JPH11248693A - Method for analyzing impurities in liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple and convenient method for analyzing impurities in liquid by using the characteristics of a silicon wafer. SOLUTION: This analyzing method comprises dipping a silicon wafer in a liquid and then analyzing matters deposited on the surface of the silicon wafer taken out of the liquid to analyze impurities contained in the liquid. In this case, after the surface of the silicon wafer is hydrotreated, it is dipped in the liquid. The hydrogenation treatment is preferably conducted by bringing the silicon wafer into contact with hydrofluoric acid and then rinsing it with water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for analyzing impurities in a liquid using a silicon wafer.

[0002]

2. Description of the Related Art A lot of washing water, storage solution, etc. are used in a manufacturing site of various products. Some products require that the concentration of impurities in the washing water, storage solution, etc. be kept below a certain value. Can be

For example, a silicon wafer for a semiconductor substrate is deteriorated in electrical characteristics when contaminated with a metal or the like. Therefore, impurities such as cleaning water and a storage solution used in each step of a method for manufacturing a silicon wafer are used. The concentration is controlled so as to be equal to or less than a certain value, and for that purpose, analysis is performed by various methods. As one of conventional methods for analyzing impurities such as metals, there is a method using a silicon wafer. This is a method of indirectly analyzing impurities in a liquid by, for example, dropping a liquid to be analyzed for impurities on a silicon wafer and then analyzing the surface of the silicon wafer. JP-A-136738, JP-A-5-251542, JP-A-9-151
No. 74 discloses this.

[0004]

However, the method disclosed in the above publication requires an operation such as concentration of a liquid serving as a sample, and thus requires an apparatus and time for concentration. . Further, in the method disclosed in the above publication, although a silicon wafer is used, it is merely used as a clean sample stage and its characteristics are not actively used.

[0005] In view of the above problems, an object of the present invention is to provide a simple method for analyzing impurities in a liquid utilizing characteristics of a silicon wafer.

[0006]

In order to solve the above-mentioned problems, the invention according to the first aspect of the present invention is to immerse a silicon wafer in a liquid and then apply the silicon wafer to the surface of the silicon wafer taken out of the liquid. A method for analyzing impurities in a liquid, comprising analyzing an attached substance to analyze impurities contained in the liquid, wherein the surface of the silicon wafer is hydrogenated, and then immersed in the liquid. And

The hydrogenation process is a process for replacing the terminal of the silicon crystal layer on the surface of the silicon wafer with hydrogen atoms. For example, the surface of a silicon wafer is treated with hydrofluoric acid (aqueous solution of hydrogen fluoride, hereinafter referred to as hydrofluoric acid).
It is known that a natural oxide film on the surface of a silicon wafer is etched by being treated with water and the terminal of the silicon crystal layer is replaced with a hydrogen atom, which is suitable for the hydrogenation treatment in claim 1. Can be used. As a specific method, as in claim 5, immersing the silicon wafer in hydrofluoric acid, or contacting the silicon wafer with hydrofluoric acid by any method such as applying hydrofluoric acid vapor to the silicon wafer, and then Rinse with water. In the invention of claim 1, the hydrogenation treatment may be performed with hydrochloric acid or the like instead of hydrofluoric acid. Alternatively, in the hydrogenation treatment, the silicon wafer may be heat-treated in an atmosphere containing hydrogen,
As described above, the epitaxial growth may be performed on the surface of the silicon wafer.

By subjecting a silicon wafer to such a hydrogenation treatment, Si—H bonds are generated on the surface of the silicon wafer, that is, most of the ends of the silicon crystal layer are replaced by hydrogen atoms. (Hydrogen termination).

According to a second aspect of the present invention, an impurity contained in the liquid is analyzed by immersing the silicon wafer in a liquid and then analyzing a substance attached to the surface of the silicon wafer taken out of the liquid. A method for analyzing impurities in a liquid, wherein a part of the surface of the silicon wafer is subjected to hydrogenation treatment and then immersed in the liquid. In claim 2, the method of hydrotreating is the same as in claim 1.

In the silicon wafer according to the second aspect of the present invention, a natural oxide film is formed on a portion of the surface other than the surface which has been subjected to the hydrogenation treatment, as in the third aspect of the invention, or in the fourth aspect of the present invention. The thermal oxide film may be formed as in the invention described in (1).

Further, in the second to fourth aspects, a portion subjected to a specific treatment or the like other than a portion subjected to a hydrogenation treatment and a portion where an oxide film is formed is formed on the surface of the silicon wafer. May be.

[0012] In the method for analyzing impurities in a liquid according to any one of claims 1 to 7, the substance adhering to the surface of the silicon wafer may be a total reflection X-ray fluorescence analysis method as in the invention according to claim 8. May be analyzed by

In the method for analyzing impurities in a liquid according to any one of the first to seventh aspects, the analysis of the substance attached to the surface of the silicon wafer as in the invention according to the ninth aspect is performed by chemical analysis. It may be performed by an analysis method. Chemical analysis methods include, for example,
The impurities attached to the silicon wafer surface are collected, and the collected liquid is further processed as necessary, and various analysis methods such as plasma emission analysis, atomic absorption analysis, ion pair chromatography, and electrophoresis are performed. Analysis method. When the impurity is a metal, it may be reacted with a specific reagent to form a complex, and the metal complex may be analyzed by these various analysis methods.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for analyzing impurities in a liquid according to the present invention will be described below. In the method for analyzing impurities in a liquid according to the present invention, the impurities contained in the liquid are analyzed by immersing the silicon wafer in the liquid and then analyzing the substance attached to the surface of the silicon wafer taken out of the liquid. In the method of analyzing impurities in a liquid, after hydrogenating the surface of the silicon wafer,
It is characterized by being immersed in the liquid.

In the present invention, the liquid to be analyzed for impurities is water or a chemical used in the manufacturing process of various industrial products. For example, a silicon wafer after polishing in a semiconductor substrate manufacturing process is stored. Water, an abrasive, a rinsing liquid for etching, and the like.

As the silicon wafer used in the present invention, a silicon wafer which has been processed and polished for a semiconductor substrate and whose surface has been subjected to a hydrogenation treatment is used. The hydrogenation process is a process for replacing the terminal of the silicon crystal layer on the surface of the silicon wafer with hydrogen atoms. By treating the surface of the silicon wafer with hydrofluoric acid (aqueous solution of hydrogen fluoride, hereinafter referred to as hydrofluoric acid) and then with water, the natural oxide film on the silicon wafer surface is etched, and the terminal of the silicon crystal layer is terminated. It is known that it is substituted by a hydrogen atom, and this can be suitably used for the hydrogenation treatment of the present invention. As a specific method, a silicon wafer is immersed in hydrofluoric acid for several tens of seconds, and then rinsed in a pure water tank for several tens of seconds. The hydrofluoric acid used here may be one generally used in a semiconductor substrate manufacturing process, and the concentration of hydrogen fluoride is 0.5% by weight or more.
50% by weight. Further, a hydrofluoric acid vapor may be applied to the silicon wafer. In this case, hydrofluoric acid having the same concentration as that in the immersion method is applied at 24 ° C. and 760 torr.
Vaporization is performed under the conditions of r, and the silicon wafer is placed in the gas. After that, similarly to the above, rinsing is performed in the pure water tank. Further, in the same manner as described above, hydrogenation treatment may be performed with hydrochloric acid, sodium hydroxide, or the like instead of hydrofluoric acid.

Further, the silicon wafer may be subjected to a heat treatment in a hydrogen atmosphere to perform a hydrogenation treatment. Further, the silicon wafer of the present invention may be a so-called epi wafer. This is because the wafer immediately after the epitaxial growth is usually in a state in which the surface is terminated with hydrogen, and can be used as the silicon wafer of the present invention.

With respect to the silicon wafer of the present invention, only a part of the surface may be hydrogenated by the above-described method. In this case, the part of the surface of the silicon wafer that has not been subjected to the hydrogenation treatment may be in a state where the natural oxide film is formed. In addition, an oxide film formed chemically, for example, an oxide film formed using a solution containing hydrogen peroxide such as a mixed solution of ammonia, hydrogen peroxide and water (SC-1 solution) used for cleaning. You may.

A thermal oxide film may be formed on a portion of the surface of the silicon wafer that has not been subjected to the hydrogenation treatment. In this case, as the thermal oxidation method, various methods such as dry O ₂ oxidation, wet O ₂ oxidation, steam oxidation, and hydrogen combustion oxidation can be used. For example, in the case of dry O ₂ oxidation, a silicon wafer is placed in a furnace at 900 ° C. to 1200 ° C., and thermal oxidation is performed by flowing a mixed gas of nitrogen and oxygen into the furnace.

Further, the surface of the silicon wafer of the present invention may have a hydrogenated portion, an oxide film formed portion, and a portion subjected to other processes. , A nitride film or the like.

In the analysis method of the present invention, the silicon wafer subjected to such a treatment is immersed in a liquid to be analyzed. By immersion, a substance that easily adheres to the silicon wafer terminated by hydrogen selectively adheres. Specifically, when a hydrogen-terminated silicon wafer is immersed in a liquid, metal atoms such as gold, silver, and copper, which have a lower ionization tendency than hydrogen atoms, are replaced with hydrogen atoms, and the silicon wafer surface is replaced with hydrogen atoms. Adhere to. The immersion time is sufficient for the impurities to be adsorbed to be sufficiently adsorbed on the surface of the silicon wafer, and is immersed for several tens of seconds to several days depending on the type of liquid and the type of impurities.

When a silicon wafer having a hydrogenated portion and an oxide film-formed portion is immersed in a liquid, the oxide film-formed portion exhibits different properties from the hydrogenated portion, Metal atoms, such as gold, silver, and copper, are unlikely to adhere and zinc, which does not adhere very much to the hydrogenated surface, selectively adheres.

After the immersion, the silicon wafer is pulled up and dried. Drying may be natural drying, forced drying, such as spinning with a spinner, drying under reduced pressure, etc., and further, if necessary, heating.

Next, impurities adhering to the surface of the dried silicon wafer are analyzed using various methods. A particularly useful analytical method is total reflection X-ray fluorescence analysis. In this analysis method, a dried silicon wafer is placed on a predetermined position of a total reflection X-ray fluorescence spectrometer, and when the silicon wafer is irradiated with X-rays, specific energy and intensity are determined depending on the type and amount of impurities. The emitted fluorescent X-rays are emitted and are detected. In addition, a chemical analysis method is also useful.
The impurities attached to the silicon wafer surface are collected, and the collected liquid is further processed as necessary, and various analysis methods such as plasma emission analysis, atomic absorption analysis, ion pair chromatography, and electrophoresis are performed. Analysis method. When the impurity is a metal, it may be reacted with a specific reagent to form a complex, and the metal complex may be analyzed by these various analysis methods.

According to the method for analyzing impurities in a liquid described above, the silicon wafer whose surface has been hydrogenated is immersed in the liquid to be analyzed, so that it can easily adhere to the silicon wafer terminated by hydrogen atoms. The substance can be analyzed. That is, it is possible to selectively analyze a specific substance by utilizing the characteristics of the surface of the silicon wafer. In addition, since the analysis method utilizes the adsorption of a specific substance on the surface of the silicon wafer, it is possible to analyze impurities without performing concentration of a liquid or the like. Become.

Further, in the method of analyzing impurities in a liquid according to the present invention, when a silicon wafer whose surface is partially hydrogenated is used, one silicon wafer is immersed in the liquid, and the hydrogenation treatment is performed. A substance that easily adheres to the surface subjected to the treatment and a substance that easily adheres to the part that has not been hydrogenated can be analyzed at a time. In this case, if a silicon wafer with an oxide film formed on the non-hydrogenated part is immersed in a liquid, a substance that easily adheres to the hydrogenated surface and a substance that adheres to the part where the oxide film is formed This makes it possible to analyze substances that are easy to perform at once, which is a more convenient analysis method.

In the present invention, since the substance adhering to the silicon wafer is analyzed by the total reflection X-ray fluorescence spectroscopy, the silicon wafer adhering to the impurities in the liquid can be directly set in a measuring instrument. It is only necessary to perform other processing on the silicon wafer, and the method for analyzing impurities is simpler.

In the present invention, impurities may be analyzed using a silicon wafer on which an oxide film is formed and another hydrogenated silicon wafer.

The method for analyzing impurities in a liquid according to the present invention is particularly useful in a semiconductor manufacturing process in which various liquids are used in multiple stages and contamination by impurities is reluctant. However, the present invention is not limited to this, and can be used for analysis of impurities such as various other industrially used cleaning liquids and immersion liquids.

Further, in the above embodiment of the present invention, a metal is exemplified as an impurity. However, an impurity to be analyzed in the present invention is one which is liable to adhere to a silicon wafer on which a hydrogenation treatment or an oxide film is formed. If this is the case, it may be an analysis target, for example, an inorganic substance other than metal, or an organic compound or protein.

[0031]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. 1. Hydrogenation treatment of silicon wafer surface A plurality of mirror-polished silicon wafers (8 inches in diameter, 725 microns in thickness) are prepared, and half of the surface is masked with a tape. Hydrofluoric acid (hydrogen fluoride, 1.5% by weight) is put into a beaker, and each of the masked silicon wafers is placed in the hydrofluoric acid for about 30 minutes.
Soaked for seconds. When the natural oxide film was removed, the wafer surface in that portion repelled the liquid (made water-repellent), and observation from the outside also revealed that the oxide film was removed. As a result, a processed wafer shown in FIG. 1 in which only half was subjected to the hydrogenation treatment was obtained. In FIG. 1, the portion A is a portion subjected to a hydrogenation treatment, and the portion B is a portion where a masked natural oxide film is formed.

2. Analysis of Impurities (1) Analysis of Water Tank for Storage of Silicon Wafer Ordinary semiconductor substrates are often stored in a water tank filled with pure water after polishing is completed. The impurities in the silicon wafer storage tank were analyzed. First, add 20 l of pure water to the water tank.
(Liter) was stored, and a polished silicon wafer for a substrate (diameter: 8 inches) was put therein and stored for 5 hours. Thereafter, all of the silicon wafers for the substrate were taken out, and then the treated wafer subjected to the hydrogenation treatment with the hydrofluoric acid obtained in 1 was immersed. The processed wafer was taken out after 240 minutes, left for 12 hours, and dried by natural drying.

The surface of the dried processed wafer was analyzed by a total reflection X-ray fluorescence analyzer (TREX610, Technos Co., Ltd.). The result is shown in FIG.
FIG. 2A shows copper (C) adhering to a silicon wafer.
The results for u) are shown, where the length of each bar indicates the density of copper atoms in that portion. In this graph, the maximum value was 100 × 10 ¹⁰ atoms / cm ² .

For comparison, a silicon wafer (unprocessed wafer) on which a natural oxide film has not been subjected to hydrofluoric acid treatment and on which a natural oxide film has been formed is also simultaneously subjected to 240 μm.
2 minutes in the water tank and analyzed in the same manner.
(B). As is clear from FIG. 2, copper is hardly adhered to the silicon wafer covered with the natural oxide film and the portion where the natural oxide film is formed, but the portion subjected to the hydrogenation treatment is not It can be seen that much copper adhered.

Therefore, it was found that copper selectively adhered to the hydrogenated silicon wafer and could be analyzed as impurities.

(2) Analysis of Water Tank for Storing Silicon Wafers Contaminated intentionally After 20 l of pure water was stored in the water tank, copper (Cu), iron (Fe), and zinc (Zn) powders were respectively added to a water tank. 8p
It was added to a concentration of pb. The treated wafer obtained in 1 was immersed in pure water to which these metals were added. It was taken out after 10 hours, left for 12 hours, and dried by natural drying.

The surface of the treated wafer after drying was analyzed with a total reflection X-ray fluorescence analyzer (TREX610, Technos Co., Ltd.). The result is shown in FIG.
FIG. 3A is for copper, and FIG.
Similarly, (c) shows the results for zinc, and the length of each bar indicates the density of atoms in that portion. The maximum value shown in these graphs is 19 for copper.
4 × 10 ¹⁰ atoms / cm ² , iron was 66 × 10 ¹⁰ atoms / cm ² , and zinc was 252 × 10 ¹⁰ atoms / cm ² . As is clear from FIG. 3, a large amount of zinc adheres to the portion where the native oxide film is formed, and almost no copper adheres, but a large amount of copper adheres to the hydrogenated portion. It can be seen that zinc does not adhere much. Also,
Iron did not adhere very much to either side.

Therefore, copper selectively adheres to the portion subjected to the hydrogenation treatment, and zinc selectively adheres to the portion where the oxide film is formed, and these can be analyzed as impurities. I understood.

Further, by selectively adhering and concentrating impurities on the surface of the wafer, unnecessary noise at the time of analysis can be reduced. In addition, in this example, only the presence / absence of impurities and qualitative evaluation results are described, but the hydrogenation method, immersion time, liquid temperature, analysis method, etc. are unified, and the By preparing a calibration curve of the impurity concentration and the amount of adhesion to the wafer, the impurities in the liquid can be quantitatively analyzed.

[0040]

According to the first, fifth, sixth and seventh aspects of the present invention, a specific substance is adsorbed on the surface of a hydrogenated silicon wafer, and the liquid is not concentrated. This makes it possible to analyze impurities, which is a simple method for analyzing impurities.

According to the second, fifth, sixth and seventh aspects of the present invention, the concentration of a liquid or the like is performed by utilizing the fact that a specific substance is adsorbed on a hydrogenated portion of the surface of a silicon wafer. The analysis of the impurities can be performed without performing the method, and the method for analyzing impurities is simple.

According to the third and fourth aspects of the present invention, by utilizing the surface characteristics of a silicon wafer, a substance which easily adheres to a surface subjected to hydrogenation treatment and a substance which adheres to a portion where an oxide film is formed This makes it possible to analyze substances that are easy to perform at once, which is a more convenient analysis method.

According to the eighth and ninth aspects of the present invention, in addition to the effects of the first to seventh aspects, the analysis can be performed more easily.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a silicon wafer used in the present invention.

FIG. 2 is a graph showing a result of analyzing impurities in a water tank for storing silicon wafers in Examples.

FIG. 3 is a graph showing a result of analyzing impurities in a water tank for storing silicon wafers intentionally contaminated in an example.

Continued on the front page (72) Inventor Hideyuki Fujisawa 1393, Ojiro, Yashiro, Nagano Prefecture Nagano Electronics Industry Co., Ltd. (72) Inventor Tadao Tanaka, 1393, Oyashiro, Daishodai, Nagano Prefecture, Japan

Claims (9)

[Claims] 1. A method for analyzing impurities contained in a liquid by immersing a silicon wafer in a liquid and then analyzing a substance attached to a surface of the silicon wafer taken out of the liquid to analyze impurities contained in the liquid. An analysis method, wherein the surface of the silicon wafer is hydrogenated, and then immersed in the liquid. 2. A method in which a silicon wafer is immersed in a liquid, and then a substance attached to a surface of the silicon wafer taken out of the liquid is analyzed to analyze impurities contained in the liquid. An analysis method, wherein a part of the surface of the silicon wafer is hydrogenated and then immersed in the liquid. 3. The method for analyzing impurities in a liquid according to claim 2, wherein a silicon wafer having a natural oxide film formed on a part other than the part of the surface is immersed in the liquid. . 4. The analysis of impurities in a liquid according to claim 2, wherein a silicon wafer having a thermal oxide film formed on a part other than the part of the surface is immersed in the liquid. Method. 5. The method according to claim 1, wherein the hydrogenation treatment is performed by bringing the silicon wafer into contact with hydrofluoric acid and then rinsing with water. Analysis method of impurities. 6. The method for analyzing impurities in a liquid according to claim 1, wherein the hydrogenation treatment is performed by heat-treating the silicon wafer in an atmosphere containing hydrogen. 7. The method for analyzing impurities in a liquid according to claim 1, wherein the hydrogenation treatment is performed by epitaxial growth on the surface of the silicon wafer. 8. The method for analyzing impurities in a liquid according to claim 1, wherein the substance attached to the surface of the silicon wafer is analyzed by total reflection X-ray fluorescence analysis. 9. The method for analyzing impurities in a liquid according to claim 1, wherein the substance attached to the surface of the silicon wafer is analyzed by a chemical analysis method.