: A polishing composition was prepared using the colloidal silica B produced in Production Example 2 of the present application so as to have the composition shown in Table 2.
E-4: Polishing composition was prepared so that it might become the composition of Table 2 using the colloidal silica B produced in this-application manufacture example 2. FIG.
E-5: A polishing composition was prepared using the colloidal silica B produced in Production Example 2 of the present application so as to have the composition shown in Table 2.
The production procedure conformed to the procedure of E-1.

In Table 2, E-1 is different in colloidal silica particle shape from the claims of the present application, and has a high Na concentration.
As for E-2, the electrical conductivity per 1 weight% of silica particles in 25 degreeC is lower than the claim of this application.
E-3 has a pH different from that of the claims of the present application.
As for E-4, the electrical conductivity per 1 weight% of silica particles in 25 degreeC is higher than the claim of this application.
E-5 has a composition in which no buffer solution is added.
Polishing compositions E-1 to E-5 were used in Comparative Examples.

<Semiconductor wafer edge polishing test>
The polishing compositions of C-1 to C-3, C-6 to C-9, C-11, and C-12 shown in Table 1-1 to Table 1-3 are shown in Tables 3-1 to 3 below. It was diluted with pure water so that the silica concentration shown in -2. Further, the polishing compositions E-1 to E-5 shown in Table 2 were diluted with pure water so that the silica concentrations shown in Table 4 were obtained. The following polishing test was conducted using the diluted polishing composition.

<Test conditions>
A polishing experiment of an 8-inch silicon wafer with a poly-Si film was performed by the method described above. The wafer edge polishing apparatus and polishing conditions used are as follows.
Polishing apparatus: EPF-200X type edge polishing apparatus manufactured by Speed Fem Co., Ltd. Wafer rotation speed: 2000 times / min Polishing time: 60 seconds / sheet Polishing composition flow rate: 3 L / min Polishing cloth: suba400 (Nita Haas Co., Ltd.) Made)
Weight: 40 N / unit 10 wafers were polished continuously, and the following evaluation test was performed on the 10th wafer.

<Evaluation>
After the edge polishing was completed, the polishing composition was washed away by flowing pure water instead of the polishing composition. The wafer was removed from the polishing apparatus and subjected to brush scrub cleaning using a 1 wt% aqueous ammonia solution and pure water. Thereafter, spin drying was performed while nitrogen blowing was performed. With respect to the wafer thus obtained, the number of particles of 0.15 μm or more adhering to the surface was measured by an SEM and a laser light scattering method surface inspection apparatus. Further, the presence or absence of haze and pits generated on the polished surface, and the presence or absence of uncut residue generated due to incomplete edge polishing were visually observed under a condensing lamp, and further observed with an 800 × optical microscope. Observation was performed on the entire circumference of the workpiece. Further, the polishing rate was determined from the difference in weight of the device wafer before and after polishing.

Examples 1-9, Comparative Examples 1-5
<Edge polishing test>
An edge polishing test was performed under the above-described conditions.
Tables 3-1 to 3-2 are examples. As a result of diluting the polishing compositions of C-1 to C-3, C-6 to C-9, C-11, and C-12 within the scope of claims of this application and performing an edge polishing test, all evaluations Good results were obtained for the items.
Table 4 is a comparative example. Since Comparative Example 1 used a polishing composition containing a large amount of Na, the number of particles adhering to the back surface of the wafer increased.
In Comparative Example 2, since the conductivity per 1% by weight of silica particles at 25 ° C. was low, the polishing rate was low and polishing residue was also generated. In Comparative Example 3, since the pH was higher than the scope of claims of the present application, haze remained on the polished surface. In Comparative Example 4, the conductivity per 1% by weight of silica particles at 25 ° C. was high, so the number of particles adhering to the back surface of the wafer increased. Since Comparative Example 5 was not a buffer solution composition, the pH of the polishing composition before and after polishing was high, and the polishing rate was low.

<Surface polishing test>
The polishing compositions of C-4, C-5, C-10 to C-12 shown in Table 1-1 to Table 1-3 were purified so that the silica concentrations shown in Table 5-1 to Table 5-2 were obtained. Dilute with water. Further, the polishing compositions E-1, E-3, E-4, and E-5 shown in Table 2 were diluted with pure water so that the silica concentrations shown in Table 6 were obtained. The following polishing test was performed using the diluted colloidal silica.

<Test conditions>
Polishing experiments were performed by the method described above. As the silicon wafer, an 8-inch etched silicon wafer having a resistivity of 0.01 Ω · cm, a crystal orientation <100>, and a conductivity type P-type manufactured by the CZ method was used. The wafer polishing apparatus used was as follows, and mirror polishing was performed under the following polishing conditions.
Polishing device: SH-24 type, speed fam Co., Ltd. Surface plate rotation speed: 70 RPM
Pressure plate rotation speed: 50 RPM
Polishing cloth: SUBA400 (made by Nitta Haas Co., Ltd.)
Load: 150 g / cm ²
Polishing composition flow rate: 80 ml / min Polishing time: 10 minutes

<Evaluation>
After the surface polishing, the polishing composition was washed away by flowing pure water instead of the polishing composition. The wafer was removed from the polishing apparatus and subjected to brush scrub cleaning using a 1 wt% aqueous ammonia solution and pure water. Thereafter, spin drying was performed while nitrogen blowing was performed. With respect to the wafer thus obtained, the number of particles of 0.15 μm or more adhering to the surface was measured by an SEM and a laser light scattering method surface inspection apparatus. Furthermore, the presence or absence of haze and pits generated on the polished surface was visually observed under a condenser lamp. Further, the polishing rate was determined from the weight difference between the wafers before and after polishing.

Examples 10-18, Comparative Examples 5-8
<Surface polishing test results>
A surface polishing test was performed under the above-described conditions.
Tables 5-1 to 5-2 are examples. As a result of diluting C-4, C-5, C-10 to C-12 polishing compositions in the scope of claims of this application and conducting an edge polishing test, good results were obtained for all evaluation items. It was.
Table 6 is a comparative example. Since Comparative Example 5 used a polishing composition containing a large amount of Na, the number of particles adhering to the wafer surface increased. In Comparative Example 6, since the pH was higher than that of the claims of the present application, haze remained on the polished surface, and at the same time, the number of particles adhering to the wafer surface increased. In Comparative Example 7, the conductivity per 1% by weight of silica particles at 25 ° C. was high, so the number of particles attached to the wafer surface increased. In Comparative Example 8, the change in pH before and after the polishing process was large. Further, the polishing rate was low, and pits were generated on the polished surface. The number of adhered particles on the wafer surface is a value including the number of pits.

  When the polishing composition according to the present invention is used, an effect of hardly causing fine particles and metal contamination in polishing of a semiconductor wafer or the like is obtained, and since it is manufactured by a build-up method, the density of silica particles is high and non-spherical. High polishing power can be obtained because of the particles. Furthermore, a stable polishing process can be performed by using a polishing composition having a pH buffering action. Therefore, the effect on related industries is extremely large.

Claims (6)

  A semiconductor wafer containing colloidal silica obtained by adding quaternary ammonium hydroxide to an active silicic acid aqueous solution obtained by hydrolyzing tetraalkoxysilane with an acid catalyst to make the pH alkaline, and heating to grow silica particles A non-spherical composition for polishing, wherein the silica particles have an average diameter in the minor axis direction of 5 to 50 nm as observed by an electron microscope and a length in the major axis direction is 1.2 to 10 times the minor axis. And the average particle size calculated by the BET method is 5 to 100 nm, and the semiconductor wafer polishing composition contains a pH buffer solution, thereby buffering at 25 ° C. between pH 8-11. A semiconductor wafer polishing composition characterized by having an action.   The composition for polishing a semiconductor wafer according to claim 1, wherein the quaternary ammonium hydroxide is choline, tetramethylammonium hydroxide, or tetraethylammonium hydroxide.   The pH buffer solution is a combination of a weak acid and a strong base, the anion constituting the weak acid is carbonate ion and / or bicarbonate ion, and the cation constituting the strong base is choline ion, tetramethylammonium ion or tetraethyl. The composition for polishing a semiconductor wafer according to claim 2, wherein the composition is ammonium ion or a mixture thereof.   By increasing the concentration of the pH buffer solution and / or having a strong acid and quaternary ammonium hydroxide salt, the conductivity at 25 ° C. is 15 mS / m or more and 200 mS / m or less per 1% by weight of silica particles. The semiconductor wafer polishing composition according to claim 3, which is prepared as described above.   It is a manufacturing method of the composition for semiconductor wafer polishing of Claim 1, Comprising: Silica concentration 1-8 mol / liter, acid concentration 0.0018-0.18 mol / liter, and water concentration 2-30 mol / liter The first step of hydrolyzing tetraalkoxysilane to prepare an active silicic acid aqueous solution with a composition in the range, the active silicic acid prepared in the first step so that the silica concentration is in the range of 0.2 to 1.5 mol / liter After diluting with water and adding quaternary ammonium hydroxide so that the pH is 8-11, the colloidal particles produced in the second step and the second step of growing colloidal particles by heating are ultrafiltered. The third step for preparing a colloidal silica solution having a silica concentration of 20 to 50% by weight by concentration with a weak acid and a fourth ammonium hydroxide so that the colloidal silica solution prepared in the third step has a pH buffer composition. Method for producing a fourth step, become more semiconductor wafer polishing composition added arm.   6. The method for producing a semiconductor wafer polishing composition according to claim 5, wherein a step of further growing colloidal particles is performed between the second step and the third step.

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