JP3216950B2 - Substrate temperature controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate temperature controller 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 for high-speed devices for computers but also for optical devices such as lasers which are indispensable for optical communication technology. These semiconductor devices are manufactured by metal organic pyrolysis, molecular beam epitaxy (MB).
E), a thin film forming method such as an organic metal molecular beam epitaxy method (MOMBE). MBE, MOMB
E is a method of irradiating a heated substrate in a vacuum vessel with a molecular beam-shaped raw 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, the temperature of the substrate holder is detected with a thermocouple, or the temperature of the substrate surface is detected with a pyrometer,
A method of feeding back these signals to a heating power supply via a temperature controller is generally used. The former measures the temperature of the holder on which the substrate is mounted, 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. Essentially, pyrometers are expected to provide more accurate control, but are not practical for the reasons described below.

[0003] In temperature measurement using a thermocouple, the thermocouple does not come into contact with the holder because the substrate is rotated, 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. Although an oxide film is formed on the surface of a substrate such as InP or GaAs, the indicated temperature of the thermocouple greatly changes depending on each holder, although the evaporation temperature is essentially constant. Further, when the growth starts, a film is deposited on the holder, so that 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 temperature control using a thermocouple in this way, 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 necessarily kept constant There is a disadvantage that there is no.

[0004] As the name implies, a compound semiconductor is composed of many elements. In the MBE and MOMBE methods, one or two evaporation sources for each constituent element and a plurality of evaporation sources for dopants are provided in a vacuum vessel in addition to a substrate.
By precisely adjusting the temperature of each evaporation source and opening and closing a shutter provided immediately above each evaporation source, a film having a desired structure and a controlled composition and carrier concentration is obtained.

[0005] The principle of the pyrometer is based on the fact that the radiant heat of a heated object follows the Stefan-Boltzmann law. The substrate temperature is determined in consideration of the emissivity (1 for a black body) of each semiconductor material. 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 is incident on the pyrometer, making accurate temperature measurement impossible. That is, when thermal radiation from the evaporation source enters in addition to 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 decreased even though the substrate temperature is not actually increased. In particular, the influence of the evaporation source heated to a high temperature of 1000 ° C. or more is greater. In order to reduce the influence, a method of devising a place where the pyrometer is installed and a method of narrowing the wavelength range of the measurement light of the pyrometer to about 20 nm have been proposed, but the problem has not been solved.

[0006]

When a substrate temperature is measured using a heat radiation spectrum from the substrate surface and the substrate temperature is controlled, heat radiation from a nearby heat source is reflected on the substrate surface and the substrate temperature is controlled. Affects measurement. In order to prevent this, the temperature control device of the present invention does not measure the temperature of the substrate surface while switching on the heat source that may disturb the temperature measurement, and based on the data stored in the memory circuit. The feature is that a constant temperature control signal is output.
That is, an object of the present invention is to provide a substrate temperature control device using a pyrometer that is not affected by heat radiation from a high-temperature evaporation source.

[0007]

A substrate temperature control device according to the present invention includes a pyrometer for measuring a temperature of a substrate, a temperature controller which receives a measurement value from the pyrometer and controls the temperature of the substrate, and A memory that stores a temperature control signal from the temperature controller, and is connected to the temperature controller;
And a changeover switch operated by an external signal, before
On the evaporation source for the dopant to the film formed on the substrate
A shutter for openably that, the provided, said shutter closing
The temperature based on the measurement value from the pyrometer.
Controlling the temperature of the substrate via a temperature controller;
To open, switch the changeover switch and
The average value of the temperature stored immediately before the shutter was
The temperature controller is driven by a corresponding temperature control signal and
The above object is achieved by controlling the temperature of the substrate while keeping the output constant .

[0008]

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

[0009]

An embodiment of the present invention will be described. FIG. 1 is a configuration diagram for explaining an embodiment of the present invention. 1 is a vacuum vessel, 2 is a substrate, 3 is a pyrometer, 4 is a temperature controller,
5 is a heating power supply, 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, 15 is TE
A G valve, 16 is a beryllium shutter, 17 is a beryllium evaporation source, 18 is a changeover switch, and 19 is a thermocouple.

[0010] InG is formed on an InP substrate by using MOMBE.
An example in which an aAs / InGaAsP-MQW laser is manufactured will be described. Phosphine for phosphorus, arsine for arsenic, trimethylindium (TMI) for indium, triethylgallium (TEG) for gallium, beryllium for p-type dopant, and tin for n-type dopant. Was. The temperature of the InP substrate 2 placed in the vacuum vessel 1 is measured using a pyrometer 3. Temperature controller 4 connected to pyrometer 3 at 505 ° C
, A signal is sent to the heating power supply 5 to heat the heater 6. When the temperature of the substrate 2 reached about 300 ° C., the phosphine valve 7 was opened, the substrate 2 was thermally decomposed by the evaporation source 8, and the substrate 2 was irradiated with phosphorus. When the state at 505 ° C. had elapsed for 5 minutes, the TMI valve 9 was opened, the light was emitted from the evaporation source 10, and InP was 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 tin evaporation source 12 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 1 degree or less.

The output signal sent from the temperature controller 4 changes every 0.1 second.
3 and are rewritten sequentially every minute. After a lapse of 30 minutes, the tin shutter 11 is closed,
Subsequently, the valve 14 for arsine and the valve 15 for TEG were opened, and an InGaAsP film was grown for 6 minutes (corresponding to a thickness of 1000 °). Next, the phosphine valve 7 is closed,
InGaAs was grown at 80 °, the phosphine valve 7 was opened, and InGaAsP was grown at 100 °. These operations were repeated six times. After that, InGaAsP is
00 grew. Arsine and TEG valves 14, 15
Was closed and the InP film was grown for 30 seconds, and then the beryllium shutter 16 was opened. 17 beryllium evaporation sources (1
(Heated to 000 ° C.) to emit beryllium and dope the InP film. At this time, the changeover switch 18 operates at the same time when the shutter 16 is opened, and the function of the temperature controller 4 is changed to the constant output operation. The output value at that time is specified by the average value immediately before opening the shutter stored in the memory circuit 13. The pyrometer reading increased to 530 ° C. at the same time as opening the shutter.
The variation in the readings was less than 1 degree. After growing 1.5 μm of beryllium-doped InP, beryllium-doped InGaAs serving as a contact layer was deposited at 2000 °.

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 in FIG. In FIG. 2, the display temperature rises sharply when the beryllium shutter is opened, but it can be seen that the indicated value of the thermocouple 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 when this method was not used increased to ² kA / cm ² or more.

In the embodiment of the present invention, in the MOMBE method, the function of the temperature controller is switched in synchronization with one dopant shutter, but it is easy to synchronize with a plurality of shutters. The MBE method is particularly effective because many evaporation sources including aluminum are heated to 1000 ° C. or higher.

[0014]

As described above, according to the present invention, a pyrometer for measuring the temperature of a substrate, a temperature controller which receives a measured value from the pyrometer and controls the temperature of the substrate, a memory for storing a temperature control signal from vessel, which is connected to a temperature controller, and a changeover switch operated by an external signal, the shape on the substrate
Openable and closable on evaporation source for dopant for film formation
And a shutter when the shutter is closed.
Via the temperature controller based on the measurement value from the pyrometer
Controlling the temperature of the substrate, and
Toggle the changeover switch to store the data in the memory.
Temperature control corresponding to the average temperature immediately before the shutter opens.
Drives the temperature controller by a control signal and keeps its output constant
Since the configuration is such that the temperature of the substrate is controlled, a device that is not affected by heat radiation from a high-temperature evaporation source can be obtained in a substrate temperature control device using a pyrometer.

[Brief description of the 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 the time course of the indicated temperature of the thermocouple during film growth.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 vacuum vessel 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 Selector switch 19 Thermocouple

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-291915 (JP, A) JP-A-7-78772 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/205 H01L 21/203 H01L 21/324

Claims (1)

(57) [Claims] 1. A pyrometer for measuring the temperature of a substrate, a temperature controller to which a measured value from the pyrometer is given and for controlling the temperature of the substrate, and a memory for storing a temperature control signal from the temperature controller. Connected to the temperature controller.
A changeover switch connected to the substrate and operated by an external signal , and an evaporation source for a dopant to a formed film on the substrate.
And an openable and closable shutter provided on the finisher
When the shutter is closed, based on the measured value from the pyrometer,
Controlling the temperature of the substrate via the temperature controller,
Toggle the switch when the shutter is open
Of the temperature immediately before the shutter is opened, which is stored in the memory.
The temperature controller is activated by a temperature control signal corresponding to the average value.
Driving and controlling the temperature of the substrate by keeping the output constant
That, the substrate temperature control apparatus characterized by.