JPH11130467A - Etching treating liquid for synthetic quartz glass jig and etching method using the liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily remove heavy metal impurities which intrude into microcracks or deposit on a rough surface by using a liquid comprising a mixture soln. of hydrofluoric acid and an inorg. acid or org. acid except for hydrofluoric acid. SOLUTION: This etching treating liquid is prepared by mixing hydrofluoric acid with an inorg. acid except for hydrofluoric acid or with an org. acid, and water in a specified proportion, and the liquid is controlled to have <=25% hydrofluoric acid concn. and <=30% inorg. or org. acid concn. When the inorg. acid or org. acid in the etching treating liquid is a strong acid, the increase in the etching rate is large, while if a weak acid is used, the increase in the etching rate is not large but the removing rate of heavy metal impurities is increased. In an etching treatment of a synthetic quartz glass jig produced by mechanical processing, the cleaning efficiency is further improved by dipping the jig in the etching treating liquid and by heating at 30 to 40 deg.C. As for the inorg. acid used together, nitric acid, sulfuric acid, phosphoric acid, chromic acid, hydrogen peroxide or the like is used, and as for the org. acid, acetic acid, formic acid or the like is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching solution for a synthetic quartz glass jig and an etching method using the same, and more particularly, to a synthetic quartz glass jig capable of easily removing metal impurities on the surface of a synthetic quartz glass jig. The present invention relates to an etching treatment solution for a tool and an etching method using the same.

[0002]

2. Description of the Related Art Quartz glass has been used as a jig for heat treatment of semiconductor devices because of its high purity and relatively excellent heat resistance. The heat treatment jig is generally used after being etched and cleaned with an aqueous solution of hydrofluoric acid so as not to contaminate the semiconductor element during use. Conventionally, an aqueous solution of hydrofluoric acid having a concentration of 5% or less has been used for this etching treatment. However, the etching treatment solution has low oxidizing ability to heavy metals such as iron and copper, and it is not easy to remove these heavy metal impurities. .

In recent years, as the degree of integration of semiconductor elements has further increased, the jigs used for heat treatment have also been required to be highly purified, and synthetic quartz glass has been used. Certainly, synthetic quartz glass has a high impurity content of 1/100 or less compared to natural quartz glass, but slightly contains heavy metal impurities, which are diffused during heat treatment of semiconductor elements.
It was contaminated and greatly deteriorated its lifetime. Heavy metal impurities remaining in the synthetic quartz glass jig are mainly present in rough surface portions generated by machining and inside micro cracks in the quartz glass bulk, but ordinary etching solutions have a slow etching rate and are rough. It takes a long time to etch the surface and open microcracks, and has a low oxidizing ability for heavy metal impurities, making it difficult to remove heavy metal impurities. Therefore, development of an etching solution that can easily remove heavy metal impurities remaining in a synthetic quartz glass jig has been eagerly desired.

[0003]

In view of the current situation,
The present inventors have conducted intensive studies, and as a result, when an inorganic acid or an organic acid other than hydrofluoric acid is added to the hydrofluoric acid aqueous solution,
In addition to the faster etching rate, the ability to oxidize heavy metals is improved, micro cracks in the synthetic quartz glass bulk are easily opened, and heavy metal impurities adhering to rough jig surfaces are easily removed by machining. It has been found that the present invention has been completed and the present invention has been completed. Ie

An object of the present invention is to provide an etching solution for a synthetic quartz glass jig having a high etching rate.

Further, the present invention provides an etching solution for a synthetic quartz glass jig which can easily remove heavy metal impurities contained in microcracks in a synthetic quartz glass bulk and heavy metal impurities adhered to a rough surface by machining. The purpose is to do.

A further object of the present invention is to provide a method for etching a synthetic quartz glass jig using the above-mentioned etching solution for a synthetic quartz glass jig.

[0007]

The present invention to achieve the above object is characterized by comprising a mixed solution of hydrofluoric acid, hydrofluoric acid, and an inorganic or organic acid other than hydrofluoric acid. The present invention relates to an etching treatment liquid for a synthetic quartz glass jig and a method for etching a synthetic quartz glass jig using the etching treatment liquid.

The etching solution for a synthetic quartz glass jig of the present invention comprises a mixed solution of hydrofluoric acid and an inorganic or organic acid other than hydrofluoric acid as described above. The acid refers to an inorganic or organic acid having an oxidizing ability and generating an acid in an aqueous solution. Specific examples of the inorganic acid include nitric acid, sulfuric acid, phosphoric acid, chromic acid, and hydrogen peroxide, and specific examples of the organic acid include acetic acid and formic acid. The concentration of the inorganic acid or the organic acid is 30% or less, preferably 5 to 20%.
When the concentration of the inorganic acid or the organic acid exceeds 30%, the etching rate of the synthetic quartz glass does not increase, and the cost increases, which is not preferable. The concentration of hydrofluoric acid used in combination with this inorganic acid or organic acid is 25% or less, preferably 5% or less. Synthetic quartz glass has a higher etching rate than natural quartz glass, but the etching rate of the synthetic quartz glass jig etching solution of the present invention is further increased, and the jig roughened by opening microcracks or machining. Etching of the surface portion becomes easy. In particular, when a short-time etching treatment is required, it is preferable to increase the hydrofluoric acid concentration within a range of 25% or less. If the hydrofluoric acid concentration exceeds 25%, the etching action is insufficient, and the synthetic quartz glass jig cannot be sufficiently cleaned.

The increase in the etching rate due to the addition of the inorganic acid or the organic acid is considered to be due to the following reasons. That is, when an aqueous solution of hydrofluoric acid is allowed to act on synthetic quartz glass, the synthetic quartz glass and hydrofluoric acid react to generate silicon fluoride, which adheres to the surface of the synthetic quartz glass in a gel form, and This suppresses the etching action of hydrofluoric acid. However, when inorganic or organic acids are present,
The silicon fluoride generated by the reaction with the synthetic quartz glass is decomposed by this inorganic acid or organic acid, and the silicon fluoride on the surface of the synthetic quartz glass is converted into a water-soluble reactant, and the surface of the synthetic quartz glass is always fresh. Etching rate is increased due to the contact of the hydrofluoric acid. Further, the inorganic or organic acid has an oxidizing ability for heavy metal impurities, forms an oxide film on the surface of the heavy metal impurities, and dissolves hydrofluoric acid to facilitate removal of the heavy metal impurities. When the inorganic or organic acid in the etching solution for synthetic quartz glass jig of the present invention is a strong acid, the etching rate is greatly increased. For example, in the case of a mixed aqueous solution of 10% hydrofluoric acid and 20% nitric acid, The etching rate is about 8 μm / hour, which is about twice the etching rate of the etching solution containing no nitric acid. However, strong acids such as nitric acid, sulfuric acid, and hydrochloric acid require special equipment for waste liquid treatment and increase the cost, so they are effective in a process where a high etching rate is particularly desired, but a weak acid when a special etching rate is not desired. It is better to use The etching rate of the etching solution containing the weak acid,
It is about 1.2 times faster than the etching rate of the etching solution not containing it, but has a high ability to remove heavy metal impurities,
Moreover, there is an advantage that the waste liquid treatment is easy and the conventional waste liquid treatment apparatus can be used as it is. In particular, hydrogen peroxide is preferable. In the case of an etching solution for a synthetic quartz glass jig containing the hydrogen peroxide solution, the used hydrogen peroxide is easily decomposed into water and oxygen, and the waste liquid treatment is simplified.

As an etching method using the above-mentioned synthetic quartz glass jig etching treatment liquid, for example, a synthetic quartz glass jig produced by machining can be immersed in a synthetic quartz glass jig etching treatment liquid. Preferably, the temperature of the etching solution is warmed to 30 to 40 ° C. By maintaining the temperature, the cleaning efficiency is further improved. The machining refers to cutting of synthetic quartz glass with a cutting jig such as a diamond wheel or a diamond saw, grinding with a grinding jig such as a diamond wheel, or polishing and grinding with abrasive grains such as green carbon.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described, but the present invention is not limited thereto.

[0012]

【Example】

Example 1 An etching treatment solution having a hydrofluoric acid concentration of 20% and a nitric acid concentration of about 25% was prepared by mixing 20 liters of a 50% aqueous hydrofluoric acid solution with 40 liters of a 61% aqueous nitric acid solution and 40 liters of pure water. did. A synthetic quartz glass rod having a diameter of 20 mm and a groove cut by a diamond wheel was immersed in the prepared etching solution for 10 minutes to perform an etching process. The microcracks present in the synthetic quartz glass rod were completely opened as shown in FIG. 1, and no heavy metal impurities remained on the surface thereof. A 12-inch Si wafer heat treatment boat was prepared using the synthetic quartz glass rod, the 12-inch Si wafer was heat-treated, and the lifetime of the Si wafer at the contact surface between the synthetic quartz glass rod and the wafer was measured to be 150 μsec. Met.

Example 2 An etching solution having a hydrofluoric acid concentration of 20% and a hydrogen peroxide concentration of about 25% was prepared by mixing 20 liters of a 50% aqueous hydrofluoric acid solution with 80 liters of a 35% aqueous hydrogen peroxide solution. Was prepared. When the synthetic quartz glass rod mechanically processed in the same manner as in Example 1 was etched using the etching solution, the microcracks were completely opened at 20 μm on the surface, and no heavy metal impurities remained on the surface. Was. Using this synthetic quartz glass rod, a 12-inch Si wafer heat treatment boat was prepared, a 12-inch Si wafer was heat-treated, and the lifetime of the Si wafer at the contact surface between the synthetic quartz glass rod and the wafer was measured. Met.

Example 3 20 liters of a 50% aqueous hydrofluoric acid solution were mixed with 80 liters of a 35% aqueous acetic acid solution to give a hydrofluoric acid concentration of 20 liters.
% And an acetic acid concentration of about 25% were prepared.
When the synthetic quartz glass rod mechanically processed in the same manner as in Example 1 was etched using the etching solution, the microcracks were completely opened and no heavy metal impurities remained on the surface. Using this synthetic quartz glass rod, a 12-inch Si wafer heat treatment boat was created, and a 12-inch Si wafer was heat-treated,
When the lifetime of the Si wafer at the contact surface between the synthetic quartz glass rod and the wafer was measured, 150 μsec
Met.

Comparative Example 1 An etching treatment solution having a hydrofluoric acid concentration of about 20% was prepared by mixing 20 liters of a 50% aqueous hydrofluoric acid solution with 80 liters of pure water. A synthetic quartz glass rod having a diameter of 20 mm and a groove cut by a diamond wheel was immersed in the prepared etching solution for 10 minutes to perform an etching process. As shown in FIG. 2, the microcracks generated in the mechanically processed synthetic quartz glass rod were not sufficiently open at about 8 μm on the surface, and heavy metal impurities remained. Using this synthetic quartz glass rod, a 12-inch Si wafer heat treatment boat was prepared, a 12-inch Si wafer was heat-treated, and the lifetime of the Si wafer at the contact surface between the synthetic quartz glass rod and the wafer was measured. Met.

COMPARATIVE EXAMPLE 2 40 liters of a 61% aqueous nitric acid solution and 40 liters of pure water were mixed with 20 liters of a 50% aqueous hydrofluoric acid solution, and etched with a hydrofluoric acid concentration of about 20% and a nitric acid concentration of about 25%. A treatment liquid was prepared. A synthetic quartz glass rod having a diameter of 20 mm and a groove cut by a diamond wheel was immersed in the prepared etching solution for 10 minutes to perform an etching process. Approximately 50% of the microcracks generated in the mechanically processed natural quartz glass rod were opened, and it was confirmed that heavy metal impurities remained on the surface. Using this natural quartz glass rod, a 12-inch Si wafer heat treatment boat was prepared, a 12-inch Si wafer was heat-treated, and the lifetime of the Si wafer at the contact surface between the natural quartz glass rod and the wafer was measured. And

[0017]

The etching solution for synthetic quartz glass jigs of the present invention contains micro-cracks generated during the production of synthetic quartz glass jigs and trace amounts of heavy metal impurities such as iron and copper adhering to rough surfaces due to machining. Can be easily removed, and even in the processing of a semiconductor element using the same, the deterioration of the lifetime due to heavy metal impurities does not occur.

[Brief description of the drawings]

FIG. 1 is a scanning electron microscope secondary electron image photograph of a synthetic quartz glass rod processed for 120 minutes with an etching solution for a synthetic quartz glass jig containing 5% hydrofluoric acid, at a magnification of 200 times. is there.

FIG. 2 is a scanning electron microscope secondary electron image photograph of a synthetic quartz glass rod processed with a conventional 5% hydrofluoric acid etching solution at a magnification of 200 times.

Claims (3)

[Claims] 1. An etching solution for a synthetic quartz glass jig, comprising a mixed solution of hydrofluoric acid and an inorganic or organic acid other than hydrofluoric acid. 2. The etching solution for a synthetic quartz glass jig according to claim 1, wherein the inorganic acid is hydrogen peroxide. 3. A synthetic quartz glass jig is treated with an etching solution for a synthetic quartz glass jig comprising a mixed solution of hydrofluoric acid and an inorganic or organic acid other than hydrofluoric acid. An etching method for a synthetic quartz glass jig.