JPS60149124A - Method for liquid-phase epitaxial growth - Google Patents

Abstract

PURPOSE:To improve the reproductivity of growing conditions by increasing the accuracy in temperature detection by using the voltage value corresponding to a saturation temperature of melt which is determined experimentaly by observing variation with time of the output voltage of a thermocouple for observation which is immersed in one of melts through a protective layer as a reference voltage value of the thermcouple for controlling a temperature of a furnace. CONSTITUTION:A tube reactor 6 is surrounded by a heater 7 in which thermocouples 21-23 for controlling an electric power are buried and in the reactor 6, a substrate holder 4 having semiconductor substrate 5 which are placed with levelling their surfaces is arranged. Also, a melt holder 3 containing plural melts 1 and 2 put on the holder 4, which is aliced to bring the melts 1 and 2 in contact with the surface of substrate 5 successively and the desired epitaxial layer is obtained. In this consitution, a thermocouple for observation 42 is immersed in the melt 1 by using an operation bar 41 coated with a protective layer consisting of BN and etc., and the voltage value corresponding to a saturation temperature of the obtained melt is used as an applied voltage of a thermocouple for temperature detection 9 which is buried in a holder 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an improvement in a crystal growth method using an epitaxial method.

(Prior art and its problems) There are various epitaxial growth methods, but the liquid phase epitaxial method produces crystals of good quality, which is especially important for manufacturing epitaxial wafers used in light emitting and light receiving devices. It is a great technology. However, the liquid phase epitaxial method requires extremely precise temperature control due to its manufacturing principle.

The principles of the liquid phase epitaxial method and the problems of conventional electric furnaces will be briefly described below based on the drawings. As an example,
The case of epitaxial growth of InP is shown. 11th Z is a drawing showing the saturation temperature when P is dissolved in In. P at an atomic fraction of X1 can be mixed into In at a temperature of Tl. In In at temperature T2, P at X2 can be mixed. 'Temperature T+ floor sauce, P
When a raw material melt in which is dissolved at an atomic fraction x1 is cooled to TQ, a supersaturated In melt containing a large amount of dissolved P corresponding to If you put it, the P of the call is In
P is deposited on the substrate to obtain a thin film crystal of InP. T
2 is set lower than Tl and within a range that does not cause spontaneous nucleation in the melt, that is, within the supersaturation limit. If necessary, a method of further cooling after contact may be used. The above is the principle of the liquid phase epitaxial method, and the relationship between the atomic fraction of the solute and the saturation temperature shown in Figure 1 is called the liquid A old gland, and has a unique relationship depending on the type of atoms involved.

In the liquid phase 1 growth method, a predetermined amount, e.g.
1 mixed with P is prepared and kept in a furnace as shown in FIG. FIG. 2 shows a cross section of a conventionally used liquid phase epitaxial furnace. The above P is mixed into the melt holder 3. Thereafter, after cooling to a required temperature, for example, T2, the melt holder 3 is moved by the operation rod 8, and the melt 1 is first brought into contact with the substrate 5, and then the melt 2 is brought into contact with the substrate 5. In this way, a two-layer epitaxial crystal is formed. can be obtained. At this time, temperature control plays an important role. If the actual melt temperature is T
If I is not reached, the predetermined amount of P will not dissolve into the melt. P is usually added by adding InP crystals onto the melt, so InP remains on the melt, and if it is cooled as it is, crystal growth will occur on the InP, and even if the melt and the substrate are brought into contact, there will be no incomplete contact with the substrate. Only the epitaxial layer can be obtained. Furthermore, if the temperature at the time of contact between the melt and the substrate is higher than T2, the epitaxial layer on the substrate may become abnormally thin, or depending on the temperature distribution, no epitaxial layer may be obtained at all, or in extreme cases, the substrate crystal may become thinner. be dissolved.

In some cases, the supersaturation limit is exceeded, and InP crystals are formed in the melt before the melt and the substrate come into contact.
Only irregular or unusually thin epitaxial layers are formed on the substrate.

Conventional liquid phase epitaxial growth is based on the temperature indicated by the thermocouple 9 inserted near the substrate, so if there is a difference in the thermocouple output or a small fluctuation in the temperature distribution inside the furnace, The degree of supersaturation of the melt varies greatly. In particular, when using conventional temperature control methods, even though the temperature difference near the epitaxial growth temperature is accurate due to the characteristics of thermocouples, sufficient accuracy is not ensured for the absolute value of temperature due to the reasons mentioned above. . That is, in the example of FIG. 1, even if the temperature difference between Ti and Tg can be set accurately, the value of T1 or T11 itself is very uncertain.

For this reason, crystal production using the liquid phase epitaxial method has been an unstable and extremely difficult technique to control.

The present invention has been made to improve the above points.

As a positive value, the melt value is experimentally determined by observing the time fluctuation of the output voltage of an observation thermocouple immersed through a protective layer into one of the multiple melts that are the raw materials for crystals. This is a liquid phase epitaxial growth method characterized by using a voltage value corresponding to the saturation temperature of the liquid.

In particular, the liquid phase epitaxial method of the present invention is equipped with a storage device for storing and holding a reference voltage to be compared with the output voltage of a thermocouple for temperature control, and furthermore, the storage device is equipped with a storage device for storing a reference voltage to be compared with the output voltage of a thermocouple for temperature control, and a crystal to be epitaxially grown is stored in the storage device. The output voltage of the thermocouple corresponding to the saturation temperature of one of the melts, which is the raw material of the melt, is held as the reference voltage.
When using an electric furnace for liquid phase epitaxial growth having an electronic circuit for controlling the temperature of the furnace based on the reference voltage, an observation thermocouple immersed in the melt through a protective layer serves as the reference voltage. It is characterized by using a voltage value corresponding to the saturation temperature of one melt, which is determined experimentally by observing the time fluctuation of the output voltage.

An example of the structure of an electric furnace for liquid phase epitaxial growth used for this purpose is shown in FIG. 48 in a structural diagram as shown in FIG.

The difference from Fig. 2 is that the operating section 4 includes the observation thermocouple 4.2.
It is to have 1. The tip of the operating tip 41 is coated with a protective layer of a material that does not contaminate the melt 1, such as BN, and reaches the melt 1 together with the viewing thermocouples 4 and 2. In this state, the temperature is raised at a constant rate, and the difference in the minute temperature fluctuation rate due to the effect of the heat of dissolution of InP between a state in which InP crystals remain in melt 1 and a state in which InP is completely dissolved can be calculated, for example. By electronically detecting the observation thermocouple 42, the output voltage value of the thermocouple 9 corresponding to the saturation temperature of Mel l-1 is stored in the storage device using an electronic circuit. The same voltage value corresponds exactly to the definition of the liquidus line, and for example, P volatilization during heating causes the P
? ! Even if there is a certain amount of movement, or if there are individual differences in thermocouples, the control of the furnace after melting is always based on the output voltage of the thermocouple corresponding to the exact saturation temperature T1. Due to the characteristics of the pair, setting the temperature difference near the growth temperature, for example, setting T i -T 2 can be much more accurate than the absolute value of TI or T2. Therefore, the present invention enables temperature control that is far more accurate and faithful to the basic principle than in the past, and in principle, instability caused by individual differences in thermocouples is completely eliminated.

The method of the present invention may be used every time liquid phase growth is performed, or may be applied every time some growth condition is updated, such as by exchanging a thermocouple, and the reference voltage stored at the time of update is used for other purposes.

Furthermore, the output voltage of the control thermocouple 22 can be used as the output voltage of the thermocouple to be used as the reference point.

Furthermore, for convenience of explanation, a 1nP liquid phase epitaxial method is taken as an example, but the present invention applies to all crystalline GaAs+ InGaAsP+ GaA crystals using the liquid phase epitaxial method.
Needless to say, it can be applied to lAs, etc.

Since the control is based on a temperature fixed point that is directly related to the fundamental principle of long-term temperature, the instability caused by the temperature detection accuracy of the conventional liquid phase epitaxial method is completely eliminated. Therefore, the reproducibility of growth conditions is dramatically improved by the present invention. As a result, the production yield of crystals by liquid phase growth method is greatly improved, and the productivity of devices using such crystals, especially semiconductor light-emitting/light-receiving devices, is greatly improved. This will greatly contribute to the development of optoelectronics.

[Brief explanation of drawings]

FIG. 1 is a drawing showing the solubility of P in an In melt. Fig. 2 is a cross-sectional view of an electric furnace used in the conventionally widely used liquid phase epitaxial growth method, and Fig. 3 is an example of the structure of an electric furnace to be used to carry out the liquid phase epitaxial growth method of the present invention. FIG. 2 is a sectional view similar to FIG. It is a cage. ■, the first melt 2, the second melt 3, the melt holder 4, the substrate holder 5, the substrate 6, the reaction tube 7, the heater 8, the operating tip 9, the temperature detection thermocouple 41, the tip of which is covered with a protective material. Positioned operating rod 42, observation thermocouple

Claims (1)

[Claims] (1) As the reference voltage value of the thermocouple for controlling the temperature of the furnace, observe the time fluctuation of the output voltage of the observation thermocouple immersed through a protective layer into one of the multiple melts that are the raw materials for crystals. A method of liquid phase epitaxial growth characterized by using a voltage value corresponding to a saturation temperature of a melt determined experimentally.