JP2021106246A - Polishing composition - Google Patents

Abstract

To provide a polishing composition capable of keeping the particle size of abrasive grains stable.SOLUTION: A polishing composition for semiconductor polishing includes silica abrasive grains, silicic acid, a basic compound, and water, and the ratio W2/W1 of the weight W2 of the silicate ion in the polishing composition to the weight W1 of the solid content of the silica abrasive grains in terms of SiO2 is 0.5 to 2.0.SELECTED DRAWING: None

Description

The present invention relates to a polishing composition.

Ultra-precision machining is an extremely important technology in the manufacture of semiconductor products. In recent years, the miniaturization of LSI devices has progressed, and along with this, the demand for surface roughness and flatness of semiconductor wafers after precision polishing tends to become stricter. Until now, in primary polishing, the emphasis has been mainly on the amount of grinding (polishing speed). On the other hand, it has become clear that the surface quality of the semiconductor wafer after the primary polishing affects the surface quality after the secondary polishing and the final polishing. Therefore, at present, even in primary polishing, it is required to realize a higher level of surface quality while maintaining the current polishing rate.

As a means for improving the surface quality of the semiconductor wafer after polishing, it is effective to reduce the concentration of abrasive grains that can cause polishing scratches and foreign matter residue. However, when the concentration of abrasive grains is lowered, there is a problem that the polishing speed is lowered.

Japanese Unexamined Patent Publication No. 9-306880 discloses a polishing liquid composition for silicon containing a water-soluble silicic acid component, colloidal silica, and an alkaline component and having a pH of 8.5 to 13. According to the publication, by adding an aqueous silicic acid component such as potassium silicate or sodium silicate to an alkaline colloidal silica suspension, the surface of the silicon wafer can be effectively reduced even if the concentration of colloidal silica is significantly reduced. It is stated that it can be polished.

Japanese Unexamined Patent Publication No. 2003-100670 includes polishing particles and soluble metal silicate, and the weight of silica in the soluble metal silicate (W2) with respect to the weight of solid content (W1) of the polishing particles. Abrasives having a ratio (W2 / W1) in the range of 0.001 to 0.08 are disclosed. The publication describes that the polishing rate of an oxide film substrate can be increased by adding a soluble metal silicate to the abrasive.

Japanese Unexamined Patent Publication No. 9-306880 Japanese Unexamined Patent Publication No. 2003-100670

As a means for increasing the polishing rate regardless of the concentration of abrasive grains, it is conceivable to increase the concentration of the basic compound in the polishing composition to increase the amount of processing by etching. However, when the concentration of the basic compound is increased, the abrasive grains may be dissolved and the particle size may change. The particle size of the abrasive grains affects the polishing rate, the surface quality and flatness of the semiconductor wafer after polishing. Therefore, it is necessary to keep the particle size of the abrasive grains stable.

An object of the present invention is to provide a polishing composition capable of maintaining a stable particle size of abrasive grains.

The polishing composition according to one embodiment of the present invention is a polishing composition for semiconductor polishing, which contains silica abrasive grains, silicic acid, a basic compound, and water, and is a solid of the silica abrasive grains. The ratio W2 / W1 of the weight W2 of the silicate ion in the polishing composition in _{terms of SiO 2 to the weight W1 of the minute is 0.5 to 2.0.}

According to the present invention, a polishing composition capable of maintaining a stable particle size of abrasive grains can be obtained.

The present inventor has made diligent studies to solve the above problems. As a result, in the polishing composition containing silica abrasive grains, silicic acid, a basic compound, and water, the silicate ions in the polishing composition are converted to _{SiO 2 with respect to the weight W1 of the solid content of the silica abrasive grains.} It has been found that by adjusting the ratio W2 / W1 of the weight W2 of the silica abrasive grains to a predetermined range, the dissolution of the silica abrasive grains can be suppressed and the particle size of the silica abrasive grains can be kept stable.

The present invention has been completed based on the above findings. Hereinafter, the polishing composition according to one embodiment of the present invention will be described in detail.

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. As the silica abrasive grains, for example, those having a secondary average particle size of 20 to 150 nm can be used.

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

[Silicic acid]
Silicic acid adjusts the concentration of silicic acid ions in the polishing composition. Silicic acids include, for example, orthosilicic acid (H ₄ SiO ₄ ), metasilicic acid (H ₂ SiO ₃ ), meta-silicic acid (H ₂ SiO ₅ ), meta trisilicic acid (H ₄ Si ₃ O ₈ ), and meta-silicic acid. It is silicic acid (H ₆ Si ₄ O ₁₁ ). Silicic acid can also be formed by dissolving silicates and silicic acid hydrates.

Silicic acid can also be formed, for example, by dissolving high-purity colloidal silica prepared 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 _{silicic acid ions in the polishing composition in terms of SiO 2 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 compound]
The basic compound efficiently reacts with the surface of the semiconductor wafer and contributes to the polishing performance of chemical mechanical polishing (CMP). The basic compound is, for example, an amine compound, an inorganic alkaline compound, or the like.

The amine compound is, for example, a primary amine, a secondary amine, a tertiary amine, a quaternary ammonium and its hydroxide, a heterocyclic amine and the like. Specifically, 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-methylpiperazin, piperazine hydrochloride, guanidine carbonate and the like. Of these, TMAH is preferably used.

Examples of the inorganic alkali compound include alkali metal hydroxides, alkali metal salts, alkaline earth metal hydroxides, and alkaline earth metal salts. Specifically, the inorganic alkaline compound is potassium hydroxide, sodium hydroxide, potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, sodium carbonate and the like.

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

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

[W2 / W1]
In the polishing composition according to the present embodiment, the ratio W2 / W1 of the weight W2 of _{silicate ions in the polishing composition in terms of SiO 2 to} the weight W1 of the solid content of the silica abrasive grains is 0.5 to 2.0. be.

_{If the weight W2 of the silicate ions in the polishing composition in terms of SiO 2} is too small with respect to the weight W1 of the solid content of the silica abrasive grains, that is, if W2 / W1 is too small, the silica abrasive grains are sufficiently dissolved. It cannot be 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 ions in the polishing composition in terms of SiO 2} is too large with respect 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 aggregate. It will be easier. The lower limit of W2 / W1 is more preferably 0.52, still 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 with a centrifuge and further removing water with a dryer. The weight of silicate ions in the polishing composition can be measured by ion chromatography after diluting the centrifuged supernatant to an appropriate concentration. Weight W2 of SiO ₂ in terms are to the measured weight, SiO ₂ and SiO ₃ ^- determined by dividing the molecular weight ratio 1.266 in a.

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.

In addition to the above, the polishing composition according to the present embodiment may optionally contain a compounding agent generally known in the field of polishing composition, such as a chelating agent, a water-soluble polymer, and a surfactant.

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

In the polishing composition according to the present embodiment, a high-purity colloidal silica prepared in advance by a sol-gel method or the like is dissolved in an aqueous solution of an amine compound to prepare an aqueous solution of silicic acid, and this aqueous solution and silica abrasive grains are used. Can also be produced by mixing. According to this method, since pure silicic acid can be obtained, contamination of the semiconductor wafer by, for example, metal ions can be suppressed.

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

Hereinafter, the present invention will be described in more detail 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 in which 3.75 parts by weight of TMAH was dissolved in pure water (DIW, the same applies hereinafter) to completely dissolve the colloidal silica. An aqueous solution of silica was prepared. To this 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 m ² / g) and 0.25 parts by weight of TMAH were further added, and a total of 0.25 parts by weight was added. Pure water was added so as to be 100 parts by weight to prepare a polishing composition.

[Composition 1-2]
The same silica abrasive grains as the silica abrasive grains of composition 1-1 (secondary average particle size: 80.7 nm, NMR specific surface area: 20.2 m ² / g) 15.5 parts by weight, TMAH 4.0 parts by weight, pure water 80.5 parts by weight were mixed to prepare a polishing composition.

[Composition 2-1]
Same as 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 of composition 1-1 are used.} To prepare a polishing composition.

[Composition 2-2]
The same silica abrasive grains as the silica abrasive grains of composition 2-1 (secondary average particle size: 123.0 nm, NMR specific surface area: 29.0 m ² / g) 15.5 parts by weight, TMAH 4.0 parts by weight, pure water 80.5 parts by weight were mixed to prepare a polishing composition.

[Composition 3-1]
Same as 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 of composition 1-1 are used.} To prepare a polishing composition.

[Composition 3-2]
The same silica abrasive grains as the silica abrasive grains of composition 3-1 (secondary average particle size: 106.7 nm, NMR specific surface area: 16.6 m ² / g) 10.5 parts by weight, TMAH 4.0 parts by weight, pure water 85.5 parts by weight were mixed to obtain a polishing composition.

[Composition 4-1]
Same as 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 of composition 1-1 are used.} To prepare a polishing composition.

[Composition 4-2]
The same silica abrasive grains as the silica abrasive grains of composition 4-1 (secondary average particle size: 122.8 nm, NMR specific surface area: 38.4 m ² / g) 10.5 parts by weight, TMAH 4.0 parts by weight, pure water 85.5 parts by weight were mixed to obtain a polishing composition.

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

The value of W2 / W1 was approximately calculated from the following formula.
W1 = compounding amount of silica abrasive grains × (secondary average particle size of silica abrasive grains in the polishing composition / secondary average particle size of mixed silica abrasive grains) ³
W2 = compounding amount of silica abrasive grains + compounding amount of silicate ions (SiO ₂ conversion) -W1

[Polishing speed]
Using these polishing compositions, a silicon wafer (P type, (100) surface) having a diameter of 200 mm was polished. As the polishing device, a single-sided polishing device manufactured by Nitta Haas Co., Ltd. was used. As the polishing pad, a suede polishing pad (SUBA800) was used. The polishing composition was diluted 31-fold and fed at a feed rate of 300 mL / min. Polishing was performed for 5 minutes under the conditions of surface plate rotation speed: 115 rpm, carrier rotation speed: 100 rpm, and polishing load: 300 g / cm ² , and the average polishing speed was calculated from the processing amount.

The results are shown in Table 1. The pH in Table 1 is a value measured at the time of measuring the secondary average particle size.

From the comparison between the composition 1-1 and the composition 1-2 and the comparison between the composition 2-1 and the composition 2-2, by setting W2 / W1 to 0.5 or more, the particles of the silica abrasive grains The amount of decrease in diameter can be reduced. Further, it can be seen that even if the amount of the blended silica abrasive grains + silicic acid ( _{converted to SiO 2} ) is the same, the polishing speed can be increased by setting W2 / W1 to 0.5 or more.

From the comparison between the composition 3-1 and the composition 3-2 and the comparison between the composition 4-1 and the composition 4-2, by setting W2 / W1 to 0.5 or more, the particles of the silica abrasive grains The amount of decrease in diameter can be reduced. Further, it can be seen that the polishing speed can be increased by setting W2 / W1 to 0.5 or more even if the amount of the blended silica abrasive grains is the same.

The embodiments of the present invention have been described above. The above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented within a range that does not deviate from the gist thereof.

Claims (2)

A polishing composition for semiconductor polishing,
With silica abrasive grains
With silicic acid
Basic compounds and
Including water
A polishing composition in which the ratio W2 / W1 of the weight W2 of _{silicate ions in the polishing composition in terms of SiO 2 to} the weight W1 of the solid content of the silica abrasive grains is 0.5 to 2.0. The polishing composition according to claim 1.
A polishing composition in which the basic compound is tetramethylammonium hydroxide.