JP2987171B2 - Concentrated composition for fine polishing of wafers - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polishing composition for polishing a surface of a wafer which is widely used as a supporting crystal of an electric integrated circuit, for smooth polishing. More specifically, the present invention relates to a fine polishing concentrate composition for smoothly polishing irregularities larger than 10 μm on the surface of a wafer.

2. Description of the Related Art Wafers widely used as supporting crystals for electric integrated circuits are usually sliced from silicon or germanium crystal ingots, and their surfaces are polished to form a surface as uneven as possible. After that, they are used for circuit formation.

This is because, when a circuit pattern is drawn on the surface of a wafer, if the surface has irregularities, it becomes difficult to draw the line precisely and precisely, and it also causes non-uniformity of the electrical characteristics of the wafer.

In order to polish the surface of such a wafer, various polishing agents have been conventionally proposed.

For example, U.S. Pat. No. 3,170,273 discloses a silica sol having a silica concentration of 2 to 50 wt.
-100% silica gel is disclosed as an abrasive.
U.S. Pat. No. 3,328,141 discloses that an alkaline compound is added to these abrasives to adjust the pH to 10.5 to 12.5, and the use of the same increases the polishing rate.

However, when the surface of the wafer polished with these abrasives is observed with a differential interference microscope or the like, it is 5 to 500 m
There are irregularities of μ, which are not sufficiently satisfactory.

Japanese Patent Publication No. 53-9910 contains quartz, silicate and hexafluorosilicate, and further contains 3 to 5 carbon atoms.
An abrasive containing monohydric alcohol and polyvinyl alcohol is disclosed.

However, even if such an abrasive is used, a sufficiently satisfactory polished surface cannot be obtained yet, and it is difficult to store these alcohol-containing abrasives stably for a long period of time.

Further, Japanese Patent Publication No. 61-14655 (US Pat. No. 4,260,396)
Corresponds to the issue specification. ) Discloses an abrasive containing water-soluble carboxymethylene gum or xanthan gum. However, there are drawbacks that the polishing time required to form a smooth polishing surface with this abrasive and that so-called empty polishing must be performed for a long time while flowing water for cleaning after polishing. Further, there is a drawback that the minimum amount of silica required to form a smooth surface is large.

(Problems to be Solved by the Invention) The present inventor has previously attempted to eliminate the disadvantages that existed in the conventional polishing composition and to solve the following problems by using a colloidal material. A concentrated composition for fine polishing of wafers is proposed in which a slurry containing silica particles contains a specific water-soluble polymer compound and further contains a specific water-soluble salt (Japanese Patent Application No. 63-313480). No.).

1. To provide an abrasive which gives a polished surface with no unevenness even when the wafer is polished when observed with a differential interference microscope.

2. Provide an abrasive that requires a short polishing time to provide a smooth surface.

3. To provide an abrasive with a minimum amount of silica required to provide a smooth surface.

4. Provide abrasives that can be stored stably for a long period of time.

Thus, the above-mentioned slurry containing colloidal silica is usually supplied in a concentrated state, and the user dilutes and uses it.Furthermore, as a result of research, in the fine polishing composition for wafers, By using a specific water-soluble polymer substance and selecting each component within a specific range, a polished surface (smooth surface) with no unevenness even when observed with a differential interference microscope can be provided. It has been found that a polishing agent having excellent storage stability even in a concentrated state is obtained while maintaining excellent polishing properties such that the polishing time for giving a surface is short, and the present invention has been completed. Another object of the present invention is to provide a concentrated polishing composition for fine wafers having excellent polishing characteristics and excellent storage stability.

(Means for Solving the Problems) That is, the gist of the present invention is to finely polish a wafer containing water, colloidal silica particles, a water-soluble polymer, and water-soluble salts. In the concentrated composition, the water-soluble polymer is at least one selected from the group consisting of polyacrylamide having a molecular weight of 100,000 or more, a modified polyacrylamide, sodium polyacrylate, polyacrylic acid, and polymethacrylic acid. A fine particle of a wafer, wherein the content of colloidal silica is 1 to 50% by weight, the water-soluble polymer is 10 to 1,000 ppm, and the number of water-soluble salts is in the range of 200 to 10,000 ppm. It is a concentrated composition for polishing.

Then, the concentrated composition according to the present invention is diluted into a polishing slurry when used, so that the water-soluble polymer is in a range of 1 to 100 ppm, and the number of water-soluble salts is in a range of 20 to 1000 ppm. Dilute.

 Hereinafter, the present invention will be described in detail.

In the practice of the present invention, useful colloidal silica is
A stable colloidal dispersion of amorphous silica in a liquid. In this liquid, the average particle size of the silica particles is 5 to 50.
It should be in the range of 0 millimicron. Average particle size 5
When the diameter is less than millimicron, the proportion of silicic acid, monomers, and oligomers contained in the colloidal dispersion increases, and when a wafer surface such as silicon is polished with such a large amount, silica adheres to the wafer surface and is preferably used. Absent. If the average particle size exceeds 500 millimicrons, the surface of the wafer is apt to be scratched, which is not preferable.

In the present invention, the average particle diameter means, when the particles are present in an isolated state without aggregation, means the average particle diameter of the particles in that state, and when the particles are present in an aggregated state Means the average particle size in that state.

In the present invention, useful colloidal silica preferably has silanol on the particle surface at an areal density of 1 to 10 co / nm ² . When the areal density of the silanol on the particle surface is in the above range, the hydration of the silica particles is improved, and the dispersion of the silanol in water is smaller than that of the abrasive containing silica powder having an areal density of less than 1 / nm ^2. The properties are excellent.

The areal density of silanol on the surface of the silica particles can be measured, for example, by the following method.

(1) First, silica sol is ion-exchanged, and sodium hydroxide is dropped into silica sol (Wg) from which metal ions have been removed by this ion exchange, and the number of moles of sodium hydroxide required until pH reaches 8 (M) How to measure. The reaction at this time is measured as proceeding as follows.

Si—OH + NaOH⇒Si—ONa + H ₂ O (2) The silica content (S wt%) in the ion-exchanged silica sol is measured by a dry method.

(3) The areal density of silanol can be calculated as follows.

Here, r means the average radius (nm) of the silica particles.

Colloidal silica having silanol at an areal density of 1 to 10 cores / nm ² can be obtained by subjecting silica to polycondensation reaction with reduced sodium ions in water glass to form silica particles.

Details of the method for producing such colloidal particles are described in “The ch
emist-ry of silica: Solubility, polymerization, coll
oid and surface properties, and biochemistry "Ralpf
It is described in Chapter 3 of K.ller JOHN WILEYSONS (1979).

The polishing concentrate composition according to the present invention contains a water-soluble polymer compound. The water-soluble polymer compound is selected from the group consisting of polyacrylamide, modified polyacrylamide, sodium polyacrylate, polyacrylic acid and polymethacrylic acid. Examples of the modified polyacrylamide include those having the following molecular structures.

These water-soluble polymer compounds show a high drug reduction effect even at a low concentration.

The drag reduction effect refers to an effect that turbulence hardly occurs even under the condition that the number of Reynolds nozzles of the fluid is high. The high drag reduction effect of the polishing composition according to the present invention means that the polishing composition maintains a laminar flow and is unlikely to become turbulent even in polishing under a pressurized state. When the wafer is polished, the water-soluble polymer compound forms a clean laminar flow between the polishing cloth and the surface of the wafer in the sliding direction of the polishing cloth, and makes the wafer surface smoother. Perform the function.

The above water-soluble polymer has a molecular weight of 100,000 or more. If the molecular weight is less than 100,000, a laminar flow is not formed between the polishing pad and the wafer surface during polishing, which is not preferable. In the present invention, the molecular weight of the polymer compound is
It refers to a value measured by a light scattering method (for example, see New Experimental Chemistry Lecture Vol. 19, pp. 571 to 585 published by Maruzen Co., Ltd. in 1978).

The above-mentioned water-soluble polymer compound can be produced by a known method using a corresponding monomer (monomer) such as polyacrylamide, polyacrylic acid, or polymethacrylic acid.

The content of the water-soluble polymer in the polishing concentrate composition according to the present invention is 10 to 1,000 ppm. When this is diluted to obtain a polishing slurry having a silica concentration of 0.1 to 5%,
It is applied in a range of less than 00 ppm, and particularly preferably 1 to 50 ppm. When a wafer is polished using a polishing slurry having a content within these ranges, a laminar flow is formed in the sliding direction between the polishing cloth and the wafer surface, and the wafer surface can be further smoothed. However, when the content is less than 1 ppm, the laminar flow is difficult to be formed, and when the content is more than 100 ppm, turbulent flow tends to be formed, which is not preferable.

The polishing concentrate composition according to the present invention contains water-soluble salts. The water-soluble salts have a function of thinning the hydrated layer on the surface of the silica particles in the slurry-like fine polishing composition. Thereby, during polishing of the wafer with the polishing composition, the amount of mechanical action exerted by the silica particles on the wafer increases, the mechanical polishing ability increases, and the polishing efficiency improves. As specific examples of the water-soluble salts, the cation is selected from the group consisting of lithium ion, sodium ion, potassium ion, cesium ion and amonium ion, and the anion is hydrofluoric acid ion, chloride ion, Selected from a combination of one selected from the group consisting of bromate, iodate, sulfate, nitrate, perchlorate, carbonate, formate, acrylate, and oxalate ions Refers to a compound.
The water-soluble salts may be used alone or in combination of two or more. Among them, in the polishing composition presenting a slurry state,
Potassium chloride and potassium perchlorate, which have high ion dissociation degree and have a large cation atom radius, are preferred.

The content of the water-soluble salts in the concentrated composition for fine polishing of a wafer according to the present invention is 200 to 10,000 ppm. When this concentrated composition is diluted to obtain a polishing slurry having a silica concentration of 0.1 to 5%, it is usually applied in the range of 20 to 1,000 ppm, and particularly preferably in the range of 100 to 500 ppm. By including water-soluble salts, the thickness of the hydrated layer formed on the surface of the silica particles can be reduced.
If the amount is less than ppm, this effect is not sufficiently exhibited, which is not preferable. When the concentration is 1000 ppm or more, an alkaline compound can be added to the concentrated composition for fine polishing of a wafer, if necessary, in order to adjust the pH of the composition to 8 to 12.

As the alkaline compound, hydroxides of alkali metals, amines or ammonia can be used. Examples of the alkali metal hydroxide include potassium hydroxide, sodium hydroxide, rubidium hydroxide, and cesium hydroxide. Among them, potassium hydroxide and sodium hydroxide are preferred. Examples of the amines include triethylamine, triethanolamine, monoethanolamine, diisopropanolamine, ethylenediamine, tetraethylpentamine, triethylpentamine, diethylenetriamine, and hexamethylenediamine.

(Effects of the Invention) The present invention has the following particularly remarkable effects.
Its industrial utility value is extremely large.

(1) The concentrated composition for fine polishing according to the present invention is extremely advantageous in transportation and the like because of its stability at a high concentration. Is easy.

(2) When polishing a wafer by diluting the concentrated composition for fine polishing according to the present invention, a water-soluble polymer exhibiting a high drag reduction effect forms a laminar flow between the polishing cloth and the wafer, Suppress turbulence. Therefore, the surface of the polished wafer can be obtained as a smooth polished surface without any irregularities even when observed with a differential interference microscope.

(3) Since the concentrated composition for fine polishing according to the present invention contains, as silica particles, colloidal silica having silanol groups on the surface of the particles at an area density of ¹ to 10 co / nm ² ,
The silica particles have higher water affinity and are superior in water dispersibility as compared with an abrasive containing silica powder containing silica particles having only 1 silanol group / nm ² or less on the particle surface.

(4) A polishing slurry is prepared using the concentrated composition for fine polishing according to the present invention, and when a wafer is polished with the polishing composition, water-soluble salts mixed in the slurry may cause
Since the thickness of the hydrated layer on the surface of the colloidal silica particles in the slurry is small, the amount of mechanical action exerted on the wafer of the silica particles when colliding with the wafer of the silica particles is increased, and thus the mechanical polishing ability is increased. The efficiency of fine polishing is higher than that of polishing with a composition containing no salt.

(Examples) Next, the present invention will be described more specifically with reference to examples and comparative examples.
It is not limited to the following example.

(1) Adjustment of polishing composition Cloidal silica having an average particle diameter of 60 millimicrons, containing 50% by weight of silica particles, and having a silanol surface density of 8 particles / nm ² on the particle surface; a water-soluble polymer As a compound, an aqueous solution (0.5% by weight) of polyacrylamide (trade name: Diaclear MN3000, manufactured by Mitsubishi Kasei Co., Ltd.) (hereinafter referred to as “PAAM”), a modified polyacrylamide (trade name, manufactured by Mitsubishi Kasei Co., Ltd.) Diamond Clear MN3000H) (hereinafter “MN300
0H. " ), And KCl and NH ₄ Cl; as salts dissolved in water, were mixed with pure water to obtain a polishing composition having a silica content of 20%. The water-soluble polymer compound and the water-soluble salts are adjusted to have the proportions shown in Table 1 when the above-mentioned polishing composition is diluted 20-fold to obtain a polishing slurry having a silica content of 1% by weight. Weighed.

(2) Fine polishing test of wafer The above polishing concentrate composition was diluted 20 times with pure water using a soft swed type polishing cloth using a Speed Fam polisher, SPAW36, and diluted per minute. The silicon wafer was polished for 5 minutes while supplying at a rate of 11. The polishing pressure at this time was 100 g / cm ² , the relative speed between the wafer and the polishing cloth was 1 m / sec, and the temperature of the polishing cloth during polishing was 40 ° C. After polishing by the polishing machine, rinse polishing was performed for 30 seconds while flowing water instead of the above polishing composition. The irregularities on the polished surface of the wafer after the rinse polishing were observed with a differential interference microscope.
Table 1 shows the results.

(3) Long-term storage stability test of concentrated polishing composition The concentrated polishing composition obtained in (2) above was stored at room temperature, and the gelation time was measured. The results are shown in Table 1.

The following is clear from Table 1.

1.When the polishing concentrate composition according to the present invention is diluted and polished as a polishing slurry, the polished surface thereof is observed with a differential interference microscope, and as a result, a smooth surface without unevenness is obtained, which is suitable as an abrasive. It is.

2. Also, it is economical because the polymer content in the slurry required to achieve fine polishing is small.

3. In the storage test of the polishing composition according to the present invention, each of the polishing compositions does not gel for 3 months or more and is stable for a long period of time.

On the other hand, when the content of the water-soluble polymer compound is large as in Comparative Example 1, fine polishing is not achieved.
Also, when the content of water-soluble salts is large as in Comparative Example 2, fine polishing is not achieved and the long-term storage stability is lacking.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/304 B24B 37/00

Claims (1)

(57) [Claims] 1. A concentrated composition for fine polishing of a wafer comprising water, colloidal silica particles, a water-soluble polymer, and water-soluble salts, wherein the water-soluble polymer has a molecular weight of 10 10,000 or more polyacrylamide, polyacrylamide modified product, sodium polyacrylate, at least one selected from the group consisting of polyacrylic acid and polymethacrylic acid, and the content of colloidal silica is 1
A concentrated composition for fine polishing of wafers, characterized in that the number of water-soluble salts is in the range of 200 to 10,000 ppm, the water-soluble polymer being in the range of 200 to 10,000 ppm.