JPH08203838A - Manufacture of compound semiconductor - Google Patents

Abstract

PURPOSE: To lighten the limitation on the thickness of an epitaxial growth layer, expand a thickness adjusting range of the growth layer, and lessen the decline of a compositional ratio of a salute along with the growth of the layer by raising a temperature at least once during the lowering of the temperature. CONSTITUTION: A solution for growth 9 is heated to an equilibrium temperature of about 920 deg.C and then is maintained at that temperature for about 60 minutes. Then, a slider 3 is operated to supply the solution from a supply vessel 4 to a growth vessel 1. Immediately after a space between substrates 7 and 8 is filled with the solution, the solution is cooled at a cooling speed 1 deg.C/min for about 60 minutes. During the lowering of the temperature, the solution is heated at a heating speed of 5 deg.C/min for about four minutes. This cooling and heating cycle is repeated four times more. When the solution is cooled down at a cooling speed of 1 deg.C/min to about 600 deg.C, a slider 5 is operated to collect the solution for growth 9 in the growth vessel 1 into an exhaust vessel 6, when the crystal growth is finished. By this method, a variation in a compositional ratio of compound semiconductors can be lessened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a compound semiconductor by liquid phase epitaxial growth.

[0002]

2. Description of the Related Art Conventionally, as a manufacturing method of this type, for example, when forming an AlGaAs mixed crystal, as shown in FIG. Between 11 and 11, A of about 900 ℃
l-Ga-As growth solution (solution in which Ga is a solvent and single crystal GaAs, Al, etc. are dissolved in a solute) 13 is interposed, and the Al-Ga-As solution 13 is heated to about 700 ° C.
Without raising the temperature on the way, the temperature is lowered at a constant cooling rate, or the temperature is gradually lowered at two types of cooling rates, and the substrate 11,
A common method is to grow AlGaAs epitaxial layers on the 11 facing surfaces. At this time, the growth amount (growth film thickness) d of the epitaxial layer is, as shown in FIG. 4 and FIG. 5, the thickness (solution thickness) D of the growth solution interposed between the substrates 11 and 11 facing each other, and It depends on the cooling rate V of the growth solution 13. As the solution thickness D is increased, the grown film thickness d increases substantially linearly, and eventually reaches the ceiling. Further, as the cooling rate V is increased, the grown film thickness d decreases.

[0003]

Therefore, in the conventional method described above, even if the solution thickness and the cooling rate are optimally adjusted to increase the grown film thickness, there is a limit to increase the grown film thickness. . Specifically, the film thickness is about 150 μm for GaAs growth and about 100 μm for Al _X Ga _{1 -X} As (x = 0.7) growth with low solubility in one growth step.

Further, for example, in the above AlGaAs growth, the Al in the solution is taken into this layer as the epitaxial layer grows, and the concentration of Al in the solution decreases, so that the epitaxial layer grows. Accordingly, the mixed crystal ratio of Al in the layer becomes low. When an LED is manufactured using the epitaxial layer grown in this way, the width of the energy band region related to light emission becomes narrow.

An object of the present invention is to provide a method capable of reducing the limitation on the thickness of the epitaxial growth layer and widening the range of adjusting the thickness of the growth layer. It is another object of the present invention to provide a method for producing a compound semiconductor by liquid phase epitaxial growth, which can alleviate the decrease in the mixed crystal ratio of the solute accompanying the layer growth.

[0006]

As a result of intensive studies to achieve the above object, the present inventor has found that a solute in a growth solution has a vector that moves to an upper layer or a lower layer of the solution due to buoyancy of the solvent. Therefore, paying attention to the fact that there is a solute concentration gradient in the direction of gravity, in which the concentration of solute becomes higher in the upper layer of the solution and becomes lower as it goes to the lower layer, or vice versa, the substrate is moved horizontally up and down through the growth solution. When arranging and growing the epitaxial layer on the substrate surface by gradually lowering the temperature while adding a temperature raising process to the solution while lowering the temperature, the substrate surface on the side where the solute concentration in the solution is low and / or the substrate The layer that has grown on the surface dissolves, and the vector when the dissolved substance diffuses to the upper layer or the lower layer of the solution due to the buoyancy between the solvent and the above-mentioned solute existing in the solution is moved upward or downward. I vector coupled with, becomes larger vector, to promote the growth of epitaxial layers to the substrate of the solute concentration is higher side in the solution, it was found that can significantly improve the growth film thickness obtained.

That is, the present invention relates to the following manufacturing method. A method for producing a compound semiconductor in which a substrate is placed horizontally above and below via a growth solution, and an epitaxial layer is grown on the substrate surface by lowering the temperature of the growth solution, at least during the temperature drop. A method for producing a compound semiconductor, which comprises raising the temperature once. The method according to the above, characterized in that the temperature is gradually decreased while repeating the temperature decrease and the temperature increase. The growth solution is a Ga-As solution or Al-Ga-As
It is a solution, The manufacturing method of the said or above characterized by the above-mentioned.

In the present invention, as the substrate for growing the epitaxial layer and the growth solution, a combination conventionally used in the liquid phase epitaxial growth method can be used without particular limitation. Specifically, for example, a single crystal GaAs substrate and a Ga solvent are used for polycrystal GaAs and Al.
And so on, and a combination of a single crystal Si substrate and a solution of polycrystalline Si as a solute in an In solvent.

The temperature rising rate in the present invention may be appropriately selected. However, if the temperature rising rate is too fast, the solute in the solution near the substrate where the solution concentration is high, that is, the substrate where high growth is desired, is abrupt. Since the temperature rises to an unsaturated state, the growth of the layer grown on the surface of the substrate on which high growth is desired may be dissolved, which may lower the growth efficiency.On the other hand, if it is too slow, it takes a long time to grow. As a result, productivity is lowered, so 1 to 10 ° C./min
The degree is preferable and practical. In addition, the temperature rise time and the number of times of temperature rise in a series of temperature decrease (growth operation) are:
The thickness can be appropriately selected according to the target film thickness, and the film thickness can be increased by increasing the temperature rising time and increasing the number of times of temperature rising. Therefore, the temperature rise time and the number of times of temperature rise may be appropriately adjusted within the range in which the temperature of the solution can be gradually lowered as a whole, in the range of the target film thickness and the productivity, in relation to the above-mentioned temperature rise rate.

In the present invention, the locus pattern of the temperature decrease due to the temperature decrease and the temperature increase of the solution can be appropriately determined. For example, the temperature decrease and the temperature increase may be continuously repeated to decrease the temperature as a whole. Alternatively, the temperature may be lowered by repeatedly lowering and raising the temperature so that the constant temperature is maintained for a certain period after the temperature is raised.

Further, as the temperature decreasing rate in the present invention,
Without particular limitation, it can be carried out within a well-known range in the slow cooling method by liquid phase epitaxial. Further, the film thickness and mixed crystal ratio (composition ratio) of the epitaxial growth layer obtained by the present invention are appropriately determined depending on the mixing ratio of solutes in the growth solution, the rate of temperature increase and decrease, the temperature increase and decrease time, the number of times of temperature increase, etc. Can be adjusted.

As the substrate interval in the present invention, as shown in FIG. 4, it may be carried out under appropriate conditions so as to obtain a target film thickness.

[0013]

The substrate is placed horizontally above and below the growth solution, and when the temperature of the solution is lowered, the epitaxial layer begins to grow on the surface of the substrate. At this time, when the specific gravity of the solute in the dissolved state is smaller than that of the solvent, for example, when Ga is the solvent and Al and As are the solutes, a concentration gradient occurs in which the concentration of the solute is higher in the upper layer of the solution. In comparison with the above, the growth amount on the upper substrate is large. Therefore, when the temperature of the solution is raised while the temperature of the solution is being lowered, the grown epitaxial layer starts to dissolve again, but due to the concentration gradient of the solute, the substrate on the side where the solute concentration in the upper and lower layers of the solution is low (the growth amount is small). Of the growth layer, while the solution in the vicinity of the substrate with a high solute concentration (the above-mentioned substrate with a large growth amount) is saturated or near saturation, the dissolution of the growth layer It can be extremely reduced.

Then, when the temperature of the solution is lowered again, the growth on the substrate with the higher solute concentration (the substrate with the larger growth amount) becomes larger than that on the other substrate. Therefore, it is possible to efficiently promote the growth of the substrate on the higher solute concentration side among the substrates arranged above and below. Further, since the growth can be performed by lowering the temperature while adding the solute by raising the temperature, it is possible to reduce the decrease in the mixed crystal ratio in the growth layer of the solute.

[0015]

EXAMPLES The features of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the first embodiment, A for LED
The case of growing an lGaAs mixed crystal will be described. FIG. 1 shows an outline of a manufacturing apparatus used in this example. In the figure, the symbol g indicates the direction of gravity. In the above-mentioned manufacturing apparatus, the jig plates 2 and 2 are horizontally arranged in the growth tank 1 at a predetermined distance apart from each other, and a growth solution supply tank 4 is mounted on the growth tank 1 via a slider 3. ing. The slider 3 is provided with a hole 3 ', and the hole 1'provided in the upper plate of the growth tank 1 and the hole 4'provided in the bottom plate of the supply tank 4 can be in communication or non-communication. It has a valve function. A discharge tank 6 is attached below the growth tank 1 via a slider 5. Similar to the slider 3, the slider 5 also has a hole 5 ′ that allows the hole 1 ″ provided in the bottom plate of the growth tank 1 and the hole 6 ′ provided in the upper plate of the discharge tank 6 to communicate with each other. A valve function capable of being disconnected is provided, and a heater (not shown) capable of adjusting the temperature of the whole is provided.

Disc-shaped single crystal GaAs substrates 7 and 8 each having a diameter of about 13 mm and serving as seed crystals are fixed to the jig plates 2 and 2 with a distance of about 4 mm. Then, using Ga as a solvent, Al and polycrystal GaAs as solutes, and a growth solution 9 with a weight ratio of Ga: Al: GaAs = 100: 0.6: 5, an equilibrium temperature was measured as shown in FIG. 920
After heating to about 0 ° C. and holding this for about 60 minutes, the slider 3 is operated to supply the material from the supply tank 4 into the growth tank 1 to fill the space between the substrates 7 and 8 and immediately cool it at a cooling rate of 1
The mixture was cooled at a heating rate of about 5 ° C./min for about 4 minutes, and this cooling and heating cycle was repeated four more times. Subsequently, the temperature was cooled to about 600 ° C. at a cooling rate of about 1 ° C./min, and the slider 5 was operated to collect the growth solution 9 in the growth tank 1 into the discharge tank 6 to complete the crystal growth.

An Al _0.3 Ga _0.7 As epitaxial layer having a film thickness of about 200 μm was grown on the surface of the upper substrate 7 obtained as described above. Further, this epitaxial layer showed only a slight decrease in the mixed crystal ratio of Al in the growth direction, and was extremely excellent in that the energy band region could be widened when it was used for manufacturing an LED.

Next, the case of growing a GaAs crystal will be described as a second embodiment. The growth solution 9 was prepared by using a solution in which Ga was a solvent, single crystal GaAs was used as a solute, and the weight ratio of Ga: GaAs was 20: 3, and the solution temperature was lowered from about 920 ° C. to about 600 ° C. Epitaxial growth was performed under the same conditions as in the first embodiment.

On the surface of the upper substrate 7 obtained as a result, a GaAs epitaxial layer having a film thickness of about 250 μm was grown. In the first and second embodiments, no impurities (dopants) were added to the growth solution, but in the present invention, well-known dopants such as Si, Zn, Ge, Te are appropriately added to the solution, It is also possible to manufacture an epitaxial growth layer containing impurities.

As a comparative example, the cooling rate is 0.2 ° C./m.
After cooling in for 600 minutes and maintaining this temperature for 60 minutes, epitaxial growth was performed under the same conditions as in the above-mentioned first example except that the temperature was lowered at a cooling rate of 0.5 ° C./min. A grown on the surface of the obtained upper substrate
The film thickness of the 1GaAs epitaxial layer was only 90 μm.

[0021]

According to the present invention, it is possible to obtain an epitaxially grown layer of a compound semiconductor having a thickness that cannot be obtained by the conventional method, and it is possible to make the width of the grown film thickness that can be designed extremely wide. Further, according to the present invention, it is possible to significantly reduce the variation in the mixed crystal ratio of the compound of the compound semiconductor obtained by the conventional liquid phase epitaxial growth method, and the resulting compound semiconductor is used in the manufacture of semiconductor devices such as LEDs. It is extremely useful.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a crystal growth apparatus used in first and second embodiments of the present invention.

FIG. 2 is a temperature (T) -time (t) graph showing a trajectory pattern of temperature drop of a solution in the first example of the present invention.

FIG. 3 is a schematic sectional view illustrating a conventional liquid phase epitaxial growth method.

FIG. 4 Solution thickness (D) in liquid phase epitaxial growth
5 is a graph showing the relationship between the growth thickness and the grown film thickness (d).

FIG. 5 is a graph showing a relationship between a cooling rate (V) of a solution and a grown film thickness (d) in liquid phase epitaxial growth.

[Explanation of symbols]

 7,8 GaAs substrate 9 Al-Ga-As solution g Gravity direction

Claims (3)

[Claims] 1. A method for producing a compound semiconductor, wherein a substrate is placed horizontally above and below via a growth solution, and the temperature of the growth solution is lowered to grow an epitaxial layer on the surface of the substrate. A method for producing a compound semiconductor, characterized in that the temperature is raised at least once during the lowering. 2. The method according to claim 1, wherein the temperature is gradually decreased by repeating the temperature decrease and the temperature increase. 3. The growth solution is a Ga-As solution or Al-
It is a Ga-As solution, It is characterized by the above-mentioned.
The manufacturing method described in.