JPH0222195A - Method for liquid-phase crystal growth and apparatus therefor - Google Patents

Abstract

PURPOSE:To uniformize the thickness of a grown crystal in a temperature- difference continuous liquid-phase growth process by using a substrate smaller than the opening of a melt tank and placing the substrate just above the area encircled by a cavity in a cooling plate having a specific shape and area. CONSTITUTION:The bottom opening of a melt tank 11 containing a melt 13 for crystal growth is closed with a slider 15. A substrate 19 having smaller area than the area of the opening of the tank 11 is placed in the recess 17 at the center of the slider 15, which is slid on a hollow rail 23 of a cooling plate 21. A cavity 25 is formed in the cooling plate 21 under the circumferential part of the melt tank 11 in such a manner as to encircle the region corresponding to the substrate 19. The inner wall of the cavity 25 has nearly the same area as that of the substrate 19 or the recess 17. The substrate 19 is placed just above the area encircled by the cavity. A metal 31 melting at the growth temperature is partially filled in the cavity 25 to leave an upper space 33 filled with an atmospheric gas.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to liquid phase crystal growth, and in particular to a process in which a certain temperature difference is created in a melt containing dissolved solute, and the solute is continuously transported from a high temperature area to a low temperature area. This paper relates to continuous liquid phase growth using a temperature difference method in which crystals are grown in a low-temperature region.

[Prior Art] Liquid phase crystal growth is widely used especially as a crystal growth technique for compound semiconductors. As liquid phase crystal growth methods, slow cooling method, temperature difference method, etc. are known.

The slow cooling method is, for example, a method in which a crystalline material is heated and melted in a crucible, and then gradually cooled and crystallized. It is divided into the Stockburger method, Bridgman method, etc. depending on the cooling method, crucible shape, etc.

The temperature difference method is a method in which a high-temperature zone and a low-temperature zone are formed with a certain temperature difference (or temperature gradient), and raw materials are supplied from the high-temperature zone and crystals are precipitated in the low-temperature zone. However, in a narrow sense, it refers to a method in which a temperature difference is created in a solution (melt), the solute is dissolved (supplied) in the high temperature part, and the solute is precipitated from a supersaturated solution in the low temperature part, that is, temperature difference method liquid phase crystallization. Growth method uses growth material (solute)
A method in which a temperature difference is applied to a solution (melt) in which the solute is dissolved, and the solute is transported toward the substrate by the temperature gradient and diffusion, and crystals are grown on the substrate. Because the crystal can be grown at a constant temperature, a uniform impurity concentration and composition can be achieved. This method allows a large number of crystals with good crystallinity to be obtained in succession.

For example, in the case of a GaAlAs-based crystal, a melt made of a Ga solution is placed in a melt tank made of graphite,
Light emitting diodes, lasers, etc. with excellent characteristics are manufactured by this method, in which crystal growth is performed with a temperature difference of 10°C to 200°C between 1000°C and 1000°C.

[Problems to be Solved by the Invention] In order to transport solute toward the substrate, a temperature difference is created in the direction perpendicular to the substrate surface. However, in order to grow uniformly over the substrate surface, it is necessary to provide a uniform temperature distribution in the in-plane direction. However, it is not easy to achieve both a temperature difference perpendicular to the surface and a uniform temperature within the surface.

Conventionally, as disclosed in Japanese Patent Publication No. 59-43087, attempts have been made to make the temperature distribution within the substrate surface uniform by balancing the heating furnace body and the cooling source.

However, it is difficult to achieve a uniform temperature distribution using these methods, and there are many growth results with uneven thickness distribution as shown in Figure 12, and slight differences in the growth system of the furnace body. , the thickness distribution changes due to the fluctuation.

Such non-uniform thickness distribution is directly linked to variations in luminous efficiency in the production of single light emitting diodes, and is a major cause of reduction in production yield.

Therefore, one object of the present invention is to provide a temperature difference method liquid phase crystal growth technique that can realize a uniform in-plane temperature distribution.

[Studies conducted to solve the problems] In order to solve the above problems, we investigated the mechanism of crystal growth in continuous liquid phase crystal growth using the temperature difference method.

FIG. 5 schematically shows an example of a temperature difference method liquid phase growth apparatus. Inside the entrance side preliminary chamber 51 is a slider 53 on which a semiconductor substrate is placed.
are housed therein, and are successively pushed up through the gate valve 62 by the slider push-up mechanism 55. Preferably, the entrance side preliminary chamber 51 is preheated in a preliminary heating furnace 59.
The pushed-up slider is sent into the growth chamber 57 through the gate valve 63 by the slider driving a-ellipse 61. A melt tank 64 is provided in the growth chamber 57, and a main heater 67
is heating the melt tank 64. The substrate 69 on the slider 53 contacts the melt at the lower part of the melt tank 64 to perform crystal growth.The slider carrying the substrate on which the crystal growth has been completed is sent out of the growth chamber 57 via the gate valve 73, and is received by the slider. The mechanism 77 stores the liquid in the outlet side preliminary chamber 79 via the gate valve 74.

FIG. 6 is an enlarged explanatory view of one example of the melt tank 64 portion.

Solutes AI and GaAs are dissolved in Ga, which is a solvent, and stored in a P melt tank 65 and an N melt tank 66. Further, as impurities, Zn is dissolved in the P melt tank 65, and Te is dissolved in the N melt tank. In order to make the bandgap of the N-type region to be grown later larger than that of the P-type region, the amount of AI in the N-melt tank 66 is preferably larger than the amount of AI in the P-melt tank 65. For example,
Red light emitting Ga AI As light emitting die No. 1-x
In order to obtain the x-do, the composition ratio X of AlAs in the p-type region is set to about 0.35. A vertical temperature difference as shown on the right side of the figure is set in the two melt tanks 65 and 66 in which the amounts of AI and GaAs are determined to be about 0.6-0.85 in the n-type region. For example, at a temperature of 800℃-toooo℃, the temperature difference is 1
Set the temperature between 0°C and 200°C. To continuously supply solute, the solute is floated above the melt, which is a high-temperature part, or a solute storage part is created and brought into contact with the melt. The solute dissolves to saturation solubility in the high temperature section and is transported to the low temperature section by diffusion.

Since the solubility usually increases with temperature, it becomes a supersaturated solution in a low temperature region, and is in a state where it can be precipitated. A large number of six substrates are sequentially brought into contact with such a melt low temperature section. For example, a growth time of about 60 minutes yields a growth layer of 50-60 μm.

As can be seen from Figure 7, which shows the relationship between temperature and time, the temperature distribution is kept constant. Initially, the first substrate is in contact with the bottom of the P melt, and the P type layer is grown.First, the slider is moved so that the first substrate is in contact with the bottom of the N melt, and the second substrate is in contact with the bottom of the P melt. do it like this. Therefore, respective growth layers are formed. Now, on the first substrate, a P-type layer is grown on the bottom and an N-type layer is grown on top, forming a diode. In this way, epitaxial growth is performed on a large number of substrates.

Now, crystal growth can occur in the low-temperature area at the bottom of the melt, but the melt and the heat-resistant material that makes up the melt tank, which is usually graphite, have different thermal properties such as thermal conductivity. One of the issues that must be solved in order to achieve uniform in-plane temperature distribution at the bottom of the melt is the relationship between the melt surrounded by graphite and the substrate.

Therefore, we considered the following cases separately.

[A, When the size of the bottom surface of the melt and the size of the substrate are almost equal] (See Figures 8 and 9) If the growth rate of the peripheral part 83 is slower than that of the vicinity 81 of the substrate center, the inner wall of the melt tank It is thought that one cause is that there is no supply of solute from It is considered that the temperature gradient in the peripheral part 83 is smaller than that in the peripheral part 83, and therefore the concentration gradient is small and the growth rate in the peripheral part 83 is slow.

[B. When the size of the bottom surface of the melt is larger than the size of the substrate] (See FIGS. 10 and 11) Since the size of the substrate is smaller than the size of the bottom surface of the melt, the peripheral part 87 of the substrate also becomes the side wall of the melt tank. The difference in temperature gradient between the center of the substrate 85 and the periphery 87 of the substrate is not as large as that of Al, and the temperature distribution within the substrate surface is also more uniform than that of Al. Therefore, the growth rate is relatively uniform in the plane compared to [Al].

However, the bottom surface of the melt in the peripheral portion 89 outside the substrate is in contact with the slider 53 made of graphite, which has a higher thermal conductivity than the substrate and on which crystals cannot be epitaxially grown. Therefore, the peripheral part 89 outside the board
At 85.87, the same or more heat flows from the melt toward the slider than in the plane of the substrate. Namely.

Even in this region, solute transport by diffusion is always occurring. However, since there are no substrate crystals, the transported solute becomes supersaturated, causing microcrystals to precipitate in the melt near the slider surface. Since the solute is constantly being transported, these microcrystals serve as seeds and are continuously precipitated into microcrystals.

Due to the precipitation of microcrystals within the melt in the peripheral portion 89 outside the substrate, the transport of solute in the inner peripheral portion 87 of the substrate is affected, and the growth rate of the inner peripheral portion 87 of the substrate is lower than that in the central portion 85 .

[A] [B] In either case, growth with a uniform thickness distribution is not achieved, and for example, as shown in FIG. 12, the growth thickness at the periphery tends to be smaller than at the center.
[B] In either case, if temperature fluctuation occurs due to the movement of the slider, the effect cannot be sufficiently absorbed, resulting in variations in thickness and distribution when a large number of sheets are grown in succession.

Based on the above study, it is considered that if the precipitation of microcrystals in the eight melts around the outer periphery of the substrate is suppressed in [B], crystal growth with a more uniform thickness will be possible.

[Means for solving the problem] According to the present invention, a solution (melt) in which a growth material is dissolved
is placed in a melt tank with an opening at the bottom, a temperature difference is set so that the upper part is higher than the lower part, the substrate is brought into contact with the melt at the opening of the melt tank, and the temperature at which crystals are epitaxially grown from the melt on the substrate is set. In differential method liquid phase crystal growth, the substrate is made smaller than the opening of the melt tank, and a cavity is provided inside the cooling plate at the bottom of the outside of the substrate so as to surround the substrate when viewed from above, and the inner periphery of this cavity is The area of the substrate is set to be approximately the same as that of the substrate, and the thermal resistance on the outside of the substrate is increased to suppress the heat flowing through this area.

Furthermore, it is preferable to fill this cavity with o-100% of a metal that becomes liquid at the growth temperature (liquid metal).

This method is applicable to GaP, GaAsInP, as well as GaAlAs.
InGaAsP in a sense, Zn5eZnTe, Hg
It can be applied to the growth of CdTe and other crystals by the temperature difference liquid phase epitaxial crystal growth method.

[Function] As illustrated in FIGS. 1 and 2, the central portion 27 of the cooling plate 21
A cavity 25 is formed surrounding the cavity 25, and gas and liquid are filled in the cavity. For example, the substrate 19 may be placed on a graphite cooling plate 21.
25 is made to surround the central part 27 having approximately the same cross-sectional area as
It is partially filled with a metal 31 that becomes liquid at the growth temperature, such as Ga, and an atmospheric gas such as H2 or Ar is introduced into the upper space 33. Thermal conductivity depends on the material of the cooling plate (>liquid metal).Since the heat flow is gas, the heat flow is restricted in the cavity and mainly passes through the central part 27 surrounded by the cavity. Since this part has almost the same area as the board, it is possible to increase the thermal resistance of the peripheral area on the outside of the board.
Precipitation of microcrystals within the melt is suppressed, making it easier to maintain uniform thermal conditions within the plane of the substrate.

Furthermore, when a metal (eg Ga) that becomes liquid at the growth temperature is placed in this cavity, the liquid metal moves by thermal convection.

Even if there is a non-uniform temperature distribution within the substrate surface, the temperature is equalized. Local non-uniform temperature distribution is made uniform by convection within the liquid metal, making it easier to obtain a uniform temperature distribution within the substrate surface. .

Furthermore, by adjusting the amount of this liquid metal, it is possible to change the volume of the space and change the thermal resistance around the outside of the substrate. Adjustment can be compensated.

Since there is no cavity under the substrate and the thermal resistance is not greatly affected, the growth rate is almost the same as in the conventional example, and the growth thickness necessary for high brightness light emitting diodes is ensured.

[Embodiment] FIGS. 1 and 2 partially show a liquid phase crystal growth apparatus according to an embodiment of the present invention.

The melt tank 11 contains a melt 13 for crystal growth. The bottom of the melt tank 11 is open and the slider 15
is designed to cover the opening at the bottom. A recess 17 is provided in the center of the slider 15, and a semiconductor substrate 19 serving as a growth base is housed therein. Therefore, the upper surface of the semiconductor substrate 19 is in contact with the bottom central portion of the melt 13. The slider slides within the concave rail 23 of the cooling plate 21 and moves in a direction perpendicular to the plane of the drawing. Inside the cooling plate, there is a cavity 25 below the periphery of the melt tank so as to surround an area corresponding to the substrate. is formed. In this embodiment, the outer circumferential dimension of the cavity is approximately the same as that of the slider 15.

Although not limited to this, the cavity 2 preferably has a cross-sectional area that is approximately the same as or larger than the cross-sectional area of the melt 13.
The inner wall of 5 is designed such that the central part 27 has approximately the same cross-sectional area as the substrate 19 or the recess 17 of the slider. Furthermore, a communication hole 29 is formed that connects this cavity 25 with the outside, allowing liquid metal and atmospheric gas to enter and exit. When a liquid metal (for example, Ga) 31 is poured into the cavity 25, the liquid comes into contact with the side surface of the central portion 27 of the cooling plate. Also at this time, a space 33 remains above the liquid level around the central portion 27. As the liquid level increases, the space 33 gradually becomes smaller, and the central portion 27 comes to be partially submerged in the liquid metal 31.

Melt tank 11. Slider 15. The cooling plate 21 is made of a heat resistant material such as graphite. The melt 13 normally uses one of the constituent elements of the semiconductor material to be grown as a solvent. G5As, GaAlAs, GaAIAsP, GaP
, GaSb, etc. use Ga, and InAs, InAsP, etc. use In. The liquid metal 31 may be made of Ga, In, Hg, etc. as long as it is liquid at the operating temperature (crystal growth temperature). It is often preferable to match the main components of the melt 13 and the main components of the liquid metal from the viewpoint of preventing impurities and thermal design. It is desirable that the temperature distribution is uniform within the plane and the temperature gradient is also uniform within the plane, and that microcrystals are not generated in the portion 89 outside the substrate 19. To achieve this, uniform heat flow within the cross-sectional area of the substrate 19 is desirable. flows from top to bottom.

On the outside it is desirable that the heat flow from top to bottom is restricted.

Within the cross-sectional area of the substrate 19, from above, the melt 13 substrate 19, the slider 15. The upper part of the cooling plate 21, the central part 27 of the cooling plate.
Heat flows to the lower part of the cooling plate 21.

Outside thereof, a gas space 33 or liquid metal 31 is present inside the cooling plate 21 .

The structure is uniform within the cross-sectional area of the substrate 19, making it easy to create a uniform heat flow.

On the outside of the substrate 19, a cavity 25 (substrate space 3) is formed in the thermal circuit.
3 or liquid metal 31) enters. The thermal conductivity of gas is much lower than that of heat-resistant materials such as graphite by λ, so the heat flow is greatly restricted.

Therefore, precipitation of microcrystals in the portion 89 outside the substrate 19 is suppressed.

For example, the thermal conductivity (300°K) of the constituent materials [W/c
Representative examples of [m-deg] are as follows.

H20,0018 Ga 0. 335 Graphite 1,2 GaAs 0.54 Furthermore, the liquid metal 31 within the cavity 25 can transport heat not only by thermal conduction but also by thermal convection.

It plays the role of equalizing heat by convection when temperature distribution is uneven.

By equalizing the temperature by thermal convection of the liquid metal 31 and suppressing the precipitation of microcrystals in the outer peripheral region 89 of the substrate.

A grown crystal of uniform thickness is obtained.

An example of the expected thickness distribution of the grown crystal is shown in FIG.

Since the structure below the substrate is the same as the conventional one, the thermal resistance is not greatly affected. Therefore, the growth rate is almost the same as in the conventional example, and the growth thickness necessary for a high-brightness light emitting diode is secured.

Furthermore, since the space provided on the upper surface of the liquid metal is connected to the external atmosphere through the pores, there is no risk of internal pressure increasing even at high temperatures.

Furthermore, by adjusting the volume of the space 33 on the top surface of the liquid metal in the peripheral area, it is possible to adjust the thermal resistance in the direction perpendicular to the substrate surface in the eight peripheral areas outside the substrate. Due to slight differences in the growth system. It is also possible to adjust and compensate for differences in growth conditions.

This method applies not only to GaAlAs but also to GaPGaAs.
InP, InP, InGaAsP or Zn5e
, ZnTe, HgCdTe, and other crystals by the temperature difference liquid phase picture epitaxial growth method.

FIG. 4 shows an example in which a wafer for light emitting diodes is manufactured by continuously growing P layers and N layers.

A crystal growth mechanism 37 made of graphite is housed in a reaction tube 35 made of quartz, and heated by heaters 38 and 39.

The slider 15 slides on the cooling plate 21 and moves from right to left in the figure. The substrate 19 on the slider 15 is first coated with P melt 4.
1, the P layer grows under the primary N melt 42.
undergo layer growth. A cavity 43.44 is provided in the lower part of each melt, in the center of which there is a central part 45.46 of a cooling plate having a cross-sectional shape substantially parallel to the substrate 19. There is a space 47.4 on the outer periphery of
8 is formed. A constant temperature gradient in the vertical direction is formed in the melt 41, 42 as shown by the cloth in the figure.

With this configuration, the substrate 19. Creates a uniform heat flow on top,
By suppressing crystal precipitation on the outside, it is possible to manufacture light-emitting diodes with good characteristics at a high yield.

[Effects of the invention] As described above, the thermal resistance of the peripheral area outside the substrate can be increased, and when liquid metal is used, it can be equalized by heat convection.
Precipitation of microcrystals in the melt around the outside of the substrate is suppressed, and grown crystals with a uniform thickness can be obtained.

Therefore, epitaxial wafers for light emitting diodes with uniform luminous efficiency can be manufactured at a high yield, and light emitting diodes with high luminous efficiency can be supplied in large quantities at low cost.

[Brief explanation of the drawing]

FIG. 1 is a partial schematic diagram of a liquid phase crystal growth apparatus according to an embodiment of the present invention, FIG. 2 is a partial cross-sectional view of FIG. 1, and FIG. FIG. 4 is a partial schematic diagram of a liquid phase crystal growth apparatus according to another embodiment, and FIG. 5 is a schematic diagram of a conventional liquid phase crystal growth apparatus. FIG. 6 is a partially enlarged view of FIG. 5, FIG. 7 is a graph of temperature versus time to explain the growth operation, FIG. 8 is a partially enlarged view of a conventional liquid phase crystal apparatus, and FIG. Cross-sectional view of, No. 10
The figure is a partially enlarged view of a conventional liquid phase crystallization device, and FIG. 11 is a cross-sectional view of FIG. 10. FIG. 12 is an example of measuring the thickness of a grown layer using the conventional technique. Explanation of symbols 11 Melt tank Melt slider Concave part of slider Substrate Cooling plate Concave rail of cooling plate Central part of cavity cooling plate Communication hole Liquid metal space Reaction tube Crystal growth v1 structure Heater Heater P Melt N Melt cavity Cavity Central part of cooling plate central space space

Claims (4)

[Claims] (1) A melt tank made of heat-resistant material that holds the melt containing the growth material and has an opening at the bottom; a slider made of heat-resistant material that holds the crystal substrate on top; Using a cooling plate made of heat-resistant material that is slidably held in contact with the opening side, a temperature difference is created in the melt so that the upper part is higher than the lower part, and the slider is placed so that the substrate is in contact with the opening of the melt tank. In the liquid phase crystal growth method using the temperature difference method, in which the substrate is brought into contact with the melt at the opening of the melt tank and crystals are epitaxially grown from the melt on the substrate, the substrate is made smaller than the opening of the melt tank, and A cavity is provided inside the lower cooling plate so as to surround the substrate when viewed from the direction perpendicular to the substrate surface, and the area created by the inner circumferential wall of this cavity is approximately the same as that of the substrate, and the area surrounded by this cavity is A liquid phase crystal growth method characterized by placing a substrate directly above and epitaxially growing a crystal from a melt. (2) The method for liquid phase crystal growth according to claim 1, wherein the cavity contains a metal that becomes liquid at the crystal growth temperature. (3) A melt tank made of heat-resistant material and having an opening at the bottom to hold the melt containing the growth material; a slider made of heat-resistant material to hold the crystal substrate on top; a cooling plate made of a heat-resistant material for slidably holding and contacting the slider with the opening side of the melt tank;
Create a temperature difference in the melt so that the upper part is hotter than the lower part, move the slider so that the substrate is in contact with the opening of the melt tank, bring the substrate into contact with the melt at the opening of the melt tank, and crystallize from the melt onto the substrate. In a liquid phase crystal growth apparatus using a temperature difference method for epitaxial growth, a cavity is provided inside a cooling plate below the outside of the substrate so as to surround the substrate when viewed from a direction perpendicular to the substrate surface. A liquid phase crystal growth apparatus characterized in that the area formed by the peripheral wall is approximately the same as the substrate, the substrate is placed directly above the area surrounded by the cavity, and the crystal is grown epitaxially from the melt. (4) The liquid phase crystal growth apparatus according to claim 3, wherein the cavity contains a metal that becomes liquid at the crystal growth temperature.