JPS6056240A - Cryostat for optical - Google Patents

Abstract

PURPOSE:To improve accuracy of measurement of infrared spectroscopic measurement, by fitting lens means in a light-trasmission window mounted in a pair of parallel side-walls and installing a heat sump in the light-collecting position located between both lens means to accommodate a pecimen holder. CONSTITUTION:Infrared rays re collected through a light inlet window 2 consisting of a lens fit into a side-wall 1 of a cryostat 10 and a focus is built on a specimen 5, such as of silicone chip, etc. The speciment 5 is held at low temperature at approx. 77 deg.K or less by a heat sump 6 and the infrared rays, after passing through the specimen 5, are collected by a light outlet window 3 consisting of a lens and absorbed in a detector 7. By this arrangement, effective convergence of the infrared rays can be realized and further, incidence into the specimen can be attained without any discontinuities and concentrations of impurities, etc. included in a semiconductor crystal can be measured with high precision.

Description

[Detailed description of the invention] The present invention relates to a cryostat for optical measurements.

More specifically, the present invention relates to a lyostat that is useful for measuring the absorption spectrum of impurities such as oxygen and carbon in a semiconductor such as a silicon crystal at a low temperature using light in the infrared wavelength region. .

Background of the Technology When manufacturing LSIs from semiconductor crystals, crystal defects such as micro defects and stacking defects occur due to a variety of causes. These crystal defects must be reduced in order to improve yield, miniaturize devices, and increase integration.

By the way, impurities contained in the crystal, especially the presence of oxygen, are thought to be the main cause of crystal defects, so it is necessary to quantitatively know the concentration and distribution of such impurities and to investigate the occurrence of crystal defects during the I and S manufacturing processes. Defects can be advantageously controlled.

Prior Art and Problems Methods for measuring the impurity concentration in semiconductor crystals include physical measurement methods, optical measurement methods, and electrical measurement methods. In particular, optical measurement methods, especially infrared spectrometry methods, are relatively simple and non-destructive, and are therefore widely used in this technical field. Furthermore, when performing infrared spectrometry, it is common to cool the sample using a so-called cryostat in order to improve the measurement accuracy. However, in this case, the light guide window must be made small to prevent heat radiation from the outside, and most of the light introduced through the window must be turned off.

Cutting off the light incident on the sample inevitably reduces measurement accuracy, thus negating the benefits of using a cryostat.

Purpose of the present invention The purpose of the present invention is to:
It is possible to absorb light without cutting off the light incident on the sample, thus improving the measurement signal-to-noise ratio by improving the measurement speed by 1 degree. It's about doing.

Structure of the Invention In order to achieve the above object, the present inventors have discovered, as a result of research, a light introduction window and a light guide t formed in the side wall of a cryostat.
J! It has been found that it is effective to fit lens means capable of condensing light having a predetermined wavelength into each opening of the T window. That is, the cryostat for optical measurement according to the present invention has at least a pair of parallel m1ll! I;
4 and 0;
a pair of leading windows separated by 'ltl and vlj, a lens means fitted in each of the light guides and capable of condensing light having a predetermined wavelength, and a light convergence position located between the lens means. ; for holding the sample in the ri;
The sample holder is characterized in that the sample holder includes a heat sink for cooling the sample S(4+Jd).

Here, the "lens means" includes a general lens. It has been found that as such a lens means, for example KR3-5 glass made of Krylam halide can be used advantageously.

Embodiments of the Invention Next, please refer to the attached FIG. 1! A detailed explanation of the present invention will be given below.

As an infrared light source (not shown), for example, a glober light source made of a rod made of sintered silicon carbide is used. Infrared rays from this light source are focused by a light introduction window 2 made of a KRS-5 lens fitted into the side wall 1 of the cryostat 10. As shown, the side t1 of the cryostat is a pair of parallel side walls, and has a pair of light guiding windows (light introducing window 2 and light leading window 6) in corresponding parts. The side wall 1 is made of stainless steel. Since the sample 5 (here, a silicon chip formed by cleavage) is placed at the condensing position of the light introducing window 2, the infrared rays condensed by the window 2 are focused on the sample 5. As shown in the figure, the sample 5 is made of copper (preferable because of its excellent thermal conductivity) equipped with a heat sink (liquid nitrogen or liquid helium) 6 to cool it to a low γ crystal (below 77°). The specimen is held by a specimen holder 4 (of which copper is used).

Furthermore, although not shown in the drawings, it is also possible to attach a Somura copper radiation shield to this sample holder 4. After passing through the sample 5, the light incident on the sample 5 is focused again by a light output window 6 made of a KR3-5 lens in the same way as the light introduction window 2, and is absorbed by a detector 7 placed outside the cryostat 1o. be done. The infrared #18 absorption spectrum can be observed with the detector 7 (for example, a HyOdTθ photoconductive type detector).

In implementing the present invention, the direction of incidence of infrared rays incident on the light introduction window 2 does not matter (because this window has a light condensing function). That is, diagonal incidence of infrared light is also possible.

Effects of the Invention According to the present invention, incident infrared light can be effectively converged and made incident on the sample without being cut.
Measurement accuracy can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a preferred example of a cryostat for optical measurements according to the present invention. In the figure, 1 is a side wall, 2 is a light introduction window, 3 is a light output window, 4 is a sample holder, 5 is a sample, 6 is a heat sink, 7 is a detector, and 10 is a cryostat.

Claims (1)

[Claims] 1. At least a pair of parallel side walls, a pair of leading windows opened at a certain distance from each other in corresponding parts of the side walls, and light having a predetermined wavelength fitted in each of the light guiding windows is collected. comprising a lens means capable of transmitting light; and a sample holder for holding a sample at a light focusing position located between the lens means and provided with a heat sink for cooling the sample. A cryostat for optical measurements featuring: