JPS6127904B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for measuring the impurity concentration of a semiconductor, and more specifically, a method for measuring the two-dimensional distribution of oxygen and carbon concentrations in a silicon wafer using a semiconductor laser in the infrared wavelength region. Regarding the method.

When oxygen and carbon exist as impurities in a silicon crystal, when irradiated with an infrared beam, oxygen absorbs a beam of 9.00μ and carbon absorbs a beam of 16.50μ depending on the concentration. The impurity concentration can be evaluated by measuring this absorption coefficient.

Conventionally, a method has been used in which a resistance heating element such as silicon carbide is used as an infrared light source, the light emitted from the element is separated into spectra using a diffraction grating or a prism, and a beam in a specific wavelength range is produced using a slit. In this method, the white light emitted from the light source is separated, so the light intensity is low, and the light beam diameter is large due to the characteristics of the resistive heating element. Therefore, it has been impossible in principle to measure the impurity concentration in a micro region, that is, 1 to 10 ⁶ μ ² in a silicon wafer.

In order to reduce the diameter of the light beam,
A method using a Pb ₁ - _x Sn _x Te (x=0.10 to 0.20) semiconductor laser as a light source has been proposed. The beam diameter of this laser beam can be focused within the range of 1 to 10 ³ μm.

The method of the present invention uses the above-mentioned semiconductor laser as a light source, and the laser light emitted from the laser beam is divided into spectra using a diffraction grating or a prism. In other words, when measuring the distribution of oxygen atoms, the distribution of oxygen atoms is 9.00μ, and when measuring the distribution of carbon atoms, it is 16.50μ. The laser beam is divided into μ laser beams, and the beam diameter is narrowed down to 20 to 30 μ using a slit. The silicon wafer is automatically moved two-dimensionally by a drive mechanism in a plane perpendicular to the optical axis plane of this laser beam, and the laser beam that is irradiated onto and transmitted through the silicon wafer is measured. Thereby, it is possible to accurately and quickly measure the absorption coefficient of oxygen or carbon present in each minute region of about 1 to 10 ⁶ μ ² on the silicon wafer, and to measure the concentration of these impurities.

FIG. 1 is an explanatory diagram of a spectroscopic system used in the method of the present invention. Pb ₁ ― _x Sn _x Te (x=0.10~
0.20) The semiconductor laser 1 is housed in the cryostat 2, and its temperature is maintained in the range of 1 to 100〓, preferably around 77〓. Power supply 3 stably supplies constant current in the range of 0.1 to 3A, and ± around the constant current value.
500mA current sweep is possible. When measuring the concentration of oxygen or carbon, first this current is
At 2A±500mA, change the wavelength of the oscillated laser beam and select the wavelength in the maximum absorption region of impurities.

In this way, the laser beam emitted from the laser 1 is converged through the lens 4, and then separated into spectra by the diffraction grating spectrometer 5. When the impurity to be detected is oxygen, it is extracted as 9.00μ, and when it is carbon, it is extracted as 16.50μ. Thereafter, the laser beam is converged with a lens 6, and further narrowed down to a beam diameter of 30 μm with a slit 7. The silicon wafer sample 8 is two-dimensionally moved by a sample drive device 9 in a plane perpendicular to the optical axis at intervals of 30 μm, which is the same as the diameter of the laser beam. The light transmitted through sample 8 is HgCdTe
The light intensity is measured by a semiconductor detector 10, the output of the detector 10 is amplified by an amplifier 11, and the output is amplified by a recorder 12.
Record with .

As described above, according to the present invention, since the semiconductor is scanned with a laser beam, it is possible to measure the impurity concentration two-dimensionally. Furthermore, since it is a laser beam, it is also possible to measure local impurity concentrations.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an apparatus for carrying out the method of the present invention. 1... Compound semiconductor laser, 2... Cryostat, 3... Constant current power supply, 4, 6... Lens, 5... Diffraction grating spectroscopy system, 7... Slit, 8
...Silicon wafer sample, 9...Sample driving device,
10...detector, 11...amplifier, 12...recorder.

Claims (1)

[Claims] 1 In a method of measuring the impurity concentration of a semiconductor by irradiating the semiconductor with a light beam and measuring the absorption coefficient, a wavelength-tunable Pb ₁ - _x Sn _x Te
(x = 0.10 to 0.20) By controlling the temperature and oscillation current of the semiconductor laser, the wavelength of the laser beam is fixed to the maximum absorption wavelength of the impurity, and the silicon wafer, which is the semiconductor, is irradiated, and the transmitted laser beam is The two-dimensional distribution of the impurities in the silicon wafer is measured by measuring the light intensity with an HgCdTe semiconductor detector and by moving the silicon wafer and the laser beam relatively. Method for measuring impurity concentration in semiconductors.