JPH0566352B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multilayer liquid phase epitaxial growth method using a slide boat, and in particular, to a method for controlling thin and thick layers on a substrate regardless of the stacking order. This method relates to a method for achieving good growth, and if applied to the manufacturing process of SBDs (shotkey barrier diodes) and LDs (laser diodes), which have a multilayer structure of thin and thick layers, it will be extremely easy to manufacture them.

[Prior Art] Compound semiconductor epitaxial wafers usually have a multilayer structure, and the slide boat method, which is one of the liquid phase epitaxial growth methods, is generally used to obtain the multilayer structure. ing.

In this slide boat method, as shown in FIG.
A device configured to be brought into sequential contact with the growth solutions 14a and 14b of b is inserted into the furnace and used.

The work order is as follows: First, the temperature inside the furnace is raised to the growth temperature in the state shown in FIG. Next, as shown in FIG. 5, slow cooling starts at time h, and at time i, the substrate 10
is moved under the first growth solution 14a to start growing the first layer. At time j when the growth of the first layer is finished, the substrate 10 is again slid and moved under the second growth solution 14b, and the growth of the second layer is started. Then, at time R, the substrate 10 is slid to end the growth.

[Problems to be Solved by the Invention] However, in the conventional method described above, when trying to grow the first layer thicker and the second layer thinner, the first layer Since the time from i to j, which is the growth time of , becomes longer, the degree of supercooling ΔT ₂ of the growth solution of the second layer becomes much larger than the degree of supercooling ΔT ₁ of the first layer. When the degree of supercooling ΔT ₂ becomes large, a large phase transition occurs when the substrate 10 is brought into contact with the second layer growth solution 14b, so that the growth rate is fast and a thick crystal film grows in a short time. Put it away. Therefore, it is very difficult to control the crystal film thickness, and it has been impossible to grow a thin epitaxial layer of about 0.1 to 0.3 μm while maintaining in-plane uniformity and with good reproducibility.

By the way, in order to avoid increasing the degree of supercooling in the second layer even when the temperature is gradually lowered, when using a growth solution, the amounts of solvent and solute must be weighed with high precision to ensure that the appropriate amount is used when contacting the substrate. There is a way to obtain the degree of supercooling. In other words, in the case of a growth solution that forms a thin layer, the solvent should be adjusted so that the temperature is slightly supercooled at the second layer growth start time (time j in Figure 5) during slow cooling. Weigh the amount of solute relative to the amount of solute.

However, this method requires highly accurate weighing, making measurement very difficult, and also requires accurate control of the absolute value of temperature, making it difficult to implement with good reproducibility.

[Object of the Invention] An object of the present invention is to eliminate the above-mentioned conventional problems, to be able to accurately and easily control the degree of supercooling of a growth solution without requiring high-precision weighing, and to be able to control the degree of supercooling of a growth solution in a thick tank. A multilayer epitaxial layer consisting of thin layers can be grown on the same substrate with good uniformity and reproducibility,
Moreover, it is an object of the present invention to provide a liquid phase epitaxial growth method that enables these growths regardless of the order of lamination.

[Summary of the Invention] The present invention, which achieves the above object, is a slide boat method using a distribution method, in which each growth solution is distributed at different temperatures when distributed to distribution solution reservoirs.

This will be explained based on FIGS. 1 and 2, which correspond to embodiments.

First, a solvent and a slightly excess amount of solute are put into the growth solution reservoirs 3a and 3b of the slide boat device 1, respectively. Here, a slightly excessive amount means an amount sufficient to make the growth solutions 6a and 6b saturated solutions at each predetermined temperature described later.

Next, the device 1 is inserted into the furnace and the temperature is increased, and when the predetermined temperature T ₁ is reached, this temperature is maintained.
The solute is dissolved in the solvent of No. 1 until it is saturated (FIG. 1a), and then the saturated growth solution 6b from which the excess solute freed from the solvent is removed is transferred into the distribution solution reservoir 4b of No. 1 ( Figure 1 b).

After this transfer, the temperature is further increased, and when the predetermined temperature _T2 of the other 1 is reached, this temperature is maintained, and after dissolving the solute in the solvent of the other 1 until it is saturated, the excess free from the solvent is The saturated growth solution 6a from which solutes have been removed is transferred into another distribution solution reservoir 4a (FIG. 2c). Here, the other transferred distribution solution 1 has become a saturated solution, but the already transferred distribution solution 1 has been cut off from the growth solution 6b in the growth solution reservoir 3b, and is in the solvent. Since there is no supply of solute to dissolve in the solution, it becomes an unsaturated solution.

In this manner, the transfer operation is performed under different temperatures for each growth solution, and the transfer operation is completed (FIG. 1d).

After these transfer operations are completed, the raised temperature is slowly cooled and lowered, and when the temperature reaches a predetermined degree of supercooling ΔT ₁ minute lower than the predetermined temperature T2 of the other ₁ , the lower temperature of the distribution solution reservoir 4a of the other 1 is reached. An epitaxial layer is grown on the substrate 7 by sliding the substrate 7 into contact with the solution.
Longer contact times result in thicker layers, while shorter times result in thinner layers.

When a predetermined film thickness is formed, the substrate 7 is again slid and moved below the distribution solution reservoir 4b of 1, and the next epitaxial layer is grown on the substrate 7. Here again, the layer thickness changes depending on the length of the contact time.

By sliding the substrate sequentially under and contacting each solution in this manner, multiple epitaxial layers are grown on the same substrate.

Therefore, by arbitrarily setting the contact time with each growth solution, a multilayer epitaxial layer having an arbitrary layer thickness can be grown. In this case, in this process, unlike the conventional method in which the growth solution remains saturated even if the temperature rises as long as there is free solute, the growth solution is transferred from the growth solution reservoir to the distribution solution reservoir under a predetermined temperature. By once transferring the saturated growth solution and cutting off the supply of solute, the growth solution becomes unsaturated when the temperature exceeds a predetermined temperature, so that, for example, the first layer can be grown thicker. Even if the growth start temperature of the second layer becomes too low due to this, the saturation temperature of the growth solution for the second layer can be kept low, so that the degree of supercooling will not become large.

Furthermore, since the solute may be added in excess of the solvent, there is no need to weigh the amounts of the solvent and solute with high precision, nor to accurately control the absolute value of the temperature, as in the conventional method.

The present invention can be applied to liquid phase epitaxial growth of - group compound semiconductors including GaAs, mixed crystal compound semiconductors such as GaAlAs, and further, - group compounds and their mixed crystals.

[Example] An example of the present invention will be described below based on FIGS. 1 to 3.

FIG. 1 shows a slide boat apparatus 1 for carrying out the method of the invention.

Reference numeral 2 denotes a growth solution holder having growth solution reservoirs 3a and 3b, which is slidably provided on the distribution solution holder 5 which has distribution solution reservoirs 4a and 4b, and depending on the amount of slide, the growth solution holder is provided with growth solution reservoirs 3a and 3b. The growth solutions 6a and 6b are distributed to the solution reservoir 4.
a and 4b, respectively.

A slider 8 that holds the substrate 7 is provided at the bottom of the distribution solution holder 5, and this slider 8 is slidably provided on a boat 9, and the slide sequentially moves the substrate into the distribution solution reservoirs 4a and 4b. is configured to come into contact with the solution.

Now, the work order in the above configuration will be explained.

First, the substrate 7 is set on the slider 8, and the growth solutions 6a and 6b, which will be the raw materials for the first layer (thick film) and second layer (thin film), are placed in the first and second growth solution reservoirs 3a and 3b. Put in. Each growth solution consists of a solvent and a solute, and a sufficient amount of solute is set in the solvent to become a saturated solution under each growth temperature T ₁ and T ₂ described later. The slide boat device 1 thus set in the state shown in FIG. 1a is inserted into a reactor (not shown).

Next, the temperature of the furnace into which the slide boat device 1 was inserted was raised to the first growth temperature _T1 , as shown in FIG.
The temperature is maintained from time a to b. At the first growth temperature T ₁ , the solute is dissolved in each growth solution, especially the solvent that will become the second layer growth solution, until it is saturated. Since solute is added in excess, undissolved free solute exists, but this free solute accumulates in the upper layer of the growth solution 6b, and there is no free solute in the lower layer. Here, the growth solution holder 2 is slid to transfer the second layer of saturated growth solution 6b from the second growth solution reservoir 3b to the second distribution solution reservoir 4b (Fig. 1b). Since the lower layer of the growth solution 6b is transferred, the second distribution solution reservoir 4b contains a saturated solution from which free excess solute has been removed.

After transferring the second layer growth solution 6b in this way,
As shown in FIG. 1c, there is also a growth solution holder 2.
to cut off the communication between the second distribution solution reservoir 4b and the second growth solution reservoir 3b, while allowing the first growth solution reservoir 3a to communicate with the first distribution solution reservoir 4a, Thereafter, the temperature of the furnace is increased to the second growth temperature _T2 , and this temperature is maintained from time c to d.
hold until. By maintaining the second growth temperature _T2 , the first layer growth solution 6a is
is the saturated solution, and the saturated solution without free solute is the first
into the distribution solution reservoir 4a. At this time,
2 trapped in the second distribution solution reservoir 4b
The layer growth solution 6b is in an unsaturated state because the supply of the solute to be newly dissolved is cut off. The growth solution holder 2 is further slid to complete the transfer and distribution operation of the solutions for the first and second layers (FIG. 1d).

After these transfer and distribution operations are completed, the second growth temperature _T2 is slowly cooled down with a predetermined temperature gradient.
At the time e when the temperature of the growth solution 6a in the distribution solution reservoir 4a falls somewhat below the second growth temperature _T2 and reaches a supercooled state by _ΔT1 , slide the slider 8 to start the growth of the first layer. The solution 6a and the substrate 7 are brought into contact. This contact is maintained for a long period of time from e to f to grow a relatively thick first epitaxial layer on the substrate 7.

When the time f when the growth of the epitaxial layer of a predetermined thickness is completed, the slider 8 is slid again to bring the second layer growth solution 6b into contact with the substrate 7. At this time f, the temperature of the solution for growing the second layer is a very low temperature, which is ΔT ₃ lower than the second growth temperature T ₂ .
When viewed from the first growth temperature _T1 , the degree of supercooling is only _ΔT2 , which is a small amount.

That is, the second layer growth solution 6b confined within the second distributed solution reservoir 4b is saturated at the first growth temperature _T1 because it is confined.
If it is higher than this, it will be unsaturated, and if it is lower than this, it will be supersaturated, so even if there is a large temperature drop of ΔT ₃ from the second growth temperature T ₂ which is higher than the first growth temperature T ₁ , the Supercooling degree ΔT ₂ (=T ₁
−T ₃ ) is small. Therefore, even if the substrate 7 is contacted for a time f, the growth rate is slow and a thin epitaxial layer can be grown. This contact time is maintained for a short period f to g to grow a very thin second epitaxial layer on the substrate 7.

Thus, as shown in Figure 3, the first layer is 10~
Even when growing a 20 μm thick epitaxial layer, by setting ΔT ₂ to around 2 to 3 degrees Celsius,
A thin epitaxial layer 21 of 0.3 μm can be grown with good uniformity and reproducibility. This is particularly effective when growing a thin layer of 0.05 μm after growing several μm, such as in a semiconductor LD.

In this way, according to this example, even when the first layer is made thicker, the degree of supercooling of the solution in the second layer can be reduced. The crystal film does not grow in a short period of time, nor is it difficult to control the crystal film thickness. In addition, since the solution in contact with the substrate is separated from the solution in the growth solution reservoir in which free solutes remain, it is difficult to weigh and measure with high precision so that free solutes do not remain in the contact solution. There is no need to accurately control the absolute value of the temperature.

In the above example, a case was described in which a thin layer was grown on a thick layer, but the slow cooling temperature was reduced to 2.
By repeating this process several times, it can be applied even when a thin layer is grown first, and the number of growth solution reservoirs is not limited to two, but can also be applied when there are three or more.

[Effects of the Invention] In summary, the present invention exhibits the following excellent effects.

(1) By transferring and distributing each growth solution at different temperatures, the temperature at which the saturated state is maintained can be set separately for each growth solution, unlike conventional systems that distribute at the same temperature. Therefore, by arbitrarily determining the width between these set temperatures, the degree of supercooling of the growth solution can be appropriately determined regardless of the order in which thick layers and thin layers are stacked. Therefore, an epitaxial layer having a laminated structure of thick and thin layers can be grown with good uniformity and reproducibility.

(2) By transferring the saturated growth solution, which removes the excess solute released from the solvent after saturation, into the distribution solution reservoir, it is possible to
It is not necessary to weigh the solute with high accuracy, and only a rough weighing of the solute in excess of the solvent is sufficient, making the work extremely easy.

[Brief explanation of the drawing]

Fig. 1 is a process diagram of an embodiment of the present invention, Fig. 2 is a diagram showing an example of the relationship between temperature rise of the furnace, gradual cooling temperature fall, and time in the process of Fig. 1, and Fig. 3 is a diagram of the present invention. 4 is a cross-sectional view of a conventional liquid phase epitaxial growth apparatus, and FIG. 5 similarly shows the relationship between furnace temperature and time. FIG. In the figure, 3a, 3b are growth solution reservoirs, 4a, 4
b is a distribution solution reservoir, 6a and 6b are growth solutions,
7 is a substrate.

Claims (1)

[Claims] 1. Distributing a portion of each saturated solution contained in each of the plurality of growth solution reservoirs of the growth solution holder to each distribution solution reservoir of the distribution solution holder, and sequentially bringing the substrate into contact with each of these distributed solutions. In a liquid phase epitaxial growth method in which multiple epitaxial growth layers are laminated on a substrate, after each of the plurality of growth solution reservoirs is filled with a solvent and an excessive amount of solute, the temperature in the furnace is started to increase, During the temperature rise, each time the solution in each growth solution reservoir reaches a different predetermined temperature, the furnace temperature is maintained at the same temperature for a predetermined period of time.
At that temperature, the saturated solution obtained by removing the excess solute released from the solution in the corresponding growth solution reservoir is distributed to the distribution solution reservoir, and after all the distribution operations are completed, the inside of the furnace is gradually reduced. Each time the temperature drops by a predetermined amount from the temperature at each distribution operation,
A liquid phase epitaxial growth method characterized by moving a substrate under each distribution solution reservoir and sequentially bringing it into contact with each solution.