JPH063268A - Infrared absorption spectroscopic method for interstitial oxygen or substituted carbon concentration of silicon wafer - Google Patents

Abstract

PURPOSE:To provide an infrared absorbing spectroscopic method for interstitial oxygen or substituted carbon concentration of silicon wafer capable of more precisely determining oxygen concentration value. CONSTITUTION:An infrared absorbing spectroscopic method for interstitial oxygen or substituted carbon concentration of silicon wafer comprises the step of spline-interpolating the base line of absorption peak on the basis of the base line near the localized vibration absorption peak of oxygen or substituted carbon on the difference absorbance spectrum of a measuring wafer to a standard wafer; the step of determining the vibration absorbing coefficient of the oxygen or substituted carbon according to incident infrared ray spectroscopic method of parallel polarization angle by using the peak height from the base line of the spline interpolation to the localized vibration absorbing peak of the oxygen or substituted carbon; and the step of converting the vibration absorbing coefficient to interstitial oxygen concentration or substituted carbon concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared absorption spectroscopy method for measuring the concentration of interstitial oxygen or substitutional carbon in a silicon wafer, particularly a silicon wafer manufactured by the CZ method.

[0002]

2. Description of the Related Art Conventionally, as an infrared absorption spectroscopy method of interstitial oxygen or substitutional carbon concentration of a silicon wafer (in the following description, interstitial oxygen concentration is taken as an example), an infrared light transmission characteristic of a measurement wafer is used. And a reference wafer (oxygen-free FZ
It has been proposed that the interstitial oxygen concentration of the measurement wafer be obtained by measuring the infrared light transmission characteristics of the wafer.
204316).

As a method of measuring the interstitial oxygen concentration of a silicon wafer of this type, the present inventor measures the infrared light transmission characteristics of a measurement wafer and the infrared light transmission characteristic of a reference wafer to determine the interstitial oxygen concentration of the wafer. Suggested to seek. Further, the present inventor further proposed that when the measurement wafer and the reference wafer have different thicknesses, the thickness is corrected in calculating the interstitial oxygen concentration of the measurement wafer (Japanese Patent Application No. 4-75561). ). That is, the inventor has a first step of measuring the incident parallel polarized light intensity, a second step of measuring the light transmission characteristic of the reference wafer by making parallel polarized light incident on the reference wafer at Brewster's angle, and a measurement wafer. To the third step of measuring the light transmission characteristics of the measurement wafer by making parallel polarized light incident at Brewster's angle, the incident parallel polarization intensity measured in the first step, and the light of the reference wafer measured in the second step. A silicon wafer interstitial oxygen concentration measuring method including a fourth step of calculating the interstitial oxygen concentration of the measurement wafer from the transmission characteristic and the light transmission characteristic of the measurement wafer measured in the third step was proposed.

Conventionally, the oxygen concentration in a non-double-sided mirror-polished wafer such as a double-sided mirror-polished wafer, a single-sided mirror-polished wafer, a double-sided etched wafer, a mechanically-polished (lap) wafer, etc. has been measured by parallel polarization Brewster angle incident infrared spectroscopy. When measuring, the baseline of the absorption peak is linearly interpolated based on the baseline near the local vibration absorption peak of oxygen on the differential absorption spectrum of the measurement wafer with respect to the reference wafer, and oxygen or The vibration absorption coefficient of oxygen is obtained according to the parallel polarization Brewster angle incident infrared spectroscopy with the peak height up to the localized vibration absorption peak of the substitutional carbon as the absorbance, and the vibration absorption coefficient is converted to the interstitial oxygen concentration.

For example, as shown in FIG. 1, 1106c on the differential absorption spectrum of the measurement wafer with respect to the reference wafer.
The baseline of the absorption peak due to the localized vibration of interstitial oxygen around m ⁻¹ is obtained by linear interpolation.

[0006]

By means of parallel polarization Brewster angle incidence infrared spectroscopy, especially single-sided mirror-polished wafers,
When measuring the oxygen concentration in non-double-sided mirror-polished wafers such as double-sided etched wafers and mechanically-polished (lapped) wafers, if linear interpolation is used, the baseline curvature will be large and correct baseline interpolation will not be possible. There is a drawback that the oxygen concentration value slightly deviated from the oxygen concentration can be obtained.

An object of the present invention is to provide an infrared absorption spectroscopy method of interstitial oxygen or substitutional carbon concentration of a silicon wafer, which can eliminate such drawbacks and more accurately determine the oxygen concentration value. That is.

[0008]

According to the present invention, the baseline of the absorption peak is determined based on the baseline in the vicinity of the localized vibration absorption peak of oxygen or substitutional carbon on the differential absorption spectrum of the measurement wafer with respect to the reference wafer. Spline interpolation step and vibration absorption of oxygen or substitutional carbon according to parallel polarization Brewster angle incident infrared spectroscopy with the peak height from the baseline of spline interpolation to the localized vibrational absorption peak of oxygen or substitutional carbon as absorbance. The gist is infrared absorption spectroscopy of interstitial oxygen or substitutional carbon concentration of a silicon wafer, which includes a step of obtaining a coefficient and a step of converting a vibration absorption coefficient into an interstitial oxygen concentration or a substitutional carbon concentration.

[0009]

[Examples] When measuring the interstitial oxygen concentration of a silicon wafer by parallel polarization Brewster angle infrared spectroscopy, the localized vibration peak of interstitial oxygen in the infrared absorption band related to oxygen, that is, the wave number of 1106 cm ^-1 band Use a nearby baseline. An example of the actual procedure for estimating the baseline is as follows.

First, the baseline in the case where there is no 1106 cm ^-1 band (that is, in the absence of oxygen) is based on the baseline in the vicinity of the 1106 cm ^-1 band on the difference absorbance spectrum between the measurement wafer and the double-sided mirror-polished reference wafer. Is spline-interpolated.

Next, the vibration absorption coefficient of oxygen or substitutional carbon is determined according to parallel polarization Brewster angle incidence infrared spectroscopy, using the peak height from the baseline of spline interpolation to the localized vibration absorption peak of oxygen as the absorbance. That is,
The baseline is subtracted from the difference absorbance spectrum between the measurement wafer and the double-sided mirror-polished reference wafer to obtain the absorbance spectrum (band) based on the local vibration of oxygen, and the peak height there is determined. The vibration absorption coefficient Ve is obtained by substituting in the following equation 1.

A = Ve · d / cosSr Equation 1 Here, Ve is a vibration absorption coefficient of localized vibration of oxygen (at a wave number of 1106 cm ⁻¹ ) d is a thickness of a measurement wafer Sr is a refraction angle (16. 3 °) Finally, the vibration absorption coefficient is converted into the interstitial oxygen concentration or the substitutional carbon concentration. That is, the interstitial oxygen concentration [Oi] is calculated according to the following equation 2.

[Oi] = K × Ve Equation 2 Here, K is a conversion coefficient.

Illustrative Example As shown in FIG. 1, the baseline of the absorption peak due to the localized oscillation of interstitial oxygen near 1106 cm ⁻¹ on the differential absorption spectrum of the measurement wafer with respect to the reference wafer is determined by spline interpolation to determine the interstitial oxygen concentration or Determine the substitutional carbon concentration.

A specific description will be given with reference to FIG. Diameter 5
The differential absorption spectrum between the measurement wafer and the double-sided mirror-polished reference wafer is measured by a parallel polarization Brewster angle incidence method with respect to a silicon wafer of inch (100) both sides (both front and back surfaces are mechanically polished (lapped)). On this differential absorption spectrum, three wave number regions 7 shown by arrows near the absorption band of the localized vibration of oxygen at 1106 cm ^-1
50 to 960 cm ^-1 , wave number region 1180 to 1190 cm
⁻¹ and the wave number region 1300 to 1460 cm ⁻¹ as a baseline, the baseline when there is no absorption at 1106 cm ⁻¹ (that is, when there is no oxygen) is spline-interpolated.

The vibration absorption coefficient of oxygen is determined according to parallel polarization Brewster angle incident infrared spectroscopy with the peak height from the baseline of spline interpolation to the localized vibration absorption peak of oxygen as the absorbance. That is, the interstitial oxygen concentration is calculated based on the peak height from the interpolated baseline. The conversion coefficient is 3.14 × 10 ¹⁷ atoms / cm ² .

As a result of actually measuring the silicon wafer by such a measuring method, the [Oi] of the double-sided mirror-polished reference wafer of the same [Oi] sampled from the same region in the same ingot as the reference wafer is 1.03 × 10. ¹⁸ atom
In contrast to s / cm ³ , the [Oi] measured on the measurement wafer was 1.02 × 10 ¹⁸ atoms / cm ³ , and both measured values were almost the same.

On the other hand, in linear interpolation, [Oi] is 0.
It is 983 × 10 ¹⁸ atoms / cm ³ , which does not match the standard [Oi] of the double-sided mirror-polished wafer.

Further, [Oi] was obtained according to the same procedure for similar measurement wafers (three laps) having different [Oi]. As a result, the results shown in Table 1 were obtained.

[Table 1] Double-sided mirror-polished wafer Present invention (spline interpolation) Conventional (linear interpolation) 0.280 × 10 ¹⁸ 0.293 × 10 ¹⁸ 0.245 × 10 ¹⁸ 1.939 × 10 ¹⁸ 0.947 × 10 ¹⁸ 0.893 × 10 ¹⁸ 0.732 × 10 ¹⁸ 0.746 × 10 ¹⁸ 0.704 × 10 ¹⁸ (unit atoms / cm ³ ) From the results of Table 1, the effectiveness of the present invention was confirmed.

The silicon wafer referred to in this specification is 1
Not only those having a thickness of 1 mm or less but also those having a thickness of 1 mm or more are included.

Modifications The present invention is not limited to the above-mentioned embodiments. For example, the present invention can be applied to a method of measuring the substitutional carbon concentration in the same manner as the interstitial oxygen concentration in the measurement wafer. In that case, the wave number caused by the vibration is set to 607 cm ⁻¹ instead of 1106 cm ⁻¹ , and the conversion coefficient K is 3.14 × 10 ¹⁷
To 0.81 × 10 ¹⁷ atoms / cm ² instead of pieces / cm ^2.

[0023]

According to the present invention, it is possible to measure the interstitial oxygen concentration or the substitutional carbon concentration in a measurement wafer with high accuracy even when the baseline is greatly curved in parallel polarization Brewster angle incidence infrared spectroscopy. Became. Of course, the present invention can be applied even when the linear interpolation of the baseline is sufficient.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of linear interpolation of a conventional method and an example of spline interpolation of a method of the present invention regarding a difference absorbance spectrum of a measurement wafer that has been mechanically polished (lapped) on both sides with respect to a reference wafer for double-sided mirror polishing.

FIG. 2 is a graph showing an example of linear interpolation of a conventional method and an example of spline interpolation of the method of the present invention with respect to a differential absorbance spectrum of a measurement wafer that has been mechanically polished (lapped) on both sides with respect to a reference wafer for double-sided mirror polishing. The absorbance is represented by log ₁₀ T ^-1 × 100, where T is the transmittance. The baseline of the spline interpolation is exaggerated and bent more than the actual one for the sake of clarity. ◆

Claims (1)

[Claims] 1. Infrared absorption spectroscopy of interstitial oxygen or substitutional carbon concentration of a silicon wafer, including the following steps. (A) a step of spline-interpolating the baseline of the absorption peak based on the baseline near the localized vibration absorption peak of oxygen or substitutional carbon on the differential absorption spectrum of the measurement wafer with respect to the reference wafer; and (b) the spline. A step of obtaining a vibrational absorption coefficient of oxygen or substitutional carbon according to parallel polarization Brewster angle incidence infrared spectroscopy, using a peak height from a baseline of interpolation to a localized vibrational absorption peak of oxygen or substitutional carbon as absorbance, c) A step of converting the vibration absorption coefficient into an interstitial oxygen concentration or a substitutional carbon concentration.