JPH04310513A - Measurement of concentration of impurities in polycrystalline silicon - Google Patents

Abstract

PURPOSE:To enable to finely and repeatedly measure the concentration distribution of impurities in polycrystalline silicon even by an IR ray absorption method by thermally treating a measurement specimen of the polycrystalline silicon, and subsequently subjecting the treated specimen to a surface finishing treatment. CONSTITUTION:The measurement is characterized by heating a measurement specimen of polycrystalline silicon at a temperature of >=1200 deg.C in a non- oxidative atmosphere for one hr or longer, and subsequently subjecting the treated specimen to a surface-finishing treatment so that the thickness of the measurement specimen is substantially the same as that of a standard specimen. A leading time until the measurement is thereby shortened.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for easily measuring impurity concentration in polycrystalline silicon.

0002

[Prior Art] Conventionally, silicon (Si)
) has only been measured for single crystal silicon. The outline will be explained with reference to a block diagram of a double beam spectrometer used in the infrared absorption method shown in FIG. The luminous flux from the light source 1 is alternately switched by a luminous flux switch 2 to the sample luminous flux side where the measurement sample 3 is located and the standard luminous flux side where the standard sample 4 is located, and the intensity difference between the two luminous fluxes is incident on the detector 5 as an alternating current signal. The output of the detector 5 is amplified by an amplifier 6a, etc., and the servo motor 7 is operated to move the beam attenuator 8 placed on the standard beam side, thereby balancing the intensities of both beams. When the intensities of both light beams are balanced, the output of the detector 5 becomes 0 and the servo motor 7 stops. At this time, the amount of movement of the luminous flux attenuator 8 is the ratio C of the sample luminous flux intensity Is and the standard luminous flux intensity Ir.
Is/Ir (C is a constant), and the amount of movement of the light flux attenuator 8 is recorded on the recorder 9. Therefore, the recording curve records the transmittance Is/Ir, and the transmittance curve can be obtained immediately.

On the other hand, for polycrystalline silicon, the absorption peak of impurities cannot be measured because the transmittance Is/Ir varies greatly. For this reason, the impurity concentration of the single crystal silicon is measured either by activation analysis, which is a destructive test, or by pulling a single crystal by the floating zone method and then measuring the impurity concentration in the obtained single crystal silicon by an infrared absorption method.

0004

[Problems to be Solved by the Invention] However, since activation analysis is a destructive test, there is a problem in that it is not possible to measure the impurity concentration at immediately adjacent points or to repeatedly measure it. Furthermore, when monocrystalline silicon is produced using the floating zone method, the impurity concentration can be measured as an average value for the entire polycrystalline silicon, but there is a problem in that the impurity concentration in a limited portion cannot be measured.

The present invention was made in order to eliminate the drawbacks of the prior art, and an object of the present invention is to provide a method for measuring the impurity concentration in polycrystalline silicon, which allows detailed and repeated measurements of the impurity concentration distribution in polycrystalline silicon. It is said that

[0006]

[Means and effects for solving the problems] In order to achieve the above object, the present inventors have continued their intensive research. As a result, they discovered that by heat-treating a polycrystalline silicon measurement sample, then surface-finishing it, and then measuring the impurity concentration using an infrared absorption method, the impurity concentration can be measured with high accuracy using an infrared absorption method.

That is, the heating temperature is 120℃ in a non-oxidizing atmosphere.
By heat-treating at 0°C or higher for 1 hour or more and finishing the surface so that the thickness of the measurement sample is almost the same as that of the standard sample, it is possible to precisely and repeatedly measure the impurity concentration distribution of polycrystalline silicon. We have found the advantage of shortening the lead time and solved the above problems.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the method for measuring impurity concentration in polycrystalline silicon according to the present invention will be explained in detail with reference to the accompanying drawings. FIG. 1 is a schematic process diagram showing a method for measuring carbon concentration in polycrystalline silicon according to an embodiment of the present invention.

First, in the first step shown in FIG. 1, a sample with a length of 15 mm or more is obtained from a round rod of polycrystalline silicon, and in the second step, a square shape of 15 x 20 mm or more is cut from this sample using a diamond cutter. Cut out the measurement sample. In the third step, this measurement sample is roughly processed by grinding with a grinder, ultrasonic cleaning, and etching.

[0010] In the fourth step, the rough-processed measurement sample is heated in a non-oxidizing atmosphere at 1200° C. or more for 1 hour or more to perform heat treatment. The preferred heating temperature is 1250-1300℃
It is.

In the fifth step, the heat-treated measurement sample is finished by lapping, ultrasonic cleaning, etching, and mirror finishing with diamond paste. In the case of a simple method, only etching may be used.

In the sixth step, the carbon absorption peak of the finished measurement sample is measured by an infrared absorption method and converted into carbon concentration using a standard calibration curve.

FIG. 2 is a transmittance curve of a measurement sample subjected to heat treatment according to the present invention, where the vertical axis shows the transmittance and the horizontal axis shows the wavelength. Since the baseline of the absorption peak in the transmittance curve is almost flat, the absorption peak (Pc) of carbon can be measured. For comparison, FIG. 3 shows a transmittance curve (prior art) of the measurement sample before heat treatment. The transmittance curve fluctuates greatly and the carbon absorption peak (Pc) cannot be measured.

FIG. 4 is a chart showing the relationship between heat treatment conditions and carbon concentration, where the vertical axis is the carbon concentration and the horizontal axis is the heat treatment time. Carbon concentration can be measured if the heat treatment temperature is 1200℃ or higher, but the preferable heat treatment temperature is 1250-1
The temperature is 300°C.

FIG. 5 shows transmittance curves of various thicknesses of the measurement sample according to the present invention when the thickness of the standard sample is 1880 μm, and FIG.
B) shows a case where the thickness is 1880 μm, and FIG. 2C shows a case where the thickness is 1860 μm. As shown in Figure (B), if the thickness of the measurement sample and the standard sample are the same, the baseline is almost flat. Therefore, if the difference in thickness between the measurement sample and the standard sample is kept within 10 μm, good.

FIG. 6 shows transmittance curves for various carbon concentrations of the measurement sample according to the present invention, and (A) of the same figure shows the absorption coefficient α
is 1.108 cm-1, carbon concentration [Cs] is 0.8
In the case of 2 x 1017 atoms/cc, the same figure (B) shows that the absorption coefficient α is 0.435 cm-1 and the carbon concentration [Cs]
When is 0.32×1017 atoms/cc, the same figure (
In C), the absorption coefficient α is 0.141 cm-1 and the carbon concentration [Cs] is 0.11×1017 atoms/cc. In the same figure (D), the absorption coefficient α is 0 and the carbon concentration [Cs]
Indicates the case where is not measurable. From these results, 0.11
Absorption peaks (Pc) can be measured up to a carbon concentration [Cs] of x1017 atoms/cc.

FIG. 7 shows an example of the oxygen concentration of a measurement sample according to the present invention. FIG. A peak (Pc) is observed. The same figure (B) is the transmittance curve (prior art) of the measurement sample before heat treatment, and 11
Although the absorption peak decreases around 0.05 cm-1, it cannot be measured because the width of the absorption peak is too wide.

As explained above, according to the present invention, impurities can be detected by infrared absorption method by heat treating a polycrystalline silicon measurement sample and keeping the difference between its thickness and that of a standard sample within 10 μm. Concentration can be measured. Therefore, the impurity concentration distribution of polycrystalline silicon can be precisely and repeatedly measured, and the lead time until measurement can be shortened.

[Brief explanation of the drawing]

FIG. 1 is a schematic process diagram showing a method for measuring carbon concentration in polycrystalline silicon according to an example of the present invention.

FIG. 2 is a chart showing transmittance curves of measurement samples subjected to heat treatment according to the present invention.

FIG. 3 is a chart showing transmittance curves of measurement samples before heat treatment in the prior art.

FIG. 4 is a chart showing the relationship between heat treatment conditions and carbon concentration.

FIGS. 5A, 5B, and 5C are charts showing transmittance curves of various thicknesses of measurement samples according to the present invention.

FIG. 6 (A), (B), (C), and (D) are charts showing transmittance curves of various carbon concentrations of measurement samples according to the present invention.

FIG. 7 (A) is a chart showing the oxygen transmittance curve of a measurement sample subjected to heat treatment, and FIG. 7 (B) is a chart showing the oxygen transmittance curve of the measurement sample before heat treatment. .

FIG. 8 is a block diagram of a double beam spectrometer used in infrared absorption method.

[Explanation of symbols]

2... Luminous flux switch 3...Measurement sample 4...Standard sample 8... Luminous flux attenuator

Claims (3)

[Claims] 1. A method for measuring impurity concentration in polycrystalline silicon, which comprises heat-treating a polycrystalline silicon measurement sample, surface-finishing the sample, and then measuring the impurity concentration by an infrared absorption method. 2. The method for measuring impurity concentration in polycrystalline silicon according to claim 1, wherein the heat treatment is performed in a non-oxidizing atmosphere at a heating temperature of 1200° C. or more and a heating time of 1 H or more. 3. Measurement of impurity concentration in polycrystalline silicon according to claim 1, wherein the surface finishing is performed so that the thickness of the measurement sample is approximately the same as the thickness of the standard sample. Method.