JPH04165320A - Optical device - Google Patents

Abstract

PURPOSE:To facilitate measurement of photo luminescence beams from a semiconductor crystal and to effect measurement of a microregion on a condition in a range of from a normal temperature to a vary low temperature by a method wherein the cold head of a cryopump forms a sample table and placed within the working distance of the objective lens of a microscope through an optical window. CONSTITUTION:A cryostat to produce a very low temperature uses the cold head 15 of a cryopump and the cold head is contained in a chamber 14a. In a system wherein the cold head forms a sample table for measuring a very low temperature, an optical window 12 is located between an objective lens 6 of a microscope installed to the outside of the chamber and the sample table 13, and the sample table is positioned within the working distance of the objec tive lens. Thus, from the outside of the chamber, engineering measurement of the very low temperature in the microregion of a sample can be carried out. This constitution facilitates measurement of the photo luminescence beams of a semiconductor crystal and performs the measurement of the microregion on a condition in a range of from a normal temperature to a very low tempera ture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an optical device that enables optical measurement of photoluminescence light in a minute area.

[Summary of the Invention] The present invention facilitates the measurement of photoluminescence light from semiconductor crystals by using the cold head of a cryopump as a sample stage and placing it within the working distance of the objective lens of a microscope through an optical window. , and can be carried out in minute areas under conditions ranging from room temperature to extremely low temperatures.

[Prior art] The photoluminescence method has the advantage of being able to fix the types of impurities and lattice defects in semiconductor substrates and thin films, and to measure lattice strains in a non-destructive and non-contact manner, making it possible to obtain important information about semiconductor crystals. It is a means. This photoluminescence method irradiates a sample with excitation laser light and measures photoluminescence light (PL light) generated from the sample. PL light reflects various energy levels within the sample, but at room temperature thermal energy becomes a disturbance factor, causing the peak wavelength of PL light to become broad, causing shifts in the wavelength of PL light, splitting, and changes in the spectral shape. It is impossible to observe in detail. Therefore, measurement at low temperatures is important.

To obtain PL light that accurately reflects the energy level of the sample, extremely low temperatures ranging from liquid helium strength (4.2 K) to tens of degrees are required. The device used to obtain low temperatures is commonly known as a cryostat, and the methods used include immersing the sample directly in liquid helium or attaching the sample to the outer wall of a chamber containing liquid helium. Similar measurements have also been made using liquid nitrogen. Adjusting the temperature with this method is extremely difficult.

As a device for measuring PL light in a minute area, the device shown in FIG. 2 is known.

In the figure, 50 is a cryostat, 51 is a liquid nitrogen tank, 52 is a liquid helium tank, 53 is an X-Y sample stage, and 5
4 is a sample, 55 is a microscope, 56 is an objective lens, 57 is a half mirror, 158 is a mirror, 59 is a filter, 60 is a spectrometer, 61 is a photodetector, 62 is an Ar ion laser-1
63 is a Clarasen filter, 64 is a beam expander, 65 is a chopper, 66 is a lock-in amplifier, 6
7 is an A-D converter, and 68 is a microcomputer.

As shown in the figure, the apparatus with the above configuration includes a liquid helium tank with a liquid nitrogen auxiliary cooling tank inside the vacuum chamber, a pure copper sample stage attached to the bottom of the liquid helium tank, and an optical window (
The PL light is collected using a microscope from the bottom of a liquid helium tank through a transparent glass (made of quartz glass, sapphire glass, Kovar glass, etc.), and then put into a spectrometer to measure the wavelength and intensity.

[Problems to be Solved by the Invention] In the device configured as described above, measurement is performed from the bottom of the liquid helium tank because the liquid helium constantly evaporates and the upper part of the liquid helium tank is exposed to volatilized helium gas. This is thought to be because the desired temperature cannot be obtained and the temperature becomes unstable. Furthermore, since light propagates through space from the microscope to the monochromator, if the monochromator is not installed close to the microscope, the PL light will attenuate, which poses a problem in the spatial arrangement of the device.

[Object of the Invention] An object of the present invention is to provide an optical device that can easily optically measure photoluminescence light of semiconductor crystals, etc., and that can perform optical measurements of minute regions from room temperature to extremely low temperatures. .

[Means for Solving the Problems] The present invention houses a cold head of a helium compression refrigerator in a chamber, uses the cold head as a sample stage for cryogenic measurement, and measures the sample using a microscope installed outside the chamber. In an optical device for optically measuring a sample placed on a table, a transparent optical window is provided in a chamber between an objective lens of the microscope and the sample table, and the sample table is placed within a working distance of the objective lens. By locating the chamber, it is possible to optically measure a minute region of the sample at extremely low temperatures from outside the chamber.

[Function] In the optical device with the above configuration, the cold head of the helium compression refrigerator is used as the sample stage, and by placing the sample stage within the working distance of the objective lens of the microscope through the optical window, a minute area of the sample is kept at room temperature. It can be carried out under extremely low temperature conditions.

[Embodiment] FIG. 1 is a block diagram of an optical device according to an embodiment of the present invention.

In the figure, 1 is a microscope, 2 is a condensing lens, 3 is an optical filter for cutting excitation light, 4 is a beam expander, 5 is a half mirror, 16 is an objective lens, 7 is a mirror holder,
8 is an Ar ion laser which is an excitation light source; 19 is an optical fiber; 10 is a fast Fourier transform spectrometer; 11 is an X-
Y table, 12 is an optical window made of transparent quartz glass, sapphire glass, Kovar glass, etc., 14 is the cryostat main body, 14a is a chamber, 15 is a cold head, 16 is a heat shield, 17 is a thermocouple, 18 is helium compression freezing 19 is a microcomputer, and 20 is a sample.

In the above configuration, the cold head 15 of the cryo (low temperature) pump, which is used as an ultra-high vacuum pump using a helium compression refrigerator, reaches about ten extremely low temperatures.

Therefore, the sample stage 13 is installed in the cold head 15 of the cryopump, and it can be used as a cryostat for cryogenic cooling. The cold head 15 can be placed in any position, including upright, inverted, and sideways.

A cryostat that realizes extremely low temperatures uses the cold head 15 of a cryopump, and this cold head is housed in a chamber 14a.In a system in which the cold head is used as a sample stage for cryogenic measurement, a microscope installed outside the chamber is used. By providing an optical window 12 between the objective lens 6 and the sample stage 13 and positioning the sample stage within the working distance of the objective lens, it is possible to optically measure a minute area of the sample at extremely low temperatures from outside the chamber. Become.

The cold head 15 has a temperature control mechanism of 12 to 30
Any measurement temperature can be selected up to 0K. The inside of the chamber 14a can be maintained at a vacuum level of 10-'torr, and together with the heat shield 16 inside the chamber, it is designed to block out all but the radiant heat that enters from the optical window 12.

The microscope is upright, and the PL focused by the microscope system
The spatial limitations of the apparatus can be released by incorporating the optical fiber 9 into the lens system of the microscope and guiding the PL light to the spectrometer 10 through the optical fiber, instead of directly entering the monochromator.

That is, the spectrometer may be installed adjacent to the microscope or at a different location, as long as the optical fiber can reach it.

[Effects of the Invention] As described above, according to the present invention, the cold head of the cryopump is used as a sample stage, and the sample stage is configured to be placed within the working distance of the objective lens of the microscope through the optical window. Therefore, photoluminescence light measurement of semiconductor crystals and the like can be easily carried out in minute regions under conditions ranging from room temperature to extremely low temperatures. Another advantage is that the microscope can be used while standing upright.

Furthermore, according to the present invention, since an optical fiber is incorporated into the lens system of the microscope, light emitted from a specific area within the field of view of the microscope can be easily guided to the measurement system without attenuating it, and the measurement system can also be used as a microscope. Since it is no longer necessary to be close to each other, the degree of freedom of the device can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an optical device showing an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional optical device. 1...Microscope, 2...Condensing lens, 3...Optical filter for cutting off excitation light, 4...Eyes, group, Beam expander, 5.
・・・・・・・・・Half mirror-16・・・・・・・・・
Objective lens, 7... Mirror body holder, 8...
・Old...Ar ion laser-19...Group・Optical fiber, IO......Fast Fourier & search method spectrometer, II......X-Y table , 12
......Optical window, 13... Sample stage, 14... Cryostat body,
14a・・・・・・Chamber, 15・Old...
...Cold head, 16...Heat shield, 17...Old thermocouple, 18...
- Helium compression refrigerator, 19... Microcomputer, 20... Sample. Patent Applicant Glarion Co., Ltd. Agent Patent Attorney Nagai 1) Takeshi Part 1 Figure f19 Go to Figure 2 2

Claims (2)

[Claims] (1) A cold head of a helium compression refrigerator is housed in a chamber, the cold head is used as a sample stand for cryogenic measurement, and a microscope installed outside the chamber is used to optically measure the sample placed on the sample stand. In the optical device for the purpose of An optical device characterized by being capable of optical measurement at extremely low temperatures in a region. (2) The optical device according to claim 1, wherein the microscope is provided with an optical fiber that guides light to the measurement system, and a condenser lens that focuses the light within the mirror onto the optical fiber.