JPH0750281A - Cleaning method for silicon wafer - Google Patents

Abstract

PURPOSE:To obtain a silicon wafer of high cleanness wherein adhesion of metal is restrained after the silicon wafer is cleaned with cleaning fluid containing sulfuric acid or hydrochloric acid. CONSTITUTION:After a silicon wafer is cleaned with cleaning fluid containing sulfuric acid or hydrochloric acid, e.g. mixed solution (SPM) of sulfuric acid and hydrogen peroxide or mixed solution (HPM) composed of hydrochloric acid, hydrogen peroxide, and ultra-pure water, the wafer is treated with aqueous solution of hydrofluoric acid or aqueous solution of buffer hydrofluoric acid (BHF).

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a cleaning method for obtaining a highly clean silicon wafer used for manufacturing semiconductor devices.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have been highly integrated, it has been strongly desired to further clean the surface of a silicon wafer as a substrate. Contaminants such as fine particles and metal impurities adhere to the silicon wafer surface during the silicon wafer manufacturing process and semiconductor device manufacturing process.
Unless these removal measures are taken, various inconvenient problems are caused in the device manufacturing yield and the device performance. The fine particles adhering to the surface of the silicon wafer may cause disconnection or short circuit of the wiring of the device, or cause abnormal diffusion of dopant or abnormal oxide film thickness in the diffusion or oxidation process. On the other hand, metal impurities such as Fe and Cu diffuse inside the silicon oxide film and the silicon wafer in the heat treatment process, and reduce the dielectric breakdown voltage and the carrier lifetime. Therefore, in the silicon wafer maker and the device maker, various kinds of cleaning are performed to remove these contaminants attached to the silicon wafer. For example, a typical cleaning method called RCA cleaning is
A mixture of ammonia water, hydrogen peroxide water, and ultrapure water (hereinafter A
(Abbreviated as PM) is heated to 60 to 90 ° C. to remove fine particles and organic substances on the silicon wafer, and then a mixed solution of hydrochloric acid, hydrogen peroxide and ultrapure water (hereinafter abbreviated as HPM) is heated to 50 to 100 ° C.
This is a cleaning method that is a combination of methods in which the metal impurities on the silicon wafer are removed by heating to the above. In addition, a mixed solution of sulfuric acid and hydrogen peroxide water (hereinafter abbreviated as SPM) is 80 to 1
The cleaning liquid heated to 50 ° C. is used for decomposing and removing organic substances such as photoresist or removing metal impurities. After these cleanings, if the chemical solution components remain on the surface of the silicon wafer and proceed to the next step, this has various adverse effects on the subsequent steps. For example, A
The ammonia component in the PM cleaning etches silicon, causing the surface of the silicon wafer to become rough,
Further, acid components such as sulfuric acid and hydrochloric acid in the SPM cleaning or HPM cleaning may cause corrosion of the device in the subsequent process.
Therefore, usually, after cleaning these, the silicon wafer is rinsed with ultrapure water in order to remove the chemical liquid component remaining on the surface of the silicon wafer.

[0003]

However, there is a problem that it is difficult to completely remove the chemical liquid component adhering to the surface of the silicon wafer by only rinsing with ultrapure water. It is considered that this is because the surface of the silicon wafer is very active. Originally, SPM cleaning and HPM
The cleaning is effective for removing the metal impurities on the surface of the silicon wafer, but the surface of the surface after the cleaning is conversely liable to be contaminated with the metal impurities. It became clear by. This is
When the cleaning tank is contaminated with metal in the ultrapure water rinse after the SPM cleaning or HPM cleaning, or the metal adheres to the silicon wafer in the process after the cleaning where metal contamination is likely to occur such as ion implantation or plasma etching. It becomes a problem that it is easy to do. Therefore, SPM cleaning and HPM
It is indispensable to remove the chemical component remaining after the cleaning in order to prevent the metal from adhering. At present, however, no countermeasure other than the rinse with ultrapure water has been taken for this purpose.

An object of the present invention is to clean a silicon wafer after cleaning with a cleaning solution containing sulfuric acid or hydrochloric acid to remove the chemical liquid component remaining on the surface of the silicon wafer, thereby suppressing the adhesion of metal impurities in the subsequent steps. It is to provide a cleaning method for obtaining.

[0005]

According to the present invention, a silicon wafer is washed with a washing liquid containing sulfuric acid or hydrochloric acid and then treated with a hydrofluoric acid aqueous solution or a buffered hydrofluoric acid aqueous solution. Regarding the cleaning method.

The silicon wafer to which the cleaning method of the present invention is applied is generally used for manufacturing semiconductor devices, and its specifications are not particularly limited.

A typical example of the cleaning solution containing sulfuric acid in the present invention is an SPM cleaning solution used for removing organic substances such as resist and metal impurities. A typical example of the cleaning solution containing hydrochloric acid is an HPM cleaning solution used for removing metal impurities. The SPM cleaning is performed by heating a mixed solution of sulfuric acid and hydrogen peroxide solution. Washing conditions are not particularly limited as long as the intended function is satisfied, but generally the composition is such that the volume ratio of concentrated sulfuric acid to 30 wt% hydrogen peroxide solution is (4 to 8) to 1, Washing temperature is 80-15
A range of 0 ° C is often used. On the other hand, the HPM cleaning is performed by heating a mixed solution of hydrochloric acid, hydrogen peroxide solution and ultrapure water. Similar to SPM cleaning, the cleaning conditions are not particularly limited as long as the function is satisfied, and the composition is such that the volume ratio of concentrated hydrochloric acid, 30 wt% hydrogen peroxide solution and ultrapure water is 1: 1: 6. Is typically used, and the washing temperature is generally in the range of 50 ° C to 100 ° C. In SPM cleaning or HPM cleaning, a thin natural oxide film is formed on the surface of a silicon wafer by hydrogen peroxide solution which is an oxidizing agent, but at the same time, chemical liquid components such as chlorine ions and sulfate ions adhere to the surface of this oxide film. These cannot be removed sufficiently by rinsing with ultrapure water.
The present invention removes the above chemical components by immersing a silicon wafer washed with a washing liquid containing sulfuric acid or hydrochloric acid in a hydrofluoric acid aqueous solution or a buffered hydrofluoric acid aqueous solution (hereinafter referred to as BHF) in the next step. is there.

The hydrofluoric acid aqueous solution used in the present invention is an aqueous solution prepared by diluting hydrofluoric acid with ultrapure water. Alternatively, as BHF, an aqueous solution obtained by diluting hydrofluoric acid and ammonium fluoride with ultrapure water is used. Preparation of these aqueous solutions can be performed at room temperature by a conventional method.

Although the concentration of hydrofluoric acid in the hydrofluoric acid aqueous solution or BHF is not particularly limited,
If it is too low, the controllability during liquid preparation will be poor, and if it is too high, the cost will be high, which is not economical. The concentration is preferably in the range of 0.5 to 20% by weight, more preferably 0.5 to 20% by weight.
A range of 10% by weight is adopted.

The concentration of ammonium fluoride in the BHF aqueous solution is not particularly limited, and a composition having a composition suitable for a desired etching rate of the silicon oxide film may be used. Generally, those in the range of 30 to 40% by weight are used.

The quality of the hydrofluoric acid aqueous solution and BHF used in the present invention is preferably as high as possible in order to avoid the inconvenience of contaminating the silicon wafer with the metal impurities therein, and specifically, It is desirable to use electronic grade chemicals.

Although the action of the aqueous solution of hydrofluoric acid or BHF is not clear, when the natural oxide film is etched by hydrofluoric acid, the above chemical solution components adhering to the surface of the natural oxide film are also peeled off from the surface of the silicon wafer. At the same time, it is presumed that hydrogen fluoride terminates the surface of the silicon wafer with hydrogen and stabilizes it, so that metal adhesion is suppressed.

The cleaning procedure in the present invention will be described below. After cleaning with a cleaning solution containing sulfuric acid or hydrochloric acid, first, ultrapure water rinsing is performed in order to wash away most of the chemical solution components adhering to the surface of the silicon wafer. Rinsing with ultrapure water is performed under general conditions, for example, at a room temperature for 1 to 15 minutes by a method in which ultrapure water overflows from the cleaning tank. After that, the silicon wafer is immersed in a fluororesin cleaning tank containing a treatment solution containing a hydrofluoric acid aqueous solution or BHF, and the residual chemical solution components are removed by etching the natural oxide film.

The processing temperature is not particularly limited, but room temperature is sufficient as generally used for etching a natural oxide film.

The treatment method with the aqueous solution of hydrofluoric acid or BHF of the present invention can be applied not only to the dipping method but also to the spray method and the spin method. Further, it goes without saying that similar results can be obtained not only in batch type processing but also in single wafer processing.

The processing time varies depending on the thickness of the natural oxide film formed by cleaning with a cleaning solution containing sulfuric acid or hydrochloric acid and the concentration of hydrogen fluoride in the processing solution, but the hydrogen fluoride concentration is within the range of 1 to 10 minutes. It is enough. After treating a silicon wafer with a hydrofluoric acid aqueous solution or BHF, excess chemical liquid adhering to the wafer surface is rinsed with ultrapure water and removed. An overflow method is generally used for the rinse, but a spray method may be used. Then, the silicon wafer is dried by a commonly used method such as spin drying. According to the method of the present invention, it is possible to prevent the silicon wafer from being contaminated with metal impurities in the next step, but it is particularly effective for elements such as Fe, Cr and Al.

[0017]

According to the cleaning method of the present invention, it is possible to obtain a highly clean silicon wafer in which adhesion of metal impurities to the surface of the silicon wafer is suppressed even after cleaning with a cleaning solution containing sulfuric acid or hydrochloric acid. It is extremely useful for manufacturing semiconductor devices.

[0018]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the example, the plane orientation (100), the specific resistance 3 ~
An n-type silicon wafer of 6 Ω · cm was used, and the quantitative determination of metal impurities attached to the silicon wafer was performed by total reflection X-ray fluorescence analysis. A standard solution for atomic absorption analysis was used as a metal source for contaminating the silicon wafer. Further, the concentrations of metal impurities in the chemicals used such as hydrochloric acid, sulfuric acid, hydrofluoric acid and BHF were all 10 ppb or less.

Example 1 In order to adjust the cleanliness of the surface before cleaning, a silicon wafer was precleaned by immersing it in a 1% by weight aqueous solution of hydrofluoric acid for 1 minute. Next, 96% by weight of sulfuric acid and 30% by weight of hydrogen peroxide were mixed at a volume ratio of 4: 1 and immersed in a liquid at 120 ° C. and washed for 10 minutes. Then rinse with ultrapure water for 10 minutes,
After soaking in 1% by weight hydrofluoric acid aqueous solution for 1 minute,
It was immersed for 10 minutes in ultrapure water containing 50 ppb of e. After rinsing with ultrapure water for 5 minutes and drying, the Fe concentration adhering to the surface of the silicon wafer was analyzed and found to be 8.5 × 1.
It was 0 ⁹ atoms / cm ^2.

Example 2 After prewashing in the same manner as in Example 1, 36% by weight of hydrochloric acid was added.
The silicon wafer was dipped in a liquid of 80% by mixing 30% by weight of hydrogen peroxide water and ultrapure water at a volume ratio of 1: 1 to 6, and washed for 10 minutes. After rinsing with ultrapure water for 10 minutes, immersing in 1 wt% hydrofluoric acid aqueous solution for 1 minute, and then immersing in ultrapure water containing 50 ppb of Fe for 10 minutes. After rinsing with ultrapure water for 5 minutes and drying, the concentration of Fe adhering to the surface of the silicon wafer was analyzed and found to be 7.8 × 10 ⁹ atoms / cm ² .

Comparative Example 1 After SPM cleaning in the same manner as in Example 1, rinsed with ultrapure water for 10 minutes and immersed in ultrapure water containing 50 ppb of Fe for 10 minutes. The Fe concentration on the silicon wafer surface after rinsing with ultrapure water for 5 minutes and drying was 4.3 × 10 ¹² atoms / c.
It was m ² .

Comparative Example 2 After washing with HPM in the same manner as in Example 2, rinsed with ultrapure water for 10 minutes and immersed in ultrapure water containing 50 ppb of Fe for 10 minutes. The Fe concentration on the surface of the silicon wafer after rinsing with ultrapure water for 10 minutes and drying was 8.6 × 10 ¹¹ atoms / c.
It was m ² .

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[Procedure amendment]

[Submission date] June 13, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

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[Claims]

Claims (3)

[Claims] 1. A method for cleaning a silicon wafer, which comprises cleaning a silicon wafer with a cleaning solution containing sulfuric acid or hydrochloric acid, and then treating the silicon wafer with a hydrofluoric acid aqueous solution or a buffered hydrofluoric acid aqueous solution. 2. The method for cleaning a silicon wafer according to claim 1, wherein the cleaning liquid is a mixed liquid containing sulfuric acid and hydrogen peroxide solution. 3. The method for cleaning a silicon wafer according to claim 1, wherein the cleaning solution is a mixed solution containing hydrochloric acid and hydrogen peroxide solution.