JPH0566915B2 - - Google Patents

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 as a crystal growth technique, especially for compound semiconductors. A slow cooling method, a temperature difference method, and the like are known as liquid phase crystal growth methods.

The gradual 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, Bridgeman 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), and the solute is dissolved (supplied) in the high temperature part, and the solute is precipitated from the supersaturated solution in the low temperature part. That is,
In the temperature difference method liquid phase crystal growth method, the growth material (solute)
A method in which crystals are grown on the substrate by applying a temperature difference to a solution (melt) in which the solute is dissolved and transporting the solute toward the substrate by temperature gradient and diffusion. Because it can grow at a constant temperature, it can achieve a uniform impurity concentration and composition. 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 bath made of graphite, and crystal growth is performed at 800°C-1000°C with a temperature difference of 10°C-200°C. Using this method, light emitting diodes, lasers, etc. with excellent characteristics have been manufactured.

[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 shown 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 and the cooling source.

However, it is difficult to achieve a uniform temperature distribution with these methods, and the growth results often have an uneven thickness distribution as shown in Figure 12. Also, due to slight differences and fluctuations in the growth system of the furnace body, The thickness distribution will fluctuate.

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

Therefore, an 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, the mechanism of crystal growth in continuous liquid phase crystal growth using the temperature difference method was investigated.

FIG. 5 schematically shows an example of a temperature difference method liquid phase growth apparatus. A slider 53 carrying a semiconductor substrate is housed in the entrance side preliminary chamber 51 and is successively pushed up through the gate valve 62 by the slider push-up mechanism 55 . The entrance side preliminary chamber 51 is a preliminary heating furnace 5
Preferably, it is preheated at 9. The pushed-up slider is sent into the growth chamber 57 through the gate valve 63 by the slider drive mechanism 61. A melt tank 64 is provided in the growth chamber 57, and the main heater 67 heats the melt tank 64. The substrate 69 on the slider 53 comes into contact with the melt at the bottom of the melt tank 64 to cause crystal growth. The slider carrying the substrate on which crystal growth has been completed is sent to the outside of the growth chamber 57 via the gate valve 73, and is sent to the exit side preliminary chamber 7 via the gate valve 74 by the slider receiving mechanism 77.
It can be stored in 9.

FIG. 6 is an enlarged explanatory view of one example of the melt tank 64 portion. Solutes Al and GaAs in the solvent Ga
is melted, and the P melt tank 65 and the N melt tank 66
is housed in. 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 that will grow later larger than that of the P-type region, the amount of Al in the N-melt tank 66 is preferably made larger than the amount of Al in the P-melt tank 65. for example,
To obtain the red-emitting Ga _1-x Al _x As light-emitting diode,
The amounts of Al and GaAs are determined so that the AlAs composition ratio x is about 0.35 in the p-type region and about 0.6-0.85 in the n-type region. A vertical temperature difference is set between both melt tanks 65 and 66 as shown on the right side of the figure. for example,
The temperature is 800℃-1000℃ with a temperature difference of 10℃-200℃. To continuously supply the 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 at low temperatures and becomes ready for precipitation. A large number of substrates 69 are sequentially brought into contact with such a melt low temperature section. For example, 50-60μm with a growth time of about 60 minutes.
A layer of growth is obtained.

FIG. 7 shows the relationship between temperature and time. As can be seen from the figure, the temperature distribution remains constant. Initially, the first base contacts the bottom of the P melt and grows a P type layer. Next, move the slider so that the first board is
The second substrate should touch the bottom of the P-melt. 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 of the melt and the size of the substrate are almost equal] (See Figures 8 and 9) The growth rate in the peripheral area 83 is slower than in the vicinity of the center of the substrate 81. This is due to the inner wall of the melt tank. One reason is thought to be that there is no supply of solutes from the Further, the thermal conductivity of the side wall of the melt tank (graphite) is higher than that of the melt (Ga). Therefore, the temperature gradient in the peripheral portion 83 is smaller than that in the vicinity 81 of the substrate center. Therefore, the concentration gradient is small and the peripheral area 83
It is thought that the growth rate 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 is also on the side wall of the melt tank. The temperature gradient difference "A" between the center part 85 of the substrate and the peripheral part 87 of the substrate away from the substrate is not large. Moreover, the temperature distribution within the substrate surface is also more uniform than in [A]. Therefore, the growth rate becomes relatively uniform within the plane than in [A].

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, in the peripheral part 89 outside the board, the inside of the board 8
At 5,87, an equal or greater amount of heat flows from the melt toward the slider. That is, 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, this microcrystal becomes the main component, and further precipitation into microcrystals occurs continuously. Due to the precipitation of microcrystals within the melt in the peripheral area 89 outside the substrate, solute transport in the internal peripheral area 87 of the substrate is affected, and compared to the central area 85 , the transport of solutes in the internal peripheral area 87 of the substrate is affected.
7 growth rate becomes smaller.

[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 in the peripheral area tends to be smaller than that in the central area. Furthermore, in both [A] and [B], if temperature fluctuation occurs due to slider movement, 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 melt in the outer peripheral portion 89 of the substrate is suppressed in [B], crystal growth with a more uniform thickness will be possible.

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

Furthermore, it is preferable to fill this cavity with 0-100% of a metal that becomes liquid at the growth temperature (liquid metal).

This method is applicable to GaAlAs as well as GaP GaAsInP.
InGaAsP can be applied to the growth of ZnSeZnTe, HgCdTe, and other crystals by temperature difference liquid phase epitaxial crystal growth.

[Function] As illustrated in FIGS. 1 and 2, a cavity 25 is formed surrounding the central portion 27 of the cooling plate 21, and gas and liquid are filled in the cavity. For example, a central portion 2 having approximately the same cross-sectional area as the substrate 19 is attached to the graphite cooling plate 21.
25 is made to surround 7, and is partially filled with a metal 31 that becomes liquid at the growth temperature, such as Ga, to fill the upper space 3.
Atmospheric gas such as H2 or Ar should be introduced into 3. Since the thermal conductivity is as follows: material of cooling plate>liquid metal>>gas, heat flow is restricted in the cavity and mainly passes through the central part 27 surrounded by the cavity. Since this area has almost the same area as the substrate, it increases the thermal resistance of the peripheral area outside the substrate, suppresses the precipitation of microcrystals in the melt there, and makes it easier to maintain uniform thermal conditions within the substrate plane. .

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 non-uniform temperature distribution within the substrate surface, the temperature can be equalized. Since the locally non-uniform temperature distribution is made uniform by convection within the liquid metal, it becomes 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.

Inside the melt tank 11 is a melt 13 for crystal growth.
is accommodated. The bottom of the melt tank 11 is open, and the slider 15 closes the bottom opening. 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 covered with the melt 13.
It touches the center of the bottom. 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.
5 is formed. In this embodiment, the outer circumferential dimension of the cavity is approximately the same as that of the slider 15;
Not limited to these. However, it is preferable that the cross-sectional area is approximately the same as or larger than the cross-sectional area of the melt 13. The center portion 27 of the inner wall of the cavity 25 is connected to the substrate 1.
9 to have approximately the same cross-sectional area as 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. Cavity part 2
When a liquid metal (for example, Ga) 31 is poured into the cooling plate 5, 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.

The melt tank 11, slider 15, and cooling plate 21 are 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. GaAs, GaAlAs,
For GaAlAsP, GaP, GaSb, etc., Ga, InAs,
In the case of InAsP etc., In is used. The liquid metal 31 only needs to be liquid at the operating temperature (approximately the crystal growth temperature), and Ga, In, Hg, etc. are used. It is often preferable to match the main components of the melt 13 with the main components of the liquid metal from the viewpoint of impurity prevention, thermal design, etc. To obtain crystal growth with uniform thickness, substrate 1
The temperature distribution on the substrate 9 is uniform in the plane, and the temperature gradient is also uniform in the plane, and furthermore, the temperature distribution on the substrate 19 is uniform in the plane.
9, it is desirable that no microcrystals be generated. For this purpose, it is desirable that a uniform heat flow flows from top to bottom within the cross-sectional area of the substrate 19, and that heat flow from top to bottom is restricted outside of the cross-sectional area.

Within the cross-sectional area of the substrate 19, heat flows from above to the melt 13 substrate 19, the slider 15, the upper part of the cooling plate 21, the central part 27 of the cooling plate, and 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 33 or liquid metal 31) enters the thermal circuit. Since the thermal conductivity of gas is much lower than that of heat-resistant materials such as graphite, heat flow is greatly restricted.
Therefore, precipitation of microcrystals in the portion 89 outside the substrate 19 is suppressed.

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

H ₂ 0.0018 Ga 0.335 Graphite 1.2 GaAs 0.54 Furthermore, since the liquid metal 31 in the cavity 25 can transport heat not only by thermal conduction but also by thermal convection,
If uneven temperature distribution occurs, convection plays a role in equalizing the temperature.

By equalizing the temperature by heat convection of the liquid metal 31 and suppressing the precipitation of microcrystals in the outer peripheral region 89 of the substrate, a grown crystal with a uniform thickness can be 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, thermal resistance is not greatly affected. Therefore, the growth rate is almost the same as that of the conventional example, and the growth thickness necessary for a high-brightness light emitting diode is ensured.

Furthermore, since the space provided on the upper surface of the liquid metal is connected to the outside 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 upper surface of the liquid metal in the peripheral area, the outer peripheral area 89 of the substrate can be adjusted.
It is also possible to adjust the thermal resistance in the direction perpendicular to the substrate plane, and to compensate for differences in growth conditions due to slight differences in growth systems such as heating furnaces and cooling sources.

This method is applicable not only to GaAlAs but also to
GaPGAAsInP, InP, InGaAsP, or
It can be applied to the growth of crystals such as ZnSe, ZnTe, HgCdTe, etc. 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. Substrate 19 on slider 15 first undergoes P layer growth under P melt 41 and then N layer growth under N melt 42. Cavities 43 and 44 are provided in the lower part of each melt, and central portions 45 and 46 of cooling plates having substantially the same cross-sectional shape as the substrate 19 are located in the center of the cavities 43 and 44 in alignment with the substrate 19. Spaces 47 and 48 are formed around the outer periphery of the central portions 45 and 46. Melt 41, 42
A constant temperature gradient is formed in the vertical direction as shown on the right side of the figure.

With this configuration, a uniform heat flow is created on the substrate 19, crystal precipitation on the outside thereof is suppressed, and light emitting diodes with good characteristics can be manufactured at a high yield.

[Effects of the invention] As described above, by increasing the thermal resistance of the peripheral area outside the substrate, and when using liquid metal, it is possible to equalize the temperature by heat convection, and to prevent the precipitation of microcrystals in the melt around the outside of the substrate. growth crystals with 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 drawings]

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, FIG. 3 is an example of the film thickness distribution of the grown layer, and FIG. 4 is a partial schematic diagram of a liquid phase crystal growth apparatus according to another embodiment,
Figure 5 is a schematic diagram of a conventional liquid phase crystal growth apparatus;
The figure 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 crystallization device, and Fig. 9 is a cross section of Fig. 10 is a partially enlarged view of a conventional liquid phase crystal device, FIG. 11 is a cross-sectional view of FIG. 10, and FIG.
FIG. 2 shows an example of measuring the thickness of a grown layer using the conventional technique. Explanation of symbols, 11...Melt tank, 13...Melt, 15...Slider, 17...Slider recess, 19...Substrate, 21...Cooling plate, 23...Concave rail of cooling plate, 25... Cavity, 27...Central part of cooling plate, 29...Communication hole, 31...Liquid metal, 33...Space, 35...Reaction tube, 37...Crystal growth mechanism, 38...Heater, 39...Heater ,
41...P melt, 42...N melt, 43...
Cavity, 44...Cavity, 45...Central part of cooling plate,
46...Central part of cooling plate, 47...Space, 48...
…space.

Claims (1)

[Scope of Claims] 1. A melt tank made of a heat-resistant material and having an opening at the bottom and holding a melt in which a growth material is dissolved; a slider made of a heat-resistant material and holding a crystal substrate thereon;
This slider is slidably held and brought into contact with the opening side of the melt tank using a cooling plate made of a heat-resistant material, and a temperature difference is created in the melt so that the upper part is hotter than the lower part, and the substrate is placed at the opening of the melt tank. In the liquid phase crystal growth method using the temperature difference method, in which the slider is moved so that it is in contact with the melt at the opening of the melt tank, and the crystal is epitaxially grown from the melt on the substrate, the substrate is brought into contact with the melt at the opening of the melt tank. A cavity is provided inside the cooling plate below the outside of the substrate so as to surround the substrate when viewed from a direction perpendicular to the substrate surface, and the area formed by the inner circumferential wall of this cavity is approximately the same area as the substrate, A liquid phase crystal growth method characterized by placing a substrate directly above the area surrounded by the cavity and epitaxially growing a crystal from a melt. 2. The method of 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, and this slider. It has a cooling plate made of heat-resistant material to slidably hold and contact with the opening side of the melt tank, and the board is placed in the opening of the melt tank by creating a temperature difference in the melt so that the upper part is hotter than the lower part. Move the slider so that it touches
In a liquid phase crystal growth apparatus using a temperature difference method for epitaxially growing crystals from the melt on the substrate by bringing the substrate into contact with the melt at the opening of the melt tank, the substrate is placed inside a cooling plate below the outside of the substrate. A cavity is provided to surround the substrate when viewed from the direction perpendicular to the plane, the area created by the inner peripheral wall of this cavity is approximately the same area as the substrate, and the substrate is placed directly above the area surrounded by this cavity. A liquid phase crystal growth apparatus characterized in that a crystal is grown epitaxially from a crystal. 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.