JPH0585517B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to compound semiconductor crystal growth, and particularly to a crystal growth method for forming an epitaxial layer of a compound semiconductor on a seed crystal. Application development of compound semiconductors is actively being carried out. In particular, since various band gaps can be obtained, their use as optical semiconductor devices is progressing. Therefore, it is required to provide a compound semiconductor or a compound semiconductor mixed crystal with excellent crystallinity. However, there are only a limited number of crystals that can be easily obtained as substrate crystals, such as Si, GaAs, and GaP. Therefore, there is a need for a technology that uses these easily available crystals as a substrate crystal, forms an epitaxial layer thereon, and further forms a compound semiconductor (including mixed crystal) having a desired composition. [Prior Art] When a semiconductor crystal with good crystallinity is required for an optical semiconductor device or the like, a buffer layer is once grown on a seed crystal, and then the desired crystal is grown thereon. Particularly when the seed crystal has a different composition from the crystal of the portion forming the device, it is important to grow a buffer layer with good crystallinity. FIGS. 2A and 2B show a conventional liquid phase growth apparatus for compound semiconductors. As shown in FIG. 2A, a solvent 32 made of constituent elements or other elements is housed in a growth ampoule 31, and a source crystal 33 and a seed crystal 3 are contained in the solvent 32.
Place 5. The seed crystal 35 is placed on a heat sink 36, and a cylindrical quartz presser 34 is placed and fixed thereon. Such a growth ampoule is heated above the growth temperature and melt alloyed for a certain period of time. After that, it is placed in a crystal growth furnace having a temperature distribution as shown in FIG.
The crystal raw material is transported to the seed crystal 35 above the seed crystal 6, and the crystal is grown on the seed crystal 35. FIGS. 3A and 3B show a conventional compound semiconductor vapor phase growth apparatus. As shown in FIG. 3A, a source crystal powder 23 and a halogen 25 such as iodine as a transport agent are placed in the lower part of a quartz ampoule 21, and the upper part of the ampoule is tapered (θ=60 to 70 degrees). Surface orientation (111)
A seed crystal 27 that had been grown and a quartz rod 29 were arranged and vacuum sealed. This growth ampoule is placed vertically in a vertical furnace,
A predetermined temperature distribution as shown in FIG. 3B is set. Convection diffusion occurs due to the temperature difference in the vertical direction,
The following reactions occur in the high-temperature room and the low-temperature section. High temperature: R〓R〓＋X ₂ →R〓X ₂ +1/2R〓 _2Low temperature: R〓R〓＋X ₂ ←R〓X ₂ +1/2R〓 ₂ R〓... Group atom R〓... Group atom X ... ...Halogen atoms Due to this reaction, the source material is halogenated in the high temperature section, and the source material is precipitated again in the low temperature section, producing halogen gas. In order to transport the raw material in the lower part of the quartz ampoule 21 to the seed crystal 27 in the upper part, a temperature distribution is formed in which the lower part is a high temperature part and the upper part is a low temperature part. In this way, the source material is transported and grown on the seed crystal. The above-mentioned conventional techniques each have their own problems. The liquid phase crystallization method shown in Figures 2A and B is as follows: (1) Due to differences in thermal properties such as the solvent contained in the ampoule, the heat sink, and the material of the ampoule,
It is difficult to make the shape and thickness of the grown layer constant. (2) Since growth uses a solvent, the amount of solvent must be increased accordingly in order to grow a film on a large wafer. As a result, problems arise such as the heater capacity required to form an appropriate temperature distribution in the solvent increases, its control becomes complicated, the cost of materials increases, and the risk of explosion due to high vapor pressure increases. do. As described above, in liquid phase crystal growth, when trying to grow a large crystal on a large wafer, there are many problems and it is not possible to obtain much benefit from increasing the scale. The vapor phase crystallization method shown in FIGS. 3A and 3B also has the following problems. (1) Due to the ampoule shape, crystal growth is limited. That is, if the crystal 27 is made larger, the ampoule 21 becomes even larger, so there is a volume limit. (2) Since the growth uses halogen as a gas phase medium, the halogen gets into the crystal, making it difficult to obtain high-purity growth. [Problems to be Solved by the Invention] As described above, according to the conventional techniques, it has been difficult to grow a uniform, highly pure and high quality epitaxial crystal of a compound semiconductor. An object of the present invention is to provide a compound semiconductor crystal growth method that can grow a high-quality, high-purity epitaxial crystal with a uniform thickness on a seed crystal. [Means for Solving the Problems] According to the present invention, a high temperature chamber and a low temperature chamber are provided, the high temperature chamber and the low temperature chamber are effectively connected via an intermediate region having a small cross-sectional area, and the intermediate region is connected to the intermediate region. Using a compound semiconductor crystal growth apparatus having a vapor pressure control chamber connected by a tube with an effectively small cross-sectional area, a compound semiconductor source crystal is placed in the high temperature chamber, and the vapor pressure is controlled in the vapor pressure control chamber. A vapor pressure source containing the component to be controlled is placed, a heat sink is placed in the cold room, a seed crystal having a (111) B plane orientation of less than ±10 degrees is placed on the heat sink, and the vapor pressure source is removed from the source crystal. A crystal growth method is provided in which a buffer layer is grown on the seed crystal. [Operation] Since the source material is transported using temperature difference without using a transport gas, highly pure crystals grow without taking in a transport agent. Furthermore, since no transport agent is used, the pressure inside the ampoule during crystal growth can be lowered. A region with an effective small cross-sectional area is provided between the high temperature chamber where the source crystal is placed and the low temperature chamber where the seed crystal is placed, and the vapor pressure of the constituent elements is controlled by supplying steam from the vapor pressure control chamber. crystal growth can be performed while controlling the deviation from the stoichiometric composition. By appropriately selecting the plane orientation, crystals with uniform, high-quality surfaces can be grown. [Example] Figures 1A and B show a crystal growth apparatus 1 used in the present invention.
A schematic diagram is shown. A crystal growth apparatus 1 includes a high temperature chamber 3 in which a source crystal 2 of a compound semiconductor is placed, a low temperature chamber 5 in which a seed crystal 4 is placed, and a vapor pressure control room in which a vapor pressure source 6 of a constituent element of the compound semiconductor or its compound is placed. 7, and has 3 high temperature chambers and 5 low temperature chambers.
However, an intermediate region 1 with an effectively small cross-sectional area is formed by inserting a solid quartz rod 9 in the middle.
1 is connected. A material with high thermal conductivity such as carbon, pyrolytic boron nitrogen (PBN), or quartz is arranged as a heat sink 13 in the lower part of the cold room 5, and a seed crystal 4 is arranged on the heat sink 13. seed crystal 4
A cylindrical quartz tube 17 is placed on top as a seed crystal holder.
to ensure that the seed crystal 4 is in close contact with the heat sink 13. Furthermore, the vapor pressure control chamber 7 is connected to a region 11 having an effectively small cross-sectional area at the upper part of the low-temperature chamber 5 in which the seed crystals are placed through a pipe 8 having a small cross-sectional area. That is, the vapor pressure control room 7 is effectively connected to the cold room 5 by a pipe with a small cross-sectional area. For example, the diameter of high temperature chamber 3 is approximately 12 mm, and the solid quartz rod 9 is
The length of the cold room 5 is about 50 mm, the space of the cold room 5 is about 8 mm in diameter and about 50 mm long, the length of the heat sink 13 is about 10 mm, and the tube 8 is about 3.8 mm in diameter. A temperature distribution as shown in FIG. 1B is set in this crystal growth apparatus 1. The source crystal 2 is maintained at source temperature T1 and generates a constant raw material vapor pressure.
Constituent elements or their compounds 6 are vapor pressure source temperature T2
The vapor pressure of the constituent elements is supplied to the source crystal chamber 3. In the case shown in the figure, T1>T2, and by adjusting the temperature of the vapor pressure control chamber 7, the vapor pressure of the constituent elements in the seed crystal chamber 5 can be controlled. Seed crystal 4 is
The crystal growth temperature T3 is maintained where T1>T3. The gas phase material transported from the source crystal chamber 3 grows epitaxially on the seed crystal 4. The vapor pressure control chamber 7 is connected by a thin tube 8 to an area of effectively small cross-sectional area, and the vapor pressure control component is supplied to the crystal growing in the seed crystal chamber 5. For this reason, vapor pressure can be controlled during crystal growth, making it possible to control the stoichiometric composition of the grown crystal. A crystal growth method using the above-mentioned crystal growth apparatus will be described below, taking ZnSe, a − group semiconductor, as an example. A seed crystal 4 having a (111) B plane orientation is sliced, polished with alumina, and chemically etched as a seed crystal 4 on a heat sink 13 at the bottom of a quartz ampoule 10 having the structure shown in FIG. 1A.
A ZnSe single crystal is placed, and a seed crystal 4 is fixed with a cylindrical quartz tube 17. In addition, as the vapor pressure source 6,
Zn or Se, which is a constituent element of ZnSe, is introduced into the vapor pressure control chamber 7. A recess 18 for supporting a spacer 9 is formed on the seed crystal chamber 5 of the ampoule body, a solid quartz rod is inserted as the spacer 9, and a region 11 with an effectively small cross-sectional area is created around the recess 18. A ZnSe polycrystal produced at a temperature lower than the growth temperature as a source crystal 2 on the spacer 9, e.g.
CVD polycrystalline ingots, e.g. 10 ^-6 Torr
Vacuum-seal at a high vacuum. Note that the quartz ampoule and the solid quartz rod inserted as a spacer are washed with hydrofluoric acid, further washed with acid, and then air-fired in a vacuum. The growth ampoule thus prepared is placed vertically in a vertical furnace having a predetermined temperature distribution as shown in FIG. 1B. When each part of the ampoule reaches a predetermined temperature, the vapor evaporated from the source crystal 2 in the seed crystal chamber 3 forms a primary raw material gas, which is effectively supplied to the seed crystal chamber 5 through a region with a small cross-sectional area. . On the other hand, from the vapor pressure control chamber 7, the controlled vapor pressure is effectively supplied to the region 11 having a small cross-sectional area, and together with the above-mentioned primary material gas, forms a material gas having a desired configuration. The seed crystal 4 is set at a lower temperature than the source crystal 2 so that such raw material gas is transported due to the temperature difference. The source gas supplied through the narrow region 11 is made to have a kinetic energy that is in equilibrium with the temperature, causing epitaxial growth on the surface. In this way, under vapor pressure control, the temperature difference causes the separation from the high temperature (source crystal chamber) 3 to the low temperature chamber (seed crystal chamber).
5, the source material is transported in a gas phase through a region 11 having an effectively small cross-sectional area. Seed crystal 4 is thermally cooled by heat sink 13, and a crystal grows thereon. It was found that the surface morphology of the epitaxial crystal layer on the seed crystal grown in this manner changes depending on the plane orientation of the seed crystal.
The growth rate depends on the growth temperature T3 and the temperature difference ΔT=T1−T3. Regarding the plane orientation, as shown in FIG. 4, good epitaxial crystal growth was obtained on the (111) B plane. Disturbances in morphology were observed when the off-angle exceeded 10 degrees when deviating from the B plane, and the morphology deteriorated considerably when the off-angle exceeded 30 degrees. Although the film thickness distribution was also good near the (111) B plane,
When the off angle exceeded 10 degrees, the distribution began to show a variation of more than 30%. Table 1 shows typical film thickness distribution and surface morphology.

[Table] However, the growth conditions are Tg=950℃, ΔT=10℃,
The vapor pressure due to Zn was 4.2 Torr. The uniformity of the film thickness is the best value obtained under the same conditions, and is expressed as [(difference from average film thickness)/(average film thickness)]×100. As is clear from Table 1, the uniformity of the film thickness on the (111)A surface is improved to about ±10%, but the surface morphology is not so favorable on the step. Compared to these, when grown on the (111) B plane, the film thickness is extremely uniform at ±5%, and the surface morphology becomes mirror-like. When such an epitaxial layer is used as a buffer layer, an excellent, high-quality device epitaxial layer can be grown thereon. Although we have explained the case where a - group epitaxial layer is grown on a - group seed crystal, Si,
A compound semiconductor having a lattice constant difference within about 0.3% may be epitaxially grown on a seed crystal such as Ge, GaAs, or GaP. For example, if you use (111) Ge as a substrate, grow the crystal at a growth temperature of 900°C, and use ZnSe _0.9 S _0.1 as a source crystal under the same conditions as the other crystals, an epitaxial layer of ZnSe _0.9 S _0.1 with a uniform thickness will be grown on Ge. You get layers. In other words, since Ge has a melting point of 958°C, the growth temperature should be lower than this, and ZnSe _0.9 S _0.1 , a mixed crystal of ZnSe (5.6687 Å) and ZnS (5.409 Å), which almost matches the lattice constant of Ge, 5.6461 Å, is lattice matched. can grow. The same is true when growing ZnSe on GaAs, but since the vapor pressure of As from GaAs is high and dissociation of As occurs during crystal growth, the growth temperature is 700°C.
In order to obtain a good growth layer, it is preferable to keep the temperature at a low temperature of .degree. C. or lower. Existing liquid phase growth and vapor phase growth such as MOCVD require various auxiliary equipment, which inevitably makes the entire equipment large-scale.Due to the structure of the growth system, sources such as solvent and carrier gas and seed crystal However, according to the method described above, the same level of crystallinity as obtained by the conventional method can be easily obtained using a simple device. Moreover, it can be grown with good yield. [Effects of the Invention] Compared to liquid phase growth, since growth is performed by vapor phase growth, it is less affected by distortions and the like due to differences in thermal properties of constituent materials. In addition, uniform conditions can be easily obtained, making it easier to grow on large wafers. Since a transport medium is not used and vapor pressure can be controlled, a high purity and high quality epitaxial layer can be provided. Since it is a closed tube gas phase method, the yield from the raw material is better than the open tube gas phase method. Since the plane orientation is selected, the uniformity of the film thickness and the surface morphology are excellent.

[Brief explanation of drawings]

1A and 1B show crystal growth of a compound semiconductor used in an example of the present invention, FIG. 1A is a cross-sectional view of a crystal growth apparatus, FIG. 1B is a temperature distribution diagram, and FIG. 2A,
B shows liquid phase crystal growth using the conventional technique, FIG. 2 A is a cross-sectional view of the crystal growth apparatus, FIG. 2 B is a graph of temperature distribution, and FIGS. 3 A and B show vapor phase crystal growth using the conventional technique. , FIG. 3A is a cross-sectional view of the crystal growth apparatus, FIG. 3B is a graph showing temperature distribution, and FIG. 4 is a conceptual diagram showing preferred surface orientations. In the figure, 1... Ampoule of crystal growth apparatus,
2... Source crystal, 3... Source crystal chamber (high temperature chamber), 4... Seed crystal, 5... Seed crystal chamber (low temperature chamber), 6... Vapor pressure source, 7... Vapor pressure control room, 8 ...Pipe with small cross-sectional area, 9 ...Spacer,
11... intermediate region having a small cross-sectional area, 13...
…heat sink.

Claims (1)

[Scope of Claims] 1 A high temperature chamber and a low temperature chamber are provided, the high temperature chamber and the low temperature chamber are connected through an intermediate region having an effective small cross section, and the intermediate region is connected to a tube having an effective small cross section. Using a compound semiconductor crystal growth apparatus having a connected vapor pressure control chamber, a compound semiconductor source crystal is placed in the high temperature chamber, and a vapor pressure source containing a component whose vapor pressure is to be controlled is placed in the vapor pressure control chamber. Then, place a heat sink in the cold room, and place (111) B side ± on the heat sink.
Place a seed crystal with a plane orientation of less than 10 degrees,
A crystal growth method in which vapor phase components are transported from a source crystal onto a seed crystal to grow an epitaxial layer on the seed crystal.