JP2010232623A - Hetero epitaxial growth method, hetero epitaxial crystal structure, hetero epitaxial crystal growth apparatus, and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hetero epitaxial growth method, a hetero epitaxial crystal structure, a hetero epitaxial crystal growth apparatus, and a semiconductor device for growing a ZnO based semiconductor crystal on a heterogeneous substrate at a high temperature. <P>SOLUTION: The hetero epitaxial growth method, the hetero epitaxial crystal structure, the hetero epitaxial crystal growth apparatus, and the semiconductor device include a process of forming a buffer layer 42 formed with an orienting film of an oxide or an orienting film of nitride on a heterogeneous substrate 40, and a process of performing crystal growth of a ZnO based a semiconductor layer 44 or 46 on the buffer layer using a halogenated group II metal and an oxygen material. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a heteroepitaxial growth method, a heteroepitaxial crystal structure, a heteroepitaxial crystal growth apparatus, and a semiconductor device. The present invention relates to a crystal growth apparatus and a semiconductor device.

  ZnO crystal is a direct transition type semiconductor with a band gap of about 3.37 eV, the exciton binding energy of holes and electrons in solids is as large as 60 meV, and it is stable even at room temperature. The load is small and it is expected as a light emitting device from the blue region to the ultraviolet region.

  ZnO crystals have a wide range of uses other than light-emitting devices, and are expected to be applied to light-receiving elements, piezoelectric elements, transistors, transparent electrodes, etc., and establishment of high-quality ZnO crystal growth technology with excellent mass productivity is desired. Yes.

  The following methods are known as methods for producing high-quality ZnO-based semiconductors. For example, in the molecular beam epitaxy (MBE) method, zinc and radicalized (plasmaized) oxygen are supplied as molecular beams and reacted on a growth substrate to grow a high-quality ZnO-based semiconductor. ing. In the pulsed laser deposition (PLD) method, a ZnO-based semiconductor is deposited on a growth substrate by depositing a ZnO-based semiconductor evaporated by irradiating a laser beam onto a ZnO-based semiconductor sintered body or crystal. Growing semiconductors.

  However, when a ZnO-based semiconductor is grown by the MBE method and the PLD method described above, it is difficult to form a film with a large area, and it is necessary to perform growth in a vacuum. There is a problem that it is difficult.

  Therefore, as a method for manufacturing a ZnO-based semiconductor that does not require high vacuum, a ZnO-based semiconductor is formed by a metal organic chemical vapor deposition (MOCVD) method that is widely used for crystal growth of III-V group semiconductors. There are known ways to grow. In the MOCVD method, an organic metal containing zinc is decomposed in the vicinity of the substrate or on the substrate, and finally the metal element and the oxygen material react to grow a ZnO-based semiconductor.

  However, in the MOCVD method described above, the vapor pressure of zinc, which is a group II element, is extremely higher than that of group III elements. Therefore, even if zinc reaches the growth substrate at a high temperature capable of high-quality growth, the growth substrate Easy to leave. For this reason, since the ratio of zinc that can contribute to the growth of the ZnO-based semiconductor on the growth substrate is small, there is a problem that the efficiency of the material containing zinc is low.

  In addition, there is a problem that it is difficult to grow a ZnO-based semiconductor that does not contain carbon because carbon is mixed into the ZnO-based semiconductor by a hydrocarbon group generated when an organometallic material containing zinc is decomposed.

  When a ZnO-based semiconductor is grown by a vapor phase epitaxy (VPE) method, it is known as one method to use a zinc metal simple substance and an oxygen material containing oxygen (for example, oxygen) as materials. . However, the equilibrium constant of this chemical reaction is larger than the equilibrium constant of the III-V group semiconductor, and it is necessary to set the supply partial pressure of zinc having a high vapor pressure high for high-temperature growth as described above. Therefore, there is a problem that it is difficult to control the reaction.

  Therefore, as another method for growing a ZnO-based semiconductor by the VPE method, a method using zinc chloride and an oxygen material is disclosed (for example, see Non-Patent Document 1). In this method of manufacturing a ZnO-based semiconductor in Non-Patent Document 1, zinc chloride powder is placed in a reaction tube, and heated to transport zinc chloride vaporized by a carrier gas and react with oxygen to form a ZnO-based semiconductor. Is growing.

  This method is called a halide (or hydride) vapor phase epitaxy (HVPE) method using a group II metal halide as a group II material. The HVPE method is known as a method for producing a group III-V semiconductor in which a gallium nitride substrate or the like is industrially produced by using a halide (chloride) as a group III material and a hydride as a group V material. It has been. In this HVPE method, a hot wall method is generally used in which not only the growth substrate and its periphery but also the quartz tube is heated.

  However, in the method of manufacturing a ZnO-based semiconductor of Non-Patent Document 1 described above, zinc chloride is used as a zinc material. Zinc chloride has deliquescence and purity of easily available zinc chloride is about 99.9. Since zinc chloride having a low purity of about% and high purity is expensive, a high-quality ZnO-based semiconductor cannot be easily manufactured.

  When a ZnO substrate of the same material type is used as the ZnO crystal growth substrate, the ZnO crystal growth substrate is manufactured by a hydrothermal synthesis method similar to that for crystal manufacturing, and high level impurity control is required. Whether it can be industrialized in the semiconductor field is still unclear. In addition, it is considered that the fact that the ZnO substrate is brittle in physical properties makes it difficult to increase the size of the future ZnO crystal growth substrate.

  Nitride semiconductors use sapphire substrates, silicon carbide substrates, silicon substrates, etc. instead of using expensive homoepitaxial substrates, especially when used for light emitting diode (LED) applications that require cost reduction. .

  When high temperature growth is directly performed on a sapphire substrate by MBE or MOCVD, there is a phenomenon that ZnO does not grow, which is a phenomenon that does not occur in GaN.

  Group III elements typified by Ga and Al have low vapor pressure and good wettability on sapphire even at high temperatures, so crystals grow at high temperatures even without a buffer layer. This is because it is difficult to grow ZnO at a high temperature without forming a ZnO film on the substrate at a low temperature to improve the wettability.

  When growing at low temperature, the diffusion of the raw material on the substrate surface is difficult to occur, and the growth film is a collection of rod-like or core-like crystals, and although it is an alignment film, high-quality crystal growth at the semiconductor level is difficult.

  A method of growing through a buffer layer is usually used for epitaxial growth on a different substrate. In particular, in the case of GaN on a sapphire substrate, a buffer layer made of AlN or GaN is formed at a low temperature, and then grown at a high temperature, thereby succeeding in obtaining a GaN crystal with good crystallinity and excellent flatness ( For example, see Patent Document 1 and Non-Patent Document 2.)

  In the case of a ZnO-based semiconductor crystal, it has been proposed to form a buffer layer as in the case of a GaN-based semiconductor crystal (see, for example, Patent Document 2 and Non-Patent Document 3). In this method, a low-temperature growth ZnO single crystal layer having a film thickness of about 10-100 nm is grown at a low temperature lower than 600 ° C., followed by a planarization process by heat treatment, and then ZnO growth is performed at a temperature lower than 800 ° C. Is to do. However, this method is based on the MBE method, and the growth temperature for high-temperature growth is limited to about 800 ° C. Further, in the method of using a Zn simple substance or an organic metal material as a Zn raw material source, there is a problem that the raw material efficiency decreases drastically as the temperature is increased due to the high vapor pressure of Zn.

Japanese Patent No. 3257344 Japanese Patent No. 3424814

N. Takahashi, et al. “Atomospheric pressure vapor-phase growth of ZnO using chloride source”, Journal of Crystal Growth. 209 (2000), 822 H. Amano, N. Sawaki and I. Akasaki, “Metalorganic vapor phase epitaxy growth of a high quality GaN film using an AlN buffer layer”, Appl. Phys. Lett. 48 (5), 3 February 1986, 353 H.KATO, M.SANO, K. MIYAMOTO, and T. YAO, “Effect of O / Zn Flux Ratio on Crystalline Quality of ZnO Films Grown by Plasma-Assisted Molecular Beam Epitaxy”, Jpn. J. Appl. Phys. Vol. 42 (2003), 2241

  In the case of ZnO-based semiconductor crystal growth on a heterogeneous substrate such as a sapphire substrate, even when Zn halide is used as a raw material, the wettability of ZnO to the heterogeneous substrate is poor when grown at a high temperature, and ZnO on the heterogeneous substrate Does not become a film, crystal nuclei grow sparsely, and it is difficult to form a continuous film.

  Further, when high temperature growth is performed by MOCVD method or MBE method, even when a buffer layer is used as described above, it is difficult to grow ZnO by high temperature growth, and when the supply amount of Zn raw material is increased, the raw material efficiency is increased. Not only does it worsen, but Zn and the oxygen source are likely to react with each other, causing premature reaction in the gas phase and causing generation of particles.

  An object of the present invention is to provide a heteroepitaxial growth method capable of growing a ZnO-based semiconductor crystal on a heterogeneous substrate such as a sapphire substrate at a temperature higher than 800 ° C.

  Another object of the present invention is to provide a heteroepitaxial crystal structure and a semiconductor device formed by using the above heteroepitaxial growth method.

  It is another object of the present invention to provide a heteroepitaxial crystal growth apparatus for growing a ZnO-based semiconductor crystal at a temperature higher than 800 ° C. on a heterogeneous substrate such as a sapphire substrate.

  According to one aspect of the present invention for achieving the above object, a step of forming a buffer layer on a heterogeneous substrate, and a zinc oxide based semiconductor layer using a group II metal halide and an oxygen source on the buffer layer. There is provided a heteroepitaxial growth method having a step of crystal growth.

  According to another aspect of the present invention, the heterogeneous substrate, the buffer layer disposed on the heterogeneous substrate, the crystal layer disposed on the buffer layer and using a group II metal halide and an oxygen source are formed. A heteroepitaxial crystal structure comprising a zinc oxide based semiconductor layer is provided.

  According to another aspect of the present invention, a heterogeneous substrate, a buffer layer disposed on the heterogeneous substrate, an n-type zinc oxide semiconductor layer disposed on the buffer layer and doped with an n-type impurity, A zinc oxide based semiconductor active layer disposed on the n-type zinc oxide based semiconductor layer; a p type zinc oxide based semiconductor layer disposed on the zinc oxide based semiconductor active layer and doped with a p-type impurity; A semiconductor device is provided.

  According to another aspect of the present invention, there is provided a first raw material zone in which a first group II metal material containing a zinc simple substance is held, and a second group II metal material containing a group II metal other than zinc. A second raw material zone to be held; a first halogen gas supply means for supplying a first halogen gas to the first raw material zone; a second halogen gas supply means for supplying a second halogen gas to the second raw material zone; Oxygen material supply means for supplying oxygen material containing oxygen, first doping gas supply means for supplying n-type doping gas for doping n-type impurities, and p-type for doping p-type impurities. A second doping gas supply means for supplying a doping gas; a halogenated II produced from the first and second halogen gases, the n-type and p-type doping gases and the group II metal material; Heteroepitaxial crystal growth apparatus and a growth zone for reacting the metal and the oxygen material is provided.

  According to the present invention, it is possible to provide a heteroepitaxial growth method capable of growing a ZnO-based semiconductor crystal on a heterogeneous substrate such as a sapphire substrate at a temperature higher than 800 ° C.

  Moreover, according to this invention, the heteroepitaxial crystal structure and semiconductor device which were formed using the said heteroepitaxial growth method can be provided.

  In addition, according to the present invention, it is possible to provide a heteroepitaxial crystal growth apparatus for growing a ZnO-based semiconductor crystal at a temperature higher than 800 ° C. on a heterogeneous substrate such as a sapphire substrate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a heteroepitaxial growth method of a heteroepitaxial crystal structure according to a first embodiment of the present invention, in which (a) a schematic cross-sectional structure diagram showing a buffer layer forming step, and (b) a ZnO facet formed by halide vapor phase growth. The typical cross-section figure showing a formation process, (c) The typical cross-section figure showing the formation process of the ZnO layer by halide vapor phase growth. In the heteroepitaxial growth method concerning the 1st Embodiment of this invention, the typical bird's-eye view structure figure of the heteroepitaxial crystal structure in the formation process of the ZnO layer by halide vapor phase growth. It is the heteroepitaxial crystal structure formed by the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention, Comprising: (a) Optical microscope photograph of ZnO layer surface, (b) Bird's-eye view SEM photograph of ZnO layer. It is the heteroepitaxial crystal structure formed by the heteroepitaxial growth method which concerns on the comparative example of this invention, Comprising: (a) Optical microscope photograph of ZnO layer surface, (b) Bird's-eye view SEM photograph of ZnO layer. It is a heteroepitaxial crystal structure (example of VI / II ratio = 200) formed by the heteroepitaxial growth method according to the first embodiment of the present invention, (a) an optical micrograph of the ZnO layer surface, (b) Bird's-eye view SEM photograph of the ZnO layer. It is the heteroepitaxial crystal structure (example of growth time 20min) formed by the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention, Comprising: (a) Optical micrograph of ZnO layer surface, (b) ZnO layer Bird's-eye view SEM photograph. It is the heteroepitaxial crystal structure (example of growth time 60min) formed by the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention, Comprising: (a) The optical microscope photograph of the ZnO layer surface, (b) ZnO layer Bird's-eye view SEM photograph. It is the heteroepitaxial crystal structure (example of growth time 180min) formed by the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention, Comprising: (a) The optical microscope photograph of the ZnO layer surface, (b) ZnO layer Bird's-eye view SEM photograph. It is the heteroepitaxial crystal structure formed by the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention, Comprising: (a) Optical microscope photograph of ZnO layer surface, (b) Bird's-eye view SEM photograph of ZnO layer. (Example of growth time of 360 min) The X-ray rocking curve (example of ZnO (002) plane) of the ZnO crystal of the heteroepitaxial crystal structure formed by the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention. The X-ray rocking curve (example of ZnO (101) plane) of the ZnO crystal of the heteroepitaxial crystal structure formed by the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention. The relationship between the half value width FWHM (arc sec) and the crystal growth time (min) of the X-ray rocking curve of the ZnO crystal of the heteroepitaxial crystal structure formed by the heteroepitaxial growth method according to the first embodiment of the present invention is shown. FIG. (Example of ZnO (002) plane and ZnO (101) plane). The schematic diagram of the crystal growth apparatus applied to the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention. In the heteroepitaxial growth method according to the first embodiment of the present invention, (a) an optical micrograph of the surface of a ZnO buffer layer formed by reacting metal zinc and water, and (b) formed by reacting zinc chloride and water. An optical micrograph of the surface of the ZnO buffer layer. In the heteroepitaxial growth method according to the first embodiment of the present invention, (a) a bird's-eye view SEM photograph of the surface of a ZnO buffer layer formed by reacting metallic zinc and water (step 1), (b) nitrogen in a water vapor atmosphere Bird's-eye view SEM photograph of ZnO buffer layer surface heat treated with gas (step 2), (c) Bird's-eye view SEM photograph of ZnO layer surface formed by subsequently reacting zinc chloride and water (step 3). In the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention, the example of the measurement result of the X-ray-diffraction measurement (2theta-omega method) explaining the crystal orientation of the ZnO layer corresponding to each step of FIG. In the heteroepitaxial growth method according to the first embodiment of the present invention, (a) an X-ray rocking curve (example of ZnO (002) plane) for explaining the crystallinity of the ZnO layer corresponding to each step of FIG. b) X-ray rocking curve (example of ZnO (101) plane) explaining the crystallinity of the ZnO layer corresponding to each step of FIG. The figure which shows the relationship between the growth temperature and the growth time for investigating the film thickness dependence of a buffer layer in the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention. In the heteroepitaxial growth method according to the first embodiment of the present invention, (a) an optical micrograph when the buffer layer growth time is 0 min, (b) a bird's-eye view SEM photo, and (c) a buffer layer growth time. And (d) a bird's eye SEM photograph, (e) an optical microscope photograph when the growth time of the buffer layer is 30 min, and (f) a bird's eye SEM photograph, (g) the buffer layer An optical microscope photograph when the growth time is 60 min, and (h) a bird's-eye view SEM photograph. In the heteroepitaxial growth method according to the first embodiment of the present invention, (a) a bird's-eye view SEM photograph in which the growth time of the buffer layer on the a-plane sapphire substrate is 20 minutes and the growth time of the ZnO layer is 20 minutes; b) The enlarged bird's-eye view SEM photograph, (c) The bird's-eye view SEM photograph when the growth time of the buffer layer is 60 minutes and the growth time of the ZnO layer is 20 minutes on the a-plane sapphire substrate, and (d) The enlarged bird's-eye view SEM photograph. In the heteroepitaxial growth method according to the first embodiment of the present invention, an X-ray diffraction measurement (2theta-omega) after a buffer layer is formed on an a-plane sapphire substrate for 10 min and a ZnO layer is grown for 60 min by HVPE. Example) In the heteroepitaxial growth method according to the first embodiment of the present invention, an X-ray diffraction measurement (2theta-omega) after a buffer layer is formed on an a-plane sapphire substrate for 30 min and a ZnO layer is grown for 60 min by HVPE. Example) In the heteroepitaxial growth method according to the first embodiment of the present invention, an X-ray diffraction measurement (2theta-omega) after forming a buffer layer for 60 min on an a-plane sapphire substrate and then growing a ZnO layer for 60 min by HVPE method. Example) (A) In the heteroepitaxial growth method according to the first embodiment of the present invention, X-rays after a buffer layer is formed on an a-plane sapphire substrate for 30 min and 60 min, respectively, and a ZnO layer is grown for 60 min by HVPE. Examples of rocking curves (ZnO (002) plane), (b) Examples of X-ray rocking curves in the case of a ZnO (101) plane obtained by growing a ZnO layer under the same conditions. Explanatory drawing of the X-ray phi scan of the ZnO layer formed on the a-plane sapphire substrate in the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention. In the heteroepitaxial growth method which concerns on the 1st Embodiment of this invention, the measurement result of the X-ray phi scan of the ZnO (101) surface by the presence or absence of the buffer layer formed on the a surface sapphire substrate. In the heteroepitaxial growth method according to the first embodiment of the present invention, (a) a schematic cross-sectional structure diagram of a ZnO layer crystal-grown without forming a buffer layer on an r-plane sapphire substrate, (b) r The surface bird's-eye view SEM photograph after forming a ZnO layer crystal growth for 60 minutes by HVPE method without forming a buffer layer on a surface sapphire substrate. In the heteroepitaxial growth method according to the first embodiment of the present invention, (a) a schematic cross-sectional structure diagram of a ZnO layer crystal-grown after forming a buffer layer on an r-plane sapphire substrate, (b) an r-plane sapphire substrate The surface bird's-eye view SEM photograph after forming a buffer layer on the top and then growing a ZnO layer for 60 min by HVPE. In the heteroepitaxial growth method according to the first embodiment of the present invention, (a) a bird's-eye view SEM photograph in which a buffer layer is grown on a r-plane sapphire substrate at 400 ° C. for 60 min, (b) further, 1000 ° C., 60 min crystal Surface bird's-eye view SEM photograph of the grown ZnO layer. The example of the measurement result of the X-ray-diffraction measurement (2theta-omega method) of the ZnO layer formed in FIG. 1 is a schematic cross-sectional structure diagram of a semiconductor device having a heteroepitaxial crystal structure formed by a heteroepitaxial growth method according to a first embodiment of the present invention.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following, the same reference numerals are assigned to the same blocks or elements to avoid duplication of explanation and simplify the explanation. It should be noted that the drawings are schematic and different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  The following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention. In the embodiments of the present invention, the arrangement of each component is as follows. Not specific. Various modifications can be made to the embodiment of the present invention within the scope of the claims.

  In the following description, “ZnO-based compound semiconductor” means a Group II oxide semiconductor containing II element Zn.

[First embodiment]
(Heteroepitaxial growth method)
A heteroepitaxial growth method of the heteroepitaxial crystal structure according to the first embodiment of the present invention will be described with reference to FIG.

  The buffer layer forming step is expressed as shown in FIG. The formation process of the ZnO facet 44 by the halide vapor phase growth method is expressed as shown in FIG. The step of forming the ZnO layer by halide vapor phase growth is represented as shown in FIG.

(A) First, as shown in FIG. 1A, for example, an a-plane sapphire substrate is used as the heterogeneous substrate 40, and a ZnO template is formed on the heterogeneous substrate 40 by a laser ablation method. The ZnO template is composed of the buffer layer 42. The buffer layer 42 may be formed of an oxide alignment film or a nitride alignment film. Specifically, for example, an oxide alignment film made of ZnO or MgO or a nitride alignment film made of AlN or GaN can be applied. The temperature for forming the ZnO template is, for example, about 500 ° C. The buffer layer 42 has a thickness of about 0.3 μm, for example.

  As another method for forming the ZnO template, for example, a sputtering method, a pulse laser method, an MBE method, an HVPE method, or the like can be used. Alternatively, a VPE method in which Zn vapor simply reacts with water vapor can be applied. In these formation methods, the growth temperature is preferably 400 ° C. or higher, for example. This is because the higher the temperature, the better the performance of the underlying crystal substrate can be reflected in the ZnO template. The VPE method in which Zn vapor is simply reacted with water vapor will be described later with reference to FIGS.

  In particular, considering the consistency with the subsequent high-temperature growth using a group II metal halide, the HVPE method, VPE method and the like that can be realized in the same growth furnace are desirable.

  Although the growth temperature of the buffer layer 42 is not particularly defined, the orientation of the buffer layer 42 can be improved by forming the heterogeneous substrate 40 while heating it to an intermediate temperature (˜500 ° C.). The crystallinity is also improved. Although the film thickness is not particularly specified, depending on the film formation method of the buffer layer 42, if it is too thick, the orientation and flatness of the buffer layer 42 may deteriorate, and if it is too thin, it is not a continuous film. About 0.02 μm to about 0.5 μm is desirable.

  The ZnO crystal formed on the above-described a-plane sapphire substrate has a c-plane oriented in the c-axis direction.

  In addition to the above-described a-plane sapphire substrate, a silicon substrate, a SiC substrate, a GaAs substrate, a GaP substrate, a GaN-based substrate, or the like can be applied as the heterogeneous substrate 40.

(B) Next, as shown in FIG. 1B, a ZnO facet 44 is formed on the buffer layer 42 by HVPE. Specifically, halide vapor phase growth using zinc chloride (ZnCl ₂ ) and water (H ₂ O) is applied. Crystal as the growth conditions, the partial pressure P _ZnCl2 of ZnCl _2, relative to the total pressure 1 atm, for example, about 2.2 × 10 ^-5 atm or so, and Zn is oxygen and the group II element is VI element the VI / II ratio is feed ratio, for example, and about 20 to 200, the crystal growth temperature T _g, for example, about 1000 ° C., the crystal growth time, for example, to about 1 hour. Here, if the partial pressure P _ZnCl2 = 2.2 × 10 ^-5 atm of ZnCl _2, when the VI / II ratio = 20 to 200, the partial pressure of _{H 2 O P H2O = 4.4 ×} 10 -4 ~ 4.4 × 10 ⁻³ atm.

In the heteroepitaxial growth method according to the first embodiment, a high temperature growth method in which the crystal growth temperature _Tg is higher than 800 ° C. is performed. Considering the melting point 1975 ° C. of ZnO crystals, about 1 / 3-1 / 2 of the melting point is necessary, the temperature T _g of the crystal growth, it is possible to obtain a high enough good crystalline quality. Therefore, in the above example, the growth at about 1000 ° C. is performed as in the case of GaN.

(C) Next, as shown in FIG. 1C, the crystal growth time is set longer, and the ZnO facet 44 formed on the buffer layer 42 is further laterally and vertically grown by the HVPE method. Then, a ZnO layer 46 having a desired thickness is formed. Specifically, as in the formation of the ZnO facet 44, halide vapor phase growth using zinc chloride (ZnCl ₂ ) and water (H ₂ O) / N ₂ is applied. The crystal growth conditions, the partial pressure P _ZnCl2 of ZnCl _2, for example, about 2.2 × 10 ^-5 atm about a feed ratio of Zn is oxygen and the group II element is VI element VI / II the ratio, for example, and about 20 to 200, the crystal growth temperature T _g, for example, about 1000 ° C., the crystal growth time, for example, from about 1 hour to 6 hours approximately.

  In the heteroepitaxial growth method according to the first embodiment, a ZnO buffer layer is deposited on a heterogeneous substrate at a low temperature, and then a Zn raw material and an oxygen material composed of a halide of Zn at a high temperature of 800 ° C. or higher are placed in a gas phase. It is characterized in that a single crystal of ZnO is obtained by mixing in the above.

  By forming the buffer layer 42 for improving the wettability of ZnO on the heterogeneous substrate 40, such as ZnO, before the high-temperature growth using a Zn raw material made of a halide, the wettability of ZnO can be improved.

(High temperature ZnO growth on the buffer layer)
In the heteroepitaxial growth method according to the first embodiment, a schematic bird's-eye view structure of the heteroepitaxial crystal structure in the step of forming the ZnO layer by the HVPE method is expressed as shown in FIG. A state in which the ZnO facet 44 is laterally grown (GL) and vertical grown (GV) on the surface 40a of the heterogeneous substrate 40 is schematically shown.

  In the heteroepitaxial crystal structure formed by the heteroepitaxial growth method according to the first embodiment, an example of an optical micrograph of the ZnO layer surface is expressed as shown in FIG. A bird's-eye view SEM photograph of the ZnO layer corresponding to FIG. 3A is represented as shown in FIG. The examples of FIG. 3A and FIG. 3B correspond to the structures of FIG. 1B and FIG. That is, in this example, an a-plane sapphire substrate is used as the heterogeneous substrate 40, and the ZnO facet 44 is formed on the buffer layer 42 formed on the a-plane sapphire substrate.

The crystal growth conditions, the partial pressure P _ZnCl2 of ^{_{ZnCl 2, 2.2 × 10 -5 atm}} , the VI / II ratio was 20, the crystal growth temperature T _g of 1000 ° C., is set to one hour crystal growth time.

  Moreover, in the heteroepitaxial crystal structure formed by the heteroepitaxial growth method according to the comparative example of the present invention, an example of an optical micrograph of the ZnO layer surface is expressed as shown in FIG. Moreover, a bird's-eye view SEM photograph of the ZnO layer corresponding to FIG. 4A is represented as shown in FIG. The example of FIGS. 4A and 4B corresponds to an example in which a ZnO crystal is directly formed on an a-plane sapphire substrate without using the buffer layer 42 in the structure of FIG. 1B.

The crystal growth conditions, the partial pressure P _ZnCl2 of ^{_{ZnCl 2, 2.2 × 10 -5 atm}} , the VI / II ratio is 600, the crystal growth temperature T _g of 1000 ° C., is set to one hour crystal growth time.

  3 and 4, when the buffer layer 42 is present, the lateral growth (GL) of the ZnO facet 44 is promoted, and the vertical growth (GV) is also performed. On the other hand, when there is no buffer layer 42, the lateral growth (GL) of the ZnO facet 44 hardly occurs, and only the vertical growth (GV) occurs mainly. For this reason, even if the crystallinity of the ZnO crystal itself formed on the surface of the ZnO facet 44 is good, in-plane growth is not performed, and it is difficult to form a ZnO epitaxial growth layer. When ZnO was directly grown on the a-plane sapphire substrate under the same VI / II ratio = 20 condition as in FIG. 3, ZnO nucleus growth was observed only very sparsely.

  In the heteroepitaxial crystal structure formed by the heteroepitaxial growth method according to the first embodiment, an optical micrograph of the surface of the ZnO layer in the example of VI / II ratio = 20 is expressed as shown in FIG. A SEM photograph of the ZnO layer corresponding to FIG. 3A is represented as shown in FIG. Similarly, the optical micrograph of the ZnO layer surface in the example of VI / II ratio = 200 is represented as shown in FIG. 5A, and the bird's-eye SEM photograph of the ZnO layer corresponding to FIG. It is expressed as shown in 5 (b).

The crystal growth conditions, the partial pressure P _ZnCl2 of ^{_{ZnCl 2 2.2 × 10 -5 atm,}} 1000 ℃ the crystal growth temperature T _g, is set to one hour crystal growth time.

As is clear from FIGS. 3A and 3B, when VI / II ratio = 20, the partial pressure P _H2O of H ₂ O is 4.4 × 10 ⁻⁴ atm, and ZnCl ₂ Since surface migration of molecules is likely to occur, lateral growth of the ZnO facet 44 is likely to occur. On the other hand, as is clear from FIGS. 5A and 5B, when the VI / II ratio = 200, the partial pressure P _H2O of H ₂ O is 4.4 × 10 ^−3. Atm, the higher the partial pressure P _H2O of H ₂ O, the more the surface migration of ZnCl ₂ molecules is suppressed, and although the vertical growth (GV) occurs, the lateral growth (GL) hardly occurs. .

  Therefore, it can be seen that low Vl / II ratio growth is an important growth condition for promoting the lateral growth (GL) of the ZnO facet 44 and obtaining the ZnO layer 46 having a desired thickness.

  Thus, when the VI / II ratio during crystal growth is large, the rate of lateral growth becomes slow, so the VI / II ratio is preferably 100 or less, for example. In addition, when the VI / II ratio during crystal growth is small, the crystal growth rate becomes slow, so the VI / II ratio is preferably set to 1 or more, for example.

  Moreover, it is not restricted to this, For example, VI / II ratio shall be 1 or more and 100 or less (for example, 20) until facet unites and a continuous film is made, and then VI / II ratio is 100 or more. (E.g. 200).

(Dependence on growth time of high-temperature ZnO)
In the heteroepitaxial crystal structure formed by the heteroepitaxial growth method according to the first embodiment, an optical micrograph of the surface of the ZnO layer when the growth time is 20 min is represented as shown in FIG. A bird's-eye view SEM photograph of the ZnO layer corresponding to (a) is represented as shown in FIG. Similarly, an optical micrograph of the surface of the ZnO layer when the growth time is 60 min is represented as shown in FIG. 7A, and a bird's-eye SEM photograph of the ZnO layer corresponding to FIG. The optical micrograph of the surface of the ZnO layer when the growth time is 180 min is represented as shown in FIG. 8 (a), and the bird's-eye SEM photograph of the ZnO layer corresponding to FIG. 8 (a) is FIG. 8B shows an optical micrograph of the surface of the ZnO layer when the growth time is 360 minutes, which is shown in FIG. 9A, and corresponds to FIG. 9A. This bird's-eye view SEM photograph is represented as shown in FIG.

Crystal as the growth conditions, the partial pressure P _ZnCl2 a ^{_{2.2 × 10 -5 ZnCl 2 (atm}} ), VI / II ratio = 20, is set to 1000 ° C. The crystal growth temperature T _g.

  By the heteroepitaxial growth method according to the first embodiment, the high-temperature ZnO layer is subjected to the lateral crystal growth (GL), the vertical crystal growth (GV) further progresses, and the epitaxial layer grows as the crystal growth time elapses. You can see how it is done.

  High-temperature growth using a halide can reduce crystal nuclei on the buffer layer 42 as compared with MBE or MOCVD. The buffer layer 42 improves the wettability of ZnO. For this reason, similarly to the high-temperature GaN on the buffer layer by MOCVD, high-temperature growth using a halide follows a growth process in which large crystal nuclei on the buffer layer 42 are connected in the lateral direction to form a film.

  In particular, when high temperature growth and low VI / II ratio conditions are employed to promote lateral growth of crystal nuclei, crystal nuclei can be bonded at an early stage, as shown in FIGS. Allows planarization of the film.

  In the case of high-temperature growth using Zn halide, the reactivity between Zn halide and oxygen source is not as high as that of Zn and oxygen source. For this reason, high-temperature growth using a halide of Zn has less reaction in the gas phase and less generation of particles.

  This low reactivity has a great influence on the crystal nucleus growth process. That is, in the high-temperature growth using a halide of Zn, sparse crystal nuclei can be greatly grown rather than forming innumerable crystal nuclei on the buffer layer 42. It is possible to grow the ZnO layer 46 with less crystallinity and good crystallinity.

(Crystallinity of ZnO crystal)
In the heteroepitaxial crystal structure formed by the heteroepitaxial growth method according to the first embodiment, the X-ray rocking curve of the (002) plane of ZnO is expressed as shown in FIG. In FIG. 10, each curve represents an example of crystal growth times of 0 min, 20 min, 60 min, 180 min, and 360 min as parameters. The crystal growth time of 0 min corresponds to the state after the buffer layer is formed. In the ZnO crystal, the (002) plane is a plane parallel to the c-axis, and the X-ray rocking curve shown in FIG. 10 represents a tilt distribution that is fluctuation in the c-axis direction that is the growth direction. As the crystal growth time of 20 min, 60 min, 180 min, and 360 min elapses, the growth thickness of the ZnO crystal increases, the half width of the X-ray rocking curve of the ZnO crystal decreases, and the crystallinity of the ZnO crystal having the (002) plane increases. It can be seen that it has improved.

  In the heteroepitaxial crystal structure formed by the heteroepitaxial growth method according to the first embodiment, the X-ray rocking curve of the (101) plane of ZnO is expressed as shown in FIG. Similar to FIG. 10, each curve represents an example of crystal growth times of 0 min, 20 min, 60 min, 180 min, and 360 min as parameters. The crystal growth time of 0 min corresponds to the state after the buffer layer is formed. In the ZnO crystal, the (101) plane is a semipolar plane, and the X-ray rocking curve shown in FIG. 11 represents a twist distribution + tilt distribution that is fluctuation in a direction perpendicular to the semipolar plane. As the crystal growth time elapses, the growth thickness of the ZnO crystal increases, the half width of the X-ray rocking curve of the ZnO crystal decreases, and the crystallinity of the ZnO crystal is improved.

  In the heteroepitaxial crystal structure formed by the heteroepitaxial growth method according to the first embodiment, the relationship between the half-value width FWHM (arc sec) of the X-ray rocking curve of the ZnO crystal and the crystal growth time (min) is shown in FIG. It is expressed as shown in FIG. 12 shows an example of the ZnO (002) plane and an example of the ZnO (101) plane. The vertical axis in FIG. 12 represents a full width at half maximum (FWHM) (arc sec). Here, it corresponds to 3600 (arc sec) = 1 (degree).

  In the ZnO crystal heteroepitaxially grown on the sapphire substrate, the value of the half-value width FWHM of the rocking curves of the (101) plane and the (002) plane is improved with the lapse of the crystal growth time. In particular, it is lower than 0.1 (degree) = 360 (arc sec), and the crystallinity is good.

  In this embodiment, when the crystal growth time is 180 min, the ZnO crystal layer on the buffer layer grows about 1.5 μm, and when the crystal growth time is 360 min, the ZnO crystal layer on the buffer layer grows. The growth was about 3 μm. Therefore, in this embodiment, after the crystal growth time of 180 min after the ZnO crystal layer is grown by about 1.5 μm or more, the full width at half maximum FWHM is 0.1 (degree) or less for both the crystal planes (002) and (101). In particular, in the present embodiment, (101) is measured as an example of a semipolar plane, but the present invention is not limited to this. Of course, the same transition of the full width at half maximum FWHM can be obtained for other semipolar planes. Examples of other semipolar planes include (102) plane, (103) plane, (111) plane, (112) plane, (113) plane, (201) plane, (203) plane, (221) plane, (223) surface. The same half-value width can also be obtained for the nonpolar planes (100) and (110) perpendicular to the (001) plane.

(Crystal growth equipment)
As shown in FIG. 13, a schematic configuration of the heteroepitaxial crystal growth apparatus 20 applied to the heteroepitaxial growth method according to the first embodiment includes a chlorine gas supply unit 2, a carrier gas supply unit 3, and a raw material zone 4. A heating means 5, a water supply means 6, a carrier gas supply means 7, a growth zone 8, a heating means 9, and a substrate holding means 10.

  The heteroepitaxial crystal growth apparatus 20 is also provided with a configuration for applying to a heteroepitaxial growth method of MgZnO semiconductor (ZnO-based semiconductor). That is, as shown in FIG. 13, a chlorine gas supply unit 12, a carrier gas supply unit 13, and a raw material zone 14 in which a group II metal material 25 containing magnesium metal alone is held.

  The heteroepitaxial crystal growth apparatus 20 is also provided with an apparatus configuration for adding an n-type impurity or a p-type impurity in a heteroepitaxial growth method of a ZnO-based semiconductor (ZnO, MgZnO). That is, as shown in FIG. 13, a first doping gas supply means 22 for supplying an n-type doping gas for doping an n-type impurity and a p-type doping gas for doping a p-type impurity are supplied. And a second doping gas supply means 24.

  The raw material zone 4 is for holding a group II metal material 15 made of zinc metal alone. The raw material zone 4 is a zone in which the chlorine gas supplied from the chlorine gas supply means 2 and zinc are reacted to generate zinc chloride gas. The raw material zone 14 is for holding single magnesium instead of the zinc of the raw material zone 4.

  The growth zone 8 reacts with the zinc chloride gas supplied from the raw material zone 4 connected by the supply pipe and the water (water vapor) supplied from the water supply means 6 as an oxygen material, on the substrate holding means 10. This is a zone in which a ZnO semiconductor is grown on the growth substrate 16 held.

  In addition, each supply pipe | tube which connects the raw material zone 4, the growth zone 8, and each gas supply means and the growth zone 8 is comprised with quartz.

  The heating means 5 is for heating the raw material zones 4 and 14 and the water supply path. The heating means 9 is for heating the growth zone 8. With these heating means 5 and 9, the heteroepitaxial crystal growth apparatus 20 realizes a hot wall system. The heating means 5 is not limited to the illustrated configuration. For example, using the heating means 5a, 5b, 5c, and 5d (not shown), the heating means 5a heats the raw material zone 14, the heating means 5b heats the raw material zone 4, and the heating means 5c uses the water supply means 6 and carrier gas. The quartz tube of the supply unit 7 may be heated, and the heating unit 5d may heat the quartz tube of the n-type doping gas supply unit 22 and the p-type doping gas supply unit 24.

  The nitrogen gas supplied from the carrier gas supply means 3, 7 and 13 includes zinc chloride gas generated in the raw material zone 4, water supplied from the water supply means 6 and magnesium chloride gas generated in the raw material zone 14. For transporting to the growth zone 8.

  Next, a method for manufacturing a ZnO semiconductor using the heteroepitaxial crystal growth apparatus 20 described above will be described.

  First, chlorine gas and nitrogen gas are transported to the raw material zone 4 from the chlorine gas supply means 2 and the carrier gas supply means 3, respectively. In the raw material zone 4, the reaction according to the following reaction formula (1) occurs by the group II metal material 15 made of the zinc simple metal and the supplied chlorine gas, and zinc chloride gas is generated. .

Zn (s, l) + Cl ₂ (g) Ｚｎ ZnCl ₂ (g) (1)
Here, the zinc simple substance held in the raw material zone 4 is preferably highly pure, for example, 99.99999% or more. In the reaction formula, (s), (l), and (g) represent solid, liquid, and gas, respectively.

  The raw material zone 4 allows the reaction in the reaction formula (1) to proceed almost to the right side, and the surface area of the group II metal material 15 made of zinc metal alone so that the flow rate of the zinc chloride gas can be controlled by the supply amount of the chlorine gas. The structure is increased and the temperature is appropriate. In addition, as such suitable temperature, about 300 degreeC-about 450 degreeC are desirable. In addition, the temperature of the raw material zone 4 is set to about 500 ° C. or less in order to suppress the transport of zinc gas having a very high vapor pressure among the metals to the growth zone 8. Then, the zinc chloride gas generated by the above reaction formula (1) is transported to the growth zone 8 by the nitrogen gas supplied from the carrier gas supply means 3.

  Further, the water (water vapor) supplied from the water supply means 6 is transported to the growth zone 8 as an oxygen material by the nitrogen gas supplied from the carrier gas supply means 7 via another path.

  In the growth zone 8, the reaction of the following reaction formula (2) proceeds to the right side by the transported zinc chloride gas and water, so that a thin film of ZnO semiconductor grows on the growth substrate 16.

ZnCl ₂ (g) + H ₂ O (g) ⇔ ZnO (s) + 2HCl (g) (2)
Here, the temperature of the growth zone 8 is set to be higher than the temperature of the raw material zone 4 so that the zinc chloride gas does not precipitate on the way to the growth zone 8. Specifically, the temperature of the growth zone 8 is set to about 500 ° C. to about 1100 ° C.

  In the MgZnO semiconductor manufacturing method using the heteroepitaxial crystal growth apparatus 20, chlorine gas is transported to the raw material zone 14 together with the carrier gas, and magnesium chloride gas is generated in the raw material zone 14. Then, the magnesium chloride gas is transported to the growth zone 8 by the nitrogen gas supplied from the carrier gas supply means 13, and the zinc chloride gas, the magnesium chloride gas and water are reacted in the growth zone 8, whereby the MgZnO semiconductor is grown. 16 can be grown.

  In a heteroepitaxial growth method of a ZnO-based semiconductor (ZnO, MgZnO), a desired n-type impurity or p-type impurity is doped into a growth layer using an n-type doping gas supply unit 22 and a p-type doping gas supply unit 24 Can be added.

  As described above, the heteroepitaxial crystal growth apparatus 20 according to the first embodiment employs high-purity ZnO instead of zinc chloride as the group II metal material 15, so high-quality ZnO. -Based semiconductors can be easily manufactured.

  Further, by making the set temperature of the raw material zone 4 lower than the growth temperature of the growth zone 8, it is possible to prevent the zinc chloride gas generated in the raw material zone 4 from being deposited before being transported to the growth zone 8. .

  Further, by adopting water instead of simple oxygen as the oxygen material, hydrochloric acid gas is generated in the growth zone 8 instead of chlorine gas. Therefore, the reaction formula (2) is advanced to the right side in a more thermodynamically stable state. be able to.

  For example, as a group II metal material, a cadmium metal simple substance may be adopted instead of a magnesium metal simple substance.

  Further, oxygen gas may be employed as the oxygen material instead of water.

  Further, bromine gas may be employed as the halogen gas instead of chlorine gas.

  Further, the type of the Group II metal material is not limited to two, and three or more Group II metal materials may be used.

(Method for forming ZnO template)
As a method for forming a ZnO template, a VPE method in which Zn vapor is simply reacted with water vapor will be described below. In these formation methods, the growth temperature is desirably 400 ° C. or higher, for example, and the higher the temperature, the better the performance of the underlying crystal substrate can be reflected in the ZnO template.

  The crystal growth apparatus 20 can use the configuration shown in FIG. 13 for the VPE method in which Zn vapor is simply reacted with water vapor as a ZnO template formation method.

In the heteroepitaxial growth method according to the first embodiment, an optical micrograph of the surface of the ZnO buffer layer formed by reacting metal zinc and water is represented as shown in FIG. An optical micrograph of the surface of the ZnO buffer layer formed as shown in FIG. 14B. In FIG. 14, the growth temperature is about 400 ° C., and the growth time is about 60 min. 14A, the partial pressure P _H2O of H ₂ O is 2.2 × 10 ⁻² atm, and in FIG. 14B, the partial pressure P _H2O of H ₂ O is 1.32 × 10 ^−2. atm. As is clear from FIG. 14B, the optical micrograph of the surface of the ZnO buffer layer formed by reacting zinc chloride with water shows a thickness of about 0.93 μm. Formation has been observed. On the other hand, although the thickness of the optical microscope photograph of the surface of the ZnO buffer layer formed by reacting metallic zinc and water is about 0.28 μm, continuous film growth is observed.

  In the heteroepitaxial growth method according to the first embodiment, a method of growing a ZnO semiconductor thin film on the growth substrate 16 by the HVPE method after forming a ZnO buffer layer formed by reacting metal zinc and water is as follows. It is expressed as shown in

(A) First, as step 1, nitrogen gas is transported from the carrier gas supply means 3 to the raw material zone 4. In the raw material zone 4, the held group II metal material 15 made of zinc simple substance is vaporized and introduced into the growth zone 8. On the other hand, water vapor introduced from the water supply means 6 into the growth zone 8 reacts with vaporized zinc, and a ZnO semiconductor thin film grows on the growth substrate 16 according to the reaction according to the equation (3). Here, the crystal growth temperature of the ZnO buffer layer 42 is, for example, about 400 ° C. or more, and the thickness is, for example, about 0.3 μm or less.

Zn (g) + H ₂ O (g) Ｚｎ ZnO (s) + H ₂ (g) (3)
(B) Next, as step 2, heat treatment (annealing) is performed with nitrogen gas in an atmosphere of water vapor H ₂ O (g). The heat treatment temperature is about 1000 ° C., for example. By performing the heat treatment in this manner, the crystallinity and surface flatness of the ZnO buffer layer 42 can be improved.

(C) Next, as step 3, chlorine gas is transported from the chlorine gas supply means 2 to the raw material zone 4, and simultaneously, nitrogen gas is transported from the carrier gas supply means 3 to the raw material zone 4. In the raw material zone 4, a reaction according to the reaction formula (1) occurs between the held group II metal material 15 made of a single metal of zinc and the supplied chlorine gas, and zinc chloride gas is generated. Then, the zinc chloride gas generated by the reaction formula (1) is transported to the growth zone 8 by the nitrogen gas supplied from the carrier gas supply means 3. Further, the water (water vapor) supplied from the water supply means 6 is transported to the growth zone 8 as an oxygen material by the nitrogen gas supplied from the carrier gas supply means 7 via another path. In the growth zone 8, the reaction of the reaction formula (2) proceeds to the right side by the transported zinc chloride gas and water, so that a thin film of ZnO semiconductor grows on the growth substrate 16. Here, the crystal growth temperature is about 1000 ° C., for example.

  In the heteroepitaxial growth method according to the first embodiment, a SEM photograph (step 1) of the surface of the ZnO buffer layer formed by reacting metal zinc and water is represented as shown in FIG. The SEM photograph (step 2) of the ZnO buffer layer surface heat-treated with nitrogen gas in the atmosphere is expressed as shown in FIG. 15B, for example, and the SEM photograph of the ZnO layer surface formed by reacting zinc chloride and water. (Step 3) is expressed, for example, as shown in FIG.

In FIG. 15A, the growth temperature is about 400 ° C., the growth time is about 60 min, and the partial pressure P _H2O of H ₂ O is about 2.2 × 10 ⁻² atm.

In FIG. 15B, the heat treatment temperature is about 1000 ° C., the heat treatment time is about 60 min, and the partial pressure P _H2O of H ₂ O is about 4.4 × 10 ⁻³ atm.

In FIG. 15C, the growth temperature is about 1000 ° C., the growth time is about 60 min, the partial pressure P _H2O of H ₂ O is about 4.4 × 10 ⁻⁴ atm, and the VI / II ratio is about 20. is there. As shown in FIGS. 15A to 15C, it is observed that the crystallinity is improved according to steps 1 to 3.

  In the heteroepitaxial growth method according to the first embodiment, an example of the measurement result of the X-ray diffraction measurement (2theta-omega method) for explaining the crystal orientation of the ZnO crystal corresponding to each step of FIG. It is expressed as shown in In FIG. 16, the vertical axis represents the XRD intensity (a.u.), and the horizontal axis represents 2θ. The ZnO (002) plane is oriented with respect to the a-plane sapphire substrate, and the peak intensity of ZnO (002) increases as the process proceeds from step 1 to step 3, thereby improving the crystal orientation. Is observed.

  In the heteroepitaxial growth method according to the first embodiment, an X-ray rocking curve (an example of the ZnO (002) plane) explaining the crystallinity of the ZnO crystal corresponding to each step of FIG. An X-ray rocking curve (an example of the ZnO (101) plane) for explaining the crystallinity of the ZnO buffer layer corresponding to each step of FIG. 15 is represented as shown in FIG. Is done.

  As is clear from FIG. 17A, the half-value width FWHM (arcsec) of the rocking curve of the (002) plane of ZnO is about 1209 (arcsec) in step 1 and about 460 (arcsec) in step 2. 3 is about 327 (arcsec). As is clear from FIG. 17B, the value of the half-value width FWHM (arcsec) of the rocking curve of the (101) surface of ZnO is about 1458 (arcsec) in step 1 and about 702 (arcsec) in step 2. In Step 3, it is about 493 (arcsec). As is clear from FIGS. 17A and 17B, the half-value widths of the rocking curves of the (002) plane and the (101) plane decrease as the process proceeds from step 1 to step 3. From this, it can be seen that both the twist distribution and the tilt distribution of the (002) -oriented ZnO layer are reduced and the crystallinity is improved.

(Dependence of buffer layer thickness)
In the heteroepitaxial growth method according to the first embodiment, the relationship between the crystal growth temperature and the growth time is expressed as shown in FIG. When the growth time of the buffer layer is 0 min, this corresponds to the case where there is no buffer layer.

First, in FIG. 18, thermal cleaning (TC) is performed in H ₂ at a high temperature of 1000 ° C. to clean the surface of the a-plane sapphire substrate, and then the carrier gas is switched to N ₂ as Step 1. Growing the buffer layer. In order to investigate the film thickness dependence of the buffer layer, the crystal growth time of the buffer layer is changed from 0 min to 60 min. The growth temperature of the buffer layer is about 400 ° C., the partial pressure P _Zn of Zn (g) is about 4 × 10 ⁻⁵ atm, and the partial pressure P _H2O of H ₂ O is about 4.4 × 10. ^-3 atm.

Next, as step 2, heat treatment is performed. In this case, the heat treatment temperature is about 1000 ° C., the heat treatment time is about 10 minutes, and the partial pressure P _H2O of H ₂ O is about 4.4 × 10 ⁻³ atm.

Next, as step 3, crystal growth of a ZnO layer by HVPE is performed. Crystal growth temperature in this case is about 1000 ° C., the crystal growth time of about 60min, supply partial pressure P _ZnCl2 of ZnCl ₂ is about ^{2.2 × 10 -5 atm, VI /} II ratio is about 20 .

  The results obtained under the growth conditions shown in FIG. 18 are expressed as shown in FIG. FIG. 19A shows an optical micrograph of the ZnO crystal surface when the growth time of the buffer layer is 0 min, and FIG. 19B shows a bird's-eye view SEM photograph. FIG. 19C shows an optical micrograph of the surface of the ZnO crystal when the growth time of the buffer layer is 10 min, and FIG. 19D shows a bird's-eye view SEM photograph. FIG. 19 (e) shows an optical micrograph of the ZnO crystal surface when the growth time of the buffer layer is 30 minutes, and FIG. 19 (f) shows a bird's-eye view SEM photograph. FIG. 19 (g) shows an optical micrograph of the ZnO crystal surface when the growth time of the buffer layer is 60 minutes, and FIG. 19 (h) shows a bird's-eye view SEM photograph.

  As a result of examining the state of the crystal surface of the ZnO layer grown by the HVPE method by changing the film thickness (growth time) of the buffer layer formed by low temperature growth at about 400 ° C., FIG. As apparent from (h), the thicker the buffer layer (the longer the growth time), the better the crystal surface state of the ZnO layer. This is probably because the two-dimensional growth of the ZnO layer by the HVPE method is promoted as the buffer layer is thicker (growth time is longer).

  The SEM photograph of the crystal surface of the ZnO layer and the enlarged bird's-eye view SEM photograph when the growth time of the buffer layer on the a-plane sapphire substrate is 20 minutes and the growth time of the ZnO layer is 20 minutes are shown in FIG. It is expressed as shown in 20 (b). Further, the SEM photograph of the crystal surface of the ZnO layer and the enlarged bird's-eye view SEM photograph when the growth time of the buffer layer on the a-plane sapphire substrate is 60 minutes and the growth time of the ZnO layer is 20 minutes are shown in FIG. And as shown in FIG.

  As is apparent from FIGS. 20A to 20D, hexagonal growth nuclei are also generated on the crystal surface of the ZnO layer formed on the buffer layer formed at a low temperature, and these hexagonal growth nuclei are formed. Bonding to each other, a growth mode that is flattened is realized. Further, as the thickness of the buffer layer formed at a low temperature increases, the lateral growth of the ZnO layer formed thereon by the HVPE method is promoted.

(X-ray diffraction measurement (2theta-omega method))
In the heteroepitaxial growth method according to the first embodiment, after forming a buffer layer for 10 min on an a-plane sapphire substrate, the ZnO layer is grown for 60 min by the HVPE method. The measurement result of -omega method is expressed as shown in FIG. 21, for example. Similarly, an X-ray diffraction measurement result after forming a buffer layer for 30 min and then growing a ZnO layer for 60 min by HVPE is expressed as shown in FIG. 22, for example. Furthermore, the X-ray diffraction measurement result after the buffer layer is formed for 60 minutes and the ZnO layer is grown for 60 minutes by the HVPE method is expressed, for example, as shown in FIG. The results of FIG. 21 correspond to FIGS. 19 (c) and 19 (d), the results of FIG. 22 correspond to FIGS. 19 (e) and 19 (f), and the results of FIG. This corresponds to (g) and FIG.

As shown in FIG. 21, when the thickness of the buffer layer formed by low-temperature growth is thin, the orientation of the ZnO layer formed thereon by the HVPE method is not uniform, and other than the desired ZnO (002) plane ZnO (101) surface of the substrate is detected. On the other hand, as shown in FIGS. 22 and 23, when the thickness of the buffer layer formed by low temperature growth becomes thick, the orientation of the ZnO layer formed thereon by the HVPE method becomes good, and the desired ZnO (002) plane is detected (X-ray rocking curve)
In the heteroepitaxial growth method according to the embodiment, after the buffer layer is formed on the a-plane sapphire substrate for 30 min and 60 min, respectively, and then the ZnO layer (ZnO (002) plane) is grown for 60 min on the crystal by HVPE. An example of a line rocking curve is represented as shown in FIG. 24A on the (002) plane and as shown in FIG. 24B on the (101) plane.

  As is apparent from FIG. 24A, the half-value width FWHM (arcsec) of the rocking curve of the (002) plane of ZnO is 396 (arcsec) and 327 (arcsec) when the buffer layer is grown for 30 min and 60 min, respectively. ). Similarly, as apparent from FIG. 24B, the value of the half-value width FWHM (arcsec) of the rocking curve of the (101) surface of ZnO is 504 (arcsec) and, respectively, when the buffer layer is grown for 30 min and 60 min. 493 (arcsec).

  As shown in FIGS. 24 (a) and 24 (b), the two-dimensional growth is promoted, and the half-value width FWHM (arcsec) of the XRD rocking curve of the ZnO layer formed as a film is as good as 500 (arcsec) or less. Similarly to FIG. 12, it is possible to expect a decrease in the half-value width of the rocking curve as the growth film thickness further increases.

(X-ray Phiscan)
In the heteroepitaxial growth method according to the first embodiment, the X-ray phi scan of the c-axis oriented ZnO layer formed on the a-plane sapphire substrate 40 detects the ZnO (101) plane as shown in FIG. In this way, the incident X-ray and the X-ray detector are combined and rotated around the c-axis direction. The measurement result of the X-ray phi scan of the ZnO layer 46 with and without the buffer layer 42 formed on the a-plane sapphire substrate 40 is expressed as shown in FIG. When there is no buffer layer 42 (WITHOUT LT-Buffer), crystal nuclei when rotated by 30 degrees are observed in addition to a large 6-fold symmetrical peak, as shown by a broken line portion A in FIG. The crystallinity in the twist direction is disturbed. On the other hand, when the buffer layer 42 is provided (WITH LT-Buffer), the hexagonal 6-fold symmetry of the ZnO layer 46 is accurately observed. In addition, when the buffer layer 42 is provided, crystal nuclei when rotated by 30 degrees are not observed, and there is an effect of aligning crystallinity in the twist direction that is the Φ direction.

(R-plane sapphire substrate)
In the heteroepitaxial growth method according to the first embodiment, a schematic cross-sectional structure of a ZnO layer 47 crystal-grown without forming a buffer layer on the r-plane sapphire substrate 41 is as shown in FIG. It is expressed in Further, a surface bird's-eye view SEM photograph after the ZnO layer 47 is grown for 60 min by the HVPE method without forming the buffer layer on the r-plane sapphire substrate 41 is expressed as shown in FIG. As shown in FIGS. 27A and 27B, a hexagonal columnar crystal is observed as the shape of the ZnO layer 47 grown on the r-plane sapphire substrate 41 without forming a buffer layer. ing.

  On the other hand, in the heteroepitaxial growth method according to the first embodiment, a schematic cross-sectional structure of the ZnO layer 47 crystal-grown after forming the buffer layer 43 on the r-plane sapphire substrate 41 is as shown in FIG. It is expressed in Further, a surface bird's-eye view SEM photograph after the buffer layer 43 is formed on the r-plane sapphire substrate 41 and the ZnO layer 47 is grown for 60 min by HVPE is expressed as shown in FIG. An effect is recognized not only on the a-plane sapphire substrate 40 but also on the r-plane sapphire substrate 41 by the ZnO buffer layer 43 for the flattening of the ZnO layer 47 deposited on the HVPE method.

  In the heteroepitaxial growth method according to the first embodiment, a surface bird's-eye view SEM photograph in which the buffer layer 43 is grown on the r-plane sapphire substrate 41 at 400 ° C. for 60 minutes is expressed as shown in FIG. A surface bird's-eye view SEM photograph of the ZnO layer grown at 1000 ° C. for 60 minutes is expressed as shown in FIG. As can be seen from FIG. 29, the ZnO buffer layer 43 is also effective on the r-plane sapphire substrate 41 for the planarization of the ZnO layer 47 deposited thereon by the HVPE method.

  The measurement result of the X-ray diffraction measurement (2 theta-omega method) of the ZnO layer formed in FIG. 29 is expressed as shown in FIG. 30, for example. As shown in FIG. 30, since the peak of ZnO (110) is observed, an a-axis oriented ZnO layer 47 is formed on the r-plane sapphire substrate 41.

(Semiconductor device)
An example of a schematic cross-sectional structure of a semiconductor device having a heteroepitaxial crystal structure formed by the heteroepitaxial growth method according to the first embodiment is arranged on a heterogeneous substrate 40 and on the heterogeneous substrate 40 as shown in FIG. A buffer layer 42, an n-type ZnO-based semiconductor layer 52 doped with an n-type impurity, and a ZnO-based semiconductor active layer 54 disposed on the n-type ZnO-based semiconductor layer 52. And a p-type ZnO-based semiconductor layer 56 which is disposed on the ZnO-based semiconductor active layer 54 and is doped with a p-type impurity.

  The n-type ZnO-based semiconductor layer 52, the ZnO-based semiconductor active layer 54, and the p-type ZnO-based semiconductor layer 56 are all heteroepitaxial growth methods using the above-described heteroepitaxial crystal growth apparatus 20 and the above-described group II metal halide and oxygen source. It is formed by.

  A p-side electrode 60 is disposed on the p-type ZnO-based semiconductor layer 56, and an n-side electrode 70 is disposed on the surface of the n-type ZnO-based semiconductor layer 52 exposed by mesa etching. As a material of the p-side electrode 60, for example, a stacked structure of a Ni layer and an Au layer can be adopted. In addition, as a material of the n-side electrode 70, for example, a laminated structure of a Ti layer and an Au layer can be adopted.

  In the example shown in FIG. 31, the back surface 40 b of the heterogeneous substrate 40 is formed with uneven random shapes such as a roughening process in order to increase the light extraction efficiency from the ZnO-based semiconductor active layer 54. .

  As the n-type impurity supplied by the n-type doping gas, for example, any of B, Ga, Al, In, or Tl can be applied.

  As the p-type impurity supplied by the p-type doping gas, for example, any of N, P, As, Sb, Bi, Li, and Cu can be applied.

The ZnO-based semiconductor active layer 54 is, for example, a multi-quantum well (MQW) in which a barrier layer made of Mg _x Zn _1-x O (0 <x <1) and a well layer made of ZnO are stacked. Provide structure.

Alternatively, the ZnO-based semiconductor active layer 54 may have an MQW structure in which a well layer made of Cd _y Zn _1-y O (0 <y <1) and a barrier layer made of ZnO are stacked.

  The number of quantum well pairs is determined by the distance traveled by electrons and holes. That is, the recombination emission efficiency of electrons and holes is determined by the number of MQW pairs corresponding to a predetermined thickness of the ZnO-based semiconductor active layer 54 that provides the best.

Here, since the band gap energy of MgO is 7.8 eV with respect to the band gap energy of 3.37 eV of ZnO, the composition ratio x of Mg _x Zn _1-x O is adjusted to make Mg _x Zn ₁ a barrier layer made of _-x O, can be well layer made of ZnO to form a laminated MQW structure.

On the other hand, since the band gap energy of CdO is 0.8 eV with respect to the band gap energy of 3.37 eV, the composition ratio y of Cd _y Zn _{1 -y} O is adjusted to obtain Cd _y Zn _{1 -y.} It is also possible to form an MQW structure in which a well layer made of O and a barrier layer made of ZnO are stacked.

The heterogeneous substrate 40 is composed of, for example, a sapphire substrate. Alternatively, a silicon substrate, a SiC substrate, a GaAs substrate, a GaP substrate, a GaN-based substrate, a ScAlMgO ₄ substrate, or the like may be applied.

  As the buffer layer 42, an oxide alignment film or a nitride alignment film can be used. As the oxide alignment film, for example, ZnO or MgO can be used.

  As the nitride alignment film, for example, AlN or GaN can be used.

  Note that light emission (hν) from the semiconductor device can be extracted from the top surface direction and the back surface direction as shown in FIG. 31. As a final device structure, for example, a configuration in which light emission (hν) is mainly extracted from the back surface 40b of the heterogeneous substrate 40 by using a flip chip mounting structure may be adopted.

  According to the heteroepitaxial growth method of the present invention, a ZnO-based semiconductor crystal can be formed on a heterogeneous substrate such as a sapphire substrate at a temperature higher than 800 ° C.

  ADVANTAGE OF THE INVENTION According to this invention, the heteroepitaxial crystal structure and semiconductor device which were formed using the said heteroepitaxial growth method can be provided.

  According to the heteroepitaxial crystal growth apparatus of the present invention, a ZnO-based semiconductor crystal can be grown on a heterogeneous substrate such as a sapphire substrate at a temperature higher than 800 ° C.

[Other embodiments]
As described above, the present invention has been described according to the first embodiment. However, it should be understood that the descriptions and drawings constituting a part of this disclosure are illustrative and limit the present invention. Absent. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  As described above, the present invention includes various embodiments that are not described herein.

  A heteroepitaxial growth method, a heteroepitaxial crystal structure, and a semiconductor device according to the present invention include a light emitting device such as an LED or a laser diode (LD) from a blue region to an ultraviolet region, a light receiving element, a piezoelectric element, and a HEMT (High Electron Mobility Transistor). ), HBT (Hetero-junction bipolar Transistor), transparent electrodes, and the like.

DESCRIPTION OF SYMBOLS 2,12 ... Chlorine gas supply means 3, 13 ... Carrier gas supply means 4, 14 ... Raw material zone 5, 9 ... Heating means 6 ... Water supply means 7 ... Carrier gas supply means 8 ... Growth zone 10 ... Substrate holding means 15, 25 ... Group II metal material 16 ... Growth substrate 20 ... Heteroepitaxial crystal growth device 22 ... First doping gas supply means 24 ... Second doping gas supply means 40, 41 ... Sapphire substrate 40a ... Sapphire substrate surface 40b ... Sapphire substrate surface Back surface 42, 43 ... Buffer layer 44 ... ZnO facet 46, 47 ... ZnO layer 52 ... n-type ZnO-based semiconductor layer 54 ... ZnO-based semiconductor active layer 56 ... p-type ZnO-based semiconductor layer 60 ... p-side electrode 70 ... n-side electrode

Claims (28)

Forming a buffer layer on a heterogeneous substrate;
And a step of crystal-growing a zinc oxide-based semiconductor layer on the buffer layer using a group II metal halide and an oxygen source.   2. The heteroepitaxial growth method according to claim 1, wherein the crystal growth temperature is 800 ° C. or higher in the step of crystal growth of the zinc oxide based semiconductor layer.   3. The heteroepitaxial growth according to claim 1, wherein in the step of crystal growth of the zinc oxide based semiconductor layer, the supply ratio VI / II of the group VI element and the group II element is 1 or more and 100 or less. Method.   The heteroepitaxial growth method according to any one of claims 1 to 3, wherein in the step of crystal growth of the zinc oxide based semiconductor layer, the reaction gas is zinc chloride and water.   5. The step of forming the buffer layer includes a step of crystal-growing a zinc oxide based semiconductor layer on the heterogeneous substrate using a group II metal and an oxygen source. The heteroepitaxial growth method according to Item.   6. The heteroepitaxial growth method according to claim 5, wherein the step of forming the buffer layer further includes a step of performing heat treatment, laser treatment, or plasma treatment.   6. The heteroepitaxial growth method according to claim 5, wherein the step of forming the buffer layer further includes a step of heat-treating with nitrogen gas in an oxidizing atmosphere.   6. The heteroepitaxial growth method according to claim 5, wherein in the step of forming the buffer layer, the Group II metal and the oxygen source are Zn and water, respectively.   The heteroepitaxial growth according to any one of claims 1 to 8, wherein the step of forming the buffer layer and the step of crystal growth of the zinc oxide based semiconductor layer are performed in the same apparatus. Method.   The reactive gas is zinc and water in the step of forming the buffer layer, and the reactive gas is zinc chloride and water in the step of crystal growth of the zinc oxide based semiconductor layer. 2. The heteroepitaxial growth method according to claim 1. Different substrates,
A buffer layer disposed on the heterogeneous substrate;
A heteroepitaxial crystal structure comprising: a zinc oxide-based semiconductor layer disposed on the buffer layer and formed by crystal growth using a group II metal halide and an oxygen source. The heteroepitaxial crystal structure according to claim 11, wherein the heterogeneous substrate is one of a sapphire substrate, a silicon substrate, a GaAs substrate, a GaP substrate, a SiC substrate, a GaN-based substrate, and a ScAlMgO ₄ substrate. 12. The heteroepitaxial crystal structure according to claim 11, wherein the buffer layer is an oxide alignment film. The heteroepitaxial crystal structure according to claim 11, wherein the buffer layer is a nitride alignment film.   12. The heteroepitaxial crystal structure according to claim 11, wherein the buffer layer is an oxide oriented film made of ZnO or MgO.   12. The heteroepitaxial crystal structure according to claim 11, wherein the buffer layer is a nitride orientation film made of AlN or GaN. Different substrates,
A buffer layer disposed on the heterogeneous substrate;
An n-type zinc oxide based semiconductor layer disposed on the buffer layer and doped with an n-type impurity;
A zinc oxide based semiconductor active layer disposed on the n-type zinc oxide based semiconductor layer;
A semiconductor device comprising: a p-type zinc oxide based semiconductor layer disposed on the active layer and doped with a p-type impurity.   The semiconductor device according to claim 17, wherein the n-type impurity is any one of B, Ga, Al, In, and Tl.   The semiconductor device according to claim 17, wherein the p-type impurity is any one of N, P, As, Sb, Bi, Li, and Cu. The semiconductor device according to claim 17, wherein the zinc oxide based semiconductor active layer has a multiple quantum well structure in which a barrier layer made of Mg _x Zn _1-x O and a well layer made of ZnO are stacked. . The semiconductor device according to claim 17, wherein the zinc oxide based semiconductor active layer has a multiple quantum well structure in which a well layer made of Cd _y Zn _1-y O and a barrier layer made of ZnO are stacked. . 18. The semiconductor device according to claim 17, wherein the heterogeneous substrate is one of a sapphire substrate, a silicon substrate, a GaAs substrate, a GaP substrate, a SiC substrate, a GaN-based substrate, or a ScAlMgO ₄ substrate. The semiconductor device according to claim 17, wherein the buffer layer is an oxide alignment film. The semiconductor device according to claim 17, wherein the buffer layer is a nitride alignment film.   18. The semiconductor device according to claim 17, wherein the buffer layer is an oxide alignment film made of ZnO or MgO.   18. The semiconductor device according to claim 17, wherein the buffer layer is a nitride orientation film made of AlN or GaN. A first raw material zone in which a first Group II metal material containing a metal element of zinc is held;
A second raw material zone in which a second group II metal material containing a group II metal simple substance other than zinc is held;
First halogen gas supply means for supplying a first halogen gas to the first raw material zone;
Second halogen gas supply means for supplying a second halogen gas to the second raw material zone;
Oxygen material supply means for supplying oxygen material containing oxygen;
first doping gas supply means for supplying an n-type doping gas for doping an n-type impurity;
a second doping gas supply means for supplying a p-type doping gas for adding a p-type impurity;
A growth zone for reacting the oxygen material with the first and second halogen gases, the n-type and p-type doping gases and the halogenated group II metal generated from the first and second group II metal materials. And a heteroepitaxial crystal growth apparatus.   28. The heteroepitaxial crystal growth apparatus according to claim 27, wherein the supply ratio VI / II of the group VI element and the group II element is 1 to 100.