JP2002039927A - Partial analysis method for surface layer of silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a partial analysis method, in which the concentration of impurities in only the desired part of a silicon wafer can be measured with high accuracy. SOLUTION: The silicon wafer is placed on the opening of a container, in which an acid mixed solution of hydrofluoric acid and nitric acid is put. The partial surface layer part, to be analyzed of the silicon wafer, is faced with the acid mixed solution. The silicon wafer is heated from the opposite direction of a face facing the acid mixed solution. Vapor is generated from the acid mixed solution. An ammonium silicofluoride thin film is generated by the vapor on the part surface layer part of the silicon wafer. The generated ammonium silicofluoride thin film is dissolved, heated and concentrated, it is heated, gasified and introduced so as to be analyzed by an ICP mass analyzer, and metal impurities are measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial analysis method for a surface layer of a silicon wafer which can analyze a part of the surface layer of a single crystal silicon wafer.

[0002]

2. Description of the Related Art High integration of semiconductor devices requires silicon wafers of higher and higher purity. For this reason, it is required to analyze and measure the impurity concentration of the surface layer of the silicon wafer with high accuracy. Recently, it has been required to partially analyze the impurity concentration in the surface layer of a silicon wafer as a part thereof.

Conventionally, a method of measuring impurities in the surface layer of a silicon wafer is to directly dissolve the surface layer of the silicon wafer by etching using a mixed acid of nitric acid and hydrogen fluoride in a container, and to dissolve metal impurities contained in the solution. A method for measuring is known. In addition, instead of using a mixed acid solution of nitric acid and hydrogen fluoride, a method of directly dissolving a silicon wafer using a mixed acid vapor in a container and measuring metal impurities contained in the solution is also known. In particular, it has been pointed out that the latter method uses an acid vapor, so that there is no problem such as a decrease in measurement accuracy due to a trace amount of impurities contained in the acid solution of the etching solution. However, since this method involves etching in a fine condensed portion of an acid vapor generated by leaving the acid naturally, it takes time, and it is difficult to uniformly etch the entire surface layer. There is a problem that the thickness is less than 1 μm. Therefore, it is also practiced to heat the mixed acid from the outside of the container and bring it into contact with the vaporized wafer. However, even with this method, since the entire surface of the silicon wafer is etched, the partial impurity concentration in the surface layer of the silicon wafer cannot be grasped, making it difficult to cope with the production of a high-purity silicon wafer.

[0004]

SUMMARY OF THE INVENTION According to the present invention, an impurity concentration of only a desired portion of a surface layer of a silicon wafer can be measured with high accuracy. Then, a thin film of ammonium silicofluoride is formed only in a part of the silicon wafer by the vapor generated from the acid solution, and the thin film of the ammonium silicate is analyzed to measure the metal impurities in the part of the surface layer of the silicon wafer.

[0005]

According to the present invention, a silicon wafer is placed on an opening of a container containing a mixed solution of hydrofluoric acid and nitric acid, and a partial surface layer portion of the silicon wafer to be analyzed is acidified. The silicon wafer is heated in the opposite direction to the surface facing the acid mixture to generate vapor from the acid mixture, and the vapor causes a thin film of ammonium silicofluoride on the partial surface layer of the silicon wafer. Is dissolved, and the resulting thin film of ammonium silicofluoride is dissolved and concentrated by heating.
A partial analysis method for a surface layer of a silicon wafer, characterized in that metal impurities are measured by analyzing with a CP mass spectrometer (Claim 1). The silicon wafer according to claim 1 or 2, wherein the method is a partial analysis method for a surface layer of a silicon wafer according to claim 1, which has substantially the same shape as the shape (claim 2), and the acid mixture is an acid mixture further containing hydrochloric acid. This is a partial analysis method for a surface layer (claim 3).

[0006]

FIG. 1 shows a partial analysis method of a surface layer of a silicon wafer according to one embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a silicon wafer for analyzing the impurity concentration at two analysis points 2 and 3 on the surface layer. The lower surface of the surface layer of the analysis points 2 and 3 to be analyzed of the silicon wafer 1, close contact against the opening 6 of the container 5 _1, 5 ₂ containing the acid mixture 4 of hydrofluoric acid and nitric acid. The ratio of hydrofluoric acid and nitric acid used here is the same as the mixing ratio of hydrofluoric acid and nitric acid used in conventional impurity analysis of silicon wafers.
Use a hydrofluoric acid with a higher ratio than nitric acid. Also,
In the present invention, as the mixed acid used here, the above hydrofluoric acid,
What added hydrochloric acid to nitric acid can also be used.
By adding hydrochloric acid, etching becomes more uniform. In this case, the added amount of hydrochloric acid is 10 to 20% by weight of the whole acid. If the amount of hydrochloric acid is too large, the ratio of hydrofluoric acid and nitric acid decreases, and the surface layer of the silicon wafer cannot be sufficiently etched. Vessel 5 ₁ containing the mixture 4 of hydrofluoric acid and nitric _acid, 5 _second opening 6
Is airtightly inside bottom surface outer circumference in close contact with the container 5 _1, 5 ₂ of the surface layer of the analysis points 2 and 3 to be analyzed of the silicon wafer 1. The container used here is made of, for example, polytetrafluoroethylene (PTFE) or perfluoroalkoxyl (PFA) which has high acid resistance and little impurities. The silicon wafer can be brought into close contact by being placed on the opening of the container. In FIG. 1, surface impurities are measured at two portions of the silicon wafer 1. However, it is of course possible to measure impurities in one narrow area. As shown in FIGS. 2 and 3, impurities can be measured in arbitrary areas of the silicon wafers 8 and 9 indicated by broken lines. In this case, it is necessary to change the shape of the opening of the container according to the shape of the measurement area.

Next, the silicon wafer 1 faces the mixed acid.
Heat the surface opposite to the surface layer 7₁, 7 ₂I do. Here
The heating is performed by, for example, a surface heater or an infrared lamp. This
Container 5 by heating₁, 5₂From mixed acid mixture 4
Vapor is generated, and this vapor causes the surface of the silicon wafer
Ammonium silicofluoride thin film is formed on the parts 2 and 3
Is done. The heating temperature here is preferably 100 ° C
And the heating time depends on the thickness of the etching.
Of the order of minutes. When etching is completed,
Remove the lower container of the con-wafer 1 and remove the silicon wafer.
The thin film of ammonium silicofluoride formed at the bottom of the wafer
Recover with recovery liquid. The recovery liquid used here is, for example,
Mix acid, hydrochloric acid and pure water at a predetermined ratio, for example, 1: 1: 8
Use what was done. This recovered liquid is then concentrated by heating.
ICP (Inductively Coupled High Frequency Plasma)
Analyze with a mass spectrometer, etc.
The amount of metal impurities in the portion is measured.

[0008]

EXAMPLE As shown in FIG. 1, a mixed acid of hydrofluoric acid and nitric acid (hydrofluoric acid / nitric acid (weight ratio)) was placed in a container having an opening diameter of 20 mm.
= 60/50) 5 ml was put in close contact with the central portion of an 8-inch diameter silicon wafer and two places 10 mm inward from the outer periphery, and this portion was kept airtight. As hydrofluoric acid, high-purity hydrofluoric acid for ULSI (SH-16, trade name of Daikin Industries, Ltd.) was used, and as nitric acid, nitric acid for electronics industry (EL grade product manufactured by Kanto Chemical Co., Ltd.) was used. The container used was a polytetrafluoroethylene container.

In this state, the opposite side of the portion of the silicon wafer applied to each container is heated to 130
At 20 ° C. for 20 minutes, each part of the silicon wafer on the contact side of each container was etched at a thickness of 3 μm to form ammonium silicofluoride. Thereafter, each container containing the acid container was removed, and ammonium silicofluoride formed on the surface layer of the wafer was recovered with nitric acid (concentration 70%), hydrochloric acid (concentration 20%), and pure water in a ratio of 1: 1: 8. The liquid was collected in 500 ml. Next, the recovered liquid was concentrated, and the collected liquid was analyzed by a heated vaporization-introduced ICP (inductively coupled high frequency plasma) mass spectrometer to measure metal impurities in each part of the silicon wafer. The results are shown in the following table.

[0010]

[Table 1]

[0011]

As described above, according to the present invention, the analysis of partial impurities in a silicon wafer can be clearly understood. This is a matter that could not be predicted by conventional analysis of the entire surface of a silicon wafer. This makes it possible to obtain higher purity semiconductor chips from each silicon wafer. Further, according to the present invention, it is possible to easily measure a metal impurity in an arbitrary area of a silicon wafer, so that the management of the silicon wafer can be performed more strictly than before.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a partial analysis method of a surface layer of a silicon wafer according to one embodiment of the present invention.

FIG. 2 is an explanatory view showing an analysis part of a silicon wafer used in the analysis method according to one embodiment of the present invention;

FIG. 3 is an explanatory view showing another analysis portion of the silicon wafer used in the analysis method according to one embodiment of the present invention.

[Explanation of symbols]

 1, 8, 9 ... silicon wafer, 2, 3 ... analysis pieces
Place, 4 ... acid mixture, 5₁ , 5₂…… Container, 6 ……
Vessel opening, 7₁, 7₂...... Heating direction.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 1/28 K N

Claims (3)

[Claims] 1. A silicon wafer is placed in an opening of a container containing an acid mixture of hydrofluoric acid and nitric acid, and a partial surface layer portion of the silicon wafer to be analyzed faces the acid mixture. The wafer is heated from the direction opposite to the surface facing the acid mixture to generate vapor from the acid mixture, and the vapor forms a thin film of ammonium silicofluoride on the partial surface layer of the silicon wafer. 1. A partial analysis method for a surface layer of a silicon wafer, comprising: dissolving a thin film of ammonium fluoride, heating and concentrating the thin film, and analyzing the thin film by a heating-vaporization ICP mass spectrometer to measure metal impurities. 2. The method according to claim 1, wherein the shape of the opening of the container of the acid mixture is substantially the same as the shape of the portion of the silicon wafer to be analyzed. 3. The method according to claim 1, wherein the acid mixture is an acid mixture further containing hydrochloric acid.