JPH0795031B2 - Method for measuring impurity concentration in polycrystalline 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 easily measuring the impurity concentration in polycrystalline silicon.

[0002]

2. Description of the Related Art Conventionally, silicon (S
The measurement of the impurity concentration in i) is performed only for single crystal silicon. The outline will be described with reference to the block diagram of the double-beam spectroscopic device used in the infrared absorption method shown in FIG. The light flux from the light source 1 is alternately switched to the sample light flux side with the measurement sample 3 and the standard light flux side with the standard sample 4 by the light flux switch 2, and the intensity difference between the two light fluxes is incident on the detector 5 as an AC signal. The output of the detector 5 is the amplifier 6a
And the like to operate the servo motor 7 to move the luminous flux attenuator 8 placed on the standard luminous flux side to balance the intensity of both luminous fluxes. When the intensities of the two light beams are balanced, the output of the detector 5 becomes 0 and the servo motor 7 stops. At this time, 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 luminous flux attenuator 8
Is recorded in the recorder 9. Therefore, the recording curve records the transmittance Is / Ir, and the transmittance curve is immediately obtained.

On the other hand, regarding polycrystalline silicon, the absorption peak of impurities cannot be measured because the fluctuation of the transmittance Is / Ir is large. Therefore, it is measured by activation analysis which is a destructive inspection, or single crystal pulling is performed by the floating zone method once, and the impurity concentration of the obtained single crystal silicon is measured by the infrared absorption method.

[0004]

However, since activation analysis is a destructive inspection, there is a problem that it is not possible to measure the impurity concentration at a point immediately next to it or repeatedly measure it. Further, when single crystal silicon is formed by the floating zone method, the impurity concentration can be measured as an average value of the entire polycrystalline silicon, but the impurity concentration in a limited portion cannot be measured.

The present invention has been made in order to solve 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 enables fine and repeated measurement of the impurity concentration distribution in polycrystalline silicon. I am trying.

[0006]

Means and Actions for Solving the Problems In order to achieve the above object, the inventors of the present invention have conducted extensive research. As a result, it has been found that the impurity concentration can be accurately measured by the infrared absorption method by subjecting the measurement sample of polycrystalline silicon to a heat treatment, surface finishing, and then measuring the impurity concentration by the infrared absorption method.

That is, the heating temperature is 120 in a non-oxidizing atmosphere.
By heat-treating at 0 ° C or more and heating time for 1H or more, and by finishing the surface so that the thickness of the measurement sample is almost the same as the thickness of the standard sample, the impurity concentration distribution of polycrystalline silicon can be measured finely and repeatedly The present invention has solved the above-mentioned problems by finding the advantage that the lead time until the product becomes short.

[0008]

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

First, in the first step of FIG. 1, a sample having a length of 15 mm or more is obtained from a round rod of polycrystalline silicon, and in the second step, a diamond cutter is used to cut a rectangular piece of 15 × 20 mm or more from the sample. Cut out the measurement sample.
In the third step, this measurement sample is roughly processed by grinder grinding, ultrasonic cleaning and etching.

In the fourth step, the rough-processed measurement sample is heated in a non-oxidizing atmosphere at 1200 ° C. or higher × 1 H or higher for heat treatment. The preferred heating temperature is 1250 to 1300 ° C.
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 absorption peak of carbon of the finished measurement sample is measured by the infrared absorption method and converted into carbon concentration by a standard calibration curve.

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

FIG. 4 is a table showing the relationship between the heat treatment conditions and the carbon concentration. The vertical axis is the carbon concentration and the horizontal axis is the heat treatment time. If the heat treatment temperature is 1200 ° C or higher, the carbon concentration can be measured, but the preferable heat treatment temperature is 1250 to 1
It 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. 5A shows the case where the thickness is 1900 μm. B) shows the case where the thickness is 1880 μm, and FIG. 7C shows the case where the thickness is 1860 μm. If the thickness of the measurement sample is the same as that of the standard sample as shown in FIG. 7B, the baseline is almost flat. Therefore, if the thickness difference between the measurement sample and the standard sample is within 10 μm, Good.

FIG. 6 shows transmittance curves of various carbon concentrations of the measurement sample according to the present invention. FIG. 6A shows the absorption coefficient α.
Is 1.108 cm ^-1 , and the carbon concentration [Cs] is 0.8.
In the case of 2 × 10 ¹⁷ atoms / cc, the figure (B) shows that the absorption coefficient α is 0.435 cm ⁻¹ and the carbon concentration [Cs].
Is 0.32 × 10 ¹⁷ atoms / cc, the same figure (C) shows that the absorption coefficient α is 0.141 cm ⁻¹ and the carbon concentration [Cs] is 0.11 × 10 ¹⁷ atoms / cc. D) has an absorption coefficient α of 0 and carbon concentration [C
[s] indicates that measurement is impossible. From these results, 0.
Carbon concentration of 11 × 10 ¹⁷ atoms / cc [C
The absorption peak (Pc) can be measured up to [s].

FIG. 7 shows an example of the oxygen concentration of the measurement sample according to the present invention. FIG. 7A is a transmittance curve of the measurement sample subjected to the heat treatment, and shows the oxygen concentration absorption at around 1105 cm ^−1. A peak (Pc) is recognized. FIG. 11B is a transmittance curve (prior art) of the measurement sample before heat treatment.
Although it decreased at around 05 cm ^-1 , it cannot be measured because the width of the absorption peak is too wide.

As described above, according to the present invention, the sample to be measured of polycrystalline silicon is heat-treated, and the difference between the thickness of the sample and the thickness of the standard sample is set within 10 μm. The concentration can be measured. Therefore, it is possible to obtain an effect that the impurity concentration distribution of the polycrystalline silicon can be measured finely and repeatedly and the lead time until the measurement becomes short.

[Brief description of drawings]

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

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

FIG. 3 is a chart showing a transmittance curve of a measurement sample before heat treatment in a conventional technique.

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

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

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

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

FIG. 8 is a block diagram of a double-beam spectroscopic device used in the 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 the impurity concentration in polycrystalline silicon, which comprises subjecting a sample for measurement of polycrystalline silicon to a heat treatment, finishing the surface of the sample, and then measuring the impurity concentration by an infrared absorption method. 2. The method for measuring the 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 higher and a heating time of 1 H or longer. 3. The measurement of the impurity concentration in polycrystalline silicon according to claim 1, wherein the surface finish is such that the thickness of the measurement sample is substantially the same as that of the standard sample. Method.