JP7512036B2 - Polishing composition - Google Patents

Description

The present invention relates to a polishing composition.

Ultra-precision processing is an extremely important technology in the manufacture of semiconductor products. In recent years, LSI devices have become increasingly miniaturized, which has led to increasingly stringent requirements for the surface roughness and flatness of semiconductor wafers after precision polishing. Until now, the primary polishing process has focused primarily on the amount of grinding (polishing speed). However, it has become clear that the surface quality of semiconductor wafers after primary polishing affects the surface quality after secondary polishing and final polishing. Therefore, there is now a demand for a higher level of surface quality in primary polishing while maintaining the current polishing speed.

Reducing the concentration of abrasive grains, which can cause polishing scratches and residual foreign matter, is an effective way to improve the surface quality of polished semiconductor wafers. However, lowering the concentration of abrasive grains causes the problem of a slower polishing rate.

JP 09-306880 A discloses a silicon polishing liquid composition that contains a water-soluble silicic acid component, colloidal silica, and an alkaline component, and has a pH of 8.5 to 13. The publication states that by adding an aqueous silicic acid component such as potassium silicate or sodium silicate to an alkaline colloidal silica suspension, the surface of a silicon wafer can be effectively polished even if the concentration of colloidal silica is significantly reduced.

JP 2003-100670 A discloses an abrasive that contains abrasive particles and a soluble metal silicate, and in which the ratio (W2/W1) of the weight of silica in the soluble metal silicate (W2) to the weight of the solid content of the abrasive particles (W1) is in the range of 0.001 to 0.08. The publication states that by blending a soluble metal silicate with the abrasive, the polishing speed can be increased, particularly for oxide film substrates.

Japanese Patent Application Laid-Open No. 9-306880 JP 2003-100670 A

One way to increase the polishing rate regardless of the abrasive concentration is to increase the concentration of the basic compound in the polishing composition to increase the amount of processing by etching. However, increasing the concentration of the basic compound may cause the abrasive to dissolve and change the particle size. The particle size of the abrasive affects the polishing rate and the surface quality and flatness of the polished semiconductor wafer. For this reason, it is necessary to keep the particle size of the abrasive stable.

The objective of the present invention is to provide a polishing composition that can maintain a stable particle size of the abrasive grains.

A polishing composition according to one embodiment of the present invention is a polishing composition for polishing semiconductors, comprising silica abrasive grains, silicic acid, a basic compound, and water, in which the ratio _W2/ W1 of the weight W2 of the silicate ions in the polishing composition in terms of SiO2 to the weight W1 of the solid content of the silica abrasive grains is 0.5 to 2.0.

According to the present invention, a polishing composition that can stably maintain the particle size of the abrasive grains can be obtained.

The present inventor has conducted extensive research to solve the above problems. As a result, it has been found that, in a polishing composition containing silica abrasive grains, silicic acid, a basic compound, and water, the dissolution of silica abrasive grains can be suppressed and the particle size of silica abrasive grains can be kept stable by adjusting the ratio W2/W1 of the weight W2 of the silicic acid ion in the polishing composition in terms of _SiO2 to the weight W1 of the solid content of silica abrasive grains in the polishing composition within a predetermined range.

The present invention was completed based on the above findings. The polishing composition according to one embodiment of the present invention is described in detail below.

The polishing composition according to one embodiment of the present invention contains silica abrasive grains, silicic acid, a basic compound, and water.

[Silica abrasive grains]
The silica abrasive grains are, for example, colloidal silica and fumed silica, and among them, colloidal silica is preferably used. The particle size and shape (degree of association) of the silica abrasive grains are not particularly limited. For example, silica abrasive grains having a secondary average particle size of 20 to 150 nm can be used.

The content of silica abrasive grains is not particularly limited, but is, for example, 0.15 to 20 mass% of the total polishing composition (undiluted). The polishing composition is diluted 10 to 100 times before use. The polishing composition according to this embodiment is preferably diluted so that the content of silica abrasive grains is 100 to 5000 mass ppm.

[Silicate]
The silicic acid adjusts the concentration of silicate ions in the polishing composition. Examples of the silicic acid include orthosilicic acid (H ₄ SiO ₄ ), metasilicic acid (H ₂ SiO ₃ ), metadisilicic acid (H ₂ SiO ₅ ), metatrisilicic acid (H ₄ Si ₃ O ₈ ), and metatetrasilicic acid (H ₆ Si ₄ O ₁₁ ). The silicic acid can also be formed by dissolving silicate or hydrated silicate.

Silicate can also be formed, for example, by dissolving high-purity colloidal silica produced by the sol-gel method in an aqueous solution of an amine compound.

The concentration of silicic acid is preferably adjusted so that the ratio W2/W1 of the weight W2 of the silicic acid ions in the polishing composition in terms of _SiO2 to the weight W1 of the solid content of the silica abrasive grains is within a predetermined range. W2/W1 will be described later.

[Basic Compounds]
The basic compound reacts efficiently with the surface of the semiconductor wafer and contributes to the polishing performance of the chemical mechanical polishing (CMP). Examples of the basic compound include amine compounds and inorganic alkali compounds.

Examples of amine compounds include primary amines, secondary amines, tertiary amines, quaternary ammonium and their hydroxides, heterocyclic amines, etc. Specific examples include ammonia, tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrabutylammonium hydroxide (TBAH), methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, hexylamine, cyclohexylamine, ethylenediamine, hexamethylenediamine, diethylenetriamine (DETA), triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, monoethanolamine, diethanolamine, triethanolamine, N-(β-aminoethyl)ethanolamine, anhydrous piperazine, piperazine hexahydrate, 1-(2-aminoethyl)piperazine, N-methylpiperazine, piperazine hydrochloride, and guanidine carbonate. Among these, TMAH is preferably used.

Examples of inorganic alkali compounds include hydroxides of alkali metals, salts of alkali metals, hydroxides of alkaline earth metals, salts of alkaline earth metals, etc. Specific examples of inorganic alkali compounds include potassium hydroxide, sodium hydroxide, potassium bicarbonate, potassium carbonate, sodium bicarbonate, sodium carbonate, etc.

The above-mentioned basic compounds may be used alone or in combination of two or more. Among the above-mentioned basic compounds, alkali metal hydroxides, alkali metal salts, ammonia, amines, ammonium salts, and quaternary ammonium hydroxides are preferred, and quaternary ammonium hydroxides are particularly preferred.

The content of the basic compound (the total amount when two or more types are contained) is not particularly limited, but is, for example, 0.1 to 7.0 mass% of the entire polishing composition (undiluted solution). The lower limit of the content of the basic compound is preferably 1.5 mass%. The upper limit of the content of the basic compound is preferably 6 mass%.

[W2/W1]
In the polishing composition according to this embodiment, the ratio W2/W1 of the weight W2 of the silicate ions in the polishing composition calculated as SiO ₂ to the weight W1 of the solid content of the silica abrasive grains is 0.5 to 2.0.

If the weight _W2 of the silicate ion in the polishing composition in terms of SiO2 is too small relative to the weight W1 of the solid content of the silica abrasive grains, that is, if W2/W1 is too small, the dissolution of the silica abrasive grains cannot be sufficiently suppressed, and it becomes difficult to keep the particle size of the silica abrasive grains stable. On the other hand, if the weight _W2 of the silicate ion in the polishing composition in terms of SiO2 is too large relative to the weight W1 of the solid content of the silica abrasive grains, that is, if W2/W1 is too large, the silica abrasive grains tend to aggregate. The lower limit of W2/W1 is more preferably 0.52, and even more preferably 0.55. The upper limit of W2/W1 is more preferably 1.5, and even more preferably 1.0.

The weight W1 of the solid content of the silica abrasive grains can be measured by extracting the solid content in the polishing composition using a centrifuge and then removing the moisture with a dryer. The weight of the silicate ions in the polishing composition can be measured using ion chromatography after diluting the supernatant obtained by centrifugation to an appropriate concentration. The weight W2 in terms of _SiO2 is calculated by dividing the measured weight by 1.266, which is the ratio of the molecular weights ^of _SiO2 and _SiO3- .

The polishing composition according to this embodiment may further contain a pH adjuster. The pH of the polishing composition according to this embodiment is preferably 8.0 to 13.0.

The polishing composition according to this embodiment can contain any of the above-mentioned additives, such as chelating agents, water-soluble polymers, and surfactants, that are generally known in the field of polishing compositions.

The polishing composition according to this embodiment is prepared by appropriately mixing silica abrasive grains, silicic acid, a basic compound, and other compounding materials, and adding water. Alternatively, the polishing composition according to this embodiment is prepared by sequentially mixing silica abrasive grains, silicic acid, a basic compound, and other compounding materials with water. The means for mixing these components are those commonly used in the technical field of polishing compositions, such as a homogenizer or ultrasonic waves.

The polishing composition according to this embodiment can also be produced by dissolving high-purity colloidal silica, which has been prepared in advance by a sol-gel method or the like, in an aqueous solution of an amine compound to prepare an aqueous solution of silicic acid, and then mixing this aqueous solution with silica abrasive grains. This method produces silicic acid of high purity, which can suppress contamination of semiconductor wafers by, for example, metal ions.

The polishing composition described above is diluted with water to an appropriate concentration and then used to polish semiconductors. The polishing composition according to this embodiment can be suitably used for polishing silicon wafers (bare wafers), particularly for primary polishing.

The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples.

The following eight types of polishing compositions were prepared:

[Composition 1-1]
5.0 parts by weight of high purity colloidal silica prepared by the sol-gel method was added to an aqueous solution of 3.75 parts by weight of TMAH dissolved in pure water (DIW, the same applies below), and the colloidal silica was completely dissolved to prepare an aqueous solution of silicic acid. 10.5 parts by weight of silica abrasive grains (secondary average particle size: 80.7 nm, NMR specific surface area: 20.2 ^m2 /g) and 0.25 parts by weight of TMAH were further added to the aqueous solution of silicic acid, and pure water was added to make a total of 100 parts by weight to prepare a polishing composition.

[Composition 1-2]
A polishing composition was prepared by mixing 15.5 parts by weight of the same silica abrasive grains (secondary average particle size: 80.7 nm, NMR specific surface area: 20.2 m ² /g) as the silica abrasive grains in Composition 1-1, 4.0 parts by weight of TMAH, and 80.5 parts by weight of pure water.

[Composition 2-1]
A polishing composition was prepared in the same manner as in Composition 1-1, except that silica abrasive grains (secondary average particle size: 123.0 nm, NMR specific surface area: 29.0 m ² /g) different from the silica abrasive grains in Composition 1-1 were used.

[Composition 2-2]
A polishing composition was prepared by mixing 15.5 parts by weight of the same silica abrasive grains (secondary average particle size: 123.0 nm, NMR specific surface area: 29.0 m ² /g) as the silica abrasive grains in composition 2-1, 4.0 parts by weight of TMAH, and 80.5 parts by weight of pure water.

[Composition 3-1]
A polishing composition was prepared in the same manner as in Composition 1-1, except that silica abrasive grains (secondary average particle size: 106.7 nm, NMR specific surface area: 16.6 m ² /g) different from the silica abrasive grains in Composition 1-1 were used.

[Composition 3-2]
A polishing composition was prepared by mixing 10.5 parts by weight of the same silica abrasive grains (secondary average particle size: 106.7 nm, NMR specific surface area: 16.6 m ² /g) as the silica abrasive grains in composition 3-1, 4.0 parts by weight of TMAH, and 85.5 parts by weight of pure water.

[Composition 4-1]
A polishing composition was prepared in the same manner as in Composition 1-1, except that silica abrasive grains (secondary average particle size: 122.8 nm, NMR specific surface area: 38.4 m ² /g) different from the silica abrasive grains in Composition 1-1 were used.

[Composition 4-2]
A polishing composition was prepared by mixing 10.5 parts by weight of the same silica abrasive grains (secondary average particle size: 122.8 nm, NMR specific surface area: 38.4 m ² /g) as the silica abrasive grains in composition 4-1, 4.0 parts by weight of TMAH, and 85.5 parts by weight of pure water.

[Secondary average particle size of silica abrasive grains in polishing composition]
After preparing the polishing compositions, compositions 1-1, 1-2, 2-1, and 2-2 were kept at room temperature for 2 months, and compositions 3-1 and 3-3 were kept at 50° C. for 5 days (corresponding to keeping at room temperature for 2 months), and then the secondary average particle diameter of the silica abrasive grains in the polishing compositions was measured by dynamic light scattering. The secondary average particle diameter was measured using ELS-Z manufactured by Otsuka Electronics Co., Ltd.

The value of W2/W1 was approximately calculated from the following formula.
W1 = amount of silica abrasive grains blended x (secondary average particle diameter of silica abrasive grains in polishing composition / secondary average particle diameter of blended silica abrasive grains) ³
W2 = amount of silica abrasive grains + amount of silicate ions ( _SiO2 equivalent) - W1

[Polishing speed]
These polishing compositions were used to polish silicon wafers (P type, (100) surface) with a diameter of 200 mm. A single-sided polishing machine manufactured by Nitta Haas Corporation was used as the polishing apparatus. A suede polishing pad (SUBA800) was used as the polishing pad. The polishing composition was diluted 31 times and supplied at a supply rate of 300 mL/min. Polishing was performed for 5 minutes under the conditions of a platen rotation speed of 115 rpm, a carrier rotation speed of 100 rpm, and a polishing load of 300 g/ ^cm2 , and the average polishing rate was calculated from the processing amount.

The results are shown in Table 1. Note that the pH in Table 1 is the value measured when the secondary average particle size was measured.

Comparisons between Composition 1-1 and Composition 1-2, and between Composition 2-1 and Composition 2-2 show that the reduction in the particle size of the silica abrasive grains can be reduced by setting W2/W1 to 0.5 or more. In addition, even if the amount of silica abrasive grains + silicic acid ( _SiO2 equivalent) is the same, it is clear that the polishing rate can be increased by setting W2/W1 to 0.5 or more.

Comparing Composition 3-1 to Composition 3-2, and Composition 4-1 to Composition 4-2, it is clear that by making W2/W1 0.5 or more, the amount of reduction in the particle size of the silica abrasive grains can be reduced. It is also clear that even if the amount of silica abrasive grains used is the same, by making W2/W1 0.5 or more, the polishing speed can be increased.

The above describes the embodiments of the present invention. The above-mentioned embodiments are merely examples for implementing the present invention. Therefore, the present invention is not limited to the above-mentioned embodiments, and it is possible to implement the above-mentioned embodiments by appropriately modifying them within the scope of the spirit of the present invention.

Claims (2)

A polishing composition for semiconductor polishing, comprising:
Silica abrasive grains;
Silica,
A basic compound,
and water,
a ratio W2/W1 of a weight W2 of silicate ions in the polishing composition calculated as _SiO2 to a weight W1 of the solid content of the silica abrasive grains is 0.5 to 2.0;
The polishing composition , wherein the silicic acid is orthosilicic acid, metasilicic acid, metadisilicic acid, metatrisilicic acid, metatetrasilicic acid or silicic acid hydrate . The polishing composition according to claim 1,
The polishing composition, wherein the basic compound is tetramethylammonium hydroxide.