JPH0222196A - Liquid phase crystal growth method and apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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, 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 to grow crystals on the substrate. Because the crystal can be grown at a constant temperature, it has a uniform impurity concentration and composition. For example, in the case of GaAIAS crystals, a melt made of Ga solution is placed in a melt bath made of graphite, and a melt made of Ga solution is heated at 800°C-1000°C and 10°C-200°C.
Using this method of growing crystals with a temperature difference of .degree. C., light-emitting diodes, lasers, and the like 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 the temperature difference perpendicular to the surface and the uniform temperature within the surface. The attempt was made to make the temperature distribution uniform within the substrate plane by balancing the

However, it is difficult to achieve a uniform temperature distribution using these methods, and the growth results often have an uneven thickness distribution as shown in Figure 11. 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 decreased manufacturing yield.Therefore, the purpose of the present invention is to realize a uniform in-plane temperature distribution. The purpose of this invention is to provide a temperature difference method liquid phase crystal growth technology that can be used.

[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. 4 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 drive mechanism 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 bottom 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 receives one slider. It is stored in the outlet side preliminary chamber 79 by the machine 77 via the gate valve 74.

FIG. 5 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 the P melt low temperature section and the N melt tank 66. Furthermore, as impurities, Zn is dissolved in the P melt tank 65 and Te is dissolved in the N melt tank. The amount of AI in 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
To obtain the x-do, the AlAs composition ratio X should be approximately 0.35. The amounts of AI and GaAs are determined to be about 0.6-0.85 in the n-type region.A vertical temperature difference as shown by the cloth in the figure is set in the two melt tanks 65 and 66. For example, at a temperature of 800℃-1000℃, the temperature difference is 1
Set the temperature between 0°C and 200°C. In order to continuously supply the solute, a container is created in which the solute floats above the melt, which is a high-temperature part, and is 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 substrates 69 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 6, 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. 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 realize a uniform in-plane temperature distribution at the bottom of the melt is the relationship between the melt surrounded by graphite and the substrate, so let's consider 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 7 and 8) The growth rate in the peripheral area 83 is slower than in the vicinity 81 of the substrate center. This is due to the inner wall of the melt tank. One reason for this is thought to be that there is no supply of solutes. In addition, the thermal conductivity of the side wall (graphite) of the melt tank is higher than that of the melt (Ga). Therefore, the temperature gradient in the peripheral area 83 is smaller than that near the center of the substrate 81, and therefore the concentration gradient is small in the peripheral area. It is considered that the growth rate of 83 is slow.

[B. When the size of the bottom surface of the melt is larger than the size of the substrate] (See FIGS. 9 and 10) Since the size of the substrate is smaller than the size of the bottom surface of the melt, the peripheral portion 87 of the substrate also overlaps 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 large compared to AI, and the temperature distribution within the substrate surface is also more uniform than AI. Therefore, the growth rate is relatively uniform within the plane compared to [AI].

However, the bottom surfaces of the eight peripheral portions of the melt outside the substrate are in contact with a slider 53 made of graphite, which has a higher thermal conductivity than the substrate and on which crystals cannot be epitaxially grown. Therefore, the same or more heat flows from the melt toward the slider in the eight peripheral areas outside the substrate than in the in-plane areas 85,87 of the substrate. Namely.

Even in this region, transport of solute by diffusion is always carried out 6 However, since there are no substrate crystals, the transported solute becomes supersaturated, causing microcrystals to precipitate in the vicinity of the slider surface within the melt. 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 .

[AI
[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 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 provided in the cavity.
A step is provided on the upper wall of this cavity to form a downwardly directed convex portion directly below the substrate, and the upper wall surface on the outside is raised so that it is in contact with the upper surface of the liquid metal over approximately the same surface area as the substrate. A space is formed above the liquid metal without contact with the liquid metal, and this space is connected to the outside through a pore.

[Function] To explain with reference to FIGS. 1 and 2, there is a 41! larger than the substrate area inside the slider below the substrate! A cavity with a cross-sectional area is provided, and the cavity is filled with a metal that becomes liquid at the crystal growth temperature (liquid metal). Because this liquid metal moves by thermal convection, even if there is a temperature distribution in the in-plane direction of the substrate, it is not uniform. becomes heated.

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, a gas space is provided on the upper surface of the liquid metal, where the liquid metal contacts the upper wall surface of the cavity. For this reason,
Perimeter outside the board 8 where the melt is in direct contact with the slider
The thermal resistance in the direction perpendicular to the substrate surface at 9 is greater than the thermal resistance at the substrate portion 85° 87, and the heat flowing through the peripheral portion 89 outside the substrate can be suppressed.

[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 a slider 21
is designed to cover the opening at the bottom. 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 in contact with the bottom central portion of the melt 13. 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. In this embodiment, the lateral dimension of the cavity is slightly larger than the bottom area of the melt 13, but is not limited to this, but it is preferable that the cavity has a cross-sectional area that is approximately the same as or larger than the cross-sectional area of the melt 13. A downward convex portion 27 is formed on the upper wall of the portion 25 .

The convex portion 27 is designed to have approximately the same cross-sectional area as the substrate 19 or the concave portion 17 of the slider, and to have 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 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 increases, the space 33 gradually becomes smaller, and the convex portion 27 is partially submerged in the liquid metal 31.

Melt tank 11. Slider 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. GaAs
, GaAlAs, GaAIAsP, GaP, GaSb, etc., and In for InAs, InAsP, etc., In is used. The liquid metal 31 is at the operating temperature (crystal growth temperature)
If it is a liquid, Ga, In, Hg, etc. can be 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 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 furthermore, no microcrystals are 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. It is desirable for heat flow to flow downwards from the outside of the wall, with restricted heat flow outside of it.

First, within the cross-sectional area of the substrate 19, the melt 13 substrate 19 is
．． Upper part of slider 21 (including convex portion 27).

Liquid metal 31. Heat flows to the lower part of the slider 21.

On the outside, there is no convex portion 27 on the top of the slider 21, and 1
A gas space 33 is inserted 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 a 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. Heat flow is greatly restricted because the thermal conductivity of gases is much lower than that of heat-resistant materials such as graphite. For this reason, precipitation of microcrystals in the portions 8 outside the substrate 19 is suppressed.

For example, the thermal conductivity (300
K) Representative examples of [W/cl-deg] are as follows.

H20,0018 Ga 0. 335 Graphite 1,2 GaAs 0.54 By equalizing the temperature by thermal convection of this liquid gold [31] and suppressing the precipitation of microcrystals in eight peripheral regions outside the substrate, a uniform thickness as shown in Fig. 3 is obtained. A grown crystal is obtained.

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 external atmosphere through the pores, there is no risk of internal pressure increasing even if the temperature rises. By adjusting the volume, it is also possible to adjust the thermal resistance perpendicular to the substrate surface in the eight outer peripheral regions of the substrate, due to slight differences in the growth system, such as the heating furnace and the cooling source. 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 temperature difference method liquid phase epitaxial growth method.

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 whose temperature can be easily uniformized by thermal convection, the thermal resistance around the outside of the substrate can be increased, and the microcrystals in the melt around the outside of the substrate can be increased. Precipitation 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, FIG. 3 is an example of measuring the thickness distribution of a grown layer, and FIG. The figure is a schematic diagram of a conventional liquid phase crystal growth apparatus, Figure 5 is a partially enlarged view of Figure 4, Figure 6 is a graph of temperature vs. time to explain the growth operation, and Figure 7 is a conventional liquid phase crystal growth apparatus. FIG. 8 is a partially enlarged view of the device, and FIG. 8 is a cross-sectional view of FIG. 7. FIG. 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 21 Slider 25 Cavity 27 Two protrusions, communication hole Liquid metal space

Claims (2)

[Claims] (1) Using a melt tank made of heat-resistant material with an opening at the bottom that holds the melt containing the growth material, and a slider made of heat-resistant material that holds the crystal substrate on top, the upper part is placed inside the melt. Apply a temperature difference so that the temperature 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 make the temperature difference to epitaxially grow crystals from the melt on the substrate. In the liquid phase crystal growth method, a cavity is provided inside the slider below the substrate and has an outer circumference larger than the area of the substrate and communicates with the outside through a hole, and the upper wall of the cavity has a cross-sectional area approximately equal to that of the substrate. a convex portion extending downward; a metal that becomes liquid at the growth temperature is accommodated in the cavity; an upper surface of the liquid metal is brought into contact with the convex portion directly below the substrate; A liquid phase crystal growth method characterized by forming a space on the upper surface of the surrounding liquid metal to control the flow of heat. (2) A melt tank that holds a melt containing melted growth materials, has an opening at the bottom and is made of a heat-resistant material, and a slider that holds a crystal substrate on top and is made of a heat-resistant material; Create a temperature difference inside so that the top is hotter than the bottom,
In a liquid phase crystal growth apparatus using a temperature difference method, a slider is moved so that the substrate is in contact with the opening of the melt tank, and the substrate is brought into contact with the melt at the position of the opening of the melt tank, and crystals are epitaxially grown from the melt on the substrate. Inside the lower slider is a cavity that has an outer periphery larger than the substrate area and communicates with the outside through a hole, and a convex part that has approximately the same cross-sectional area as the substrate and extends downward is formed on the upper wall of the cavity. However, when a metal that becomes liquid at the growth temperature is placed in this cavity, the upper surface of the liquid metal comes into contact with the convex portion directly below the substrate, and a space is formed on the upper surface of the liquid metal around the convex portion. 1. A liquid phase crystal growth apparatus characterized in that the apparatus is configured to control the flow of heat.