JP2008182181A - Compositions for abrasion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide compositions for abrasion which is applicable to the process of forming a floating gate in a flash memory, and suitable for a CMP process in which a protrusion on a polysilicon film is flattened and polishing is stopped before exposing a ground. <P>SOLUTION: The present invention relates to compositions for abrasion for polishing a polysilicon film containing (a) abrasive grains, (b) anionic polymer salt, (c) polymer with poly-alkylene oxide structure and water, and preferably, further containing quaternary ammonium ion. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polishing composition suitable for CMP (Chemical Mechanical Polishing) of polysilicon in the manufacture of a semiconductor memory device and having excellent flatness and auto-stop characteristics.

  In order to achieve high integration of flash memory, planarization by CMP is indispensable in the formation process of the floating gate. As further miniaturization progresses in the future, the demand for flatness after CMP has become more severe, and it has become difficult to obtain sufficient flatness with conventional polishing compositions. A method for forming a floating gate structure using CMP is disclosed in Patent Document 1, Patent Document 2, and the like.

  An outline of a method for forming a floating gate using CMP will be described. 1 to 5 show a plan view and a cross-sectional view in each step of forming a floating gate using CMP. The cross-sectional view shows a cross-sectional view (b) and a cross-sectional view (c) along two directions shown in (a) the plan view, that is, the AA plane and the BB plane.

  After a diffusion layer (not shown) is formed on the surface of the silicon substrate 1, the element isolation insulating film 3 formed on the entire surface of the substrate is processed by dry etching using a photoresist pattern as a mask to remove unnecessary resist. The thickness of the element isolation insulating film is about 50 to 200 nm. Thereafter, a state in which the gate insulating film 2 is formed on the exposed surface of the silicon substrate 1 is shown in FIG.

  FIG. 2 shows a cross section after the polysilicon film 4 for the floating gate is formed by CVD (Chemical Vapor Deposition). The thickness of the polysilicon film is about twice that of the element isolation insulating film 3. Even after the polysilicon film is formed, the step of the element isolation pattern is maintained as it is. If a photoresist pattern for processing a polysilicon film is formed with such a level difference, pattern resolution failure or the like is likely to occur, and in a miniaturized semiconductor device, it causes a decrease in yield.

  Further, as shown in the cross-sectional view of FIG. 2B, since the polysilicon film is formed conformally, the film thickness in the vertical direction of the side wall portion of the element isolation pattern is increased. For this reason, when a polysilicon film is processed by anisotropic dry etching, an etching residue tends to occur in the side wall portion of the element isolation region, and a short circuit between the gates easily occurs.

  Over-etching is performed to remove this etching residue, but if the time is lengthened, the thin gate oxide film 2 is damaged and the reliability of the device is lowered. Such problems are becoming more serious in miniaturized semiconductor devices.

  In order to avoid such a problem, a method of removing the convex portion of the polysilicon film by CMP has been proposed. FIG. 3 shows the state of the polysilicon film after CMP. At this time, the protrusion on the element isolation insulating film 3 is removed, but the element isolation insulating film 3 needs to be not exposed.

  The remaining thickness of the polysilicon film 4 on the element isolation insulating film is about 1/4 to 1/2 of the thickness of the element isolation insulating film. In this state, the photoresist 5 pattern is formed (FIG. 4) and anisotropic dry etching is performed (FIG. 5). It is possible to avoid problems such as a short circuit between them and a decrease in reliability of the gate insulating film due to overetching.

  For comparison, FIGS. 6 to 8 show cross sections when a floating gate is formed without planarization by CMP. Comparing the cross-sectional view after forming the floating gate, FIG. 5 and FIG. 8, when the floating gate is formed without flattening by CMP, the unevenness after forming the floating gate is large, and when forming the control gate or the like in the upper layer In addition, it is expected that problems such as poor pattern resolution and etching residue are likely to occur.

  As described above, the planarization of the polysilicon film by CMP is extremely effective for improving the yield and reliability of the semiconductor element. However, as the semiconductor element is further miniaturized, the demand for the planarity is becoming stricter. Further, as shown in FIG. 3B, it is necessary to leave a thin polysilicon film on the element isolation insulating film. However, as the semiconductor element is miniaturized, the control becomes increasingly difficult.

  In response to these requirements, it is difficult to obtain sufficient characteristics with the conventional polishing composition for polysilicon proposed in Patent Document 3, Patent Document 4, and the like. Therefore, development of a polishing composition for polysilicon that can achieve the above controllability is strongly desired.

  Patent Documents 5 and 6 propose a floating gate forming method using CMP, but do not show a specific method for obtaining good flatness and remaining film thickness controllability.

  Patent Document 3 discloses a polishing composition for a polysilicon film to which a basic organic material is added. In this method, the selection ratio between the polysilicon film and the silicon oxide film is large, but the flatness is insufficient, and it is difficult to deal with miniaturized LSIs. Further, it is assumed that CMP is performed until the base oxide film is exposed, and it is considered difficult to control the remaining film thickness when the CMP is stopped without exposing the base.

Patent Document 4 proposes to add a nonionic surfactant in order to improve the flatness, but even with this method, the flatness is expected to be insufficient. Also in this patent, it is assumed that CMP is performed until the base oxide film or nitride film is exposed, and the controllability of the remaining film thickness when the CMP is stopped without exposing the base is not improved. it is conceivable that.
Japanese Patent Laid-Open No. 10-112531 JP 2001-135731 A Japanese Patent No. 3457144 JP 2005-175498 A Japanese Patent Laid-Open No. 10-112531 JP 2001-135731 A

(Object of invention)
The main object of the present invention is applicable to a CMP process that can be applied to a floating gate forming process in a flash memory, etc., polishing and planarizing a convex part of a polysilicon film, and stopping polishing before exposing the base. It is to provide a polishing composition. Thereby, excellent flatness and remaining film thickness controllability can be obtained, so that the yield and reliability of the semiconductor element can be improved.

  Means of the present invention for achieving the object of the present invention and solving the problems is a polishing composition for polishing a polysilicon film, which contains the following components and water.

a) Abrasive grain b) Salt of anionic polymer c) Polymer having polyalkylene oxide structure

  According to the present invention, in CMP of a polysilicon film, the polishing rate is kept low at a low pressure, and a polishing pressure dependency is obtained in which the polishing rate suddenly increases from a certain polishing pressure. By applying the polishing composition of the present invention to CMP for forming a floating gate of a semiconductor memory device, both excellent flatness and residual film controllability can be achieved. Thereby, the yield and reliability of the semiconductor memory device can be improved, and the manufacturing cost can be reduced.

  In order to clarify the above and other objects, features and advantages of the present invention, embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

  FIG. 9 is a graph schematically showing the polishing pressure dependence of the polishing rate of the polysilicon film by (a) the polishing composition of the present invention and (b) the conventional polishing composition. The dependency of the polishing rate on the polishing pressure in FIG. 9 shows the result of measurement with a wafer having no pattern. By using the polishing composition of the present invention, the polishing rate of polysilicon is kept low at a low polishing pressure, and the polishing rate increases rapidly above a certain polishing pressure, as shown in FIG. The polishing pressure dependence of speed is obtained.

  When polishing a patterned wafer having irregularities on the surface at an average polishing pressure B slightly higher than the pressure near the point at which the graph of the polishing rate bends, using the polishing composition showing such polishing pressure dependence, The pressure of the convex portion is C larger than the average polishing pressure, and the polishing pressure of the pattern concave portion is A lower than the polishing pressure.

  When the polishing rates for the polishing pressures A, B, and C of the polishing composition shown in FIG. 9A are a1, b1, and c1, the convex polishing rate is c1, and the concave polishing rate is a1. The ratio of the polishing rate of the convex portion to is expressed by c1 / a1. The larger this ratio, the faster the polishing rate of the convex portion with respect to the concave portion, the easier the step is eliminated, and the flatness is improved.

  On the other hand, the conventional polishing composition for polysilicon shows polishing pressure dependency as shown in FIG. In this case, when a wafer having irregularities is polished with an average polishing pressure B, the polishing rate of the pattern convex portion is c2, the polishing rate of the pattern concave portion is a2, and the polishing rate ratio of the convex portion to the concave portion is c2 / a2. Appear.

  As can be seen from FIGS. 9 (a) and 9 (b), the polishing composition in which c1 / a1> c2 / a2 and load dependency as shown in FIG. Compared with the composition, it has a high level difference elimination capability and provides excellent flatness.

  In addition, when the polishing composition having the polishing pressure dependency shown in FIG. 9A is used to polish a patterned wafer at an average pressure B, the pattern convex portion has a polishing rate c1 at the beginning when the pattern step is large. Although the polishing is performed, the polishing rate approaches the polishing rate b1 of the wafer having no pattern as the polishing progresses and the level difference is eliminated. This means that it has an auto-stop characteristic in which the polishing rate decreases as the pattern level difference is eliminated.

  In the polishing composition as shown in FIG. 9A, the ratio of the polishing rate when there is no pattern to the polishing rate when there is a pattern (b1) as compared with the polishing composition as shown in FIG. 9B. It can be seen that / c1, b2 / c2) are small and the auto-stop characteristic is strong. When the auto-stop characteristic is strong, the polishing rate is lowered after unnecessary convex portions are removed, so that a margin for film thickness unevenness in the wafer surface and variations in the polishing rate is increased.

  In normal CMP, since the film thickness in the wafer surface and the polishing rate vary, it is necessary to lengthen the polishing time in accordance with the portion where the convex portion is difficult to remove. At that time, the part where the convex part has been removed first will be excessively polished, but if the auto-stop characteristic is strong, the polishing rate will be reduced after the step is eliminated, so the decrease in film thickness of that part is suppressed. The

  Therefore, it is possible to achieve good flatness over the entire wafer surface and at the same time to secure a residual film thickness. In the conventional polishing composition as shown in FIG. 9B, since the change in the polishing rate is small even after the protrusion is removed, it is difficult to achieve both flatness on the entire wafer surface and controllability of the remaining film thickness. It is.

  The composition of the polishing composition of the present invention will be described.

  a) As an abrasive, ceria, silica, alumina, zirconia, or the like can be used. The average particle size of the abrasive grains is preferably 10 to 500 nm, and particularly preferably 50 to 300 nm. The abrasive grain concentration in the polishing composition is preferably 0.1 to 10 wt%, and particularly preferably 0.2 to 5 wt%. When the average particle size is less than 10 nm, the polishing rate tends to decrease, and when it exceeds 500 nm, the polishing film tends to be easily damaged. In the present invention, the average grain size of abrasive grains refers to the median diameter of volume distribution measured with a laser diffraction particle size distribution meter. Specifically, values obtained using LA-920 manufactured by Horiba, Ltd. are exemplified.

  a) As a method of dispersing abrasive grains in water, a homogenizer, an ultrasonic disperser, a ball mill, or the like can be used in addition to a dispersion treatment using a normal stirrer. Moreover, you may filter the dispersion liquid after a dispersion process with the filter produced by SUS.

  In the polishing composition of the present invention, b) the salt of the anionic polymer serves to increase the polishing rate of the polysilicon. Examples of salts of anionic polymers include polyacrylic acid, polymethacrylic acid, polymaleic acid, polystyrene sulfonic acid, and anionic polymers obtained by copolymerization of monomers used in the synthesis of these polymers, inorganic alkalis, ammonia, and amines. A salt with one or more basic substances selected from quaternary ammonium hydroxides can be used.

  Examples of other anionic polymers include polyaspartic acid, polyglutamic acid, polylysine, polymalic acid, polyamic acid, polyitaconic acid, polyfumaric acid, poly (p-styrene carboxylic acid), polyvinyl sulfonic acid, and poly-2- Examples thereof include acrylamido-2-methylpropanesulfonic acid and salts thereof. Examples of the anionic polymer salt include polyoxyethylene alkyl ether sulfate triethanolamine. Two or more of these anionic polymer salts may be used in combination.

  As a method for adding to the polishing composition, an anionic polymer and a basic substance may be added separately, even if a salt is added in advance. Further, the salt of the anionic polymer may not be completely neutralized with a basic substance, but the pH of the polishing composition is preferably 5 to 13, particularly preferably 6 to 12. When the pH is less than 5, the polishing rate of the polysilicon is lowered, and when the pH exceeds 13, the handling of the polishing composition becomes difficult. The most preferred pH range is 6-9.

  The polystyrene-equivalent weight average molecular weight of the anionic polymer is preferably 1,000 to 300,000, particularly preferably 2,000 to 100,000. The amount of the anionic polymer salt added is preferably 30 to 1,000%, particularly preferably 50 to 600%, based on the weight of the abrasive grains. The concentration in the polishing composition is preferably 0.04 to 10 w%, particularly preferably 0.1 to 6 wt%.

  c) The polymer having a polyalkylene oxide structure is preferably a polymer having a polyethylene oxide structure or a polypropylene oxide structure. As such a polymer, polyethylene oxide, polypropylene oxide, block copolymer of polyethylene oxide and polypropylene oxide (pluronic polymer), polyethylene oxide adduct of acetylene glycol, polyethylene oxide alkyl ether, polyethylene oxide alkyl phenyl ether, etc. are used. be able to. Polypropylene oxide is more preferable.

  c) The average molecular weight of the polymer having a polyalkylene oxide structure calculated based on the hydroxyl value of the polymer is preferably from 200 to 40,000, particularly preferably from 400 to 20,000. The concentration of this c) polymer in the polishing composition is preferably 0.0005 to 0.05 wt%, particularly preferably 0.001 to 0.03 wt%.

  It is considered that the polymer having a polyalkylene oxide structure is adsorbed on the surface of polysilicon and functions to suppress the polishing rate. However, simply adding these polymers to the conventional polishing composition for polysilicon will only reduce the polishing rate while maintaining the polishing pressure dependence as shown in FIG. A polishing composition having polishing pressure dependency as in a) cannot be obtained.

  Therefore, as a result of various studies, it has been found that when a polymer having c) a polyalkylene oxide structure and a salt of b) an anionic polymer are combined, a load dependency as shown in FIG. It was. An anionic polymer salt is considered to have an action of increasing the polishing rate of polysilicon.

  Further, it is considered that the salt of the anionic polymer is weakly adsorbed to the abrasive grains although it is weakly adsorbed to the polysilicon surface. Although the mechanism has not been clarified, it is expected that, due to these factors, an effect of significantly increasing the polishing rate is generated only when the polishing pressure is high and the mechanical action of the abrasive grains is strong.

  It is known that the polishing rate of polysilicon increases as the pH increases, and in the polishing composition of the present invention, in order to further increase the polishing rate in a region where the polishing pressure is high, an inorganic alkali, It is effective to raise the pH using ammonia, amine, quaternary ammonium hydroxide or the like. In particular, quaternary ammonium hydroxide is effective and effective for increasing the polishing rate of polysilicon. As the quaternary ammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, or the like can be used.

  The method for producing the polishing composition of the present invention is not particularly limited. For example, a) an abrasive is dispersed in water to prepare a dispersion, and b) an anionic polymer salt and c) a polyalkylene oxide structure. It is obtained by preparing a mixed liquid of a polymer having water and water, mixing both, and adjusting the concentration with water or the like.

  CMP using this polishing composition can be carried out using a commercially available CMP apparatus. A wafer having a polysilicon film held by a carrier is pressed against a surface plate on which a polishing pad made of polyurethane foam or the like is attached, and the surface plate and the carrier are placed in the same direction while dripping the polishing composition onto the polishing pad. CMP is performed by rotating.

  The polishing pad is not particularly limited and may be a general nonwoven fabric, foamed polyurethane, porous fluororesin, or the like, and it is preferable to perform a groove processing such that the polishing composition is accumulated on the polishing pad. The polishing conditions are not limited, but the polishing pressure applied to the polysilicon film is preferably 7 kPa to 35 kPa, for example, although it depends on the composition and addition amount of c) polymer.

  During polishing, it is preferable that the surface of the polishing pad is always covered with the polishing composition by continuously supplying it with a pump or the like. The polysilicon film after polishing is preferably washed in running water, and then dried after removing water droplets adhering to the film using a spin dryer or the like.

  When this polishing composition is used for CMP of a wafer having a cross section as shown in FIG. 6B, excellent flatness can be obtained because of the large difference in polishing rate between the concave and convex portions.

  Further, since the polishing rate decreases as the polishing progresses and the level difference of the convex portion decreases, the margin for over-polishing is large and the controllability of the remaining film is excellent. The polishing time is set so that the amount of overpolishing is appropriate according to the variation in the polishing rate within the wafer surface, the variation in the initial level difference of the pattern, and the like.

  Hereinafter, the present invention will be described using examples and comparative examples. It should be noted that the present invention is not limited to the following embodiments, and it is obvious that each embodiment can be appropriately modified and used in other fields to which CMP processing can be applied within the scope of the technical idea of the present invention.

  In the preparation of the following polishing composition, after preparing a dispersion in which abrasive grains are dispersed in water and a liquid in which components other than abrasive grains are dissolved or dispersed in water, both are mixed, and finally, an appropriate concentration The total amount was adjusted by adding water.

  In the following examples, a) ceria was used as the abrasive. The average grain size of the abrasive grains is about 200 nm. The concentration of the abrasive grains was 1 wt%. b) As the anionic polymer, a polyacrylic acid ammonium salt having a polystyrene equivalent weight average molecular weight of about 10,000 was used. The compounding quantity of the polyacrylic acid ammonium salt was 1 wt%.

  c) As the polymer having a polyalkylene oxide structure, polyethylene oxide, polypropylene oxide, and polyethylene oxide-polypropylene oxide block copolymer were used. As the polyethylene oxide-polypropylene oxide block copolymer, a propylene oxide portion having a molecular weight of about 3000 was used. These molecular weights and blending amounts are shown in Table 1. Furthermore, in Example 6, tetramethylammonium hydroxide was blended.

The pH of the polishing compositions of Examples 1 to 6 was measured with a pH meter (model number PH81 manufactured by Yokogawa Electric Corporation). Standard buffer (phthalate pH buffer solution pH: 4.21 (25 ° C), neutral phosphate pH buffer solution pH 6.86 (25 ° C), borate standard solution pH: 9.13 (25 ° C) ), The electrode was placed in the polishing composition, and the value after 2 minutes had passed and stabilized was measured. The pH of the polishing composition of Examples 1-6 was between 6-9.

  Polysilicon CMP was performed using the polishing compositions of Examples 1 to 6 shown in Table 1, and the polishing rate was measured. As the wafer, a wafer in which an oxide film of 100 nm was formed on an 8-inch silicon wafer (without a pattern) and then a polysilicon film of 500 nm was formed by CVD. An optical interference film thickness meter was used to measure the polysilicon film thickness.

A commercially available CMP apparatus for 8-inch wafers was used as the CMP apparatus, and a commercially available polyurethane foam pad was used as the polishing pad. The groove of the pad was a concentric circle. The CMP pressure was 1 to 5 psi (7 kPa to 34 kPa), the rotation speeds of the polishing platen and wafer carrier were both 80 rpm, the polishing composition flow rate was 200 ml / min, and the polishing time was 1 minute. Table 2 shows the polishing rate at each pressure when the polishing compositions of Examples 1 to 6 were used. The relationship between the polishing pressure and the polishing rate is shown in graphs in FIGS.

  As shown in FIG. 10, in Example 1, the result that the polishing rate suddenly increased from 4 psi (28 kPa) was obtained. In Examples 2 and 3, the polishing rate was increased from 3 psi (21 kPa) and 5 psi (34 kPa), respectively. A sudden rise is seen. In either case, it is considered that good flatness and auto-stop characteristics can be obtained on a patterned wafer. Since Example 3 has a sharp rise in polishing rate compared to Examples 1 and 2, polypropylene oxide is considered to be particularly effective.

  As shown in FIG. 11, in Example 4 in which the amount of polyethylene oxide added was reduced as compared with Example 1, the polishing rate increased rapidly at a lower polishing pressure than in Example 1, and the polyethylene oxide In Example 5 in which the amount added was increased, the pressure at which the polishing rate increased was shifted to a high pressure. Therefore, it is possible to control the pressure at which the polishing rate suddenly increases within an appropriate range depending on the amount of the polymer having a polyalkylene oxide structure.

  As shown in FIG. 12, in Example 6 in which tetramethylammonium hydroxide was blended, the polishing rate increased sharply at 4 psi and 5 psi compared to Example 1. It is expected that the flatness and auto-stop characteristics are better as the polishing rate increases more rapidly. In addition, an increase in the polishing rate improves productivity. From these facts, it can be seen that it is effective to add quaternary ammonium hydroxide such as tetramethylammonium hydroxide to the polishing composition of the present invention.

  In any of Examples 1 to 6, the polishing pressure dependency as shown in FIG. 9A is obtained. The pressure at which the polishing rate starts to increase suddenly can be controlled by the type and amount of the polymer having a polyalkylene oxide structure and the addition of quaternary ammonium hydroxide. As a result, a desired polishing speed can be obtained with an appropriate polishing pressure according to the type of semiconductor element and the CMP apparatus, and excellent flatness and remaining film controllability can be achieved without sacrificing throughput. it can.

(Comparative Examples 1-3)
b) No salt of anionic polymer and quaternary ammonium hydroxide were added. c) As a polymer having a polyalkylene oxide structure, polyethylene oxide was blended at a concentration shown in Table 3, and compared in the same manner as in Examples. The polishing compositions of Examples 1 to 3 were prepared. As the abrasive grains, the same ceria as in the examples was used, and the abrasive grain concentration in the polishing composition was 1 wt%.

(Comparative Example 4)
c) A polymer having a polyalkylene oxide structure and a quaternary ammonium hydroxide were not blended, and b) 1 wt% of a polyacrylic acid ammonium salt was blended as a salt of an anionic polymer. A polishing composition was prepared. As the abrasive grains, the same ceria as in the examples was used, and the abrasive grain concentration in the polishing composition was 1 wt%.

Table 4 shows the result of measuring the polishing rate of polysilicon in the same manner as in the example. FIG. 13 shows a graph of the polishing pressure dependence of the polishing rate. In Comparative Examples 1 to 3, it can be seen that when the blending amount of polyethylene oxide is increased, the polishing rate decreases, but the polishing pressure dependency as shown in FIG. 9A cannot be obtained. This is because the polishing compositions of Comparative Examples 1 to 3 do not contain ammonium polyacrylate. In this case, good flatness and residual film thickness controllability cannot be obtained in polishing the patterned wafer.

It is an example of the formation process of the floating gate using CMP of a polysilicon film, (a) is a top view, (b) is a sectional view by the AA plane of (a), (c) is by the BB plane of (a) It is sectional drawing. 1A is a plan view, FIG. 1B is a sectional view taken along the AA plane of FIG. 1A, and FIG. 1C is a sectional view taken along the BB plane of FIG. 2A is a plan view, FIG. 2B is a sectional view taken along the AA plane of FIG. 2A, and FIG. 2C is a sectional view taken along the BB plane of FIG. 3A is a plan view, FIG. 3B is a sectional view taken along the AA plane of FIG. 3A, and FIG. 3C is a sectional view taken along the BB plane of FIG. 4A is a plan view, FIG. 4B is a sectional view taken along the AA plane of FIG. 4A, and FIG. 4C is a sectional view taken along the BB plane of FIG. It is an example of the formation process of the floating gate which does not use CMP of a polysilicon film, (a) is a top view, (b) is a sectional view by the AA plane of (a), (c) is by the BB plane of (a) It is sectional drawing. 6A is a plan view, FIG. 6B is a sectional view taken along the AA plane of FIG. 6A, and FIG. 6C is a sectional view taken along the BB plane of FIG. 7A is a plan view, FIG. 7B is a sectional view taken along the AA plane of FIG. 7A, and FIG. 7C is a sectional view taken along the BB plane of FIG. It is a figure explaining the polishing pressure dependence of the polysilicon film | membrane polishing speed, (a) is a graph which shows each polishing pressure dependence by the polishing composition of this invention, (b) conventional polishing composition. . It is a graph which shows the polishing pressure dependence of the polysilicon grinding | polishing speed | rate using the polishing composition of Examples 1-3 of this invention. It is a graph which shows the polishing pressure dependence of the polysilicon grinding | polishing speed | rate using the polishing composition of Example 1, 4, 5 of this invention. It is a graph which shows the polishing pressure dependence of the polysilicon grinding | polishing speed | rate using the polishing composition of Example 1 and 6 of this invention. It is a graph which shows the polishing pressure dependence of the polysilicon grinding | polishing speed | rate using the polishing composition of Comparative Examples 1-3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Gate insulating film 3 Element isolation insulating film 4 Polysilicon film 5 Photoresist

Claims (3)

A polishing composition for polishing a polysilicon film, comprising a) abrasive grains, b) a salt of an anionic polymer, c) a polymer having a polyalkylene oxide structure and water.   The polishing composition according to claim 1, further comprising a quaternary ammonium ion.   The polishing composition according to claim 1 or 2, wherein the polymer having c) a polyalkylene oxide structure is polypropylene oxide.

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