JP2000158329A - Wafer edge polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the polishing method of an edge, in detail, having a buffering action and using the composition for polishing with a large dielectric constant, on the polishing method using an abrasive for polishing the edge of the semiconductor substrate consisting of a silicon wafer, compound wafer or the like. SOLUTION: This method polishes the edge of a semiconductor wafer by a polishing composition consisting of the colloidal solution containing silicon oxide grains. The average primary grain diameter of the silicon oxide grain is 8-500 nm and its containing amount is 1-25 wt.% for the entire liquid amount and the polishing composition consisting of the colloidal solution is adjusted as a buffering solution having a buffering action between pH 8.3-11.5 by using a weak acid and/or weak base whose logarithm value of the reciprocal of the acid dissociation constant at 25 deg.C is 8.0-12.0 and adding either combination of the weak acid and strong base, strong acid and weak base or weak acid and weak base. Thereby, the polishing method of the edge part of the semiconductor wafer is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing method using an abrasive for polishing an edge portion of a semiconductor substrate such as a silicon wafer or a compound wafer. More specifically, the present invention relates to a method for polishing an edge portion using a polishing composition having a buffering action and a high electrical conductivity.

[0002]

2. Description of the Related Art Conventionally, as a polishing composition for polishing an edge portion of a workpiece (hereinafter abbreviated as a wafer or the like) of a semiconductor substrate formed of a silicon wafer or a compound wafer, silicon oxide or a hydrate thereof is used. A suspension dispersed in a colloidal form, so-called colloidal silica, is used,
At the time of processing, a method in which a workpiece is placed on a rotary processing drum on which a polisher made of synthetic resin foam or suede-like synthetic leather or the like is spread, and processing is performed while quantitatively supplying the abrasive solution while pressing and rotating. Is common. Here, the term "polishing" refers to a step of polishing an edge portion of a wafer or the like which has been subjected to pre-processing such as beveling, lapping, and etching so as to approach a mirror surface with less irregularities.

As an abrasive, for example, US Pat. No. 332
As disclosed in Japanese Patent No. 8141, a solution in which fine colloidal silicon oxide particles are dispersed in a solution containing an alkali component is generally used. This processing is different from the so-called mechanical processing using a diamond grindstone or hard alumina-based abrasive grains before that, and the chemical action of alkali as its component, Specifically, it is an application of the erodibility to a workpiece such as a silicon wafer. That is, a thin soft erosion layer is formed on the surface of a workpiece such as a wafer due to the corrosiveness of the alkali. Processing proceeds by removing the thin layer by mechanical action of fine colloidal silicon oxide particles. The pH of the abrasive solution must be in an alkaline region of 7 or more because the processing proceeds by the chemical action of the alkaline component of the solution. That is, pH 7
As the value approaches neutrality, the power of the chemical action becomes weaker, and the polishing speed becomes slower. Also, in the strong alkali region exceeding 11 and closer to 14, the power becomes stronger and the polishing speed becomes higher. .

[0004] Therefore, in such processing, the properties of the abrasive are extremely important factors. That is, the surface of the workpiece is eroded by the alkali component to form a thin layer, and its properties and properties, specifically, its thickness and hardness, etc., affect the properties of the abrasive solution used, particularly the electrochemical properties. Therefore, it is very important that the electrochemical properties, specifically, the pH be in a stable range. If this changes easily due to external conditions such as heat, contact with the outside air, or contaminants from the outside, the depth of the eroded layer, erosion speed, uniformity, ease of removal, etc. However, it is difficult to expect precise and uniform processing. Further, since the erosion layer is removed by the mechanical action of colloidal silicon oxide particles contained as a polishing agent in the polishing composition, the particles have an appropriate size and are easily broken. It should not be or be agglomerated due to high order aggregation. That is,
The silicon oxide particles effectively remove the erosion layer formed by the alkali component by mechanical action.
Therefore, it must not affect the new mirror after removal.

Conventionally, various polishing compositions have been proposed as polishing agents for wafers and the like. For example, in US Pat. No. 3,170,273, silica sol and silica gel are proposed as abrasives. No. 33
No. 28141, the pH of the suspension is adjusted to a pH of 10.5 to 1
It is disclosed that the polishing rate is increased by setting the ratio within the range of 2.5. U.S. Pat. No. 4,169,337 discloses adding amines to the polishing composition. JP-A-2-158684 discloses a polishing composition comprising water, colloidal silica, a water-soluble polymer having a molecular weight of 100,000 or more, and water-soluble salts. Further, Japanese Patent Application Laid-Open No. 5-154760 discloses a polishing method using a polishing composition containing 10 to 80% by weight of piperazine, which is a kind of water-soluble amine, based on silica of silica sol or silica gel. These disclosed methods increase the dispersibility of the abrasive by adding various additives to a solution having a basic structure in which an abrasive composed of fine particles such as colloidal silica or silica sol is dispersed in an alkaline mother liquor. It is intended to stabilize the processing power and does not remarkably improve the conventional polishing composition processing speed.

[0006] Basically, the pre-polishing or polishing step is based on the above-mentioned method using the polishing composition, so that the processing speed is generally slow and the production efficiency is poor, and the pH is changed due to a change in external conditions. It is a processing method that often changes and lacks processing stability, is time-consuming, and has a high degree of difficulty, and is hardly a perfect method. However, in particular, with the recent increase in the degree of integration of electronic circuits and the size of the wafer itself, it has become essential to highly planarize the surfaces of silicon wafers and semiconductor device substrates.
Furthermore, in order to improve production efficiency, a polishing composition and a polishing method with a high processing speed are desired. Further, there is a strong demand for a polishing method using a polishing composition which does not cause stains after polishing.

[0007] At the same time, the importance of the processing accuracy in polishing the wafer edge portion has been highlighted as an important issue. In other words, a polishing composition for polishing the wafer edge portion to reduce the unevenness of the wafer edge surface in order to prevent the generation of particles due to cracking and contact during transport of a large wafer and to further clean the wafer, and to bring the wafer edge portion as close as possible to a mirror surface. Attempts have been made to achieve the purpose by using an object and a polishing machine. In addition,
Wafer edge polishing is required to withstand severe conditions between the workpiece and the polishing pad, to be able to be recycled several times to several tens of times, and not to increase the viscosity of the processing liquid. I have.

[0008]

SUMMARY OF THE INVENTION The present inventors have described the above
In view of the problems with the wafer edge polishing method using a conventional polishing composition, and intensive research is performed, as a polishing composition solution, a colloid containing fine silicon oxide particles,
That is, it was found that stable high-speed processing was achieved by using an aqueous alkaline solution of colloidal silica, which had a pH buffering action, and had a high conductivity as a polishing composition solution. It has been found that by polishing the edge portion with an object, it is possible to process the desired excellent edge portion, which has led to the completion of the method of the present invention. ,
Another object of the present invention is to provide a method for polishing an edge portion of a semiconductor wafer with a stable polishing composition having a high polishing rate and little change even when used repeatedly, and a method for adjusting the polishing composition. Still another object of the present invention is to provide a specific polishing method using a polishing machine.

[0009]

An object of the present invention is to provide a method for polishing an edge portion of a semiconductor wafer with a polishing composition comprising a colloidal solution containing silicon oxide particles,
The silicon oxide particles have an average primary particle diameter of 8 to 500 nm, and the content thereof is 1 to 25% by weight based on the total liquid amount.
And the polishing composition comprising the colloidal solution has a logarithmic value of the reciprocal of the acid dissociation constant at 25 ° C. of 8.0.
Using a weak acid and / or weak base of ~ 12.0, adding a weak acid and strong base, strong acid and weak base, or any combination of weak acid and weak base, pH 8.
It can be achieved by a method for polishing an edge portion of a semiconductor wafer, characterized in that the solution is adjusted as a buffer solution having a buffering action between 3 and 11.5.

Further, by using the polishing composition, the surface of the silicon oxide fine particles contained in the polishing composition is coated with aluminum.
It can withstand severe use conditions and perform stable processing. That is, the specific colloidal silica containing fine silicon oxide fine particles coated with aluminum is more stable in a neutral region and a high alkali region than ordinary colloidal silica containing uncoated silicon oxide fine particles. By using the polishing composition containing silicon fine particles, it is possible to achieve more stable high-speed processing of the edge portion of the semiconductor wafer particularly in a high alkali region.

In addition, the polishing composition of the present invention contains a water-soluble organic solvent, so that contamination of the processed semiconductor wafer can be effectively prevented. That is, in such a polishing composition for polishing, the silicon oxide fine particles are dispersed in water, but the polishing composition is increased by contact with a rise in the temperature of the liquid during processing and a flow of dry air. Is easily dried, and only the silicon oxide fine particles, which are solid portions, partially remain on the wafer surface as a gel-like dried product, and appear as white stains. In addition, if a part of the wafer or a part of the colloidal silica is dissolved in the alkali component, and the polishing composition remains unevenly on the surface after the polishing process, a dried product of these dissolved materials is used as a wafer etchant ( Dissolution promoter) to cause spot-like stains, and these stains occur in the polishing composition in a water-soluble organic solvent, particularly a monohydric alcohol or a polyhydric alcohol,
Alternatively, it can be effectively prevented by adding an organic compound containing a hydroxyl group. In particular, high-molecular-weight alcohols or polyhydric alcohols such as glycols hardly evaporate, and the effect of preventing stains is remarkable. Specific preferred examples include ethylene glycol, polyethylene glycol, glycerin and hydroxydiethylamine.

Further, as another specific method of polishing the edge portion of a semiconductor wafer, which is another object of the present invention, a polishing process in which a polisher made of synthetic resin foam, synthetic leather, nonwoven fabric, or the like is attached to a rotatable drum is used. An example is a method in which a semiconductor wafer, which is a workpiece, is gripped by a carrier using a reduced pressure suction method, and an edge portion thereof is pressed against the drum while rotating at least one of the drum and the carrier.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The fine particles of silicon oxide contained in the colloid solution used in the polishing composition of the present invention have an average primary particle diameter of 8 to 500 nm, preferably 8 to 500 nm.
~ 200 nm. These silicon oxide fine particles may be secondary aggregated. The average primary particle diameter is 8 nm
If it is smaller, the colloidal solution is likely to aggregate, and the stability as a polishing composition is reduced. Further, when the average primary particle diameter is 2
When the thickness is from 00 to 500 nm, there is no influence on the performance as a polishing composition, but it is difficult to produce a stable product and the price is disadvantageous. If the average primary particle size exceeds 500 nm, the particles deviate from the colloid dimensions, which is not preferable.

It is important that the concentration of silicon oxide be 1 to 25% by weight during actual polishing, and a more preferable range is 3 to 15% by weight. Concentration is 1% by weight
If it is less than the above, the polishing speed becomes low and is not practical.
When the concentration of silicon oxide during polishing increases, the polishing speed itself increases, but the value reaches a saturation value when the concentration exceeds about 25% by weight. In addition, silicon fine powder generated as processing waste remains in the liquid as it is and is oxidized into silicic acid or silicon oxide to increase the concentration of silicon oxide in the liquid. If the silicon oxide concentration is high from the beginning, the oxidized silicon fine powder is added,
There is a tendency that the gelation of the recycle liquid is further accelerated, and the stability as a colloid solution is lacking, and the recyclability of the polishing composition solution is significantly reduced, which is not preferable. Further, it is disadvantageous in terms of cost.

In the present invention, the pH of the polishing composition is particularly preferably in the range of 8.7 to 10.6. p
If H is 8.6 or less, the polishing rate is undesirably reduced. Further, when the pH is 10.7 or more, the stability of the polishing composition is lowered because the colloidal silica starts to aggregate, which is also not preferable. And also this pH is friction,
Heat, contact with the outside air or mixing with other components, etc., should not easily change due to possible changes in external conditions, but in the present invention, the polishing composition solution itself is It is a necessary condition to use a liquid having a so-called strong buffering action with a small change in pH with respect to a change in the target conditions. The weak acid and / or weak base forming the buffer solution preferably has a logarithmic value (pKa) of the reciprocal of the acid dissociation constant (ka) at 25 ° C. in the range of 8.0 to 12.0. When the logarithm of the reciprocal of the acid dissociation constant at 25 ° C. is 8.0 or less, it is not preferable because a large amount of a weak acid and / or a weak base needs to be added to increase the pH. If the logarithm of the reciprocal of the acid dissociation constant at 25 ° C. is greater than 12.0, the pH is adjusted to 8.7 to 1
It is not possible to form a buffer solution with a large buffer capacity that stabilizes in the range of 0.6.

One example of a weak acid used for forming a polishing composition solution having a buffering effect used in the method of the present invention is as follows.
Boric acid (pKa = 9.24), carbonic acid (pKa = 6.3)
5, 10.33), phosphoric acid (pKa = 2.15, 7.2)
0, 12.35) and water-soluble organic acids.
Also, a mixture thereof may be used. As the weak base, a water-soluble amine or a mixture thereof can be used. Specifically, for example, ethylenediamine (pKa = 7.0)
8, 9.89), monoethanolamine (pKa = 9.
52), diethanolamine (pKa = 8.90), triethylamine, ethylamine, diethylamine, 4-
Aminopyridine, piperazine (pKa = 5.59, 9.
71), piperidine (pKa = 11.1), butylenediamine, propylenediamine, butylamine, hydroxyethylpiperazine, aminoethylpiperazine (pKa
= 4.02, 9.11, 9.80), and mixtures thereof. As the strong base, an alkali metal hydroxide and a water-soluble quaternary ammonium hydroxide can be used. Further, as the strong acid, hydrochloric acid, nitric acid, sulfuric acid and the like can be used. In the case where a plurality of pKa values exist in the above-described substances, one of them may be within the range. To form a buffer solution, add (1) a weak acid and a strong base, (2) a strong acid and a weak base, (3) a salt of a combination of a weak acid and a weak base, or a salt and a base, or a salt and an acid. May be. The buffer solution described in the present invention is:
A solution formed by the above combination, in which the weak acid and / or weak base are dissociated as ions in the solution and the undissociated state are present together. It is characterized by little change in pH.

In the method of the present invention, the polishing rate can be significantly improved by increasing the conductivity of the polishing composition solution. The electrical conductivity is a numerical value indicating the ease of passing electricity in the liquid, and is a reciprocal of the electric resistance per unit length. In the present invention, the value of the conductivity per unit length (micro-Siemens) is defined as silicon oxide 1
It is shown by a numerical value converted per weight%. In the present invention,
A conductivity of at least 20 mS / m / 1% -SiO ² is preferable for improving the polishing rate, and is preferably 25 mS / m / 1.
% More preferably equal to -SiO ² or more. There are the following two methods for increasing the conductivity. One is to increase the concentration of the buffer solution, and the other is to add salts. To increase the concentration of the buffer solution, (1) a weak acid and a strong base, (2) a strong acid and a weak base, (3) a weak acid and a weak base,
In any of the combinations, only the concentration may be increased without changing the molar ratio between the acid and the base. Salts used in the method of adding salts are composed of a combination of an acid and a base.The acid may be a strong acid or a weak acid, and a mineral acid and an organic acid can be used and a mixture thereof. Is also good.
The base may be a strong base or a weak base,
Alkali metal hydroxides, water-soluble quaternary ammonium hydroxides, and water-soluble amines can be used, and a mixture thereof may be used. 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 may be changed. The above two methods may be used in combination.

In order to improve the physical properties of the polishing composition used in the method of the present invention, a surfactant, a dispersant, an antisettling agent and the like can be used in combination. Examples of the dispersant and the antisettling agent include water-soluble organic polymer substances and inorganic layered compounds. Although the polishing composition of the present invention is in the form of an aqueous solution, an organic solvent may be added. The polishing composition of the present invention may be prepared by mixing colloidal silica, a base, an additive and water during polishing. In general, a composition having a high concentration of 15 to 65% is prepared as colloidal silica, and is often used after being diluted with water or a mixture of water and an organic solvent.

[0019]

EXAMPLES Next, the polishing composition of the present invention and a polishing method using the polishing composition of the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not particularly limited thereto. Polishing compositions used in Examples and Comparative Examples were prepared by the following methods. The colloidal silica used had an average primary particle size of 60, 90 and 110 nm and a silicon dioxide concentration of 30.
It is a commercial product of weight%. A commercially available product in which the surface of a part of colloidal silica was coated with aluminum was also used. A predetermined amount of these colloidal silicas is taken, and after adding 1000 g of pure water, an acid and / or a base or a salt is added to the mixture to adjust the pH while stirring, thereby preparing a buffer solution. Further, additives such as glycerin and ethylene glycol are required. Was added sequentially according to, and then a solution prepared with a necessary amount of pure water was used as a working solution. In this state, the concentration of silicon oxide in the liquid was 10 and 1
5% by weight. Polishing conditions were such that the edge portion was polished by the following method. Polishing equipment: Speed Fam Co., Ltd. EP-200-
V type Drum rotation speed: 1800 rpm Drum vertical speed: 1
mm / min. Polishing cloth: SUBA400 (manufactured by Rodel Nitta) Polishing composition flow rate: 600 mL / min Processing time: 5 minutes Workpiece: 8-inch silicon wafer with low-temperature oxide film Edge polishing is performed by pressing a silicon wafer against a rotating drum while tilting the silicon wafer. After polishing for 5 minutes, the front and back of the wafer were reversed, and the same polishing was performed for 5 minutes. The polishing amount was determined from the difference in weight (mg / m) per silicon wafer before and after polishing for polishing on both surfaces during a processing time of 5 minutes on one surface. The pH of the polishing composition was measured using a pH meter. In the measurement, the pH was calibrated in advance with a pH standard solution of pH 6.86 and pH 9.18 before measurement. The conductivity was measured with a conductivity meter. For the evaluation of the polished surface, the surface roughness of the edge surface was measured using Surfcom Profiler M2000 (manufactured by Chapman Instruments).

Examples 1 to 10 and Comparative Examples 1 to 5 The polishing compositions of the formulas shown in Tables 1 to 3 were prepared and used by the method of preparing the polishing compositions of the examples. The surface roughness was measured. Tables 1, 2 and 3 show examples of the method of the present invention and comparative examples of the prior art. In this example, as is clear from the results in the table, the polishing of the edge portion by the slurry of each example was faster in polishing speed than that of the comparative example, and the surface roughness was excellent in the surface roughness close to the mirror polished surface. It is clear that a roughness value is obtained. In Tables 1 to 3, * 1: Aluminum colloidal silica coated with aluminum * 2: TMAOH is tetramethylammonium hydroxide * 3: Abbreviation of glycerin * 4: Abbreviation of ethylene glycol * 5: Abbreviation of monoethanolamine * 6 : Polishing amount indicates the difference in weight per wafer after double-side polishing in processing for 5 minutes on one side of the edge portion. In Examples 6 to 10 and Comparative Examples 1 to 5, an adhesion test of stains remaining after polishing was performed. Done. In this test, the carrier holding the wafer at the time of polishing is a vacuum suction method, so the place held around the carrier and the surroundings are easy to dry with wind, and the degree of the stain remaining even after washing with water following polishing completion is visually judged. Was performed in the following manner.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

As is clear from the above description, 8
The method for polishing an edge portion of a semiconductor wafer according to the present invention using colloidal silica idal silica having a buffering action under specific conditions including silicon oxide particles of ~ 500 nm has an excellent polishing rate in edge polishing of a silicon wafer. As a result, the finished surface roughness is good, a sufficient mirror surface is obtained, the contamination is small, and it is possible to sufficiently cope with the high precision of the silicon wafer.

Claims (9)

[Claims] 1. A method for polishing an edge portion of a semiconductor wafer with a polishing composition comprising a colloidal solution containing silicon oxide particles, wherein the silicon oxide particles have an average primary particle diameter of 8 to 500 nm, The polishing composition comprising the above-mentioned colloidal solution has a content of 1 to 25% by weight based on the total amount of the solution, and the logarithm of the reciprocal of the acid dissociation constant at 25 ° C is 8.0 to 12.0. Buffering between pH 8.3 and 11.5 by adding a weak acid and / or a weak base and adding any combination of a weak acid and a strong base, a strong acid and a weak base, or a weak acid and a weak base. A method for polishing an edge portion of a semiconductor wafer, wherein the method is prepared as a buffer solution having the following. 2. The edge of a semiconductor wafer according to claim 1, wherein the polishing composition is prepared as a buffer solution having a buffering action between pH 8.7 and 10.6. Part polishing method. 3. The conductivity of the polishing composition at 25 ° C.
3. The method of polishing an edge portion of a semiconductor wafer according to claim 1, wherein the polishing rate is 20 mS / m or more per 1% by weight of silicon oxide. 4. The method for polishing an edge portion of a semiconductor wafer according to claim 3, wherein the concentration of the solution is increased or
Alternatively, a method for preparing a polishing composition, wherein the conductivity at 25 ° C. is adjusted to 20 mS / m or more per 1% by weight of silicon oxide by adding a salt. 5. The method for polishing an edge portion of a semiconductor wafer according to claim 1, wherein the average primary particle size of the silicon oxide particles is from 8 to 500 nm, and the content of the silicon oxide particles with respect to the total liquid amount is from 15 to 65. % By weight, and a polishing composition comprising a colloidal solution is mixed with a weak acid by using a weak acid and / or a weak base having a reciprocal value of an acid dissociation constant at 25 ° C. of 8.0 to 12.0. A solution containing a strong base, a strong acid and a weak base or a combination of a weak acid and a weak base to form a buffer solution having a pH buffering action, and a solution containing water, an organic solvent, salts, or a mixture thereof. A method for preparing a polishing composition, characterized by diluting with a slurry. 6. The method for polishing an edge portion of a semiconductor wafer according to claim 1, wherein the surface of the silicon oxide fine particles contained in the polishing composition is coated with aluminum. 7. The method for polishing an edge portion of a semiconductor wafer according to claim 1, wherein the polishing composition contains a water-soluble organic solvent. 8. The method for polishing an edge portion of a semiconductor wafer according to claim 7, wherein the water-soluble organic solvent is a monohydric alcohol or a polyhydric alcohol, or an organic compound containing a hydroxyl group. 9. A method for polishing an edge portion of a semiconductor wafer, comprising: reducing a pressure of a semiconductor wafer as a workpiece by a polishing machine in which a polisher made of synthetic resin foam, synthetic leather or non-woven fabric is attached to a rotatable drum; 9. The method according to claim 1, wherein the carrier is gripped by a suction method and an edge portion thereof is pressed against the drum while rotating at least one of the drum and the carrier. 3. The method for polishing an edge portion of a semiconductor wafer according to item 1.