JPH06291099A - Cleaning method of silicon wafer - Google Patents

Abstract

PURPOSE:To obtain a cleaning method of a silicon wafer, in stead of the HPM treatment, wherein heavy metal on a wafer surface can be eliminated, and danger to a human body and corrosiveness little occur. CONSTITUTION:A circulation filtering system cleaning liquid tank is used, and the final finish cleaning of a wafer after APM cleaning is performed by using organic acid of pH 3 or lower as the cleaning liquid. Since low corrosive organic acid is used, corrosion resistant structure is not necessary. Hence the installation can be made small, installing is facilitated in a small space, danger to human body little occurs, operability and maintainability are excellent, MCL elimintion effect is comparable to the HPM cleaning, readhesion of heavy metal can be prevented because of chelate effect, and stable quality is obtained in the MCL lifetime.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a silicon wafer which requires high cleanliness, and removes particles such as organic substances adhering to the surface by APM cleaning,
In RCA cleaning that removes heavy metals on the wafer surface by PM cleaning, organic acid is used as an acid cleaning instead of HPM cleaning, and final finishing cleaning is performed on the wafer to obtain a stable wafer with high surface cleanliness. The present invention relates to a silicon wafer cleaning method.

[0002]

2. Description of the Related Art As a method for cleaning a silicon wafer, 1
Since 970, an immersion type cleaning device called RCA cleaning has been used and generalized. In RCA cleaning, a plurality of cleaning tanks are lined up and the wafers are immersed in order to perform a series of cleaning. First, fine particles and organic substances are removed by an APM (ammonia / hydrogen peroxide solution) tank, and then a water cleaning tank (QDR tank). The cleaning liquid is removed with a vacuum cleaner, and the natural oxide film generated by the APM process and the metal taken in the oxide film are diluted with diluted hydrofluoric acid (HF / H ₂ O: DH).
F) and buffered hydrofluoric acid (HF / NH ₄ F / H ₂ O: B
After removing the cleaning liquid in the HF tank of HF) and the washing liquid in the water washing tank, the heavy metals on the surface are removed in the HPM (hydrochloric acid / hydrogen peroxide solution) tank, and then again through the water washing tank and the final water washing tank (FR tank). Then, it is dried by centrifugal drying (SD).

Conventionally, A is used in the final cleaning of silicon wafers.
After removing surface particles with PM, an acid cleaning called HPM is performed to remove heavy metals on the wafer surface. This washing is performed using a solution in which high-purity hydrochloric acid, hydrogen peroxide solution, and ultrapure water are mixed at a fixed ratio. In general, heavy metals have high solubility in acidic solutions, so that heavy metals on a wafer can be removed. HPM cleaning is performed using this action.

[0004]

In the HPM cleaning, since hydrochloric acid is used in the HPM cleaning, the hydrochloric acid aqueous solution and the hydrochloric acid gas corrode the metal inside and outside the cleaning room of the cleaning equipment, which may cause the contamination by the corroded metal at the time of cleaning. There is a nature. In addition, there is also a problem that the equipment becomes large in size due to the corrosion resistant structure. Hydrochloric acid is a chemical that is extremely dangerous to the human body and has problems in operability and workability. Further, in terms of wafer quality, there is a large variation between wafers in terms of surface heavy metal removability, and there is a problem that stable quality cannot be obtained.

The present invention is capable of removing heavy metals on the surface of a wafer, is less dangerous to the human body, and is less corrosive.
It is an object of the present invention to provide a silicon wafer cleaning method that replaces PM processing.

[0006]

The inventors of the present invention have proposed a conventional RC
In A cleaning, since HPM cleaning uses hydrochloric acid, the gas etc. corrode the cleaning equipment and other metal parts,
There is a risk of contamination during wafer cleaning, there is a high risk to the human body that special handling is required, and in terms of wafer quality, there is a large variation in surface heavy metal removability, and MCL and lifetime are stable. Therefore, as a result of various studies on acid cleaning instead of HPM cleaning, cleaning with organic acid is particularly excellent in safety and maintainability, and also in terms of wafer quality, MCL, The present invention has been completed by finding that there is little variation in lifetime and stable quality can be obtained.

That is, according to the present invention, in an immersion type cleaning method of cleaning a wafer by immersing the wafer in a cleaning liquid tank, a final finishing cleaning of the wafer is performed by using an organic acid as a cleaning liquid. Is the way. Further, the present invention is the method for cleaning a silicon wafer, characterized in that, in the above-mentioned constitution, the pH of the organic acid cleaning liquid is set to 3 or less, and further, a circulation filtration type cleaning liquid tank is used.

In the present invention, the cleaning using the organic acid is characterized in that it is used for the final finishing cleaning of the wafer after the APM cleaning in the RCA cleaning.
The cleaning can be performed after the M cleaning, or the final finishing cleaning of the wafer can be performed in combination with other known dry cleaning and wet cleaning methods. Furthermore, not only the final finish cleaning of the wafer but also acid cleaning can be applied for the purpose of removing the metal before the heat treatment. Further, any known constitution can be adopted as the cleaning liquid tank for storing the organic acid, but since the organic acid is less dangerous to the human body and less corrosive, the circulation filtration type cleaning tank as shown in the examples is used. Can be used, and the particles in the liquid can be removed.

In the present invention, as the organic acid, citric acid, hydroxyacetic acid, acetic acid oxalic acid, lactic acid, gluconic acid, etc. may be appropriately selected according to the required cleanliness, and may be used alone or in combination. It is necessary to use as low a heavy metal concentration as possible. Preferred organic acids include tartaric acid, succinic acid, malic acid, glycolic acid, formic acid and the like. Further, a mixed organic acid may be used for adjusting the pH and preventing the generation of bacteria. The liquid concentration and liquid temperature are also appropriately selected according to the type of organic acid. Also, in terms of cleaning efficiency, 5
It is preferable to raise the temperature to about 0 ° C., and a cleaning time of about 5 minutes is sufficient. In addition, some organic acids, such as citric acid, are prone to bacteria, and IPA or H ₂ O ₂ is added as a preservative in a few% of these to prevent the generation of particles. Good. further,
In the present invention, since the pH of the organic acid is involved in the reduction of the wafer surface heavy metal MCL, it is preferable to adjust the concentration of the organic acid so that the MCL can be lowered by setting the pH to 3 or less and the required pH is obtained.

[0010]

According to the present invention, as an acid cleaning in place of HPM, cleaning is carried out using an organic acid which is less dangerous to the human body and less corrosive. As a result, a sufficient effect can be obtained even with a relatively weak acid such as an organic acid, the heavy metal MCL on the wafer surface can be reduced, and since the corrosiveness is small, there is no fear of contamination due to corrosion of the device or the like. In addition, many organic acids have a chelating effect and can prevent reattachment of heavy metals.

[0011]

【Example】

Example 1 Citric acid was used as an organic acid, and a cleaning solution p was prepared under the conditions of a concentration of 3 to 5 wt% aqueous solution, a temperature of 25 ° C., and a cleaning time of 3 minutes or more.
By changing H to 2-3, the wafer is cleaned after the APM cleaning, and then rinsed with water and dried to complete the cleaning.
The wafer surface heavy metal MCL was measured, and the relationship between the cleaning solution pH and the wafer surface heavy metal MCL is shown in FIG. pH 3
It can be seen that MCL can be lowered by washing with the following organic acid washing solution.

Example 2 In the cleaning apparatus shown in FIG. 2, a recovery tank 3 for recovering the overflowed organic acid cleaning solution 2 is provided around the cleaning tank 1 made of quartz or fluororesin. The organic acid cleaning liquid 2 is sent through a fluororesin pipe 4 to a fluororesin filter 6 by a bellows pump 5 to remove particles in the liquid, and then sent to a drain pipe 8 in front of a drain valve 7 of the cleaning tank 1 to the cleaning tank 1. It consists of a circulating structure. Since the organic acid cleaning liquid has a low corrosiveness, it can be used as a circulation type cleaning tank, and it is not necessary to have a corrosion-resistant structure such as a cleaning draft or a maintenance room cleaning room. In organic acid cleaning, no corrosion occurs in equipment and room. Further, there is almost no danger to the human body, and the operation and work can be performed safely.
On the other hand, in the conventional HPM treatment, after almost one year of use, iron and parts in the room are almost rusted and become unusable.

Example 3 Conventional APM (NH ₄ OH / H ₂ O ₂ / H ₂ O) treatment and H
The cleaning effect of the PM (HCl / H ₂ O ₂ ) treatment and the citric acid treatment of the present invention was confirmed by surface impurities (Fe, Al, Zn,
The Cu) concentration was evaluated. The result is shown in FIG. In the figure, APM processing is displayed as SC-1 and HPM processing is displayed as SC-2. The citric acid treatment conditions of the present invention are pH 2, concentration 3 wt%, temperature 25 ° C., immersion time 3 minutes, and A
PM treatment conditions are as follows: concentration NH ₄ OH: H ₂ O ₂ : H ₂ O =
1: 1: 5, temperature 80 ° C., soaking time 10 minutes, HPM treatment concentration: HCl: H ₂ O ₂ : H ₂ O = 1: 1: 5, temperature 8
It was 0 ° C. and the immersion time was 10 minutes. As is clear from FIG. 3, the MCL removal effect is equivalent to that of the HPM cleaning.

Example 4 The cleaning effect of the APM treatment and HPM treatment of Example 3 and the citric acid treatment of the present invention was evaluated by the lifetime of the wafer. The result is shown in FIG. The citric acid treatment conditions of this invention were pH 2, concentration 3 wt%, temperature 25 ° C., and immersion time 3 minutes. As is clear from FIG. 4, it is found that stable quality is obtained in MCL lifetime as compared with HPM cleaning.

[0015]

According to the cleaning method of the present invention, the organic acid is used as the acid cleaning instead of the HPM cleaning to perform the final finish cleaning of the wafer. Since the low corrosive organic acid is used, the corrosion resistance is high. Since it does not require a structure, the equipment can be downsized and can be easily installed even in a place with a small space. In addition, there is little danger to the human body and operability and maintainability are excellent. Furthermore, in terms of wafer quality, HPM
Although the MCL removal effect is equivalent to that of cleaning, since the corrosiveness is small, there is no fear of contamination due to corrosion of the device or the like.
Further, since the organic acid has a chelating effect, redeposition of heavy metals can be prevented, and stable quality can be obtained in the MCL lifetime.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a cleaning solution pH and a wafer surface heavy metal MCL.

FIG. 2 is an explanatory diagram showing a configuration of a cleaning device used in the cleaning method of the present invention.

FIG. 3 is a graph showing a relationship between a cleaning method and a wafer surface impurity concentration.

FIG. 4 is a graph showing a relationship between a cleaning method and MCL lifetime.

[Explanation of symbols]

 1 Cleaning Tank 2 Organic Acid Cleaning Solution 3 Recovery Tank 4 Piping 5 Bellows Pump 6 Filter 7 Drain Valve 8 Drain Pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunori Oka 2201 Ueda, Kamikita-machi, Kijima-gun, Saga Prefecture Sumitomo Sitix Corporation Kyushu Office

Claims (2)

[Claims] 1. A method for cleaning a silicon wafer, which comprises performing a final cleaning of a wafer by using an organic acid as a cleaning liquid in a cleaning method of immersing a wafer in a cleaning liquid tank for cleaning. 2. The method for cleaning a silicon wafer according to claim 1, wherein the organic acid cleaning solution has a pH of 3 or less.