JPH0566916B2 - - 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 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, 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 provided within 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. In other words, in the temperature difference liquid phase crystal growth method, a temperature difference is applied to a solution (melt) in which a growth material (solute) is dissolved, and the solute is transported toward the substrate by the temperature gradient and diffusion, thereby forming crystals on the substrate. This is a method of growing crystals at a constant temperature, which allows a large number of crystals with uniform impurity concentration and composition and good crystallinity to be obtained in succession.
For example, in the case of GaAlAs-based crystals, a melt made of Ga solution is placed in a melt bath made of graphite,
Crystal growth is performed at 800℃-1000℃ with a temperature difference of 10℃-200℃. 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 uniform within the substrate surface 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 11. In addition, slight differences and fluctuations in the growth system of the furnace body cause the thickness to vary. The 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. 4 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 contacts the melt at the bottom of the melt tank 64 and undergoes 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 slider receiving mechanism 7.
7 and is stored in the outlet side preliminary chamber 79 via the gate valve 74.

FIG. 5 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 in both melt tanks 65 and 66 as shown on the right side of the figure. For example, at a temperature of 800℃-1000℃, the temperature difference is 10℃-200℃
establish. 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 in a low temperature region and is in a state where it can precipitate. A large number of substrates 69 are transferred to such a melt low temperature section.
are brought into contact sequentially. For example, with a growth time of about 60 minutes,
A growth layer of 50-60 μm is obtained.

FIG. 6 shows the relationship between temperature and time. As can be seen from the figure, the temperature distribution remains constant. Initially, the first substrate 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. Such operations are repeated to perform epitaxial growth 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 FIGS. 7 and 8) The growth rate of the peripheral portion 83 is slower than that of the vicinity 81 of the substrate center. One reason for this is thought to be that no solute is supplied from the inner wall of the melt layer. 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 temperature gradient is small and the peripheral area 83
It is thought that the growth rate is slow.

[B: When the size of the bottom of the melt is larger than the size of the substrate] (See Figures 9 and 10) Since the size of the substrate is smaller than the size of the bottom of the melt, the peripheral part 87 of the substrate is also separated from the side wall of the melt tank. The difference in temperature gradient between the center area 85 of the separated substrate and the peripheral area 87 of the substrate is not large compared to [A]. 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
5, 87, or more 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, these microcrystals serve as seeds and are continuously precipitated into microcrystals. 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. 11, the growth thickness at the periphery tends to be smaller than at the center. 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, in temperature difference method liquid phase crystal growth, the cross-sectional area of the substrate is made smaller than that of the melt, and an outer peripheral portion larger than the substrate area is formed inside the slider below the substrate. A metal that becomes liquid at the growth temperature (liquid metal) is stored in the cavity, and a step is provided on the upper wall of the cavity to form a downward convex portion directly below the substrate, so that the surface area is approximately the same as that of the substrate. The upper wall on the outside thereof is made high so as not to be connected to the liquid metal, but to form a space on the upper surface of the liquid metal, and this space is connected to the outside through a pore.

[Function] To explain with reference to FIGS. 1 and 2, a cavity with a cross-sectional area larger than the substrate area is provided inside the slider below the substrate, and a metal that becomes liquid at the crystal growth temperature (liquid metal) is placed in the cavity. Since this liquid metal moves by thermal convection, even if there is a temperature distribution in the in-plane direction of the substrate, the temperature is equalized.

Directly below the substrate, a convex portion extending downward from the upper wall surface of the cavity is provided, and contacts the upper surface of the liquid metal over approximately the same cross-sectional area as the substrate, thereby forming a heat flow path. On the outside, the liquid metal does not contact the upper wall surface of the cavity, and a gas space is provided on the upper surface of the liquid metal. Therefore, the thermal resistance in the direction perpendicular to the substrate surface in the peripheral area 89 outside the substrate where the melt is in direct contact with the slider is
The peripheral portion 89 outside the board is larger than the thermal resistance at
The heat flowing through can be suppressed.

[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 21 closes the bottom opening. A recess 17 is provided in the center of the slider 21, 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 on a rail (not shown) of a guide member and moves in a direction perpendicular to the plane of the drawing. A cavity 25 is formed inside the slider below the melt tank. Although the lateral dimension of the cavity is slightly larger than the bottom area of the melt 13 in this embodiment, it is not limited thereto. 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. A downward protrusion 27 is formed on the upper wall of the cavity 25 . This convex part 2
7 is designed to have approximately the same cross-sectional area as the substrate 19 or the recess 17 of the slider and a horizontal lower surface. 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 level and the lower surface of the convex portion 27 come into uniform contact. At this time, a space 33 remains around the convex portion 27. As the liquid level rises, the space 33 gradually becomes smaller, and the convex part 27 becomes the liquid metal 3.
Halfway down in 1.

The melt tank 11 and slider 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, GaAlAsP,
Ga is used for GaP, GaSb, etc., and In is used for InAs, InAsP, etc. The liquid metal 31 only needs to be liquid at the operating temperature (approximately the crystal growth temperature), and may be 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. In order to obtain crystal growth with a uniform thickness, it is desirable that the temperature distribution on the substrate 19 be uniform within the plane and the temperature gradient be uniform within the plane, and furthermore, it is desirable that no microcrystals occur in the portion 89 outside the substrate 19. . 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 the heat flow is restricted outside the cross-sectional area.

First, within the cross-sectional area of the substrate 19, the melt 13 is applied from above.
Substrate 19, upper part of slider 21 (including convex portion 27),
Heat flows through the liquid metal 31 and the lower part of the slider 21.
On the outside thereof, the convex portion 27 does not exist on the top of the slider 21, and a gas space 33 enters instead.

The structure is uniform within the cross-sectional area of the substrate 19, making it easy to create a uniform heat flow. Furthermore, since the liquid metal 31 can transport heat not only by thermal conduction but also by thermal convection, it plays the role of equalizing the temperature by convection when the temperature distribution is uneven.

Outside the substrate 19, a space 33 (gas) enters the thermal circuit. Since the thermal conductivity of gases is much lower than that of refractory 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, typical examples of the thermal conductivity (300°K) [W/cm-deg] of the constituent materials of the crystal growth apparatus are as follows.

H ₂ 0.0018 Ga 0.335 Graphite 1.2 GaAs 0.54 By equalizing the temperature by thermal convection of the liquid metal 31 and suppressing the precipitation of microcrystals in the peripheral region 89 outside the substrate, a grown crystal with a uniform thickness as shown in FIG. 3 is grown. can get.

Since there is no space below 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.

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 ZnSe, ZnTe, HgCdTe, and other crystals by temperature difference liquid phase epitaxial growth.

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 using a cavity and a liquid metal that can easily achieve temperature uniformity through thermal convection, the thermal resistance around the substrate is increased, and the microscopic temperature inside the melt around the outside of the substrate is increased. Precipitation of crystals is suppressed and grown crystals with uniform thickness can be obtained.

Therefore, epitaxial wafers for light emitting diodes with uniform luminous efficiency can be manufactured with high yield.
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, third is an example of measuring the film thickness distribution of a grown layer, and FIG. is a schematic diagram of a conventional liquid phase crystal growth apparatus, and FIG.
6 is a graph of temperature vs. time to explain the growth operation, FIG. 7 is a partially enlarged view of a conventional liquid phase crystallization device, and FIG. 8 is a cross-sectional view of FIG. 7.
Figure 9 is a partially enlarged view of a conventional liquid phase crystallization device;
FIG. 10 is a cross-sectional view of FIG. 9, and FIG. 11 is an example of measuring the thickness of a grown layer according to the prior art. Explanation of symbols, 11...Melt tank, 13...Melt, 17...Slider recess, 19...Substrate, 2
1...Slider, 25...Cavity, 27...Protrusion,
29...Communication hole, 31...Liquid metal, 33...Space.

Claims (1)

[Scope of Claims] 1. A melt tank made of a heat-resistant material that holds a melt containing a growth material and has an opening at the bottom, and a slider made of a heat-resistant material that holds a crystal substrate on top. Move the slider so that the substrate is in contact with the opening of the melt tank, and then bring the substrate into contact with the melt at the opening of the melt tank to collect crystals from the melt onto the substrate. In the liquid phase crystal growth method using the temperature difference method for epitaxial growth, a cavity is provided inside the slider below the substrate, the outer periphery of which is larger than the area of the substrate, and which communicates with the outside through a hole. A convex portion having approximately the same cross-sectional area as the substrate and extending downward is formed, a metal that becomes liquid at the growth temperature is contained in this cavity, and the upper surface of the liquid metal and the convex portion are formed directly below the substrate. A liquid phase crystal growth method characterized by controlling the flow of heat by contacting the liquid metal and forming a space on the upper surface of the liquid metal around the convex portion. 2. It is equipped with a melt tank made of a heat-resistant material and with an opening at the bottom that holds the melt containing the growth material, and a slider made of the heat-resistant material that holds the crystal substrate on top. Create a temperature difference so that the upper part is higher 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 epitaxy crystals from the melt onto the substrate. In a liquid phase crystal growth apparatus using the temperature difference method for dual growth, a cavity is provided inside the slider below the substrate, the outer periphery of which is larger than the area of the substrate, and which communicates with the outside through a hole. A convex portion having approximately the same cross-sectional area as the substrate and extending downward is formed, and when a metal that becomes liquid at the growth temperature is contained in this cavity, the upper surface of the liquid metal and the convex portion are formed directly below the substrate. 1. A liquid phase crystal growth apparatus characterized in that a space is formed on the upper surface of the liquid metal in contact with the convex portion to control the flow of heat.