JPH03115192A - Device for growing crystal by molecular beam epitaxy - Google Patents

Abstract

PURPOSE:To provide the title device for growing crystals which can make the uniform control of the surface temp. distribution of a substrate and the control thereof to a design value by consisting the device of a vessel for epitaxial growth substrate, a source crucible for housing materials, a means for photoirradiation and a means for controlling the intensity of a light beam, etc. CONSTITUTION:While the intensity of the laser light is controlled, the spot of the laser beam is scanned on the surface of the substrate 3 for epitaxial growth and the surface temp. distribution of the substrate is controlled. This temp. distribution is measured by a heat image visualizing device 26. The signal output to the measured temp. distribution of the substrate surface and the signal output to the prescribed temp. distribution previously stored in a memory device 25 are compared and computed by a computing element 27. The results of the computation are fed back to the means 24 for controlling the intensity of the light beam and the means 23 for scanning the light beam to control the position where the means 22 for photoirradiation scans the light beam to the substrate 3 and the intensity of the light beam with which the substrate is irradiated. Since the temp. distribution of the substrate surface can be thereby controlled to the desired temp. distribution, the substrate surface is heated to the uniform temp. and the epitaxial crystal having the compsn. uniform over the entire part of the substrate 3 and the prescribed compsn. is grown.

Description

[Detailed Description of the Invention] [Summary] Regarding a molecular beam epitaxial crystal growth apparatus, the present invention is directed to a molecular beam epitaxial crystal growth apparatus capable of obtaining epitaxial crystals of a compound semidiagonal containing mercury with a predetermined composition, and an epitaxial growth vessel. a substrate for epitaxial growth placed inside the container; a source crucible placed opposite to the substrate and containing a source material for epitaxial growth; and a light irradiation means for irradiating the substrate for epitaxial growth with light. comprising: a light beam scanning means for scanning the light beam of the light irradiation means; a light beam intensity control means for adjusting the intensity of the light beam; and a storage device for storing the design value of the substrate surface temperature distribution; The light beam scanning means and the light beam intensity control means are operated according to stored information to perform epitaxial growth while controlling the temperature of the epitaxial growth substrate.

[Industrial application field]

The present invention relates to a molecular beam epitaxial crystal growth apparatus.

Photoelectric conversion devices such as infrared sensors use mercury, cadmium, and tellurium (Hg+-x), which have narrow energy band gaps.
A compound semiconductor crystal such as Cd3Te) is used.

Such infrared sensors are increasingly required to have a higher number of pixels, higher performance, and lower cost. Therefore, inexpensive and large substrates such as sapphire and gallium arsenide (GaAs) are required to be mounted on substrates that can be easily handled. Mercury, cadmium, tellurium (Hg1-X Cd
There is a need for a method and an apparatus that enable high quality compound semiconductor crystals of X Te) to be obtained.

In order to grow a Hg+-x CdXTe crystal having a lattice constant different from that of the substrate on the GaAs substrate or sapphire substrate described above, a liquid phase epitaxial growth method in which crystal growth is performed in an equilibrium state cannot obtain a good crystal. The development of vapor phase growth methods such as molecular beam epitaxial growth methods, which can obtain good crystals even on different types of substrates, is underway.

In addition, in the liquid phase epitaxial growth method, due to the high growth temperature, interdiffusion occurs between crystals with different compositions, such as the substrate and epitaxial crystal. It is difficult to realize a distributed pattern, and the development of a vapor phase epitaxial growth technique that allows low-temperature growth is awaited.

On the other hand, if the epitaxial crystal component to be grown contains mercury, which evaporates easily, the mercury adhesion coefficient to the substrate will vary significantly even with a slight difference in substrate temperature, resulting in a change in the composition of the epitaxial crystal to be formed. It doesn't become constant.

Conventional vapor phase growth technology cannot achieve sufficient temperature control;
It is desired to improve the growth apparatus so that the substrate temperature distribution can be precisely controlled according to the designed value.

[Conventional technology]

FIG. 4 is a schematic diagram of a conventional molecular beam epitaxial crystal growth apparatus. As shown in the figure, an epitaxial growth substrate 3 such as a GaAs substrate is placed on a substrate mounting table 2 above an epitaxial growth container 1.

Furthermore, the epitaxial growth substrate 3 is placed on the substrate installation stand 2.
A heater 4 for heating is built-in.

At the bottom of the epitaxial growth container 1, at a position facing the epitaxial growth substrate 3, a CdTe containing a predetermined weight of CdTe, which is a forming material of the Hg+-xCdxTe crystal to be epitaxially grown on the substrate, is placed.
A Te source crucible 5, a Hg source crucible 6 containing a predetermined weight of mercury, and a Te source crucible 7 containing a predetermined weight of tellurium are installed. A shielding plate 8 is installed between the epitaxial growth substrate 3 and each source crucible. Further, inside the epitaxial growth container, an internal side wall 9 having a double structure is provided, and liquid nitrogen is flowed into the double internal side wall to cause unreacted mercury atoms to adhere to the internal side wall during the epitaxial growth process. Furthermore, a mercury collector 11 for storing mercury attached to the inner side wall is connected to the lower part of the epitaxial growth container.

Furthermore, the entire epitaxial growth container is heated to 10"" torr.
A vacuum evacuation device 12 for evacuation to a relatively high vacuum is connected to the container.

When growing an epitaxial crystal of HgI-x Cdx Te on a substrate for epitaxial growth using such a conventional apparatus, after installing the substrate 3 for epitaxial growth on the substrate mounting table 2, each source crucible and the epitaxial growth A heater (not shown) is provided around each source crucible with a shielding plate 8 interposed between the source crucible and the source crucible.
When the temperature of the source crucible reaches a predetermined temperature, the shield plate 8 is moved to irradiate the substrate with the evaporated components of each source from the source crucible, and the epitaxial growth substrate is heated. Hg+-x on the substrate
CdXTe epitaxial crystals are grown in a vapor phase.

[Problem to be solved by the invention]

Incidentally, while source materials such as CdTe and Te are heated at high temperatures, there is a problem that mercury will not adhere to the substrate unless the temperature of the epitaxial growth substrate 3 is kept at a relatively low temperature of 200°C.

However, there is a problem in that the temperature of the surface of the substrate for epitaxial growth does not become uniform over the entire substrate due to the influence of radiant heat generated from the source material. Increasing the temperature of the entire epitaxial growth substrate makes it relatively easy to control the temperature distribution on the substrate surface, but the adhesion coefficient of mercury to the substrate is extremely reduced, making epitaxial growth of Hg+-x CdxTe impossible.

On the other hand, if the temperature of the epitaxial growth substrate 3 falls below a predetermined temperature, not only will the composition of the epitaxial crystal to be formed shift, but also the crystallinity of the epitaxial crystal to be formed will change due to excessive mercury adhering to the epitaxial growth substrate. A problem arises that gets worse.

In conventional equipment, sufficient temperature control of the substrate temperature for epitaxial growth cannot be ensured, so molecular beam epitaxial crystal growth of compound semiconductors containing mercury as a component has poor reproducibility in both composition and crystallinity, making it impractical for practical use. It has not become a technology.

Therefore, with conventional equipment such as installing a soaking plate or a heater on the back side of the substrate to make the substrate temperature uniform for epitaxial growth, it is not possible to control the absolute value and distribution of the substrate temperature with the required accuracy. Since the mercury fixation coefficient of the epitaxial crystal is not constant depending on the location or time, the composition of the epitaxial crystal differs between growth lofts, resulting in a problem that the uniformity of the composition of the epitaxial crystal deteriorates.

An object of the present invention is to eliminate the above-mentioned problems and provide a molecular beam epitaxial crystal growth apparatus in which the surface temperature distribution of a substrate can be uniformly controlled or precisely controlled according to a designed value.

[Means to solve the problem]

As shown in the principle diagram of FIG. 1, the molecular beam epitaxial crystal growth apparatus of the present invention which achieves the above object includes an epitaxial growth container l, an epitaxial growth substrate 3 placed inside the container, and an epitaxial growth substrate 3 facing the substrate. Source crucible 5.6 installed at
．． 7, a light irradiation means 22 for irradiating the epitaxial growth substrate with light, a light beam scanning means 23 for scanning the light beam of the light irradiation means, a light beam intensity control means 24 for adjusting the intensity of the light beam, The storage device 25 stores the design value of the substrate surface temperature distribution, and the information stored in the storage device 25 operates the light beam scanning means 23 and the light beam intensity control means 24 to control the epitaxial growth substrate. It is structured so that epitaxial growth is performed while controlling the temperature.

[For production]

As shown in FIGS. 1 and 2, the apparatus of the present invention controls the substrate surface temperature distribution by scanning the laser beam spot on the surface of the epitaxial growth substrate 3 while controlling the light intensity of the laser beam. ing. The temperature distribution on the substrate surface is measured by the thermal imaging device 26, and a signal output for the measured temperature distribution on the substrate surface and the storage device 25 are provided.
A predetermined temperature distribution stored in advance (design temperature distribution)
The arithmetic unit 27 compares and calculates the signal output for
The light beam is fed back to the light beam scanning means (optical scanner) 23 to control the scanning position of the light beam on the substrate of the light irradiation means (carbon dioxide laser tube) 22 and the intensity of the irradiated light beam.

Therefore, if there is a difference between the actual substrate surface temperature distribution measured by the thermal imaging device 26 and the designed value of the substrate surface temperature distribution stored in the storage device 25, the optical controlling the intensity of the light beam using an attenuator 24;
Alternatively, by changing the light beam scanning speed by the light beam scanning means 23, the substrate surface temperature distribution can be made to substantially match the designed temperature distribution.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a schematic diagram of the molecular beam epitaxial growth apparatus of the present invention.

As shown in the figure, an epitaxial growth substrate 3 made of GaAs is placed on an upper substrate installation table 2 in an epitaxial growth container 1 .

The above-described CdTe source crucible 5, Hg source crucible 6, and Te source crucible 7 are installed below the substrate, and a shielding plate 8 is provided between the epitaxial growth substrate and the source crucible.

A lens barrel 31 is provided on the side wall of the epitaxial growth container 1 so that the substrate can be viewed from below in an oblique direction, and a light transmitting substrate 21 is provided at the end of this lens barrel 31.

An infrared camera, for example, IRCCD, is used to measure the substrate surface temperature distribution of the epitaxial growth substrate on a line connecting the light-transmitting substrate 21 and the epitaxial growth substrate 3.
A thermal imaging device 26 such as the one shown in FIG.

Further, a lens barrel 32 is further provided at the bottom of the lens barrel 31, and a light transmitting substrate 21 is installed on the lens barrel 32 so as to look into the epitaxial growth substrate 3, and the substrate 21 and the epitaxial growth substrate 3 are connected to each other. As shown in FIG. 3, on the line connecting the A light beam scanning means 23 includes a Y-direction scanning mirror 42 that scans in the Y direction, a driving electromagnetic coil 43° 44 that drives the scanning mirror, and a light beam scanning means 23 that adjusts the light intensity of the laser beam to a predetermined intensity as shown in FIG. An optical attenuator 24 such as a variable beam splitter configured with a half mirror whose angle relative to the incident light is variable is installed to maintain the incident light, and the carbon dioxide laser tube 22 described above is also installed.

The light beam scanning means 23 and the optical attenuator 24 send the values measured by the thermal imaging device 26 and the values from the storage device 25 in which the design value of the substrate surface temperature is stored to the computing unit 24.
7, and according to the value obtained by the calculator 27, the movement angle of the scanning mirror in the light beam scanning means 23 is changed, or the variable beam splitter of the optical attenuator is operated. In this way, the illuminance of the laser spot light at each position on the substrate surface is changed.

The above-mentioned storage device 25 stores information on the designed temperature distribution of the epitaxial growth substrate.

This designed temperature distribution is designed to be a temperature pattern in which the entire substrate is uniform, or a temperature pattern in which the temperature of the substrate partially varies.

The thermal imaging bag W126 described above always photographs the surface of the epitaxial growth substrate 3. For objects with the same emissivity, the higher the temperature of the object, the more infrared rays it emits, so the temperature of the surface of the epitaxial growth substrate can be measured using a thermal imaging device that visualizes the intensity of this infrared ray. However, since the surface of the epitaxial growth substrate 3 is generally a mirror surface and has a large reflection coefficient (=1 - emissivity), more infrared rays are emitted from the area where it is reflected from the substrate surface when viewed from a thermal imager. If so, it will be reflected off the substrate surface and incident on the thermal imaging device, making it impossible to accurately measure the temperature distribution on the substrate surface.

In order to keep the amount of infrared rays incident on the thermal imager due to the above reflection constant and to be able to subtract it with a calculator, it is necessary to keep the temperature uniform in the area visible from the thermal imager as seen by the reflection from the substrate surface. It is desirable to install a low-temperature blackbody.

Therefore, a lens barrel 33 is further provided on the left side wall of the epitaxial growth container l so as to look into the epitaxial growth substrate 3 from an obliquely lower direction, and the lens barrel 33 is made of germanium that transmits infrared rays reflected from the substrate surface. An infrared transmitting window 34 made of a plate and a low-temperature black body 35 made of carbon that does not reflect infrared rays are installed.

In order to measure the temperature distribution of the epitaxial growth substrate with higher accuracy, it is necessary to reduce the length of the infrared rays incident on the thermal imaging device rather than keeping the infrared rays incident on the thermal imaging device constant. It is necessary to keep the black body at a low temperature.

However, in the growth of epitaxial crystals containing mercury, mercury molecules that are not fixed to the epitaxial growth substrate float inside the epitaxial growth container l and adhere to the low temperature part, so as described above, the low temperature black body 35 It is protected by a high temperature infrared transmitting window 34 to which mercury does not adhere. Since the infrared radiation from the infrared transmission window 34 has a small emissivity (=1-transmittance) of the transmission window, the amount of infrared rays incident on the thermal imaging device from the transmission window does not increase due to reflection.

Further, a vacuum evacuation device 12 for evacuating the entire apparatus and a mercury recovery device 11 for recovering unreacted mercury accumulated in the inner side wall 9 are connected to and arranged in the epitaxial growth container 1. .

The operation of such a molecular beam epitaxial growth apparatus of the present invention will be explained.

First, an epitaxial growth substrate l is placed on the substrate mounting table 2 described above.
113, the inside of the epitaxial growth container 1 is evacuated using the vacuum evacuation device 12 until a vacuum level of 10-'' torr is reached.

Next, each source crucible is heated, and when the temperature of these source crucibles reaches a predetermined temperature, the shielding plate 8 is moved laterally from the top of the source crucible.

Next, the attenuation rate of the optical attenuator 24 is lowered, and the optical scanner 23 is scanned so that the laser beam from the carbon dioxide laser tube 22 reaches a predetermined position on the epitaxial growth substrate 3.

In this state, a laser beam is irradiated onto the epitaxial growth substrate for a predetermined period of time, and when the temperature of the substrate rises to a predetermined temperature, the temperature at a predetermined position on the substrate surface is measured by the thermal imaging device 26.

Then, this temperature is compared and detected with the design value temperature of the substrate surface temperature at a predetermined position stored in the storage device 25, and this compared value is calculated by the calculator 27, and based on the calculated information, the above-described optical The scanning mirror of the scanner 23 is scanned so that the laser beam reaches a predetermined position on the substrate, and the optical attenuator 24
The intensity of the light spot of the laser light is adjusted by changing the angle of the half mirror with respect to the incident light of the laser light.

Further, in order to prevent the infrared light reflected by the substrate described above from entering the thermal imaging device and the measured values of the device being influenced by the reflected infrared light, the device of the present invention is provided. As seen from the thermal imaging device, the infrared light is transmitted through a low-temperature black body 35 that does not reflect infrared light and hardly radiates the infrared light to a position where it can be seen reflected by the substrate, By providing the infrared transmitting window 34 that emits almost no radiation, reflected infrared light does not enter the thermal imaging device, further improving the reliability of the epitaxial growth device.

As a modification of the present invention, the means for reducing infrared rays reflected on the substrate surface and incident on the thermal imaging device is a combination of a low-temperature black body and an infrared transmitting window, but it is possible to use only a black body with a uniform temperature. You may do so.

Furthermore, in the above embodiment, the measured value of the substrate surface temperature distribution measured by the thermal imaging device is fed back to the laser beam irradiation intensity, but the output from the storage device that stores the design temperature distribution information is The laser beam irradiation intensity may be controlled solely by

Further, although the temperature of the epitaxial growth substrate is controlled only by laser light, auxiliary heating means such as a heater or a temperature equalizing plate provided on the back surface of the substrate, or auxiliary temperature distribution means may be provided.

C. Effects of the Invention] As is clear from the above description, according to the present invention, the temperature distribution on the substrate surface can be made to match the designed temperature distribution. Therefore, if the above-mentioned design temperature distribution is set to be a uniform temperature, the substrate surface will have a uniform temperature. Therefore, an epitaxial crystal having a uniform and predetermined composition can be grown over the entire substrate, and if an infrared area sensor or the like is manufactured using this crystal, a sensor with uniform characteristics between pixels can be obtained.

Furthermore, by setting the design temperature distribution to partially different temperature patterns, a predetermined temperature pattern can be achieved on the substrate surface with high accuracy, and the Hgr-
An epitaxial crystal of x Cdz Te can be selectively grown at a predetermined position on a substrate, and if an infrared sensor is formed using such a selectively grown epitaxial crystal, a highly functional infrared sensor can be obtained.

[Brief explanation of drawings]

Fig. 1 is a diagram of the principle of the device of the present invention, Fig. 2 is a schematic diagram of an embodiment of the device of the present invention, Fig. 3 is a schematic diagram showing the main parts of the present invention, and Fig. 4 is a diagram of the conventional device. It is a schematic diagram. In the figure, 1 is an eviaxial growth container, 2 is a substrate installation table, 3 is an epitaxial growth substrate, 5 is a CdTe source crucible, and 6 is a CdTe source crucible.
is a Hg source crucible, 7 is a Te source crucible, 8 is a shielding plate,
9 is an internal side wall, 11 is a recovery means (mercury collector), 12 is an exhaust means (vacuum exhaust device), 21 is a light transmitting substrate, 22 is a light irradiation means (lie-Ne laser tube), 23 is a light beam scanning means (optical scanner), 24 is a light beam intensity control means (optical attenuator), 25 is a storage device, 26 is a thermal image visualization device, 27 is a computing unit, 31, 32, 33 is a lens barrel, 34 is an infrared transmitting device Window 35 indicates a low temperature black body. effusion'1l-i 1/-L tJP*;i-IINKm
Figure 3

Claims (3)

[Claims] (1) An epitaxial growth container (1) and an epitaxial growth substrate (
3), a source crucible (5, 6, 7) placed opposite to the substrate and containing a source material for epitaxial growth, and a light irradiation means (22) for irradiating light to the substrate for epitaxial growth.
), and a light beam scanning means (
23), a light beam intensity control means (24) for adjusting the light beam intensity, and a storage device (2) for storing the design value of the substrate surface temperature distribution.
5), wherein the light beam scanning means and the light beam intensity control means are operated according to information stored in the storage device to perform epitaxial growth while controlling the temperature of the epitaxial growth substrate. Line epitaxial crystal growth equipment. (2) A thermal imaging device (26) is provided to measure the surface temperature distribution of the epitaxial growth substrate, and the measured values measured by the thermal imaging device and the substrate surface temperature distribution are stored in the storage device. A calculation unit (27) performs a comparison operation with a design value of , and the light beam scanning means (23) and the light beam intensity control means (24) are operated based on the information obtained by the comparison operation. (1) The molecular beam epitaxial crystal growth apparatus described in (1). (3) The thermal imaging device (26) is provided with infrared reducing means (34, 35) for preventing infrared light reflected by the epitaxial growth substrate (3) from entering. The molecular beam epitaxial crystal growth apparatus according to 1) or (2).