JPS6353158B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses one solution bath, and forms an epitaxial layer of one conductivity type and an epitaxial layer of the opposite conductivity type or an epitaxial layer of the same conductivity type with low impurity. The present invention relates to a method for continuously growing a concentrated epitaxial layer.

The liquid phase epitaxial growth method is a widely used method for forming epitaxial layers of gallium arsenide (GaAs), gallium phosphide (GaP), gallium aluminum arsenide (GaAlAs), etc. on - group compound semiconductor substrates. It can be said to be the basic processing method for manufacturing semiconductor lasers or light emitting diodes. For example, by such a liquid phase epitaxial growth method,
One of the commonly used methods for forming a p-n junction is to prepare a solution bath containing a solution containing impurities of one conductivity type, and to first contact the semiconductor substrate with the solution in the solution bath. After growing the first epitaxial layer, impurities of one conductivity type are compensated for by adding impurities of the opposite conductivity type to the solution in the solution bath from the gas phase or solid phase, and the epitaxial layer is grown on the semiconductor substrate. There is a method of growing a second epitaxial layer of the opposite conductivity type on the epitaxially grown first epitaxial layer.

This method allows the formation of the first and second epitaxial layers using one solution tank, and the tank structure of the liquid phase growth apparatus is simple.
It is widely used in practical applications. However, in this method, compensation for impurities is required in forming the second epitaxial layer, so the impurity concentration of the second epitaxial layer is inevitably higher than that of the first epitaxial layer. Therefore, the impurity concentration of the second epitaxial layer cannot be controlled to an arbitrary value;
Furthermore, since the impurity concentration of the second epitaxial layer becomes high, the crystallinity of this layer is poor, and it is difficult to obtain a light emitting diode with sufficient light emitting output using this method.

As a method to solve this problem, the applicant has developed a method in which after growing the first epitaxial layer, the reaction system is evacuated to evaporate impurities in the solution, and the second epitaxial layer is grown again. Special request for
This has already been proposed in specification No. 54-4381. Although this method makes it easy to remove impurities in the solution, there still remains the problem that evaporated impurities and solute atoms scatter throughout the reaction system and contaminate various parts. There is still room for further improvement in terms of concentration controllability.

The present invention provides a liquid phase epitaxial growth method that eliminates the problem of post-reaction contamination due to the scattering of evaporated impurities, etc., which is generated in the above-mentioned method using vacuum evacuation, and improves controllability of impurity concentration. The present invention is characterized in that after a semiconductor substrate is brought into contact with a solution containing impurities of one conductivity type to form an epitaxial layer of one conductivity type, the reaction system is evacuated while flowing a carrier gas, and the reaction system is evacuated while flowing a carrier gas. By evaporating the impurities and removing them from the reaction system, a solution with a low impurity concentration is obtained, and this solution is then used to grow the epitaxial layer again.

Hereinafter, the liquid phase epitaxial growth method of the present invention will be explained in detail based on Examples and drawings.

FIG. 1 is a diagram showing the configuration of a liquid phase epitaxial growth apparatus used when performing GaP epitaxial growth for GaP green light emitting diodes by the method of the present invention, and FIG. FIG. 3 is a diagram showing a temperature program.

As shown in FIG. 1, the liquid phase epitaxial growth apparatus used in the present invention includes a main electric furnace 1 and an auxiliary electric furnace 2, which are arranged inside these electric furnaces 1 and 2, and one end of which has a first valve 3. A reaction tube 5 made of quartz, the other end of which is connected to a gas supply system through a second valve 4 and an exhaust system through a second valve 4, and a substrate holder 6 and a solution tank for holding a GaP substrate serving as a starting material. The main component is a growth boat consisting of 7. In addition, 8 is a GaP substrate, 9
10 is an operating handle for moving the solution tank 7; 11 is an impurity boat; 12 is an impurity contained in the boat 11; for example, zinc, Zn,
And 13 is a vacuum pump.

By the way, the GaP epitaxial growth solution 9 used for manufacturing GaP green light emitting diodes is as follows:
For example, 10g of gallium Ga as a solvent, 350mg of polycrystalline GaP as a solute, and tellurium as an n-type impurity.
This is a GaP saturated solution formed by putting 100 μg of Te into a solution bath 7 and heating it.

The process of growing an epitaxial layer will be specifically explained below based on the temperature program shown in FIG.

First, only the main electric furnace 1 is operated and heated, and after raising the temperature to T ₁ , the second valve 4 is turned on while flowing H ₂ gas from the first valve 3 at a rate of 1/min.
_The time τ ₁ ( _{approximately} 30
temperature T ₁ (1050 min) for the boat in the reaction tube
℃) to prepare a saturated solution 9 of GaP containing Te. Next, at time t ₂ , the operation handle 10 is operated to move the solution tank 7 to bring the GaP saturated solution 9 into contact with the GaP substrate 8 , and the time τ ₂ (approximately 20 minutes) until time t ₃
Keep it in this state for a long time.

Then, from time t ₃ , slow cooling is started at a cooling rate of 1° C./min, and this slow cooling is continued for a time τ ₃ until reaching temperature T ₂ (for example, 920° C.) at time t ₄ ,
An n-type epitaxial layer is grown on the GaP substrate 8.

After growing the n-type epitaxial layer in this way, _the time τ ₄ ( ₃₀ ~
40 minutes) from the first valve 3.
While flowing H ₂ gas, the vacuum pump 13 is activated to evacuate the inside of the tube. Te in the solution 9 is evaporated by this vacuum evacuation, and is discharged out of the reaction system by H ₂ gas. That is, after the time τ ₄ has elapsed, the impurity Te concentration in the solution 9 decreases to a negligible level. Next, at time _t5 , the auxiliary electric furnace 8 is operated, Zn in the impurity boat 11 is heated and evaporated, and Zn, which is a p-type impurity, is introduced from the gas phase.
From time t ₆ when time τ ₅ has elapsed, the temperature T ₃ (for example, 800
℃), and a p-type epitaxial layer is grown on the n-type epitaxial layer. Finally, at time _t7 , the contact between the GaP substrate 8 and the solution 9 is cut off, thereby ending all the processing.

In the method of the present invention described above, since there is a flow of carrier gas in the reaction system during vacuum evacuation, the impurity Te that has evaporated from the solution is discharged from the reaction system together with the carrier gas.
Since the evaporated impurities do not scatter and adhere to the impurity boat 11, the inner surface of the reaction tube 1, etc. and contaminate these parts, the controllability of the impurity concentration in the second epitaxial layer is improved. Even when performing epitaxial growth over a long period of time, there is no need to clean the reaction tube, which improves work efficiency.

In addition, the flow rate of the carrier gas flowing into the reaction tube 5 during vacuum evacuation is set to 50 to 500 ml/min to reduce the pressure inside the reaction tube.
If the gas flow rate is kept at 30 to 300 Torr, it is suitable for removing impurities; if the gas flow rate is less than 50 ml/min, the removal of impurities is insufficient;
If it is more than ml/min, the temperature inside the tube will be lowered. That is, it is desirable to select the flow rate of the carrier gas flow within the above-mentioned range.

In addition, in the above explanation, the case where the conductivity types of the first and _second epitaxial layers to be formed are made to be different has been exemplified. For example, it is also possible to form n-type epitaxial layers having different impurity concentrations.

In this case, the impurity concentration of the second epitaxial layer can be controlled by evacuation time and temperature. In addition, the present invention is applicable not only to GaP but also to GaAs,
It can also be widely applied to the manufacture of other compound semiconductor devices such as GaAlAs.

[Brief explanation of drawings]

FIG. 1 is a liquid phase epitaxial growth apparatus used in the method of the present invention, and FIG. 2 is a temperature program diagram showing an embodiment of the method of the present invention. DESCRIPTION OF SYMBOLS 1... Main electric furnace, 2... Auxiliary electric furnace, 3... First valve, 4... Second valve, 5... Reaction tube, 6... Substrate support stand, 7... Solution tank, 8 ...Substrate, 9...Solution, 10...Operation handle, 11...
...Impurity boat, 12...Impurity, 13...Vacuum pump.

Claims (1)

[Claims] 1. A solution for epitaxial growth doped with impurities of one conductivity type is placed in a liquid phase growth furnace that can be evacuated, a substrate is brought into contact with the solution, and a first impurity of one conductivity type is placed on the substrate. After forming the epitaxial layer, a carrier gas for preventing contamination of the reaction system is supplied from one side of the reaction system and vacuum is evacuated from the other side to bring the reaction system into a depressurized state, so that the reaction system is reduced in pressure. The impurities of the conductivity type are evaporated and removed from the reaction system, and then the solution after the impurity evaporation is used to form a second epitaxial layer on the first epitaxial layer.
A liquid phase epitaxial growth method characterized by forming an epitaxial layer of.