JPH04179225A - Cleaning method - Google Patents

Abstract

PURPOSE:To prevent surroundings from being contaminated, to easily control a cleaning process and to realize a high-grade cleaning operation by a method wherein an object to be cleaned is immersed in a cleaning liquid which contains an acid and hydrogen peroxide and/or ozone and it is irradiated with ultraviolet rays. CONSTITUTION:An object 8 to be cleaned is immersed in a cleaning liquid which contains an acid and hydrogen peroxide and/or ozone in a chemical-liquid tank 3. It is irradiated with ultraviolet rays from a light source 2. For the acid, e.g. sulfuric acid, hydrochloric acid or the like as an inorganic acid is used and formic acid, acetic acid or the like as an organic acid is used. The mixture ratio of the acid or an alkali agent to the hydrogen peroxide is set at 1:10 to 10:1. When ultraviolet rays are irradiated, molecules which have absorbed the ultraviolet rays are reacted with a contaminant more effectively than heated molecules, and the organic contaminant on the object to be cleaned is oxidized and decomposed. In addition, it is not required to take into consideration a drop in the temperature of a chemical liquid when the object to be cleaned is immersed; the object can be cleaned by the chemical liquid in small quantities. As a result, it is possible to always supply a new chemical liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for cleaning organic contaminants in precision processing of semiconductor wafers, etc., and particularly to a method for removing resists and the like.

[Conventional technology]

Conventionally, methods for removing organic contaminants such as resist on objects to be cleaned include a dissolution method and an oxidative decomposition method.

The dissolution method is a method in which a solvent having a dissolving power acts on a contaminant organic substance to dissolve the contaminant in the solvent and thereby remove the contaminant from the surface of the object to be cleaned. As this solvent, mainly organic solvents such as chlorinated solvents such as trichloroethylene, tetrachloroethylene, and methyl chloroform, fluorocarbons, and alcohols such as ethyl alcohol, methyl alcohol, and isopropyl alcohol are used.

Solutions of surfactants may also be used.

The oxidative decomposition method is a method in which organic pollutants are reacted with an oxidizing agent to be decomposed and removed from the surface, and there are two methods: a dry method and a wet method. Dry methods include, for example, a method of heating to several hundred degrees, a method of contacting with oxygen plasma, and a method of irradiating ultraviolet rays in the presence of ozone. The wet method is a method in which treatment is performed using a chemical solution with strong oxidizing power. Wet oxidation decomposition methods include, for example, adding nitric acid, hydrogen peroxide, etc. as an oxidizing agent to concentrated sulfuric acid and heating it, heating it with an alkaline solution of hydrogen peroxide, and immersing it in an oxidizing agent and heating it. There are methods such as applying sound waves.

[Problem to be solved by the invention]

In the method of dissolving using an organic solvent, flammable solvents such as alcohols have problems in terms of fire prevention. In addition, chlorinated solvents such as trichlorethylene have problems in terms of labor 2D treatment. There is a worldwide call for the use of fluorocarbons to be restricted or completely abolished as they cause ozone layer depletion. Furthermore, since chlorinated solvents, fluorocarbons, etc. are chemically stable substances and their decomposition methods are quite low, the amount equivalent to the amount of replenishment is discharged into the environment in some form. These organic solvents discharged into the environment cause contamination of groundwater, the atmosphere, etc. In particular, groundwater contamination is directly linked to drinking water contamination, and has become a serious problem.

The surfactant solution is used to remove oil stains (liquid organic substances with a relatively low molecular weight). However, due to their nature, surfactants strongly adsorb to the surface of the object to be cleaned, so they remain even after rinsing after cleaning, and further oxidative decomposition is required to completely remove them. Furthermore, since the hydrophilic groups of surfactants generally dissociate from alkali metal ions as counterions, they may cause metal contamination.

Wet oxidative decomposition uses highly corrosive chemicals and heats them, so sufficient safety measures are required. In addition, management of chemical solutions is important because they can volatilize, decompose, and get mixed with impurities such as reaction products, but there are few measuring instruments and purification equipment that can withstand high-temperature chemicals.

In the dry oxidative decomposition method, it takes a long time to decompose and remove organic substances, and if the amount of pollutants is large, depending on conditions such as ozone and UV irradiation, the pollutants may change in quality and become difficult to remove. There are problems such as the need for pre-cleaning with an organic solvent or the like.

As mentioned above, conventional cleaning methods do not pollute the global environment,
There have been problems such as contamination of objects to be cleaned by the cleaning chemicals, difficulty in managing the chemicals, and the need for a long time for cleaning.

The present invention does not use organic solvents such as fluorocarbons that cause environmental pollution such as depletion of the ozone layer, and the cleaning process can be easily controlled.
The purpose of this paper is to propose a method for obtaining highly cleaned objects.

[Means to solve the problem]

In order to achieve the above object, in the present invention, the object to be cleaned is
This cleaning method involves immersing the object in a cleaning solution containing acid, hydrogen peroxide, and/or ozone, and irradiating it with ultraviolet rays. This cleaning method involves immersing it in a cleaning solution containing hydrogen and/or ozone and irradiating it with ultraviolet light.

Here, examples of acids include sulfuric acid, hydrochloric acid, and inorganic acids.
Nitric acid, hydrofluoric acid, etc. can be used, and as organic acids, formic acid, acetic acid, oxalic acid, etc. can be used.

Further, as the amines, choline, diethylamine, etc. can be used.

The mixing ratio of the acid or alkaline agent and hydrogen peroxide can be 1:10 to 10:1, and 1:1 to 5.
:1 is preferable. Furthermore, it is also possible to use an acid or alkali agent, or a solution in which ozone is further dissolved in a mixed solution thereof.

In the cleaning method, the ultraviolet irradiation light source may be one that irradiates ultraviolet rays with a wavelength of 400 nm or less, including a wavelength of 200 nm with higher energy.
A light source that can irradiate light below m is more preferable.

[For production]

Many of the polymeric organic substances used in phosphorography, such as resists, absorb ultraviolet rays with a wavelength of 300 nm or less. Cleaning chemicals also absorb UV rays. For example, 188 with sulfuric acid
There is an absorption peak at 303 nm for nitric acid and 189 nm for ammonia.

On the other hand, the energy of ultraviolet light is 254 nm, which is one of the main wavelengths of a low-pressure mercury lamp, which is a typical ultraviolet light source.
at about 470 kJ/mol, and at 185 nm about 6
It is 50 kJ/mol, which is fully comparable to the bond dissociation energy of many organic substances.

Here, when a chemical solution is heated to about 100°C, the molar heat capacity is generally several tens to hundreds of J/K mol, so the heated chemical solution has an extra energy of 1) compared to room temperature. approximately + kJ/mol. For example, when sulfuric acid is heated, its molar heat capacity is approximately 140 J/-mo
+, so in heated sulfuric acid, almost all molecules in the liquid each have an extra energy of 10 to 20 kJ/mol. Furthermore, hydrogen peroxide has a molar heat capacity of approximately 9 DJ/K-mol, so 7 kJ/m
It will have an extra energy of about o1. At this time, only a small number of molecules actually react, so the energy of the remaining molecules is not used effectively.

When irradiated with ultraviolet light, molecules that have absorbed the ultraviolet light are excited and have hundreds of I/mol of extra energy, which is greater per molecule than the energy obtained by heating. , 2, the molecules that have absorbed the ultraviolet light react with the pollutants more effectively than the heated molecules 3.

Therefore, by immersing the object to be cleaned in a chemical solution and irradiating it with ultraviolet rays, the organic contaminants on the object to be cleaned are effectively oxidized and decomposed. Furthermore, since the decomposition products dissolved in the cleaning chemical solution are discharged outside the system, there is no need for complete oxidation to CO2, unlike dry methods such as UV and []3.

In addition, contamination is reduced because a heater for heating the chemical solution is not required; volatilization and deterioration of the chemical solution are suppressed because the liquid temperature is low; analysis of drug liquid crystals is easier at room temperature, so drug liquid crystalline management It has the advantage of being easy to use.

Furthermore, there is no need to consider a drop in the temperature of the chemical solution due to the introduction of the object to be cleaned, and since cleaning can be performed with a small amount of chemical solution, it is possible to constantly supply new chemical solution.

〔Example〕

The present invention will be further explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 No. 11:21 is a schematic sectional view showing an example of an embodiment of a cleaning device according to the cleaning method of the present invention. In this embodiment, the cleaning device 1 includes an ultraviolet light source 2 and a cleaning chemical tank 3. In addition, the cleaning chemical liquid tank: 3 is a chemical liquid supply port 6,
It has an overflow mechanism 4 and a chemical solution discharge lower.

The object to be cleaned 8 coated with resist as a simulated contaminant,
It was immersed in a cleaning chemical solution Tg 3, irradiated with ultraviolet rays from the ultraviolet light source 2 for 5 minutes to remove the resist, and rinsed with pure water for 5 minutes using a rinser (not shown).

Here, as cleaning chemicals, sulfuric acid and hydrogen peroxide are used as H, S
[], : ]8[]2: 112D= 3: 1
: Using a solution mixed at a ratio of 1: 20 mff/mi
Supplied at n.

Further, as the ultraviolet light source, six 40W low-pressure mercury lamps using protective tubes made of Daio quartz and capable of transmitting ultraviolet light having a wavelength of 200 nm or less were used. The object to be cleaned leaked uniformly in a dense mist of water droplets, and was judged to be clean.

) Also, the results obtained using other inorganic acids were similar.

Example 2 Using the same apparatus as in Example 1, formic acid and hydrogen peroxide were used as cleaning chemicals HCOOH: H2O2: ]70-1=1
The treatment was carried out under the same conditions except that a solution prepared by mixing 8 and dissolving it by blowing in 20 mg-[]3/d of ozone was used. The object to be cleaned leaked uniformly using the water droplet spray method, and was judged to be clean.

Moreover, the results obtained using other organic acids were also similar.

Example 3 Using the same apparatus as in Example 1, ammonia and hydrogen peroxide were used as cleaning chemicals in NIl, OH: )1202:H2
Processing was carried out under the same conditions except that 0=1:1:5 was used. The object to be cleaned leaked uniformly using the water droplet spray method, and was judged to be clean.

Example 4 Using the same apparatus as in Example 1, the cleaning chemical concentration was adjusted to J phosphorus 1.
%, IIJ was 23%, but the treatment was carried out under the same conditions. The object to be cleaned leaked uniformly using the water droplet spray method, and was judged to be clean.

Comparative Example 1 The same object to be cleaned as in Example 1 was used in a UV and ozone cleaning device using six 40W low-pressure mercury lamps.

In Comparative Example 1, it took 20 minutes for the object to be cleaned to be determined to be clean by the water droplet spray method.

Furthermore, in order to prevent the leakage of ozone gas harmful to the human body when taking out the object to be cleaned, it is necessary to provide an exhaust ozone gas treatment device.

Comparative Example 2 The same object to be cleaned as in Example 1 was treated with a high temperature mixed solution of sulfuric acid and hydrogen peroxide for 1 minute.

The object to be cleaned was determined to be clean by the water droplet spray method.

In Comparative Example 2, a heating device for the cleaning chemical solution is required, and the highly oxidizing high-temperature chemical solution requires extreme caution in handling.

〔Effect of the invention〕

Immerse the object to be cleaned in the cleaning chemical solution as described above,
The cleaning method of the present invention by irradiating ultraviolet rays can easily obtain a highly cleaned object, and compared to conventional methods, 1) Unlike cleaning methods using organic solvents, it is easy to use and discharge; There is no need to use fluorocarbons, chlorinated organic solvents, etc., which are restricted.

2) Compared to dry cleaning methods such as UV and ozone, processing can be performed in a shorter time.

3) Compared to methods using high-temperature cleaning chemicals, chemical heating equipment is not required and handling is easier.

There are advantages such as

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing an example of an apparatus used in the method of the present invention. ■...Cleaning device, 2...Ultraviolet light source, 3...Chemical solution tank, 4...Overflow mechanism, 5゛...Object holding mechanism, 6...Chemical solution supply port, 7...・Exhaust port, 8・
・Object to be cleaned, 9.・Perforated plate

Claims (1)

[Scope of Claims] 1. A cleaning method characterized by immersing an object to be cleaned in a cleaning liquid containing an acid, hydrogen peroxide and/or ozone, and irradiating it with ultraviolet rays. 2. A cleaning method characterized by immersing the object to be cleaned in a cleaning liquid containing ammonia or amines, hydrogen peroxide and/or ozone, and irradiating it with ultraviolet rays.