JPH07176494A - Substrate temperature controller - Google Patents

Abstract

PURPOSE:To provide a substrate temperature controller which is not affected by influence of heat radiation from a high-temperature evaporation source in the controller using a pyrometer. CONSTITUTION:The substrate temperature controller comprises a pyrometer 3 for measuring a temperature of a substrate 2, a temperature control unit 4 receiving a measured value from the pyrometer 3 to control the temperature of the substrate 2, a memory 13 for storing a temperature control signal from the unit 4, and a changeover switch 18 for operating according to an external signal, wherein a signal from the pyrometer 3 or a signal from the memory 13 is applied to the unit 4 by an operation of the switch 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate temperature control device for a thin film forming apparatus used for forming a compound semiconductor thin film.

[0002]

2. Description of the Related Art Compound semiconductors are widely used not only in high speed devices for computers but also in optical devices such as lasers which are indispensable for optical communication technology. For manufacturing these semiconductor elements, metal organic thermal decomposition method, molecular beam epitaxy method (MB
E), a thin film forming method such as metal organic molecular beam epitaxy (MOMBE). Of these, MBE and MOMB
E is a method of irradiating a heated substrate in a vacuum container with a molecular beam source material to deposit a thin film. Since the quality of the thin film is sensitive to the substrate temperature, it is necessary to precisely control the substrate temperature. To do this, either detect the temperature of the substrate holder with a thermocouple or the temperature of the substrate surface with a pyrometer,
It is common practice to feed these signals back to the heating power supply via a temperature controller. The former measures the temperature of the holder on which the substrate is placed, not the substrate, whereas the latter measures the temperature of the substrate itself. Therefore, the temperature of the thermocouple is a monitor of the substrate temperature and does not always match the temperature of the pyrometer. In essence, it is expected that a pyrometer will allow more accurate control, but it has not been put to practical use for the reasons described later.

In temperature measurement using a thermocouple, since the substrate is rotated, the thermocouple is not in contact with the holder and is often placed between the heater and the holder. Therefore, the indicated temperature greatly changes depending on the state of the holder, that is, the degree of metallic luster. An oxide film is formed on the surface of a substrate of InP, GaAs, etc., and although the evaporation temperature is essentially constant, the indicated temperature of the thermocouple varies greatly depending on each holder. Further, when the growth starts, a film is vapor-deposited on the holder as well, the amount of heat radiation from the holder changes, and the surface temperature of the substrate decreases even if the substrate temperature is kept constant. In such temperature control using a thermocouple, it is necessary to set the heating temperature of the substrate for each holder, and even if the indicated temperature is kept constant, the temperature of the substrate itself is not always kept constant. It has the drawback of not having it.

As its name implies, compound semiconductors are composed of many elements. In the MBE / MOMBE method, in addition to the substrate, one or two evaporation sources for each constituent element and a plurality of evaporation sources for dopants are provided in the vacuum container.
By precisely adjusting the temperature of each evaporation source and opening and closing a shutter provided directly above each evaporation source, a film having a desired structure and controlled composition and carrier concentration is obtained.

The principle of the pyrometer is based on the fact that the radiant heat of the heated object follows the Stefan-Boltzmann law. The substrate temperature is determined in consideration of the emissivity of each semiconductor material (1 in the case of a black body). However, when the shutter is opened during the film growth of MBE and MOMBE, a large amount of heat radiation is emitted from the heated evaporation source,
The heat radiation is reflected by the substrate and enters the pyrometer, making it impossible to measure the temperature accurately. That is, when thermal radiation from the evaporation source enters in addition to the radiation heat from the substrate when the shutter is opened, the display value of the pyrometer increases. This signal is fed back to the heating power supply, and the temperature is lowered even though the substrate temperature has not actually risen. In particular, an evaporation source heated to a high temperature of 1000 ° C. or higher has a great influence. In order to reduce this influence, a method of devising the installation location of the pyrometer and a method of narrowing the wavelength range of the measuring light of the pyrometer to about 20 nm have been proposed, but the problem has not been solved.

[0006]

When the substrate temperature is measured by utilizing the thermal radiation spectrum from the substrate surface and the substrate temperature is controlled, the thermal radiation from the nearby heat source is reflected on the substrate surface and the substrate temperature is reduced. It adversely affects the measurement. In order to prevent this, the temperature control device of the present invention does not measure the temperature of the substrate surface while the heat source that may disturb the temperature measurement is switched on, and based on the data stored in the memory circuit. It is characterized in that it outputs a constant temperature control signal.
That is, an object of the present invention is to provide a substrate temperature control device using a pyrometer, which is not affected by heat radiation from a high temperature evaporation source.

[0007]

The substrate temperature control device of the present invention comprises a pyrometer, a temperature controller, a memory circuit, and a changeover switch, and each component has the following functions. . That is, the pyrometer measures the substrate temperature and outputs the measured value to the temperature controller. After detecting the difference between the measured temperature measured by the pyrometer and the set temperature, the temperature controller outputs a signal to decrease the output toward the heating power source if the measured temperature is higher, and a signal to increase the output if it is lower. It has a normal temperature control function and a function to output a constant output signal stored in a memory circuit, and switches both functions by a signal from a changeover switch. The memory circuit stores the average value of the output of the temperature controller during temperature control, and outputs the stored temperature control signal to the temperature controller according to the signal from the changeover switch. The changeover switch switches the operation of the temperature controller and the memory circuit according to a signal from the outside (for example, a shutter opening / closing signal).

[0008]

When the shutter is closed, the function of the temperature controller is to change the output momentarily. When the shutter is opened, the output is switched to a constant control (its value is the average value in the memory) in synchronization with the signal. Therefore, the temperature of the substrate is kept constant even if the reading of the pyrometer fluctuates greatly.

[0009]

EXAMPLES Examples of the present invention will be described. FIG. 1 is a block diagram for explaining an embodiment of the present invention. 1 is a vacuum container, 2 is a substrate, 3 is a pyrometer, 4 is a temperature controller,
5 is a heating power source, 6 is a heater, 7 is a phosphine valve, 8 is a phosphorus evaporation source, 9 is a TMI valve, 10 is an evaporation source, 11 is a tin shutter, 12 is a tin evaporation source, 1
3 is a memory circuit, 14 is a valve for arsine, and 15 is TE.
A G valve, 16 a beryllium shutter, 17 a beryllium evaporation source, 18 a changeover switch, and 19 a thermocouple.

InG on InP substrate using MONBE
An example of producing an aAs / InGaAsP-MQW laser will be described. Phosphine is used as a raw material of phosphorus, arsine is used as a raw material of arsenic, trimethylindium (TMI) is used as a raw material of indium, triethylgallium (TEG) is used as a raw material of gallium, beryllium is used as a p-type dopant, and tin is used as an n-type dopant. I was there. The temperature of the InP substrate 2 placed in the vacuum container 1 is measured using the pyrometer 3. Set the temperature controller 4 connected to the pyrometer 3 to 505 ° C.
When set to, a signal is sent to the heating power source 5 and the heater 6 is heated. When the temperature of the substrate 2 reached about 300 ° C., the phosphine valve 7 was opened, and the substrate 2 was thermally decomposed and the substrate 2 was irradiated with phosphorus. When 5 minutes had passed at 505 ° C., the TMI valve 9 was opened, the light was emitted from the evaporation source 10, and InP was vapor-deposited on the substrate. Shutter 11 after 1 second
Then, tin was emitted from the evaporation source 12 to dope the InP film with tin. The temperature of the evaporation source 12 for tin was 770 ° C. At this time, the fluctuation of the measured value of the pyrometer due to the opening and closing of the shutter was less than 1 degree.

The output signal sent from the temperature controller 4 changes every 0.1 seconds, and the average value thereof is the memory circuit 1.
It is saved in 3 and is rewritten sequentially every 1 minute. After 30 minutes, close the tin shutter 13
Subsequently, the valve 14 for arsine and the valve 15 for TEG were opened to grow an InGaAsP film for 6 minutes (corresponding to a thickness of 1000 Å). Next, close the phosphine valve 7,
InGaAs was grown to 80 Å, then the phosphine valve was opened, and InGaAsP was grown to 100 Å, and these operations were repeated 6 times. After that, 100 InGaAsP
It grew to 0Å. Close the valves for arsine and TEG
After growing the P film for 30 seconds, the beryllium shutter 16
Opened. Beryllium is emitted from the beryllium evaporation source 17 (heated to 1000 ° C.) and doped into the InP film. At this time, the changeover switch 18 is activated at the same time when the shutter 16 is opened, and the function of the temperature controller 4 changes to the constant output operation. The output value at that time is designated by the average value stored in the memory circuit 13 immediately before the shutter is opened. The reading of the pyrometer is 530 ° C at the same time when the shutter is opened.
However, the fluctuation of the reading value of the thermocouple using the monitor was less than 1 degree. Beryllium-doped InP 1.5μ
After m growth, 2000 liters of beryllium-doped InGaAs to be a contact layer was vapor-deposited.

FIG. 2 shows the elapsed time of the display temperature of the pyrometer during the film growth, and FIG. 3 shows the time change of the indicated value of the thermocouple 19. It can be seen from FIG. 2 that the display temperature rises sharply when the beryllium shutter is opened, but the thermocouple indicated value in FIG. 3 hardly changes. The display temperature in FIG. 3 is 560 ° C., which is considerably different from the actual temperature, but the reason has already been described. The threshold current density of the laser manufactured by this method was 1 kA / cm ² . On the other hand, the current density without this method increased to ² kA / cm ² or more.

[0013]

According to the embodiment of the present invention, the function of the temperature controller is switched in synchronization with one shutter of the dopant in the MOMBE method, but it is easy to synchronize with a plurality of shutters. In the MBE method, since many evaporation sources including aluminum are heated to 1000 ° C. or higher, this method is particularly effective. As described above, according to the present invention, it is possible to obtain a substrate temperature control device using a pyrometer that is not affected by heat radiation from a high-temperature evaporation source.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of the present invention.

FIG. 2 shows a time course of a display temperature of a pyrometer during film growth.

FIG. 3 shows a time course of a display temperature of a thermocouple during film growth.

[Explanation of symbols]

 1 Vacuum Container 2 Substrate 3 Pyrometer 4 Temperature Controller 5 Heating Power Supply 6 Heater 7 Phosphine Valve 8 Phosphorus Evaporation Source 9 TMI Valve 10 Evaporation Source 11 Tin Shutter 12 Tin Evaporation Source 13 Memory Circuit 14 Arsine Valve 15 TEG Valve 16 Beryllium shutter 17 Beryllium evaporation source 18 Changeover switch 19 Thermocouple

Claims (1)

[Claims] 1. A pyrometer for measuring the temperature of a substrate,
A temperature controller that receives a measurement value from the pyrometer and controls the temperature of the substrate, a memory that stores a temperature control signal from the temperature controller, and a changeover switch that operates according to an external signal are provided, and A substrate temperature control device, wherein either the signal from the pyrometer or the signal from the memory is given to the temperature controller by the operation of the changeover switch.