JPH07149930A - Treating method for wafer and assessing method for cleanness of environmental atmosphere using wafer treated thereby - Google Patents

Abstract

PURPOSE:To obtain a wafer useful for assessing the cleanness of an environmental atmosphere by treating a silicon wafer with ultraviolet rays and ozone in an air-circulating clean bench to form a hydrophilic silicon surface contg. no nonmetallic ion on the wafer. CONSTITUTION:A hydrophilic silicon surface contg. no nonmetallic ion is formed by treating a silicon wafer with ultraviolet rays and ozone in a space separated from the outside in an air-circulating clean bench equipped with a filter contg. an active carbon or a chemical adsorbent (e. g. a pleated plastic fabric impregnated with activated carbon particles, or a chemical adsorbent, such as KMnO4, attached to activated alumina particles and encased). Thus, metallic impurities, acid or alkali ions, and org. substances are satisfactorily removed and a wafer which has a hydrophilic surface easily adsorbing an acidic or alkaline gas and is useful for assessing the cleanness of an environmental atmosphere is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor wafer cleaning method and a semiconductor manufacturing environment cleanliness evaluation method using the same.

[0002]

2. Description of the Related Art Conventionally, as a method for evaluating the environmental atmosphere cleanliness for each area in a semiconductor clean room, in addition to measurement by a dust counter, a silicon wafer from which fine particles have been sufficiently removed is left for a predetermined time. Then, the method of measuring the falling particles on the surface with a laser light scattering surface adhering particle measuring device has been performed.

In the semiconductor device manufacturing process, contaminants that adversely affect the yield and quality assurance include fine particles and metallic elements. Particularly harmful Na, Fe, Ca, etc. are suspended in the air as salt molecules, but the source is
Corrosion of workers or metal parts of the equipment is considered. Therefore,
It is necessary to evaluate the environmental atmosphere cleanliness of such metal components for each region in the semiconductor clean room.

Such evaluation of the environmental atmosphere cleanliness is carried out by leaving a cleaned silicon wafer from which metal has been sufficiently removed in an inspection area for a predetermined time, decomposing wafer surface deposits with HF vapor and collecting it in a small amount of liquid. It was carried out by analyzing the metal component by atomic absorption method or the like.

However, the environmental atmosphere cleanliness to be controlled has disappeared not only for fine particles and metals. For example,
A trace amount of HCl, HF, acidic gas such as H ₂ SO ₄ , alkaline gas such as NH ₃ , and various organic molecules that contaminate the air affect various devices in the clean room, and these are adsorbed on the wafer itself. In some cases, it has been found that the adhesion of various harmful metals is promoted, and it has become a problem that the production is hindered as the device is advanced. Even if strong local exhaust is performed to prevent this, such chemical substances leak into the clean room from the process equipment for various processes such as cleaning / etching, but cause a problem. Has a sufficient amount (about several ppb) of environmental pollution. Further, since the HEPA filter has no ability to remove gaseous impurities, the gaseous impurities in the atmosphere outside the factory pollute the clean room environment and have a similar effect.

Therefore, in various areas in the clean room, it is necessary to inspect and manage polluted non-metallic substances in the environmental atmosphere as well as particulate and metal contamination. Conventionally, an impinger or beaker containing ultrapure water in this inspection area was left for a long time to allow the acidic gas and alkaline gas in the environmental atmosphere to be absorbed by this ultrapure water, and this was analyzed to analyze the environmental atmosphere contamination level. Is being evaluated. In this case, the pollution level in the environment in question is a few ppb or less, which is considerably lower than the target concentration for general pollution problems. The law is taking place.

[0007]

However, in the conventional environmental atmosphere cleanliness evaluation method in which ultrapure water is allowed to stand for a long time to absorb the test air and used as an analysis sample, the use of an impinger requires a suction device and there are many points. It is not suitable for measurement, and using a beaker has a problem that the pure water left standing evaporates and decreases considerably quickly, which causes an error. Further, in a high temperature area such as the vicinity of the furnace, it is particularly necessary to evaluate the environmental atmosphere, but it is difficult to perform the inspection by this method because the amount of the pure water left is reduced quickly. Furthermore, setting a container containing water limits the inspection place.

By the way, the hydrophilicized wafer is supposed to adsorb on the surface a substance which is easily dissolved in water together with water in the air. Similar to the above-mentioned abandoned wafers used for the evaluation of environmental pollutant fine particles and the abandoned wafers used for the evaluation of environmental pollutant metals, evaluation of organic substances that are easily adsorbed on the acid gas, alkaline gas and silicon surface If there is a left-use wafer for the purpose, it is possible to ideally evaluate the environmental atmosphere under the same conditions by placing three left-use wafers at the same place without restriction on the inspection place. For this purpose, it is necessary to prepare a silicon wafer from which acid ions, alkali ions and organic substances are sufficiently removed, and a wafer cleaning treatment method for producing such a silicon wafer is required.

If such a wafer is produced, it is left in the inspection area for a predetermined time, the adsorbed substances on the wafer surface are eluted into a small amount of ultrapure water, and the ions of acid and alkali are measured by ion chromatography, and the organic substances are measured by TOC. The purpose of environmental atmosphere evaluation can be achieved by analyzing with a vessel.

In cleaning the wafer,
First, metallic impurities must be removed from the surface. When the metal impurities remain on the surface, there is a possibility that some of the ions adsorbed on the wafer surface will not be eluted into the ultrapure water by binding with the metal impurities. Wet cleaning with a chemical solution is considered to be most effective for removing metal impurities. For example, HCl-H ₂ O _{2 cleaning, H 2 SO 4 -H 2 O} 2 washing (performed for particular particulate _{removal) NH 4 OH-H 2 O} 2 cleaning, rare HF cleaning (especially natural oxide film , Etc.) are known and are often used.

However, in the case of washing with HCl-H ₂ O ₂ , Cl ions remain on the surface after rinsing and drying with ultrapure water, and in the case of washing with H ₂ SO ₄ —H ₂ O _2, SO ₄ ions are washed. Remains on the surface. Another NH ₄ O
In the H-H ₂ O ₂ cleaning, NH ₄ ions are more rare H
In F cleaning, there is a problem that F ions remain on the surface, and the amount of each of them is 10 ¹³ atoms /
It is known to be on the order of cm ² . Also, in all of the above four cleaning methods, C was detected by Auger electron spectroscopy on the surface after rinsing and drying with ultrapure water, and it was found that all of them have problems in terms of removing organic substances.

The inventor of the present invention forms a natural oxide film on the silicon surface in the above cleaning methods (1) and (2), so that Cl and SO ₄ ions are trapped in the natural oxide film during cleaning. It was thought that it could not be removed by a pure water rinse, and a rare HF cleaning was performed after these cleanings. However, as a result of total reflection X-ray fluorescence analysis, Cl and SO ₄
Of about ¹³ atoms / cm ² was also detected. Similar results have already been reported in academic journals by Rutherford backscattering analysis.

As a cleaning method capable of surely confirming the removal of organic substances on a silicon wafer by Auger electron spectroscopy, a dry cleaning method of irradiating with ultraviolet rays (wavelengths 1850Å and 2537Å) is known. 1850 Å generates O ₃ from O ₂ in the air, and this O ₃ absorbs 2537 Å ultraviolet rays to generate O radicals. Due to the strong oxidizing action of O ₃ and O radicals and the dissociative action / excitatory action of ultraviolet rays, organic substances are decomposed into CO, CO ₂ , and H ₂ O, which are scattered and removed. However, it is said that the inorganic salt cannot be removed by this method. In fact, the above-and-
This UV dry cleaning was performed after cleaning
O ₄ removal for could not be.

Therefore, an object of the present invention is to sufficiently remove metal impurities, acid ions, alkali ions and organic substances,
Another object of the present invention is to provide a processing method for producing a wafer having a hydrophilic surface that easily adsorbs an acidic gas or an alkaline gas and useful for evaluation of environmental atmosphere cleanliness.
Another object of the present invention is to provide a method for evaluating environmental atmosphere cleanliness using a wafer processed by the above method.

[0015]

According to the present invention, a wafer is treated with ultraviolet rays and ozone in an area isolated from the outside in an air circulation type clean bench equipped with a filter containing activated carbon and a chemical adsorbent. A method of processing a wafer is provided that is performed to form a hydrophilic silicon surface that is free of non-metal ions.

Further, according to the present invention, in a region isolated from the outside in an air circulation type clean bench equipped with a filter containing activated carbon and a chemical adsorbent, treatment with ultraviolet rays and ozone is performed to perform non-metal ion treatment. A wafer with a hydrophilic silicon surface that does not contain is formed, and the wafer is exposed to the atmosphere inspection region by sealing the wafer in an airtight case in circulating air that has been subjected to the treatment and carrying out a predetermined time. This provides a method of adsorbing impurities on a hydrophilic surface in an atmosphere and evaluating the environmental atmosphere cleanliness by analyzing the adsorbed material.

(Wafer Processing Method) In the wafer processing method of the present invention, a filter containing activated carbon and a chemical adsorbent means a combination of an activated carbon type filter and a chemical adsorbent type filter.

Activated carbon filters are especially suitable for organic substances and NH.
₃ is an effective filter for adsorption removal, such as a case packed with activated carbon particles, a pleated form by impregnating activated carbon fine particles into a plastic woven fabric, or a pleated activated carbon fiber woven fabric. There are things.

As a chemical adsorbent filter, K
It is known that a chemical adsorbent such as MnO ₄ is impregnated into activated alumina particles and packed in a case, or a woven cloth of ion exchange resin fiber is pleated, and any of these can be used. Is. K as a chemical adsorbent
When MnO ₄ is used, NO ₂ and SO ₂ are oxidized and N
These become acid ions such as O ₃ ⁻ and SO ₄ ²⁻ , and KOH, which is decomposed and produced at the same time, neutralizes this and these are captured by the filter. In the ion exchange resin fiber, both acid and alkali ions are captured by the resin. Also KMnO ₄
Alternatively, a chemical adsorbent such as iodine and alkali which is attached to the activated carbon type filter to integrate both adsorption functions can be used in the present invention. The same reaction mechanism as in the case of using KMnO ₄ is also obtained in the case of impregnating iodine with alkali.

The removal efficiency of these chemisorption filters is often about 90 to 98%. However, according to the present invention, since the air circulation type clean bench is equipped with the filter, these filters can be repeatedly acted to obtain high removal performance. gas, nO _2, sO ₂ and organic substances is to be created air the substantial absence.

In the present invention, the treatment of the wafer with ultraviolet rays and ozone is carried out in the circulating air in the above clean bench. For the treatment with ultraviolet rays, it is preferable to use one having a wavelength near 1850 Å and a low-pressure mercury lamp having a wavelength near 2537 Å in parallel, and irradiate the wafer as close as possible. The intensity of the ultraviolet light may be such that the hydrophobic surface of the wafer can be made hydrophilic by irradiation for a predetermined treatment time, for example, 10 minutes. Since ozone is generated by this 1850Å UV irradiation in ozone treatment, it is not necessary to use a special source, but of course, it is also possible to shorten the treatment time by separately providing a generator and spraying it onto the wafer. . Organic substances are first reliably removed from the surface of the wafer thus treated.

In the present invention, as the wafer to be subjected to the above treatment, a silicon wafer immediately after being subjected to a natural oxide film removal treatment after being washed with an oxidizing chemical solution for removing metal contamination on the silicon surface is used. Are suitable for removing non-metal ions.

The oxidizing chemical solution for removing metal contamination is a cleaning solution containing hydrogen peroxide such as ammonia water and hydrogen peroxide and water, hydrochloric acid and hydrogen peroxide and water, sulfuric acid and hydrogen peroxide, or concentrated nitric acid. A chemical solution containing nitric acid like aqua regia,
It is a cleaning liquid used for removing metal contamination on silicon wafers in the semiconductor industry, and may have any composition as long as a natural oxide film of 10 Å or more is formed after the cleaning treatment depending on the treatment temperature and treatment time. For example, wash with sulfuric acid and hydrogen peroxide at 130 ° C, 1
For 0 minute treatment, the preferred composition is hydrogen peroxide 1
Concentrated sulfuric acid is 1 to 5 volumes relative to the volume.

The natural oxide film removal treatment means washing with an oxidizing chemical solution, rinsing with ultrapure water for 10 minutes or more, followed by treatment with diluted hydrofluoric acid, and rinsing again with ultrapure water for 10 minutes or more. This is the process of storing in water. The concentration of dilute hydrofluoric acid may be a concentration that can reliably make the hydrophilic surface hydrophobic according to the treatment temperature and treatment time. For example, if the treatment is carried out at room temperature for 1 minute, a preferable composition is 10 to 50 water per 1 volume of hydrofluoric acid. It is good. In addition to the dilute hydrofluoric acid treatment, an organic strong alkali such as tetramethylammonium hydroxide 0.1% by weight and a nonionic surfactant such as a polyoxyethylene alkylphenol ether 0.1% by weight aqueous solution are used for 10 minutes. You may perform alkaline natural oxide film removal processing which heat-processes to a degree.

According to the present invention, it is desirable to treat the silicon wafer with ultraviolet rays and ozone immediately after the above natural oxide film removal treatment, but specifically, a wafer pulled from ultrapure water is as short as possible. It can be set in the UV / ozone treatment area in time. Once set, there is no limit to the time to start UV irradiation as long as the clean bench is operating. Therefore, it is most preferable to pull the wafer from the ultrapure water near the ultraviolet irradiator in the clean bench having the ultraviolet / ozone treatment area.

When the present inventor cleans and dries semiconductor wafers in the air circulation region in the clean bench for performing the above-mentioned processing, the ions detected in the natural oxide film are only those derived from the main component of the cleaning liquid. I found a thing. Conventionally,
It is understood that most of the Cl and SO ₄ detected on the clean wafer were always contaminated from the clean room ambient air. For example, when a wafer is treated with a cleaning solution containing HCl, only Cl ions remain in the natural oxide film at about 10 ¹³ atoms / cm ² . Further, such residual ions are 10 ¹⁰ at at the next natural oxide film removing step.
It is removed to the order of oms / cm ² , that is, to a substantially clean level.

Further, in such a natural oxide film removing process, rare H
When F is used, F ions are 10 ¹³ atoms / cm ²
Adsorb to bare silicon surface. However, when the hydrophilicity, that is, the natural oxide film (SiO ₂ film) is formed by the treatment of ultraviolet rays and ozone, the reaction of SiO ₂ + F ⁻ → SiF ₄ ↑ produces gaseous SiF ₄ at room temperature, and this natural oxide film is generated. It was found that F ions were eliminated.

When the natural oxide film is removed by treatment with an organic alkali / surfactant solution, trace amounts of these chemicals are adsorbed on the bare silicon surface, but these are completely removed by ultraviolet rays / ozone. Disassemble and scatter. The natural oxide film formed by UV / ozone treatment is extremely hydrophilic, and the contact angle of water drops is about 2 °. Therefore, this natural oxide film has the ability to strongly absorb harmful gas impurities in the environment together with moisture in the air. Therefore, the environmental atmosphere cleanliness evaluation can be easily performed by leaving the wafer. As described above, according to the treatment of the present invention, acid / alkaline gas, NO
_A clean wafer having a superhydrophilic natural oxide film containing no ₂ , SO ₂ and organic substances can be obtained.

(Evaluation of Environmental Atmosphere Cleanliness) According to the present invention, the environmental atmosphere cleanliness is evaluated using the clean wafer processed by the above method. That is, by sealing the wafer in an airtight case in the circulating air that has been subjected to the above treatment, carrying it to the atmosphere inspection region, and exposing the wafer surface for a predetermined time, impurities are adsorbed in the atmosphere on the hydrophilic surface. Then, the environmental atmosphere cleanliness can be evaluated by analyzing the adsorbed material.

As an airtight case, for example, a plastic case for carrying a silicon wafer may be thoroughly washed and further dried in a nitrogen atmosphere at 100 ° C. or higher to be used. In this cleaning, the required cleanliness can be obtained by treating with a strong organic alkaline cleaning solution for a long time.
On the other hand, this plastic case easily adsorbs organic substances and acid / alkaline gas from the environment while standing, and unless careful attention is paid to storage management after cleaning, there is a risk that these will come off during wafer storage and contaminate the wafer. There is. For this reason, it is most preferable to use an airtight case made of aluminum or an airtight case whose inner surface is made of aluminum. This is because they are extremely easy to clean and store.

The analysis of the adsorbed substance can be carried out by various methods known per se, whereby the cleanliness degree in the atmosphere can be easily controlled.

[0032]

【Example】

Example 1 A clean bench having the structure shown in FIG. 1 was assembled. That is, in the clean bench 1 of FIG. 1, a blower 2 is used for chemical filter 3 (felt-like activated carbon fiber woven cloth is pleated) and HE for removing fine particles.
After passing through the PA filter 4, the ultraviolet / ozone-treated region 5, and the suction grid 6, through the duct 7, and further through the chemical filter 8 (filled with activated alumina particles (trade name Purafil) impregnated with KMnO ₄ ), again. Air is circulated so as to return to the blower 2.

In this clean bench, the ultraviolet / ozone treatment region becomes dust cleanliness class 10 within 5 minutes after the start of operation. Also impinger put ultrapure water samples the air was analyzed by ion chromatography and TOC measurement _{device, HCl, HF, H 2 SO} 4, NO
₂ , SO ₂ 0.1 ppb or less, TOC 0.3 μg /
At m ³ (below the detection limit), it was found that the chemical pollutants in the air were substantially removed.

Next, the above-mentioned ultraviolet / ozone treatment area 5
A low-pressure mercury lamp 9 and a wafer mounting table 10 that generate ultraviolet rays of 1850Å and 2573Å are installed therein. A door that can be opened and closed is provided on the front surface of the region 5 so that the region 5 can be completely insulated from the outside air during the ultraviolet ray / ozone treatment and for a few minutes after the treatment is completed.

In the same manner as in the semiconductor manufacturing process, a so-called SC-containing 1 volume of ammonia water, 1 volume of hydrogen peroxide and 5 volumes of water is used.
The hydrophilic silicon wafer cleaned by the standard method of No. 1 is immersed in dilute hydrofluoric acid in a quartz container containing 1 volume of hydrofluoric acid and 50 volumes of water until the surface is sufficiently hydrophobicized, and then flowed in ultrapure water. Was added to rinse the wafer for 10 minutes without exposing it to the outside air, and the wafer was transferred to a region 5 in the clean bench while being kept in ultrapure water. Hydrophobic wafer 11
Was gradually pulled up from the ultrapure water 12, and after it was confirmed that no water droplets remained on the wafer, it was placed on the wafer platform 10 and irradiated with ultraviolet rays until the wafer surface became hydrophilic. In a commercially available low-pressure mercury lamp for irradiating a silicon wafer, a superhydrophilic surface having a water droplet contact angle of about 2 ° was obtained in 5 minutes or less. Therefore, it is clear that the surface is substantially free of organic matter.

This wafer was dipped in 50 ml of ultrapure water to elute NH ₄ ions, F, Cl, SO ₄ ions and NO _{2 on the surface} into ultrapure water and measured by ion chromatography. The detection limit in terms of surface concentration was 10 ¹¹ ions / cm ² or less. Therefore, a surface substantially free of acid / alkali ions, NO _{2 and} organic matter was obtained. Also, a mercury lamp that emits 2573 Å ultraviolet rays 1
When 3 is put in, most of the ozone generated in the mercury lamp 9 is decomposed, the decomposed gas is completely absorbed by the filter 3, there is no ozone leak outside the device, and the mercury lamp 9 is not irradiated. It was confirmed that the ozone in the clean bench was completely lost within a few minutes after the operation was stopped and it was completely harmless in terms of work.

Example 2 As a filter 3 of Example 1, Extraction Systems I
The same test as in Example 1 was carried out except that an iodine / alkali impregnated pleated activated carbon filter (trade name: 1073K) manufactured by nc. was used and the chemical filter 8 was omitted, but there was almost no significant difference. Results were obtained.

Example 3 HC labeled with radioisotope ³⁶ Cl in high-purity air
1 was added thereto, adjusted to 1 ppb and filled in a container of about 1 m ³ , and the wafer prepared in Example 1 was left therein for 2 hours. The radioactivity of this wafer was measured by a radioluminography technique using an imaging plate.
It was found that there was 2 μg of adsorbed HCl. The limit of detection by the ion chromatograph when the HCl adhering to the wafer surface is dissolved in 50 ml of ultrapure water is 2.5 μg. Therefore, when the wafer prepared in Example 1 was left in the environment atmosphere inspection region for 2 hours for evaluation, it was found that at least 0.1 ppb of HCl in the atmosphere could be detected.

Example 4 The wafer prepared in Example 1 was placed in an ultraviolet / ozone treatment area 5 in a clean bench, sealed in an airtight aluminum case, and carried to an atmosphere inspection area for 2 hours. Exposed and left. A beaker containing 50 ml of ultrapure water was placed at the same inspection point, and this beaker was left for 8 hours. The exposed wafer adsorbate was dissolved in 50 ml of ultrapure water and subjected to ion chromatographic analysis together with the water left in the beaker. The results are shown in Table 1. Since the trends are similar and both methods are not methods of measuring absolute airborne concentrations, but methods of relatively assessing cleanliness and controlling environmental conditions, the wafer leaving method of the present invention is sufficient. I see that I can reach my goal.

[0040]

[Table 1]

[0041]

As the wafer for environmental atmosphere evaluation obtained by the processing method of the present invention, a normal cleaned wafer in a semiconductor manufacturing process is used, and the atmosphere is left in an environment to be evaluated to remove harmful gas impurities in the atmosphere. Can be adsorbed and can be used for analysis and evaluation by an ion chromatograph or a TOC measuring instrument. Conventionally, it was left in a liquid state, but it can be sampled and analyzed by a wafer leaving method similar to that for evaluation of fine particles, and since the hydrophilicity of the wafer surface is high, it is left standing for 2 to 5 hours for evaluation. be able to.

Further, this wafer processing method can be used as a cleaning method particularly when it is necessary to remove non-metal ions and organic substances in the semiconductor device manufacturing process. The air required for this UV / ozone treatment does not require a high-purity air cylinder, etc., and can be used as it is because the environmental air is sufficiently cleaned, and the ozone generated is completely contained in the air circulation system. Therefore, it is not necessary to separately provide an exhaust ozone decomposition treatment device. Therefore, in the treatment method of the present invention, the ultraviolet / ozone treatment device essentially requires only a mercury lamp in a clean bench,
Extremely simplified. Since this method is generally applicable to the case where a wafer-shaped object is treated with ultraviolet rays or ozone, it has a very high industrial value.

[Brief description of drawings]

FIG. 1 is a diagram showing the structure of a clean bench for carrying out the treatment method of the present invention used in Example 1.

[Explanation of symbols]

 1: Clean bench 2: Blower 3: Chemical filter 4: HEPA filter 5: UV / ozone treatment area 7: Duct 8: Chemical filter

Claims (4)

[Claims] 1. A hydrophilic wafer that does not contain non-metal ions by treating a wafer with ultraviolet rays and ozone in an area isolated from the outside in an air circulation type clean bench equipped with a filter containing activated carbon and a chemical adsorbent. A wafer processing method for forming a silicon surface. 2. The silicon wafer immediately after being subjected to a natural oxide film removal treatment after being washed with an oxidizing chemical solution for removing silicon surface metal contamination is used as the wafer to be subjected to the treatment. Wafer processing method. 3. Hydrophilicity that does not contain non-metal ions by treatment with ultraviolet rays and ozone in an area isolated from the outside in an air circulation type clean bench equipped with a filter containing activated carbon and a chemical adsorbent. By making a wafer with a silicon surface formed, sealing the wafer in an airtight case in circulating air that has been treated, and carrying it to the atmosphere inspection area, and exposing the wafer surface for a predetermined time, the hydrophilicity is improved. Impurity is adsorbed on the surface in the atmosphere and the adsorbed material is analyzed to evaluate the cleanliness of the atmosphere. 4. The environmental atmosphere evaluation method according to claim 3, wherein at least the inner surface of the hermetic case is aluminum.