JP2013251388A - Sapphire material-cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sapphire material-cleaning method allowing simple and effective cleaning of a sapphire material with gas-dissolving water obtained by dissolving a low-cost and safe gas.SOLUTION: In a cleaning method where a sapphire material is cleaned by contacting the sapphire material with a cleaning liquid, the cleaning liquid is nitrogen gas-dissolving water and a supersonic wave is applied in cleaning. The pH of the nitrogen gas-dissolving water is preferably greater than 7. The concentration of the nitrogen gas in the nitrogen gas-dissolving water is preferably 8 mg/L to 20 mg/L. After alkaline cleaning of the sapphire material, it is preferable to clean with the nitrogen gas-dissolving water.

Description

  The present invention relates to a method for cleaning a sapphire material used as a semiconductor manufacturing apparatus member, a substrate or the like, and more particularly to a method for cleaning a sapphire material using nitrogen gas-dissolved water in which nitrogen gas is dissolved.

  Sapphire has characteristics such as light transmittance, high hardness, and heat resistance, and is widely used as a semiconductor manufacturing apparatus member and a compound semiconductor substrate material.

  The sapphire member is required to be surface-cleaned for yield improvement and quality improvement. For example, in a semiconductor manufacturing apparatus, substances (B, P, As, Al, etc.) used in the process adhere on the sapphire member. If this is peeled off or dropped due to a difference in thermal expansion or the like, the object to be processed is contaminated and the product quality is deteriorated. Therefore, the sapphire member must be periodically cleaned. Further, when sapphire is used as a compound semiconductor substrate material, if particles or the like are present on the surface, crystal defects starting from the particles are generated in the CVD film forming process, and the product quality is lowered. Therefore, it is necessary to sufficiently clean the surface of the sapphire substrate material before the film forming process. Since there are many polishing processes by CMP such as colloidal silica before the CVD process, it is necessary to clean and remove these abrasives from the sapphire substrate material.

  Patent Document 1 describes that after surface polishing of sapphire, the colloidal silica is removed by alkali cleaning. However, when removing colloidal silica only by alkali cleaning, high temperature and high concentration alkali is required. Further, the alkali in which the silica is dissolved becomes an alkali silicate (such as sodium silicate) and easily gels, so that the waste water treatment is difficult.

  As a method for cleaning the sapphire surface, Patent Document 2 describes cleaning the sapphire surface with a cleaning liquid composed of fluoride and citric acid. Patent Document 3 describes that the surface of the sapphire is cleaned with a cleaning liquid containing an anionic polymer and a chelating material.

  Patent Document 4 describes that an electronic component or the like is cleaned using an acidic or alkaline solution in which ozone or hydrogen is dissolved.

JP 2010-109329 A JP2008-153272 JP2011-190405A JP-A-9-255998

  In the method using the cleaning chemical solution as in Patent Documents 2 and 3, the chemical cost increases and the cleaning waste liquid treatment cost is high.

  In the method of Patent Document 4, since hydrogen gas or ozone gas has flammability or toxicity, an exhaust gas treatment facility is essential as a safety measure. Further, since it is not a general-purpose gas, a separate gas production apparatus and supply piping are required.

  An object of this invention is to provide the cleaning method of the sapphire material which can wash | clean a sapphire material simply and effectively with the gas solution water which melt | dissolved the low-cost and safe gas.

  The cleaning method for a sapphire material of the present invention is a cleaning method for cleaning a sapphire material by bringing a cleaning liquid into contact with the sapphire material, wherein the cleaning liquid is nitrogen gas-dissolved water, and an ultrasonic wave is applied during cleaning. is there.

  According to the method for cleaning a sapphire material of the present invention, the sapphire material can be sufficiently cleaned using nitrogen gas-dissolved water that is inexpensive and does not require an exhaust gas treatment facility.

It is a microscope picture of the sapphire substrate surface before cleaning. It is a microscope picture of the sapphire substrate surface after washing.

  In the sapphire material cleaning method of the present invention, the sapphire material is cleaned with nitrogen gas-dissolved water.

  Examples of the sapphire material to be cleaned include a semiconductor manufacturing apparatus member (insulating material), a polarizing plate, a coating material, and a sapphire substrate.

  In the present invention, preferably, nitrogen gas is dissolved in ultrapure water to produce nitrogen gas-dissolved water, and preferably, an alkaline solution is further added to adjust the pH to be alkaline to obtain a cleaning liquid. To remove particles on the surface of the sapphire material.

[Method for producing nitrogen gas-dissolved water]
In order to produce nitrogen gas-dissolved water, nitrogen gas is dissolved in pure water, preferably ultrapure water, using a gas-dissolving device such as a gas-dissolving membrane device. In order to increase the dissolution efficiency of nitrogen gas, it is preferable to degas ultrapure water in advance.

  The nitrogen gas concentration of the nitrogen gas dissolved water is preferably 8 to 20 mg / L. If it is less than 8 mg / L, the cleaning effect is low because the gas concentration is low, and if it exceeds 20 mg / L, the gas is supersaturated and bubbles are generated, so the ultrasonic cleaning effect is low.

  The pH of the nitrogen gas-dissolved water is not particularly limited, but the alkaline region is preferable, and pH 8.5 to 11 is particularly preferable.

[Cleaning method]
The sapphire material is cleaned with the cleaning liquid made of the nitrogen gas-dissolved water thus manufactured. The cleaning method can be either batch type or single wafer type.

  In the present invention, ultrasonic waves are applied when cleaning the sapphire material. The ultrasonic frequency is preferably 28 kHz to 2 MHz, and more preferably 39 kHz to 1 MHz. The temperature of the cleaning liquid at the time of cleaning is preferably 20 to 80 ° C., particularly preferably 20 to 60 ° C., which has a low ultrasonic cavitation threshold.

  When the cleaning method of the present invention is applied to a process in which a sapphire substrate is diced from an ingot, polished, and washed with an alkali, the sapphire substrate after the alkali cleaning is preferably cleaned by the method of the present invention. Even in a normal temperature and low concentration alkali cleaning, the colloidal silica is sufficiently removed by the cleaning step according to the present invention. By removing colloidal silica mainly in the nitrogen gas-dissolved water washing step, the generation of sodium silicate is reduced, and the wastewater treatment load is reduced.

  Hereinafter, examples and comparative examples will be described.

[Example 1]
The colloidal silica solution was diluted with ultrapure water, and the supernatant of the aqueous solution was applied to a commercially available sapphire substrate (diameter: 2 inch) with a spinner to intentionally contaminate with a SiO ₂ particle having a particle size of 0.5 μm for 1 day. The substrate was cleaned.

  Nitrogen gas dissolved in ultrapure water was dissolved at 16 mg / L, and nitrogen gas-dissolved water adjusted to pH 7.0 with ammonia water was used as a cleaning solution.

  The substrate is immersed in an ultrasonic cleaning tank accommodated in 30 L of this cleaning liquid, and the substrate is cleaned for 3 minutes while irradiating 39 kHz ultrasonic waves at room temperature. Then, the substrate is taken out from the cleaning tank, rinsed with ultrapure water for 3 minutes. And then spin-dried.

  The surface of the sapphire substrate before and after cleaning was observed with an optical microscope, the number of particles having a particle size of 0.5 μm or more was counted, and the particle removal rate was determined. The results are shown in Table 1. 1 and 2 show micrographs of the surface of the sapphire substrate before and after cleaning.

[Example 2]
The sapphire substrate was washed in the same manner as in Example 1 except that the pH was adjusted to 9.4 with aqueous ammonia. Table 1 shows the measurement results of the particle removal rate.

[Comparative Example 1]
The sapphire substrate was washed in the same manner as in Example 1 except that the nitrogen gas was not dissolved. Table 1 shows the measurement results of the particle removal rate.

[Comparative Example 2]
The sapphire substrate was washed in the same manner as in Example 2 except that the nitrogen gas was not dissolved. Table 1 shows the measurement results of the particle removal rate.

[Comparative Example 3]
The sapphire substrate was cleaned in the same manner as in Example 1 except that a cleaning solution in which 1.4 mg / L of hydrogen gas was dissolved was used instead of nitrogen gas. Table 1 shows the measurement results of the particle removal rate.

[Comparative Example 4]
The sapphire substrate was cleaned in the same manner as in Example 2 except that a cleaning solution in which 1.4 mg / L of hydrogen gas was dissolved was used instead of nitrogen gas. Table 1 shows the measurement results of the particle removal rate.

[Comparative Example 5]
The sapphire substrate was cleaned in the same manner as in Example 1 except that 20 mg / L of ozone gas was dissolved instead of nitrogen gas, and a cleaning liquid adjusted to pH 5.3 with carbon dioxide gas was used. Table 1 shows the measurement results of the particle removal rate.

[Comparative Examples 6 and 7]
The sapphire substrate was cleaned in the same manner as in Examples 1 and 2 except that the ultrasonic wave was stopped. Table 1 shows the measurement results of the particle removal rate.

  As shown in Table 1, according to Examples 1 and 2, the particle removal rate is extremely high. It can be seen that the particle removal rate is higher in the case of pH = 9.4 than in the case of pH = 7.0.

  Further, as is clear from the comparison between Examples 1 and 2 and Comparative Examples 6 and 7, the cleaning efficiency becomes extremely high by applying ultrasonic waves.

[Comparative Example 8, Examples 3-8]
The sapphire substrate was cleaned in the same manner as in Example 1 except that the nitrogen gas dissolution concentration was 0, 2, 4, 8, 16, 20 or 24 mg / L as shown in Table 2 and no ammonia water was added. The pH of the cleaning solution was 7. Table 2 shows the measurement results of the particle removal rate.

As shown in Table 2, when the nitrogen gas dissolution concentration is equal to or lower than the saturation dissolution concentration (about 16 mg / L at room temperature), the particle removal rate is higher as the nitrogen gas concentration is higher, and the nitrogen gas saturation concentration is 16 mg / L. Highest. When the supersaturated dissolution concentration is reached, the particle removal rate decreases. This is presumably because N ₂ gas becomes bubbles due to supersaturation, and the bubbles interfere with the straightness of the ultrasonic waves or serve as a cushion for cavitation.

[Example 9]
In Example 1, the sapphire substrate was cleaned in the same manner as in Example 1 except that the intentionally contaminated sapphire substrate was allowed to stand for 7 days and the object to which the dirt was firmly attached was the object to be cleaned. Table 3 shows the measurement results of the particle removal rate.

  As shown in Table 3, when the dirt adheres firmly after 7 days from the intentional contamination, the particle removal rate is lower than in the case of Example 1 after one day from the intentional contamination.

[Example 10]
In Example 9, the sapphire substrate to be cleaned was immersed in 1% NaOH for 30 minutes and then cleaned in the same manner. Table 3 shows the particle removal rate. As shown in Table 3, by performing alkali cleaning (NaOH cleaning) before cleaning with nitrogen gas-dissolved water, the particle removal rate is improved.

[Comparative Example 9]
The sapphire substrate was cleaned in the same manner as in Example 9 except that nitrogen gas was not dissolved in the cleaning solution. Table 3 shows the measurement results of the particle removal rate. As shown in Table 3, the particle removal rate in this case is as extremely low as 2%.

[Comparative Example 10]
The sapphire substrate was cleaned in the same manner as in Example 10 except that nitrogen gas was not dissolved in the cleaning liquid. Table 3 shows the measurement results of the particle removal rate. As shown in Table 3, even if alkaline cleaning is performed, if ultrasonic cleaning is performed without using nitrogen gas-dissolved water, the particle removal rate is as low as 15%.

Claims (5)

  A cleaning method for cleaning a sapphire material by bringing a cleaning solution into contact with the sapphire material, wherein the cleaning solution is nitrogen gas-dissolved water, and an ultrasonic wave is applied during cleaning.   2. The method for cleaning a sapphire material according to claim 1, wherein the pH of the nitrogen gas-dissolved water is higher than 7.   3. The method for cleaning a sapphire material according to claim 1, wherein the concentration of nitrogen gas in the nitrogen gas-dissolved water is 8 mg / L to 20 mg / L.   4. The method for cleaning a sapphire material according to claim 1, wherein the applied ultrasonic wave is 28 kHz to 2 MHz. 5.   5. The method for cleaning a sapphire material according to claim 1, wherein the sapphire material is washed with an alkali and then washed with the nitrogen gas-dissolved water. 6.

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