EPITAXIAL GROWTH METHOD AND APPARATUS THEREFOR

Abstract: In an epitaxial growth method a first gas (21) consisting of a hydrogen diluted gas containing a Group V element is con­ tinuously flowed on a monocrystalline substrate (16) that is placed in a reaction chamber, the monocrystalline substrate (16) is arranged in a gas mixing region where the first gas and a second gas containing a halogenide of a Group III element are mixed adjacent to the monocrystalline substrate, and a Group III-V compound semiconductor (25) is grown on the mono­ crystalline substrate.

Description: The present invention relates to a method and apparatus for epitaxially growing a Group III-V compound semiconductor on a monocrystalline substrate. As methods for epitaxially growing a Group III-V compound semiconductor on a monocrystalline substrate, a vapor phase epitaxy (VPE) method, a metal organic chemical vapor deposition (MOCVD) method, and a molecular beam epitaxy (MBE) method are known. In a hydride VPE method, a Group III material is converted into a halogenide, and is supplied into a reaction tube together with H₂ diluted gas containing a Group V element so as to grow a Group III-V compound semiconductor on a substrate. By this method, in the case of homo-epitaxial growth wherein a crystal is grown on a substrate of the same type material, a crystalline film having a high purity and good crystallinity can be easily obtained. Therefore, this method is widely applied to the manufacture of a Group III-V compound (e.g., GaAs, GaP, InP, and the like) semiconductor device. The conventional hydride VPE method using GaP growth will now be described with reference to Figs. 11(A) and 11(B). Ga 3 (Group III material) stored in a boat 2 and a GaP monocrystalline substrate 4 are arranged inside a reaction tube 1. An electrical oven (not shown) is arranged around the reaction tube 1, so as to keep the temperature distribution inside the reaction tube, as shown in Fig. 11(B). A gas mixture 6 containing PH₃ and H₂ is introduced from an introduction tube 5 inside the reaction tube and a gas mixture 7 containing HCl and H₂ is introduced through a gas inlet (not shown). The introduced HCl reacts with the heated Ga as follows. Ga + HCl → GaCl + 1/2H₂ (1) A gas mixture 8 containing H₂ and GaCl produced by the reaction given by reaction formula (1) is supplied toward the downstream side. PH₃ is decomposed into P₄ and is mixed with the gas mixture 8 containing GaCl and H₂ in a baffle 9 placed on a high-temperature area, thereby forming a gas mixture 10 containing P₄, GaCl, and H₂. The gas mixture 10 passes the high-temperature region and then flows into the low-temperature region. As the temperature of gas mixture 10 is reduced, GaP grows on the GaP monocrystalline substrate 4 placed on the low-temperature region by the reaction expressed by reaction formula (2). 2GaCl + 1/2P₄ + H₂ → 2GaP + 2HCl (2) In the case of homo-epitaxial growth wherein GaP is to be grown on the substrate 4 of a GaP single crystal, GaP can be grown epitaxially as described above. When an Si single crystal is used as the substrate 4, GaP cannot be grown for the following reasons. The reaction tube is normally made of silica glass (SiO₂) because of its good heat processibility, and working properties. When HCl is brought into contact with the silica glass which is heated to high temperature, H₂O is produced by the following reaction: SiO₂ + (4-n)HCl + nH₂ → SiHnCl 4-n + 2H₂O (3) (where n = 0 to 3) H₂O is supplied above the Si substrate on the downstream side together with the H₂ gas and reacts with Si, thereby producing SiO₂. The thus produced SiO₂ covers the Si substrate surface and prevents the GaP growth on the Si substrate. The article of H. Huber and G.H. Winstel (Siemens Forschungs und Entwicklungsberichte; 2 (1973) pp. 171-174) describes an example wherein an electrical oven for annealing is provided in addition to the electrical growth oven. The Si substrate is annealed in the H₂ atmosphere to remove a natural oxide film, and immediately thereafter, the substrate is moved to a growth region so as to grow GaP. However, in this case, since the substrate is exposed to the HCl atmosphere at a high temperature of about 800°C, a formation of SiO₂ on the Si substrate cannot be avoided. For this reason, the growth reproducibility is poor, and even if grown, the resultant crystal has a poor crystallinity and cannot be used as a substrate for practical application. For the above reasons, the hetero-epitaxial growth of the Group III-V compound semiconductor on the Si substrate has not yet been realized by the epitaxial growth method containing halogenide such as HCl. Several attempts have been made to grow a Group III-V compound semiconductor on a Si substrate by the MOCVD or MBE. However, these methods cannot provide a crystal having a crystallinity comparable to that of a crystal which is homo-epitaxially grown by the epitaxial growth method containing a halogenide. M. Akiyama et al. reported a GaAs crystal which is grown on an Si substrate by the MOCVD method (Journal of Crystal Growth, Vol. 68, pp. 21-26, 1984). With this report, a GaAs film which was deposited on the Si substrate by decomposing trimethyl gallium and AsH₃ at 400°C was annealed at 750°C, and mirror-surface-like monocrystalline GaAs could be obtained. However, even when GaAs was grown on the resultant GaAs film by a conventional method, such as the MOCVD or hydride VPE method, the resultant crystal could not provide the same crystallinity as that of a crystal which was grown on a GaAs substrate. It was revealed by an impurity analysis in the depth direction of the resultant film that CH₃ as a constituting molecule of trimethyl gallium is left in the film without being decomposed and degrades the crystallinity since a first film is deposited at a low temperature of 400°C. Attempts for developing a device for integrating many or various functions on an identical substrate have been made. For example, an optical-electronic device in which optical devices and electronic devices are integrated on an identical substrate is known. When devices made of different materials are integrated on an identical substrate, in order to fabricate the next device so as not to impair the previously fabricated device, the steps for growing the respective materials must be performed at low temperature. However, in the conventional method, when growth is carried out under the condition of decreased substrate temperature, a crystal is deposited on a region of the inner wall of the reaction tube corresponding to a temperature, at which the growth is conventionally performed, on the upstream side of the substrate position, and no crystal is grown on the substrate. In this manner, hetero-epitaxial growth for integrating many or various functions on an identical substrate cannot be achieved by the conventional hydride VPE method. Summary of the Invention In other known epitaxial growth methods as described in GB-A-2 055 774 and US-A-4 504 329, there is used the technique of growing a Group III-V semiconductor crystal layer on a semiconductor substrate. In the known reactors used to this end, there are provided mixing and deposition zones which are separated from each other, with a maximum temperature level being maintained in the mixing zones so as to obtain an optimal mixture of the two types of gas flows. The present invention is based on the task of obviating the prior art shortcomings and providing a method as well as an apparatus enabling a satisfactory growth rate in growing a Group III-V compound semiconductor of high quality, preferably of uniform characteristics, on a monocrystalline substrate. According to the present invention, this task is solved in an epitaxial growth method for growing a Group III-V compound semiconductor onto a monocrystalline substrate by the steps of placing said substrate in a reaction chamber; flowing a first gas consisting of a hydrogen diluted gas containig a Group V element continuously along said substrate in the reaction chamber; mixing a second gas containig a halogenide of a Group III element with said continuously flowing first gas in a gas mixing region in the immediate vicinity of the substrate upon reaching predetermined temperature conditions in said gases and the zone in which the substrate is disposed, said mixture contacting the substrate in the reaction chamber; making the thus produced gas mixture to contact the monocrystalline substrate in the gas mixing region for growing said Group III-V compound semiconductor onto said substrate; and maintaining the temperature of the gas mixing region and of the substrate at the same and essentially constant predetermined level whilst the growing process of the Group III-V compound semiconductor on said monocrystalline substrate takes place in this gas mixing region. According to another aspect of the present invention for solving this task there is suggested an epitaxial growth method for growing a Group III-V compound semiconductor onto a monocrystalline substrate placed in a reaction chamber, which method comprises the steps of flowing a first gas consisting of a hydrogen diluted gas containing a Group V element along said substrate in the reaction chamber and a second gas containing a halogenide of a Group III element along a flow path different from that of said first gas to be mixed with said first gas; in a first step, and upon reaching predetermined temperature conditions in said gases and the zone in which the substrate is disposed, mixing said first and second gases in the immediate vicinity of the substrate immediately before making the mixture thus produced to contact said monocrystalline substrate for growing of the Group III-V compound semiconductor onto said monocrystalline substrate, which growth takes place whilst maintaining the temperature of the gas mixing region and of the substrate at the same and essentially constant predetermined level; interrupting said first step growing; and as a second step, performing a further growing of a Group III-V compound semiconductor on said Group III-V compound semiconductor grown by the first step. In order to put the method according to the invention into practice in a most appropriate and expedient manner, there is further suggested an epitaxial growth apparatus for growing a Group III-V compound semiconductor onto a monocrystalline substrate, the apparatus comprising: a reaction chamber; a first flow path, formed in said reaction chamber, for flowing a first gas consisting of a hydrogen diluted gas containing a Group V element; a second flow path, formed in said reaction chamber, for flowing a second gas containing a halogenide of a Group III element; a support member for a monocrystalline substrate arranged in said reaction chamber; and end portions of said first and second flow paths in said reaction chamber arranged so as to constitute a mixing region in which said first and second gases are mixed; wherein said support member is arranged to move said monocrystalline substrate into and out of said mixing region between the latter and a region in which only said first gas flows, so as to determine the starting and concluding of the growth of the Group III-V compound semiconductor on the surface of said monocrystalline substrate; the end portion of said first flow path adjacent to said mixing region has a smaller sectional area than that of the other portion of said first flow path; and said first flow path is arranged parallel to said second flow path. In order to further improve the handling of the apparatus, the gas inlet of said first flow path may be formed in said reaction chamber so as to oppose a gas inlet of said second flow path. Brief Description of the Drawings Embodiments of the present invention will now be described with reference to the accompanying drawings. In these Figs. 1(A) and 1(B) show an epitaxial growth apparatus according to an embodiment for performing the method according to the present invention, in which Fig. 1(A) is a sectional view taken along a longitudinal direction of the apparatus, and Fig. 1(B) is a sectional view taken along a line IB-IB in Fig. 1(A); Fig. 1(C) is a graph showing the temperature distribution of such apparatus; Figs. 2(A) to 2(D) are reflection high energy electron diffraction (RHEED) photographs of a GaP crystal which is grown when utilising the method of the present invention; Fig. 3 is a graph showing the relationship between the growth time and the film thickness of GaP which is grown on an Si (111) substrate; Figs. 4(A) and 4(B) show another embodiment of an epitaxial growth apparatus according to the present invention, in which Fig. 4(A) is a sectional view taken along a longitudinal direction of the apparatus, and Fig. 4(B) is a sectional view taken along a line IVB-IVB in Fig. 4(A); Fig. 5 is a graph showing semiconductor growth rate characteristics in a gas mixing region and a downstream side region thereof; Fig. 6 is a graph showing the relationship between the film thickness of GaP grown on an Si (100) substrate and the PH₃ flow rate; Fig. 7 is a graph showing the relationship between the film thickness of GaP grown on an Si (100) substrate and the substrate temperature; Figs. 8(A) to 8(C) are reflection electron beam diffraction photographs of a GaP crystal which is grown on an Si (100) substrate by a two-step growth method according to the present invention; Fig. 9 is a graph showing the relationship between the substrate covering ratio with a GaP layer and the substrate temperature; Figs. 10(A) and 10(B) are sectional views showing a still another embodiment of an epitaxial growth apparatus according to the present invention; Fig. 11(A) is a sectional view of a conventional epitaxial growth apparatus; and Fig. 11(B) is a graph showing the temperature distribution of the apparatus shown in Fig. 11(A). Description of the Preferred Embodiments Example 1 Figs. 1(A) and 1(B) show an epitaxial growth apparatus according to a first embodiment for putting the method of the present invention into practice, and Fig. 1(C) shows temperature distribution in this apparatus. A reaction tube 11 which is made of silica glass constitutes a double tube structure together with a Group III element source chamber (to be referred to simply as a source chamber hereinafter) 12 made of silica glass. The reaction tube 11 need not have a cylindrical shape as shown in Fig. 1(B) but may well have any other sectional shapes. The sectional shape of the source chamber 12 need not be of a semicircular shape as shown in Fig. 1(B) but can be of any other suitable shape such as a rectangular shape. The two ends of the reaction tube 11 are shielded from an outer atmosphere, respectively, by a lid 11A, a flange 11B, and an O-ring 11G, and a lid 11C, a flange 11D, and an O-ring 11G'. A gas inlet 11E is formed on the lid 11A, and a gas outlet 11F is formed on the lid 11C. One end portion of the source chamber 12 is shielded from the outer atmosphere by a lid 12A, a flange 12B, and an O-ring 12E. A gas inlet 12C is formed on the lid 12A. The other end portion of the source chamber 12 has an opening portion 12D which is open to the reaction tube 11. The opening portion 12D has a downwardly inclined portion, and its opening end is formed to be substantially parallel to the surface of a substrate (to be described later) which is arranged therebelow. A Group III element 13 is stored in the source chamber 12 while being housed in a boat 14. A substrate support table 15 is arranged below the opening portion 12D in the reaction tube 11, and a substrate 16 on which a crystal is to be grown is supported thereby. Preference numerals 17 and 18 denote electrical ovens for heating the reaction tube 11. The seal method of the two ends of the reaction tube 11 and locations of the gas inlet and the gas outlet are not limited to those illustrated in Figs. 1(A) and 1(B), and various other known methods can be used. A method for growing GaP on an Si monocrystalline substrate having a (111) plane using the apparatus shown in Figs. 1 (A) and 1(B) will now be described. Ga is used as the Group III element 13. The surface of the Si substrate 16 having a (111) plane is cleaned by chemical etching or the like, and a natural oxide film formed on the surface is removed by a hydrogen fluoride (HF) solution. Then, the substrate 16 is set on the substrate support table 15. A gas mixture 21 containing phosphine (PH₃) and hydrogen (H₂) as source materials of a Group V element is introduced from the gas inlet 11E into the reaction tube 11, and an H₂ gas 22 is introduced from the gas inlet 12C into the source chamber 12. After the air inside the apparatus has been sufficiently substituted by the introduced gases, the reaction tube 11 is heated. The temperature distribution of the reaction tube 11 is as shown in Fig. 1(C). More specifically, the electrical ovens 17 and 18 are controlled such that high temperature is obtained at the position of the Ga 13 and low temperature is obtained at the position of the substrate 16. When the desired temperature distribution is obtained, e.g., when the Ga temperature (T S ) reaches 500°C to 900°C, preferably, 750°C to 850°C and the substrate temperature (T G ) reaches 400 to 800°C, preferably, 600°C, then hydrogen chloride (HCl) gas is supplied from the gas inlet 12C to convert the gas flow 22 to be a gas mixture containing (HCl + H₂). PH₃ contained in the gas flow 21 is decomposed by heat to become a gas flow 23 containing (P₄ + H₂). Meanwhile, HCl produces GaCl by reaction given by reaction formula (1) and forms a gas flow 24 containing (GaCl + H₂). The gas flow 24 containing the Group III element Ga and the gas flow 23 containing the Group V element P flow along independent flow paths, and are mixed near the opening portion 12D of the source chamber 12. Thus, a GaP crystal 25 is grown on the substrate by a reaction given by reaction formula (2). An exhaust gas 26 is exhausted from the gas outlet 11F. With the method of this example, the substrate surface before crystal growth is exposed to a (PH₃ + H₂) or (P₄ + H₂) atmosphere and, hence, will not be oxidized. GaCl and P₄ pass a high temperature region separately, and produce GaP near the low-temperature substrate. Therefore, a high degree of super saturation of crystal growth can be realized, and hence, a high growth rate can be achieved. The atmosphere surrounding the substrate has a low oxygen content, and H₂O produced by a reaction given by reaction formula (3) reaches the substrate after the growth of the crystal. Therefore, the substrate will not be oxidized, and the GaP crystal can grow satisfactorily onto the Si substrate. The Si substrate 16 is located immediately below the opening portion 12D. The distance between the substrate surface and the opening portion 12D is preferably as short as possible so as not to interfere with the reaction given by reaction formula (2) after the gas flows 23 and 24 are mixed. In this example, the distance from the surface of the substrate 16 to the opening portion 12D is about 2 mm. The GaP crystal growth starts upon introduction of HCl, and is stopped when the introduction of HCl is stopped. When the Ga temperature was 850°C, the PH₃ flow rate was 5 x 10⁻⁵ mol/min, and the HCl flow rate was 5 x 10⁻⁵ mol/min, and the substrate temperature was 600°C, a 0.35-µm thick GaP crystal was grown in five minutes. When the substrate temperature was changed while other conditions remained the same, the GaP crystal growth was possible within the substrate temperature range of 350°C to 800°C. Figs. 2(A) to 2(D) show reflection high energy electron diffraction (RHEED) images of the GaP crystal which was grown as described above. As the substrate temperature increases, the resultant crystal has good crystallinity. A GaP single crystal having the same (111) plane as that of the substrate can be obtained at the substrate temperature of 350°C or higher. Even if the Ga temperature is changed from 500°C to 900°C, the growth rate and the crystal quality are not affected. Fig. 3 shows the relationship between the growth time and the thickness of a grown crystal film. The temperature of the Si substrate is 350°C. The GaP thickness on the Si (111) plane is increased in proportion to the growth time. In this example, the opening portion 12D has the downwardly inclined portion, and its opening end is substantially parallel to the substrate surface. However, the opening end of the downwardly inclined portion need not be parallel to the substrate. In addition, the opening portion 12D need not be inclined downwardly, but can extend to be parallel to the substrate surface. Furthermore, the opening portion 12D can have a tapered nozzle portion whose opening faces the substrate surface. Example 2 Figs. 4(A) and 4(B) show an epitaxial growth apparatus according to a second embodiment for putting the present invention into practice. Differences between the first and second embodiments are that the interior of the reaction tube 11 is partitioned by a partition wall 31 and that a substrate support table 32 is movable inside the reaction tube by means of a substrate moving rod 33. The seal method of the two ends of the reaction tube 11, the locations of the gas inlet and the gas outlet, and the electrical ovens for heating the reaction tube 11 are the same as those in the first embodiment, and are omitted from Figs. 4(A) and 4(B). The Group III element 13 is stored in the boat 14 and is placed on the partition wall 31. An end portion 31A of the partition wall 31 on the downstream side of the gas flow is bent downward to guide the gas flow above the partition wall downwards. The substrate support table 32 can be moved under the end portion 31A of the partition wall 31. The temperature inside the reaction tube 11 is controlled by the electrical ovens so that the high temperature is obtained at the position of the Group III element and the low temperature is obtained at the position of the substrate, in the same manner as shown in Fig. 1(C). A GaAs crystal was grown on an Si (111) substrate using the apparatus shown in Figs. 4(A) and 4(B). The substrate 16 whose surface was cleaned in the same manner as described in Example 1 was located below the end portion 31A of the partition wall 31, as shown in Fig. 4(A). Ga was used as the Group III element. A gas mixture 34 containing arsine (AsH₃) and H₂ was flowed below the partition wall 31, and an H₂ gas 35 was flowed thereabove. After air inside the reaction tube 11 had been sufficiently substituted, the reaction tube 11 was heated. After the temperature distribution inside the reaction tube as shown in Fig. 1(C) was obtained such that the Ga portion was at high temperature and the substrate position was at low temperature, for example, after the Ga portion (T S ) reached 850°C and the substrate temperature (T G ) reached 300°C to 700°C, HCl was mixed with the gas flow 35 to form a gas mixture containing (HCl + H₂). AsH₃ in the gas flow 34 was mainly decomposed in the form of As₄ by heat, and formed a gas mixture flow 36 containing (As₄ + H₂). Meanwhile, HCl was reacted with Ga to produce GaCl, and formed a gas mixture flow 37 containing (GaCl + H₂). The gas flow 37 containing the Group III element Ga and the gas flow 36 containing the Group V element As were flowed along independent flow paths, and were mixed for the first time near the end portion 31A of the partition wall 31. Then, these two gases reacted and a GaAs crystal 38 was grown or the substrate 16. Reference numeral 39 denotes an exhaust gas. GaAs precipitation and growth are started upon introduction of HCl, and stopped when the introduction is stopped. After the Ga temperature was 850°C, the substrate temperature was 600°C, the AsH₃ flow rate was 5 x 10⁻⁵ mol/min, and the HCl gas was flowed for five minutes at the flow rate of 5 x 10⁻⁵ mol/min, the reaction tube 11 was cooled and then the substrate 16 was unloaded. A 0.35-µm thick GaAs crystal was grown on the substrate. When the resultant crystal was observed by RHEED, the resultant crystal was a single crystal having the same (111) plane as that of the substrate when the temperature of the substrate 16 was 300°C or higher. The GaAs crystal growth can be started and stopped not only by introduction of the HCl gas but also by moving the substrate. More specifically, the substrate support table 32 is located below the partition wall 31 so that the substrate 16 does not contact with the gas flow 37, the reaction tube 11 is heated to a desired temperature, and the HCl gas is mixed in the gas flow 35. In this state, the substrate support table 32 is moved to a position shown in Fig. 4(A), and the gas flows 36 and 37 can be mixed and reacted near the substrate surface. After a predetermined period of time has passed, when the substrate support table 32 is moved below the partition wall 31 so as to separate the substrate from the gas mixing region, the GaAs growth is stopped. The quality of the resultant GaAs crystal and the growth rate in this case are the same as those when the crystal growth is controlled by introduction of the HCl gas. The end portion 31A of the partition wall 31 on the downstream side of the gas flow is bent downward, so that the sectional area of the flow path of the gas flow 36 adjacent to the gas mixing region near the end portion 31A of the partition wall 31 is decreased. As a result, the velocity of the gas flow 36 is increased through the narrow region, and an undesirable reverse flow of a gas and the like toward the flow path of the gas flow 36 can be prevented. The moving mechanism of the substrate support table can be added to the apparatus shown in Fig. 1(A). Example 3 A GaP crystal was grown on an Si (100) substrate using the apparatus shown in Fig. 4(A). A substrate 16 was located at a position below the partition wall 31 so as not to contact the gas flow 37. Only an H₂ gas was flowed as the gas flows 34 and 35. After any air inside the reaction tube 11 was sufficiently substituted, the reaction tube was heated by the electrical ovens to keep the temperature of the substrate 16 at 800°C to 1,000°C for 15 minutes, so that contamination, a natural oxide film, and the like on the substrate were removed by cleaning. The temperature distribution inside the reaction tube was controlled as shown in Fig. 1(C), so that the Ga source portion was set at high temperature and the position of the substrate was set at low temperature. In this example, the temperature T S was kept at 800°C, and the temperature T G was kept at 350°C to 450°C. A gas mixture 34 containing PH₃ and H₂ and a gas mixture 35 of HCl and H₂ were introduced. After the gas flows were stabilized, the substrate was moved to the downstream side of the end portion 31A of the partition wall 31, as shown in Fig. 4(A), and this state was maintained for five minutes. The gas flow 36 containing P₄ and the gas flow 37 containing GaCl were mixed and reacted near the end portion 31A, and as a result, GaP was grown on the substrate 16. In this first step, a uniform amorphous GaP layer was grown on the Si substrate. The thickness of the GaP layer varies in accordance with the PH₃ and HCl flow rates and the substrate temperature. When the PH₃ flow rate was 0.1 mℓ/min and the HCl flow rate was 0.5 mℓ/min, the thickness was 20 nm. Thereafter, the substrate 16 on which the GaP layer was grown was returned to a position at which it could not contact the gas flow 37, e.g., a position below the partition wall 31, and HCl introduction was then stopped. In order to prevent P of the GaP layer deposited on the substrate 16 from evaporating, the gas mixture flow 34 of H₂ diluted gas containing a Group V element was flowed and then the substrate temperature was increased to 600°C to anneal the substrate. The gas mixture containing HCl and H₂ was again introduced. After the gas flow was stabilized, the substrate 16 was moved to the downstream side of the end portion 31A of the partition wall 31, and the second-step growth was carried out. 10 minuted later, a 0.5-µm thick GaP monocrystalline layer was grown on the substrate 16. The resultant crystal had a full width at half maximum of 40" of the X-ray rocking curve of the double crystal method. Thus, it was demonstrated that the resultant crystal had good crystallinity equivalent to that of a crystal which was homo-epitaxially grown on a normal GaP substrate. According to this embodiment, since the epitaxial layer is grown by moving the substrate 16 under the end portion 31A of the partition wall 31, a uniform semiconductor film can be grown. Fig. 5 shows the GaP growth rate characteristic on a substrate around the gas mixing region and the downstream region thereof. As can be seen from this characteristic, the semiconductor growth rate around the gas mixing region near the end 31A of the partition wall 31 is noticeably high. Since this rate is much higher than the rate at which an oxide film is formed on the substrate surface, a hetero-epitaxially grown semiconductor of high quality can be obtained at high yield. Since the sectional area of the flow path of the gas flow 36 adjacent to the gas mixing region is smaller than the other portion of the flow path of the gas flow 36, a gas such as HCl which adversely affects the substrate cannot flow to the upstream side of the gas flow 36 from the gas mixing region. For this reason, the substrate surface will not be contaminated with such gas before, during, and after the semiconductor epitaxial growth onto the substrate. As described above, the thickness of the GaP layer in the first-step growth varies in accordance with the growth conditions. When the PH₃ flow rate is increased, the film thickness is increased as shown in Fig. 6. When the PH₃ and HCl flow rates were fixed at 0.1 mℓ/min and 0.5 mℓ/min, respectively the film thickness was increased as the substrate temperature increased, as shown in Fig. 7. The film thickness shown in Figs. 6 and 7 corresponds to that after a growth time of five minutes has passed. Figs. 8(A), 8(B), and 8(C), respectively, show RHEED patterns of the GaP layers which were obtained at the substrate temperatures of 500°C, 600°C, and 700°C, respectively. It is demonstrated that as the substrate temperature increases, crystallinity is improved, and a single crystal GaP having the same (100) plane as that of the substrate can be obtained at the substrate temperature of 600°C or higher. It can be considered that the grown film is annealed upon an increase in temperature during the transition from the first to second step, and the crystallinity is improved, thereby facilitating the growth in the second step. Furthermore, after the amorphous GaP layer was grown on the substrate which was kept at 350°C, the substrate was not moved, and the HCl flow was stopped, thereby stopping GaP growth. Thereafter, the substrate temperature was increased up to 600°C. Thereafter, the HCl gas was again introduced to grow a GaP crystal on the substrate. The full width at half maximum of the X-ray rocking curve of the double crystal method was the same as that of the GaP crystal obtained in the second-step growth by moving the substrate. Example 4 GaP was epitaxially grown on an Si (100) substrate in combination of the method shown in Example 3 and the conventional method. After the first-step growth of GaP in Example 3, the substrate 16 was unloaded from the reaction tube. As described above, in this step, GaP on the Si (100) substrate is amorphous. GaP was then grown on this substrate by the conventional method. The substrate on which the amorphous GaP layer was grown was placed at a position of the substate 4 in the conventional apparatus shown in Fig. 11. Then, the temperature conditions shown in Fig. 11(B), i.e., the temperature at the position of the Ga source 3 of 900°C, the substrate temperature of 750°C to 800°C, and the temperature gradient at the position of the substrate of 5 to 10°C/cm were set while supplying the gas mixture 6 containing PH₃ and H₂ from the supply tube 5. Then, the gas mixture 7 containing HCl and H₂ was supplied to initiate epitaxial growth. After the epitaxial growth was performed for 20 minutes under the conditions of the PH₃ and HCl flow rates of 1 mℓ/min, respectively, a 2-µm thick GaP monocrystalline layer was grown on the substrate. The crystallinity of the resultant crystal was the same as that of the crystal shown in Example 3. The same result was obtained when the second-step growth was conducted by the MOCVD method using trimethyl gallium and PH₃. In Examples 3 and 4, the first-step growth is started and stopped upon movement of the substrate. Alternatively, the substrate can be initially located at the downstream side of the end portion 31A of the partition wall 31, and after the interior of the reaction tube 11 is set in the temperature distribution, i.e., the Ga source temperature is set at 800°C and the substrate temperature is set at 350°C, amorphous GaP having a desired thickness can be grown on the substrate upon introduction of HCl. Thereafter, when the second-step growth was performed in accordance with the above examples, a single crystal having the same crystallinity could be obtained. Group III-V compound semiconductor hetero-epitaxial growth on an Si substrate depends on the fact that oxidation of an Si surface is suppressed to allow the growth of a first Group III-V compound semiconductor thin film layer. In the second-step growth of the present invention, the first layer is grown on the Si (100) substrate at a relatively low temperature, as described above. When the first layer is grown at a high temperature of 500°C or higher, an oxygen component which is contained in the HCl gas and is produced by reaction of the reaction tube and HCl is reacted with Si before the growth of the GaP layer. Thus, the oxygen component forms an SiO₂ layer on the Si surface, and interferes with the growth of the GaP layer. When the substrate temperature is set at 450°C or lower, the GaP growth rate becomes faster than the SiO₂ growth rate, and a uniform film can be formed. Fig. 9 is a graph showing the relationship between the substrate temperature and the covering ratio of the Si (100) substrate with the GaP layer. Fig. 9 reveals that a region on which no GaP is deposited is formed on the substrate at about 500°C. Therefore, in order to obtain a uniform GaP film, growth must be performed at 450°C or lower. The film which is grown at 450°C or lower does not always have good crystallinity and is found to have a quality between polycrystalline (450°) and amorphous (350°) upon observation by RHEED. Therefore, the film cannot be utilized for manufacturing a device such as an LED. In the present invention, the second step is carried out at a temperature at which a film is to be grown normally by the VPE method, and after the amorphous or polycrystalline film of the first step is annealed, the GaP layer having good crystallinity can be grown thereon. This crystal can be utilized for manufacturing a device such as an LED. Example 5 Fig. 10(A) is a sectional view of an epitaxial growth apparatus according to another embodiment of the present invention. The same reference numerals in Fig. 10(A) denote the same parts as in Fig. 1(A), and a detailed description thereof will be omitted. Although the electrical ovens for heating the reaction tube 11 are omitted from the drawing, they are controlled to heat the reaction tube to obtain the temperature distribution as shown in Fig. 1(C). The principal difference between this embodiment and the embodiment shown in Fig. 1(A) is a gas introduction portion of a gas (containing a Group V element) (to be referred to as a Group V gas introduction portion hereinafter). A Group V gas introduction portion 41 has a gas inlet 41A at one end thereof. Supplied gas 21 is returned by the other end of the Group V gas introduction portion and continues to flow. The returning portion corresponds to a storage portion 41B of the substrate support table 42. An end portion 41C of the storage portion 41B is bent downwards so as to guide gas flow 24 containing a Group III element downwardly. The two gas flows 23 and 24 are mixed and first reacted near the end portion 41C. The substrate support table 42 can be moved by the moving rod 42A inwardly and outwardly with respect to the storage portion 41B. The height from the substrate 16 supported on the substrate support table 42 to the end portion 41C must fall within the range within which mixing of the gas flows 23 and 24 is not interfered, and is preferably 1 mm to several cm, and more preferably 2 to 5 mm. The gas inlet 11E of the reaction tube 11 can have the same arrangement as that of Fig. 1(A). This embodiment has a good operatability and processability such as an easy change of the type of a Group III element or a substrate used, easy cleaning of the interior of the reaction tube, and the like. The epitaxial growth of the Group III-V semiconductor using the apparatus of this embodiment can be performed in the same manner as in Examples 2 to 4. Fig. 10(B) is a sectional view for explaining another embodiment for supplying gas flows in opposing directions. The same reference numerals in Fig. 10(B) denote the same parts as in Figs. 4 and 10(A). The operation of this embodiment is substantially the same as that in the embodiment shown in Fig. 10(A), except that a gas flow 35 flowing through the source chamber is returned by the partition wall in the opposite direction and is then mixed with a gas flow 36 in the vicinity of an end portion 31A. HBr or HI can be used instead of HCl as a gas which reacts with the Group III element and produces a halogenide gas. The hetero-epitaxial growth wherein a different material such as a Group III-V compound is grown on an Si substrate has been described. The present invention can be applied to homo-epitaxial growth wherein a crystal is grown on a substrate of the same type of material, as a matter of course. The two-step crystal growth according to the present invention can be applied to other planes and other substrates in addition to the Si (100) substrate, and can advantageously improve the quality of a grown crystal. According to the present invention as described above, a substrate is placed in an H₂ gas atmosphere containing a Group V element, and a gas containing a Group III halogenide is mixed with the H₂ gas containing a Group V element immediately above the substrate, so as to grow a crystal. Therefore, a Group III-V compound semiconductor can be hetero-epitaxially grown on an Si substrate. Therefore, electronic and optical devices using GaP, GaAs, and the like can be manufactured using an inexpensive Si substrate instead of an expensive Group III-V compound semiconductor substrate. Since a Group III-V compound semiconductor crystal can be grown at a low substrate temperature of 600°C or lower, a highly functional device which is constituted by different materials and is arranged on an identical substrate can be realized.

Claims: An epitaxial growth method for growing a Group III-V compound semiconductor onto a monocrystalline substrate, the method comprising the steps of a) placing said substrate in a reaction chamber; b) flowing a first gas consisting of a hydrogen diluted gas containing a Group V element continuously along said substrate in the reaction chamber; c) mixing a second gas containing a halogenide of a Group III element with said continuously flowing first gas in a gas mixing region in the immediate vicinity of the substrate upon reaching predetermined temperature conditions in said gases and the zone in which the substrate is disposed, said mixture contacting the substrate in the reaction chamber; d) making the thus produced gas mixture to contact the monocrystalline substrate in the gas mixing region for growing said Group III-V compound semiconductor onto said substrate; and e) maintaining the temperature of the gas mixing region and of the substrate at the same and essentially constant predetermined level whilst the growing process of the Group III-V compound semiconductor on said monocrystalline substrate takes place in this gas mixing region. A method according to claim 1, wherein the growth of said Group III-V compound semiconductor is started and stopped upon supply and termination thereof, respectively, of said second gas to said gas mixing region. A method according to claim 1, wherein said monocrystalline substrate is moved from a region in which only said first gas flows to the region in which said first and second gases mix, thereby growing said Group III-V compound semiconductor on said monocrystalline substrate. A method according to claim 1, wherein said monocrystalline substrate is moved from a region in which only said first gas flows to the region in which said first and second gases mix, thereby growing said Group III-V compound semiconductor on said monocrystalline substrate, and is then returned to the region in which only said first gas flows, so as to stop the growth of the semiconductor thereon. A method according to claim 1, wherein said monocrystalline substrate is a silicon substrate. A method according to claim 1, wherein an end portion of the flow path of said first gas adjacent to said gas mixing region has a smaller sectional area than that of the other portion of said flow path. A method according to claim 1, wherein the surface of said monocrystalline substrate is cleaned before said monocrystalline substrate is placed in said reaction chamber so as to remove a natural oxide film formed thereon. An epitaxial growth method for growing a Group III-V compound semiconductor onto a monocrystalline substrate placed in a reaction chamber, the method comprising the steps of a) flowing a first gas consisting of a hydrogen diluted gas containing a Group V element along said substrate in the reaction chamber and a second gas containing a halogenide of a Group III element along a flow path different from that of said first gas to be mixed with said first gas; b) in a first step, and upon reaching predetermined temperature conditions in said gases and the zone in which the substrate is disposed, mixing said first and second gases in the immediate vicinity of the substrate immediately before making the mixture thus produced to contact said monocrystalline substrate for growing of the Group III-V compound semiconductor onto said monocrystalline substrate, which growth takes place whilst maintaining the temperature of the gas mixing region and of the substrate at the same and essentially constant predetermined level; c) interrupting said first step growing; and d) as a second step, performing a further growing of a Group III-V compound semiconductor on said Group III-V compound semiconductor grown by the first step. A method according to claim 8, wherein the second step comprises the steps of flowing the first gas consisting of the hydrogen diluted gas containing the Group V element on said monocrystalline substrate that is placed in said reaction chamber, flowing said second gas containing the halogenide of the Group III element along a flow path different from that of said first gas, placing said monocrystalline substrate in said gas mixing region where said first and second gases are mixed, and growing said Group III-V compound semiconductor on said monocrystalline substrate. A method according to claim 8, wherein in the first and second steps, the growth of said Group III-V compound semiconductor is started and stopped upon supply and termination thereof, respectively, of said second gas to said gas mixing region. A method according to claim 8, wherein in the first and second steps, said monocrystalline substrate is moved from a region in which only said first gas flows to the gas mixing region in which said first and second gases mix, thereby growing said Group III-V compound semiconductor on said monocrystalline substrate. A method according to claim 8, wherein in the first and second steps, said monocrystalline substrate is moved from a region in which only said first gas flows to the gas mixing region in which said first and second gases mix, thereby growing said Group III-V compound semiconductor on said monocrystalline substrate, and is then returned to the region in which only said first gas flows, so as to stop the growth of the semiconductor thereon. A method according to claim 8, wherein in the first or second step, the growth of said Group III-V compound semiconductor is started and stopped upon supply and termination thereof, respectively, of said second gas to said gas mixing region. A method according to claim 13, wherein in the remaining first or second step, said monocrystalline substrate is moved from the region in which only said first gas flows to said gas mixing region in which said first and second gases mix, so that said Group III-V compound semiconductor is grown on said monocrystalline substrate, and said monocrystalline substrate is then returned to the region that only said first gas flows to stop the growth of the semiconductor. A method according to claim 8, wherein in the second step, said first and second gases are satisfactorily mixed before they reach the substrate in said reaction chamber, and the gas mixture is supplied onto said monocrystalline substrate that is held at a temperature higher than the temperature in the first step, thereby growing said Group III-V compound semiconductor. A method according to claim 8, wherein said monocrystalline substrate is a silicon substrate. A method according to claim 8, wherein an end portion of the flow path of said first gas adjacent to said gas mixing region has a smaller sectional area than that of the other portion of said flow path. A method according to claim 8, wherein the surface of said monocrystalline substrate is cleaned before the first step so as to remove a natural oxide film formed thereon. An epitaxial growth apparatus for growing a Group III-V compound semiconductor onto a monocrystalline substrate (16), the apparatus comprising: a reaction chamber (11); a first flow path (23;36), formed in said reaction chamber, for flowing a first gas consisting of a hydrogen diluted gas containing a Group V element; a second flow path (24;37), formed in said reaction chamber, for flowing a second gas containing a halogenide of a Group III element (13); a support member (15;32;42 for a monocrystalline substrate arranged in said reaction chamber; and end portions (12D;31A;41C) of said first and second flow paths in said reaction chamber arranged so as to constitute a mixing region in which said first and second gases are mixed; wherein said support member is arranged (33;42A) to move said monocrystalline substrate into and out of said mixing region between the latter and a region in which only said first gas flows, so as to determine the starting and concluding of the growth of the Group III-V compound semiconductor on the surface of said monocrystalline substrate; the end portion of said first flow path adjacent to said mixing region has a smaller sectional area than that of the other portion of said first flow path; and said first flow path is arranged parallel to said second flow path. An apparatus as claimed in claim 19, wherein the gas inlet (41a) of said first flow path (23) is formed in said reaction chamber (11) so as to oppose a gas inlet (11E) of said second flow path (24).

Inventors: MORI, HIDEFUMI 4-16-8, MINAMIOGIKUBO, TSUZUKI, NOBUYORI 4-10, HAMADACHO, YAMAMOTO, MITSUO 1282, JOSUIHONCHO
Applicants: NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Application year: 1987
Main classification: C30B25
IPC codes: C30B25, H01L21