JPS59223293A - Molecular beam epitaxial growth device - Google Patents

Abstract

PURPOSE:To stabilize the intensity of a molecular beam for a long time and to decrease considerably the consumption of a sample until said intensity stabilizes by detecting the intensity of the molecular beam emitted from a molecular beam source and controlling the heating electric power for the molecular beam source so that the detected value is maintained at a prescribed value. CONSTITUTION:A pressure sensor 13 for detecting the intensity of a molecular beam as a pressure, a pressure measuring device 14 and a heating control device 15 are provided to a molecular beam cell 5 to control a heating power source 6 of a heater 2. The intensity of the molecular beam is then directly detected without delay in the value thereof and the heating is adequately controlled so that the detected value is maintained constant. Such control is basically the same as direct control of the surface temp. of a sample and therefore there is no need for considering the temp. difference between a crucible 1 and a sample 10. The deviation of time with respect to a temp. fluctuation is minimized and the time until the intensity of the molecular beam is stabilized is considerably reduced.

Description

Detailed Description of the Invention The present invention relates to molecular beam epitaxial growth, in which a single or multiple molecular beams are emitted at an appropriate intensity or intensity ratio onto a substrate heated under a supersieve vacuum, and the beams are deposited to grow crystals. The present invention relates to an apparatus for controlling the molecular beam intensity or molecular beam intensity ratio to a desired value, and the object of the present invention is to provide an apparatus that makes it possible to obtain an excellent epitaxially grown film.

A conventional device for controlling molecular beams is shown in FIG.

Crucible containing sample 10 to be made into molecule 1I111 1
, a heater 2 for heating this crucible 1 , a molecular beam cell 5 consisting of a thermocouple 3 for measuring the crucible temperature, and a heat shield plate 4 for preventing heat escape, and a heater 2
It consists of a heating power source 6 for heating the crucible, and a temperature control device 7 for controlling the output heater power of the heating power source 6 in response to the temperature signal obtained from the thermocouple 3, thereby keeping the crucible temperature constant.

Thereby, the intensity or intensity ratio is controlled to be constant. The rate at which the sample 10 in the crucible 1 becomes the molecular beam 11 is closely related to the specific vapor pressure P of the sample 10, and the relationship between the vapor pressure P and the temperature T' is expressed by the following equation. There is a relationship.

Noog P=--)-Blog T-)-C...
(1) Here, A, H, and C are values unique to the sample.

When considering keeping the molecular beam intensity constant, it is necessary to pay attention to the fact that the pressure P generally changes greatly with changes in temperature. For example, if arsenic (As) is used as sample 10, 5
If the temperature changes by ±0.5°C near 03°, the vapor pressure P
A fluctuation of about 10 inches occurs.

Moreover, it is necessary to maintain this temperature within ±0.5℃ for a long time.
It is extremely difficult to achieve this goal, and currently the goal is barely achieved through extremely complex control (pH) control.

As mentioned above, conventional methods are part of the crucible.

To maintain a constant temperature at the thermocouple insertion point.

It has not always been possible to completely control the temperature of the sample surface, which is the key factor that determines the molecular beam intensity. The reason for this is that the temperature measurement unit is not able to properly cope with and follow the difference in thermal conductivity between the materials of sample 10 and crucible 1, and changes in heat capacity due to changes in the sample surface shape over time. etc.

This is particularly noticeable when the sample 10 is a sublimable substance such as arsenic (As). In history, when the molecular beam cell is heated to obtain a predetermined molecular beam intensity, when the temperature starts to rise, no matter how sophisticated the temperature detection and control based on it, the 2-time axis is the horizontal axis. A phenomenon in which the molecular beam intensity taken in this direction greatly overshoots as shown by curve A in FIG. 2 is observed. This phenomenon is more severe as the vapor pressure of the sample 10 is higher, and the shorter the heating time is, the more severe this phenomenon is. Here, curve A in Figure 2 shows the change in the intensity of the molecular beam when the temperature is increased in a short period of time.

Curve B shows the temperature change of the crucible at that time. Curve C shows the change in molecular beam intensity when the temperature is increased over a long period of time.

Curve 9 shows the temperature change of the crucible at that time.

Now, epitaxial growth is actually performed only after the molecular beam intensity becomes constant. Therefore, all the samples consumed during heating are wasted.2For example, Jr.
When the tL element is heated in about 20 minutes and the temperature is stabilized, due to this overshoot, the amount of HTL element equivalent to about 26 hours of consumption after stabilization contributes to growth. It is consumed without being consumed.

Since it normally takes about 1 hour to form a 1 μm thick GaAs film, the amount of wasted consumption is actually 26 times that amount.

The present invention overcomes the drawbacks of conventional thermocouple temperature control as described above. It was created with the aim of significantly improving the drawbacks of the difficulty of maintaining stable molecular beam intensity over a long period of time and the excessive amount of sample consumed until the nine-molecular beam intensity stabilizes. . The present invention will be explained below using the figures.

FIG. 3 is a block diagram of one embodiment of the present invention. The configuration of the apparatus of the present invention is as follows: from the molecular beam cell 5 to the thermocouple 3 shown in FIG.
and temperature control device 7, and in their place a pressure sensor 13 for detecting single molecule beam intensity as pressure.
A pressure measuring device 14 and a heating control device 15 are installed to control the heating power supply 6.

As this pressure sensor 13, a device 2 which measures steam pressure in a vacuum, such as a device also called a vacuum gauge, can be used. As a method of controlling the molecular beam intensity, the intensity of the molecular beam generated by heating a heater to raise the temperature of the sample is detected and measured using a pressure sensor and a pressure measuring device as described above, and the output of this pressure measuring device is The signal is input to the heating control device, and the heating control device compares the signal with a signal corresponding to a preset desired pressure value, and adjusts the power of the heating power source so that the difference between the two falls within an appropriate error range. control. According to the control method of the present invention as described above, the value of the molecular beam intensity can be directly detected without delay.

Appropriate heating control is performed to keep this detected value constant.

Therefore, in this case, it is no different from directly controlling the temperature of the sample surface, so there is no need to keep in mind the temperature difference between the crucible ■ and the sample 10.

The time lag caused by temperature fluctuations is also extremely small compared to the conventional method, and the drawbacks of the conventional method are greatly improved.

In particular, the present invention is particularly effective for substances with high vapor pressure such as nitrogen (As) and phosphorus (P).

FIG. 4 shows how the molecular heat intensity rises when the apparatus of the present invention is used.

This is compared to the second time course of change using the conventional method on the same scale.
Comparing with the figure, it can be seen that the time it takes for the single molecule beam intensity to stabilize is extremely short.

2. The method of the present invention can reduce the amount of time required for growth to about 0.59 hours, whereas the conventional method wastes time for the sample to reach 26 hours, as mentioned above. was proven by experiment. If wasteful consumption is allowed to the same level as in the past, the time it takes to stabilize the bimolecular beam intensity will be extremely short, 1/10 to 1/100 of the conventional time.

As described above, according to the present invention, the time required for crystal growth, including the initial adjustment of the bimolecular beam intensity, can be significantly shortened, and the amount of sample consumed can also be significantly reduced.

Although the above description has been made regarding the case where there is one molecular beam cell as the evaporation source, the present invention is not limited to the case where there is a single evaporation source. FIG. 5 shows a molecular beam intensity control method using the apparatus of the present invention in the case of a plurality of evaporation sources. The configuration of each control section is the same as that in FIG. 3.

Here, for example, by inserting the molecular beam separator 20 as shown in FIG. 5, the pressure sensor 31 or 32 will detect only the molecular beam emitted from the molecular beam cell 2 or 22. The intensity of each of the molecular beams 41 and 42 can be controlled independently. Also, in the above explanation, it was stated that a general vacuum gauge can be used as the pressure sensor 13, but it can be placed in a space through which a bimolecular beam passes, and, like a vacuum gauge, it can ionize the molecular beam and open its ion current. It is clear that any type that can be used side by side can be effectively used for heating, etc. using this pressure sensor.

Furthermore, it is also possible to use the control method of the present invention and the conventional temperature control method in conjunction with a plurality of evaporation sources. There is nothing wrong with the effectiveness of this device. That is, the implementation of the present invention is not limited to the above-described embodiments.

Please note the following: The idea of detecting molecular beam intensity using a pressure sensor has existed in the past. However, when crystal growth is performed using a plurality of molecular beams, there are problems such as the concern that the two molecular beams may influence each other, and for this reason, this has not been used to control pure molecular epitaxial growth. There has also been no attempt to control the temperature of a molecular beam cell using pressure measurement signals as in the present invention. simple +
14) Therefore, the present invention, which makes it possible to economically obtain an epitaxially grown film of excellent quality, has high technical value and can be said to be a useful invention. .

[Brief explanation of drawings]

FIG. 1 shows a conventional device for temperature control. FIG. 2 shows the temporal changes in molecular beam intensity and crucible temperature at the start of heating obtained by the conventional apparatus. FIG. 3 shows an apparatus for controlling the molecular beam intensity of the present invention. FIG. 4 shows the temporal change in molecular beam intensity using the apparatus of the present invention. FIG. 5 is a schematic diagram of an apparatus in which the apparatus of the present invention is applied to a plurality of molecular beams. In the figure, 1 is a crucible, 2 is a heater, and 3 is a thermocouple. 4 is a heat shield plate, 5 is a molecular beam cell, 6 is a heating power source, 7 is a temperature control device, 10 is a sample, 11 is a molecular beam, 12 is a substrate,
13 is a pressure sensor, 14 is a pressure measuring device, 15 is a heating control device, 20 is a molecular beam GIL plate, 2122 is a molecular beam cell in the case of plurality, and 3132 is a pressure sensor in the case of plurality. FIG.3

Claims (1)

[Claims] A detector that measures the molecular beam intensity emitted from the molecular beam source, and a heating control device that controls the heating power of the molecular beam source so as to maintain the molecular beam intensity measured by the detector at a predetermined value. A molecular beam epitaxial growth apparatus characterized by: