JPH07104333B2 - Method for measuring oxygen concentration in silicon - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring oxygen concentration in silicon, and more particularly to a method for preparing a sample used for oxygen concentration measurement by an inert gas dissolution analysis method and a vacuum dissolution method.

[0002]

2. Description of the Related Art In recent years, due to advances in semiconductor technology, particularly advances in microfabrication technology, high integration and miniaturization of devices have been progressing.

Under such circumstances, the purity of silicon used as a substrate has a great influence on the device characteristics and becomes a very serious problem.

Although various aspects have been measured to measure the purity of silicon, the oxygen concentration in silicon has a great influence on device design.
Various methods have been investigated to obtain accuracy.

To measure the oxygen concentration in silicon, activation analysis, secondary ion mass spectrometry, sub-infrared absorption method, inert gas dissolution analysis method or vacuum dissolution method is used.

Of these, the inert gas dissolution analysis method and the vacuum dissolution method are methods in which silicon of a predetermined size is heated and melted in an inert gas or in a vacuum, and oxygen generated during melting is measured.

In adopting this method, conventionally, a sliced piece of silicon in a wafer is diced into a predetermined size, and several pieces of the sliced pieces are used as a sample.

In this case, the surface area per weight of the sample is increased, the possibility of contamination and oxidation of the surface is increased, and the melting method is varied. There is a problem that the internal oxygen concentration cannot be measured.

[0009]

As described above, in the conventional measurement of the oxygen concentration of silicon, a sliced piece of silicon in a wafer is diced into a predetermined size, and several pieces are piled up as a sample. Since it is used, there is a problem that surface contamination and oxidation are likely to occur, and highly accurate internal oxygen concentration measurement cannot be performed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method capable of highly accurately measuring the internal oxygen concentration.

[0011]

Therefore, in the present invention, the silicon to be measured is cut into a bulk of a desired size, and this is used as a sample piece by heating and melting it in an inert gas or vacuum to generate it. I try to measure the oxygen concentration.

Further, preferably, the sample piece is a rectangular parallelepiped.

It is also desirable that the sample piece be a cube.

More preferably, the sample piece is spherical.

[0015]

According to the above method, since the silicon to be measured is cut into a bulk of a desired size and used, the dissolution state is constant and there is little variation, and the surface area per weight of the sample is reduced. It is possible to reduce the size, prevent contamination and oxidation of the surface, and improve the measurement accuracy.

Further, by making the shape of the sample piece into a rectangular parallelepiped, the surface area can be further reduced, the preparation of the sample piece and the calculation of the surface area are facilitated, and the conversion considering the oxygen concentration due to surface oxidation is facilitated. It can be performed, and the measurement accuracy can be further improved. Desirably, length: width: height = 1 ± 0.2: 1 ± 0.2: 1 ± 0.2
So that If the edge is rounded by chemical polishing or the like, damage to the edge when handling the sample can be prevented.

Furthermore, by making the shape of the sample piece a cube, the surface area can be further reduced, and the measurement accuracy can be further improved.

Further, by making the shape of the sample piece spherical, the surface area can be minimized and the measurement accuracy can be further improved.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Example 1 First, as shown in FIG. 1, after bulk silicon 1 is obtained by dicing, chemical polishing is performed to smooth the surface, and then the surface oxide film is removed by hydrofluoric acid treatment.

5 mm in length and 5 mm in height obtained in this way
Bulk silicon 1 mm is put in a crucible 2 made of carbon, and while flowing He gas as a carrier gas, 300
The infrared detector 3 detects the concentration of carbon monoxide CO generated by the reaction of oxygen in silicon with the carbon in the crucible by heating to 0 ° C. (a temperature above the melting point of silicon).
As shown in FIG. 2 and FIG. 3, the measurement results show that the measurement value can be obtained with very little variation according to this method.

For comparison, length 4 mm width 4 mm thickness 0.5 mm
As a sample, four silicon wafers were stacked and the same measurement was performed. The results are shown in FIGS. 4 and 5.

From a comparison of these results, it can be seen that the method of the present invention can significantly reduce variations in measured values.

Although the oxygen concentration is measured by using the infrared detector in the above-mentioned embodiment, it is needless to say that it is also effective when the oxygen concentration is measured by using the thermal conductivity detector.

Example 2 First, as shown in FIG. 6, a cube-shaped silicon 1 having a side of 4 mm obtained through a chemical polishing and a surface oxide film removing process after dicing was put in a carbon crucible, and Example 1 was used.
In the same manner as above, while flowing He gas as a carrier gas, it is heated to a temperature higher than the melting point of silicon (for example, 3000 ° C.), and the concentration of carbon monoxide CO generated by the reaction between oxygen in silicon and carbon in the crucible is detected by infrared ray To detect with a vessel.

Also in this case, it was possible to obtain measured values with very little variation, as in Example 1.

Example 3 First, as shown in FIG. 7, spherical silicon 1 having a radius of 2.7 mm obtained through a chemical polishing and a surface oxide film removing process after dicing was put in a crucible made of carbon, and Example 1 was used. In the same manner as 2 and 2, while flowing He gas as a carrier gas, heating to a temperature equal to or higher than the melting point of silicon (for example, 3000 ° C.), the concentration of carbon monoxide CO generated by the reaction between oxygen in silicon and carbon in the crucible Detect with infrared detector.

Also in this case, it was possible to obtain measured values with less variation than in Examples 1 and 2.

[0029]

As described above, according to the method of the present invention, the silicon to be measured is cut into a bulk of a desired size for use, so that the melting state is constant and varies. In addition, the surface area per weight of the sample can be reduced, contamination and oxidation of the surface can be prevented, and the measurement accuracy can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a method according to a first embodiment of the present invention.

FIG. 2 is a diagram showing measurement results of oxygen concentration obtained by the method of the first embodiment of the present invention.

FIG. 3 is a chart showing coefficient of variation obtained from the measurement results.

FIG. 4 is a diagram showing measurement results of oxygen concentration obtained by a method of a conventional example.

FIG. 5 is a chart showing the coefficient of variation obtained from the measurement results.

FIG. 6 is a diagram showing a sample used in the method of the second example of the present invention.

FIG. 7 is a diagram showing a sample used in the method of the third example of the present invention.

Claims (4)

[Claims] 1. A sample piece preparation step of cutting silicon to be measured into a bulk of a desired size , and heating and melting the sample piece in an inert gas or vacuum ,
And an oxygen concentration measuring step of measuring the generated oxygen concentration. 2. The method for measuring the oxygen concentration in silicon according to claim 1, wherein the sample piece is a rectangular parallelepiped. 3. The method for measuring oxygen concentration in silicon according to claim 1, wherein the sample piece is a cube. 4. The method for measuring the oxygen concentration in silicon according to claim 1, wherein the sample piece is spherical.