Semiconductor stack, semiconductor element, and method for manufacturing semiconductor element

Abstract

The present invention provides a semiconductor stack comprising at least a substrate, a buffer layer, and a crystalline metal oxide semiconductor film having a corundum structure containing at least one metal element. The semiconductor stack comprises the buffer layer directly or via another layer on the main surface of the substrate, and the crystalline metal oxide semiconductor film on the buffer layer. The buffer layer is a stacked structure of multiple buffer films having different compositions, and at least two of the multiple buffer films have a thickness of 200 nm to 650 nm. This provides a semiconductor stack having a high-quality corundum-type crystalline metal oxide semiconductor film with suppressed crystal defects, warping, and cracking, even when formed by heteroepitaxial growth.

Description

Technical Field

[0001] The present invention relates to a semiconductor stack, a semiconductor element, and a method for manufacturing the semiconductor element. Background Art

[0002] As a next-generation switching element that can achieve high withstand voltage, low loss and high heat resistance, semiconductor elements using gallium oxide (Ga2O3) with a large band gap are attracting attention and are expected to be suitable for power semiconductor devices such as inverters.

[0003] In particular, corundum-type α-Ga2O3 metal oxide can be epitaxially grown using a relatively inexpensive sapphire substrate, and can further be applied to normal pressure processes such as spray CVD (chemical vapor deposition) (Patent Document 1) or HVPE (Hydride Vapor Phase Epitaxy) (Patent Document 2). Therefore, it is expected that it can be manufactured at a cost lower than that of existing power semiconductor devices.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-28480

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-34882

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 2018-002544 Summary of the Invention

[0009] Technical Problems to be Solved by the Invention

[0010] On the other hand, in heteroepitaxial growth as described above, stress generated by lattice mismatch or differences in thermal expansion coefficients between the substrate and epitaxial layer can lead to problems such as crystal defects such as dislocations, warping, and cracking. These problems become particularly pronounced when forming films on large substrates, making production difficult.

[0011] Patent Document 3 describes an example of a corundum-structured InAlGaO-based semiconductor film with a thickness of 3 μm or greater, free of cracks within an area of ​​300 μm or greater, formed using a substrate substrate having two or more oxide layers formed thereon. However, the crack suppression shown in the example described in Patent Document 3 is limited to small-diameter substrates with diameters less than 4 inches (approximately 10 cm), and is insufficient when using practical-sized substrates (diameters of 4 inches or greater). Furthermore, even with small-diameter substrates, substrate warping cannot be suppressed.

[0012] The present invention has been implemented to solve the above-mentioned problems, and its object is to provide a semiconductor stack and a high-performance semiconductor element having a high-quality corundum-type crystalline metal oxide semiconductor film with suppressed crystal defects, warping and cracking even when formed by heteroepitaxial growth.

[0013] Technical means to solve technical problems

[0014] The present invention is implemented to achieve the above-mentioned purpose and provides a semiconductor stack, which at least includes a substrate, a buffer layer and a crystalline metal oxide semiconductor film with a corundum structure containing at least one metal element. The semiconductor stack has the buffer layer directly or through other layers on the main surface of the substrate, and has the crystalline metal oxide semiconductor film on the buffer layer. In the semiconductor stack, the buffer layer is a stacked structure composed of multiple buffer films with different compositions, and at least two of the multiple buffer films have a film thickness of not less than 200 nm and not more than 650 nm.

[0015] In addition, the present invention provides a semiconductor stack, which includes at least a substrate, a buffer layer and a crystalline metal oxide semiconductor film with a corundum structure containing at least one metal element. The semiconductor stack has the buffer layer directly or via other layers on the main surface of the substrate, and has the crystalline metal oxide semiconductor film on the buffer layer. In the semiconductor stack, the buffer layer is a stacked structure composed of multiple layers of buffer films with different compositions, and the film thickness of the multiple layers of buffer films are all greater than 200 nm and less than 650 nm.

[0016] Since such a buffer layer can effectively alleviate the stress caused by the lattice mismatch between the substrate and the crystalline metal oxide semiconductor film, a semiconductor stack having a high-quality crystalline metal oxide semiconductor film with reduced incorporation of crystal defects and further suppressed cracks and warping can be obtained.

[0017] In this case, it is preferable that the buffer film contains a main component metal element that is contained most among the metal elements contained in the crystalline metal oxide semiconductor film.

[0018] Furthermore, the buffer layer is preferably a stacked structure formed by stacking the plurality of buffer films in such a manner that the composition ratio of the main component metal element of the crystalline metal oxide semiconductor film increases from the substrate side of the buffer layer toward the crystalline metal oxide semiconductor film side.

[0019] This further enhances the stress relaxation effect of the buffer layer, thereby further improving the quality of the crystalline metal oxide semiconductor film on the buffer layer.

[0020] In this case, it is preferable that the buffer film contains a main component metal element that is contained most among the metal elements contained in the substrate of the buffer layer.

[0021] Furthermore, the buffer layer is preferably a stacked structure in which a plurality of buffer films are stacked such that the composition ratio of the main component metal element of the substrate of the buffer layer decreases from the base side of the buffer layer toward the crystalline metal oxide semiconductor film side.

[0022] This further enhances the stress relaxation effect of the buffer layer, thereby further improving the quality of the crystalline metal oxide semiconductor film on the buffer layer.

[0023] In this case, it is preferable that the substrate of the buffer layer is the base, and the main component metal element of the base is aluminum.

[0024] From the viewpoint of quality and cost, a wafer containing aluminum as a main component metal element, such as a sapphire wafer, can be suitably used as the substrate.

[0025] In this case, it is preferable that the main component metal element of the crystalline metal oxide semiconductor film is gallium.

[0026] The gallium oxide film has a large band gap and can be suitably used as the crystalline metal oxide semiconductor film of the present invention.

[0027] In this case, the thickness of the crystalline metal oxide semiconductor film is preferably 1 μm or more.

[0028] This further improves the quality of the crystalline metal oxide semiconductor film.

[0029] In this case, the main surface area of ​​the substrate is preferably 10 cm 2 above.

[0030] This further improves the quality of the crystalline metal oxide semiconductor film and increases the degree of freedom in device design.

[0031] In this case, it is preferable to provide a semiconductor element including at least the buffer layer and the crystalline metal oxide semiconductor film in the semiconductor stack described above.

[0032] This results in a high-performance semiconductor element with excellent electrical characteristics.

[0033] In addition, the present invention provides a method for manufacturing a semiconductor element, which is a method for manufacturing a semiconductor element having at least a crystalline metal oxide semiconductor film and an electrode, comprising: a process of forming a multilayer buffer film as a buffer layer on the main surface of a substrate, the multilayer buffer film comprising two or more layers of buffer films having respective different compositions and a thickness of not less than 200 nm and not more than 650 nm; a process of forming a crystalline metal oxide semiconductor film having a corundum structure on the buffer layer; and a process of forming an electrode on at least the crystalline metal oxide semiconductor film.

[0034] In addition, the present invention further provides a method for manufacturing a semiconductor element, which is a method for manufacturing a semiconductor element having at least a crystalline metal oxide semiconductor film and an electrode, comprising: a process of forming a plurality of buffer films having different compositions and a thickness of not less than 200 nm and not more than 650 nm as a buffer layer on the main surface of a substrate; a process of forming a crystalline metal oxide semiconductor film having a corundum structure on the buffer layer; and a process of forming an electrode on at least the crystalline metal oxide semiconductor film.

[0035] Since the formation of such a buffer layer can effectively alleviate the stress caused by the lattice mismatch between the substrate and the crystalline metal oxide semiconductor film, a high-performance semiconductor element can be obtained using a high-quality crystalline metal oxide semiconductor film with reduced mixing of crystal defects and further suppressed cracks and warping.

[0036] Effects of the Invention

[0037] As described above, the present invention provides a semiconductor stack, a semiconductor device, and a method for manufacturing a semiconductor device having a high-quality corundum-type crystalline metal oxide semiconductor film with suppressed crystal defects, warping, and cracking, even when formed by heteroepitaxial growth. Furthermore, by using a semiconductor stack having a crystalline metal oxide semiconductor film according to the present invention, a high-performance semiconductor device can be manufactured. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a diagram showing one embodiment of the structure of the semiconductor stack of the present invention.

[0039] Figure 2 This is a diagram showing another embodiment of the structure of the semiconductor stack of the present invention.

[0040] Figure 3FIG1 is a diagram showing an example of a Schottky barrier diode of the present invention.

[0041] Figure 4 FIG1 is a diagram showing an example of a high electron mobility transistor (transistor) of the present invention.

[0042] Figure 5 FIG. 1 is a diagram showing an example of a semiconductor field-effect transistor according to the present invention.

[0043] Figure 6 FIG. 1 is a diagram showing an example of an insulated gate bipolar transistor according to the present invention.

[0044] Figure 7 This is a diagram showing an example of a light-emitting diode according to the present invention. DETAILED DESCRIPTION

[0045] Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[0046] As described above, a semiconductor stack has been sought that includes a high-quality corundum-type crystalline metal oxide semiconductor film with suppressed crystal defects, warping, and cracking even when formed by heteroepitaxial growth.

[0047] The inventors of the present application have conducted in-depth research on the above-mentioned technical problems and found that a semiconductor stack can effectively alleviate the stress caused by the lattice mismatch between the substrate and the semiconductor film, thereby obtaining a high-quality semiconductor stack that reduces the mixing of crystal defects and further suppresses cracks and warping, thereby completing the present invention. The semiconductor stack at least includes a substrate, a buffer layer and a crystalline metal oxide semiconductor film having a corundum structure containing at least one metal element, the semiconductor stack having the buffer layer directly or via other layers on the main surface of the substrate, and having the crystalline metal oxide semiconductor film on the buffer layer, in the semiconductor stack, the buffer layer is a stacked structure composed of multiple buffer films that are different in composition, and at least two of the multiple buffer films have a film thickness of not less than 200 nm and not more than 650 nm, or the buffer layer is a stacked structure composed of multiple buffer films that are different in composition, and all of the multiple buffer films have a film thickness of not less than 200 nm and not more than 650 nm.

[0048] In addition, the inventors of the present application discovered that a semiconductor element manufacturing method can be used to obtain a semiconductor element using a high-quality crystalline metal oxide semiconductor film with reduced crystal defects and further suppressed cracks and warping, thereby completing the present invention. The manufacturing method of the semiconductor element is a manufacturing method of a semiconductor element having at least a crystalline metal oxide semiconductor film and an electrode, which comprises: a process of forming a multilayer buffer film including two or more layers of buffer films having different compositions and a thickness of 200 nm to 650 nm on the main surface of a substrate as a buffer layer; a process of forming a crystalline metal oxide semiconductor film having a corundum structure on the buffer layer; and a process of forming an electrode at least on the crystalline metal oxide semiconductor film, or a process of forming a multilayer buffer film including two or more layers of buffer films having different compositions and a thickness of 200 nm to 650 nm on the main surface of a substrate as a buffer layer; a process of forming a crystalline metal oxide semiconductor film having a corundum structure on the buffer layer; and a process of forming an electrode at least on the crystalline metal oxide semiconductor film.

[0049] Hereinafter, description will be given with reference to the accompanying drawings.

[0050] (Semiconductor stack)

[0051] Figure 1 、 Figure 2 Each of the figures shows a configuration of a semiconductor stack according to the present invention. The semiconductor stack having a crystalline metal oxide semiconductor film (hereinafter sometimes simply referred to as a "semiconductor stack") 100, 200 according to the present invention basically comprises: a substrate 101, 201; a buffer layer 112, 212; and a crystalline metal oxide semiconductor film 103, 203. The semiconductor stack is composed of the buffer layer 112, 212 formed on the main surface of the substrate 101, 201, and the crystalline metal oxide semiconductor film 103, 203 further formed on the buffer layer 112, 212.

[0052] (Matrix)

[0053] The substrates 101 and 201 are not particularly limited as long as they contain a crystal as their main component and can be any known substrate. They can be insulators, conductors, or semiconductors, and can be single crystal or polycrystalline. Furthermore, it is preferred to use a substrate in which aluminum is the most abundant main component metal element among the metal elements contained in the substrate. Sapphire wafers are particularly preferred for quality and cost reasons.

[0054] The orientation of the principal surface of the substrate is not particularly limited. In the case of a sapphire wafer, for example, a principal surface such as the c-plane, m-plane, or a-plane can be used. Alternatively, a surface having an off-angle relative to the just plane may be used. The off-angle is not particularly limited, but is preferably 0° to 15°.

[0055] The thickness of the substrate 101, 201 is not particularly limited, but is preferably about 200 to 800 μm from the perspective of cost. In addition, the area of ​​the main surface of the substrate 101, 201 is preferably 10 cm 2 The diameter of the substrate 101 or 201 is preferably greater than or equal to 10 cm (4 inches). By using a substrate 101 or 201 with a large diameter, the quality and productivity of the crystalline metal oxide semiconductor film 103 or 203 formed on the substrate 101 or 201 are further improved. Furthermore, the degree of freedom in device design is increased. The shape of the substrate 101 or 201 is not particularly limited in the present invention.

[0056] (Buffer layer)

[0057] The buffer layers 112 and 212 may be Figure 1 As shown in FIG. 1 , it may be formed directly on the substrate 101 or may be formed via other layers. For example, when a peeling layer for separating the crystalline metal oxide semiconductor film from the substrate is introduced as the other layer, the crystalline metal oxide semiconductor film may be formed directly on the substrate 101 or may be formed via other layers. Figure 2 As shown, it is formed on the release layer 204.

[0058] (Buffer film)

[0059] The buffer layers 112 and 212 are stacked structures of multiple buffer films 102a, 102b, 102c, 202a, 202b, and 202c with different compositions. The buffer films have different compositions. More preferably, they contain the main component metal element that is contained in the largest amount among the metal elements contained in the crystalline metal oxide semiconductor films 103 and 203 described later, or the main component metal element that is contained in the largest amount among the metal elements contained in the substrate containing the buffer layers 112 and 212. Of course, they may also contain both the main component metal element of the crystalline metal oxide semiconductor films 103 and 203 and the main component metal element of the substrate of the buffer layers 112 and 212. Here, the main component metal element of the substrate of the buffer layers 112 and 212 refers to, Figure 1 In the scheme of the main component metal element of the matrix 101 or Figure 2 The main component metal element of the peeling layer 204 in the scheme.

[0060] In addition, Figure 1 and Figure 2In the scheme, although the buffer layer is composed of three layers of buffer films, the present invention is not limited to this. As long as two or more layers (multilayers) of buffer films with different compositions are formed, the number of layers and composition of the buffer film as a whole can be appropriately adjusted according to conditions such as the thickness of the crystalline metal oxide semiconductor film. At this time, the thickness of each of at least two layers of the buffer film of the two or more layers (multilayers) is set to be greater than 200nm and less than 650nm. Although the thickness of at least two layers of buffer films can be all the same thickness or different thicknesses, if it is less than 200nm, the full effect cannot be obtained. In addition, if it is greater than 650nm, the stress will become significant and warping and defects will be mixed in. Preferably, the thickness of the buffer film of the two or more layers (multilayers) is all greater than 200nm and less than 650nm.

[0061] Furthermore, when the buffer film includes the main component metal element of the crystalline metal oxide semiconductor film 103, 203, it is preferable to stack the buffer film in such a manner that the composition ratio of the main component metal element of the crystalline metal oxide semiconductor film 103, 203 increases from the substrate 101, 201 side toward the crystalline metal oxide semiconductor film 103, 203 side. Furthermore, when the buffer film includes the main component metal element of the substrate of the buffer layer 112, 212, it is preferable to stack the buffer film in such a manner that the composition ratio of the main component metal element of the substrate of the buffer layer 112, 212 decreases from the substrate 101, 201 side toward the crystalline metal oxide semiconductor film 103, 203 side. For example, in Figure 1 In the scheme, when forming a crystalline metal oxide semiconductor film of α-Ga2O3 on an Al2O3 wafer, it is preferred to use (Al x Ga 1-x )2O3 (0<x<1) forms a buffer film, and the value of x decreases from the buffer film 102a toward the buffer film 102c.

[0062] Furthermore, it is preferable to use a substrate in which aluminum is the most abundant main component metal element among the metal elements contained in the substrate, and to use the substrate as the base of the buffer layer. This is advantageous in terms of quality and cost.

[0063] (Crystalline Metal Oxide Semiconductor Film)

[0064] The main component of the crystalline metal oxide semiconductor film 103, 203 is not particularly limited as long as it is a crystalline metal oxide having a corundum structure. For example, a crystalline metal oxide containing any one of aluminum, titanium, vanadium, chromium, iron, gallium, rhodium, indium, and iridium can be used as the main component. The main component metal element contained in the crystalline metal oxide semiconductor film 103, 203 is more preferably gallium. Specifically, it is Al2O3, Ti2O3, V2O3, Cr2O3, Fe2O3, Ga2O3, Rh2O3, In2O3, Ir2O3, and Ga2O3 is particularly preferred in the present invention. This is because Ga2O3 has a large band gap and can be expected to be used as a variety of semiconductor devices. In addition, when two elements selected from the above-mentioned metal elements are set as A and B, it can be (A x B 1-x )2O3(0<x<1) is a binary metal oxide, or when three elements selected from the above metal elements are set as A, B, and C, it can be (A x B y C 1-x-y )2O3(0<x<1, 0<y<1) is a ternary metal oxide represented by.

[0065] Furthermore, the crystalline metal oxide semiconductor films 103 and 203 may have a single layer structure of the above-mentioned metal oxide, or may have a stacked structure of a plurality of crystalline films having different compositions or dopant contents.

[0066] The thickness of the crystalline metal oxide semiconductor films 103 and 203 is preferably 1 μm or more, more preferably 3 μm or more. By setting the film thickness to such a level, the orientation of the crystals can be improved, and a higher quality crystalline metal oxide semiconductor film can be formed.

[0067] Furthermore, in order to impart conductivity, the semiconductor stack of the present invention may be doped with impurities according to the design of the semiconductor element to which it is applied. For example, when the semiconductor films 103 and 203 contain at least gallium, any one of silicon, germanium, tin, magnesium, and copper, or a combination thereof, may be suitably used as the impurity. Furthermore, the conductivity type at this time is n-type. The concentration of the impurity added by doping varies depending on the design of the target final product, but is generally 1×10 16 cm -3 Above 8×10 22 cm -3 In particular, the crystalline metal oxide semiconductor films 103 and 203 may be stacked layers of crystalline films to which impurities are added at different concentrations. Furthermore, the buffer layers 102 and 202 may also be made conductive by similar doping.

[0068] (Semiconductor components)

[0069] In addition, using the semiconductor stack of the present invention as described above, a semiconductor element having at least a buffer layer and a crystalline metal oxide semiconductor film in the semiconductor stack can be provided. Such a semiconductor element can be a semiconductor element including a substrate or a semiconductor element without the substrate. The semiconductor element of the present invention is a semiconductor element using a high-quality crystalline metal oxide semiconductor film that reduces the incorporation of crystal defects and further suppresses cracking and warping, and is a high-quality semiconductor element. Application examples (specific examples) of the semiconductor element are described in detail later.

[0070] (Method for Manufacturing Semiconductor Stack)

[0071] The method for producing the semiconductor stack of the present invention is not particularly limited. A substrate and a buffer layer can be appropriately selected according to the type of crystalline metal oxide semiconductor film or the semiconductor device to which it is applied, and a film can be formed on the substrate to obtain a semiconductor stack. The film formation method is not particularly limited and can be achieved using a wide range of well-known techniques such as plasma CVD, LPCVD (reduced pressure CVD), APCVD (atmospheric pressure CVD), spray CVD, HVPE, sputtering, and ion plating.

[0072] (Method for manufacturing semiconductor element)

[0073] In addition, a buffer layer is formed directly or across other layers on the main surface of the substrate. The buffer layer is formed by film-forming in the form of a buffer film including two or more layers having different compositions and a thickness of 200 nm or more and 650 nm or less. It is preferred that the thickness of the multilayer buffer film constituting the buffer layer is all set to 200 nm or more and 650 nm or less for film-forming. On the buffer layer, a crystalline metal oxide semiconductor film having a corundum structure is formed to obtain a semiconductor stack of the present invention. Then, an electrode is further formed on the crystalline metal oxide semiconductor film to manufacture a semiconductor element. At this time, a semiconductor stack including a substrate, a buffer layer and a crystalline metal oxide semiconductor film can be used directly, or the substrate can be removed and the buffer layer and the crystalline metal oxide semiconductor film can be left, or the substrate and the buffer layer can be removed and only the crystalline metal oxide semiconductor film can be left. Thus, it is possible to manufacture a high-performance semiconductor element using a high-quality crystalline metal oxide semiconductor film that reduces the mixing of crystal defects and further suppresses cracks and warping.

[0074] (Examples of Applicable Semiconductor Elements)

[0075] Semiconductor stacks having such crystalline metal oxide semiconductor films have reduced defect density, excellent electrical properties, and are industrially useful. Such semiconductor stacks having such crystalline metal oxide semiconductor films can be suitably used in various semiconductor devices and are particularly useful in power devices.

[0076] In addition, the semiconductor stack having the crystalline metal oxide semiconductor film of the present invention can be classified into a lateral element (lateral device) in which an electrode is formed on a single side of the crystalline metal oxide semiconductor film and a vertical element (vertical device) having electrodes on both the inner and outer sides of the crystalline metal oxide semiconductor film. In the present invention, although it can be suitably used in both lateral devices and vertical devices, it is preferably used in vertical devices. As semiconductor elements, for example, Schottky barrier diodes (SBDs), metal semiconductor field effect transistors (MESFETs), high electron mobility transistors (HEMTs), semiconductor field effect transistors (MOSFETs), junction field effect transistors (JFETs), insulated gate bipolar transistors (IGBTs), or light emitting diodes (LEDs) can be listed.

[0077] The following describes preferred examples of applying the crystalline metal oxide semiconductor film of the present invention to an n-type semiconductor layer (e.g., an n+-type semiconductor or an n--type semiconductor layer) using the accompanying drawings. However, the present invention is not limited to these examples. Furthermore, the semiconductor elements exemplified below may further include other layers (e.g., an insulator layer or a conductor layer), and intermediate layers or buffer layers (buffer layers) may be omitted as appropriate.

[0078] Figure 3 The SBD 300 is an example of an SBD of the present invention and includes an n-type semiconductor layer 301 a doped at a relatively low concentration, an n+ type semiconductor layer 301 b doped at a relatively high concentration, a Schottky electrode 302 , and an ohmic electrode 303 .

[0079] The materials of the Schottky electrode 302 and the ohmic electrode 303 can be well-known electrode materials. Examples of the electrode materials include metals such as aluminum, molybdenum, cobalt, zirconium, tin, niobium, iron, chromium, tantalum, titanium, gold, platinum, vanadium, manganese, nickel, copper, hafnium, tungsten, iridium, zinc, indium, palladium, neodymium or silver, or alloys thereof; metal oxide conductive films such as tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO); organic conductive compounds such as polyaniline, polythiophene or polypyrrole; or mixtures thereof and laminates thereof.

[0080] The Schottky electrode 302 and the ohmic electrode 303 can be formed by a known method such as vacuum evaporation or sputtering. More specifically, when the Schottky electrode is formed using two of the metals, a first metal and a second metal, the Schottky electrode can be formed by stacking a layer composed of the first metal and a layer composed of the second metal, and patterning the layer composed of the first metal and the layer composed of the second metal using photolithography.

[0081] When a reverse bias is applied to the SBD 300, a depletion layer (not shown) diffuses in the n-type semiconductor layer 301a, resulting in a high-voltage SBD. Furthermore, when a forward bias is applied, electrons flow from the ohmic electrode 303 to the Schottky electrode 302. Therefore, the SBD of the present invention is excellent for high-voltage and high-current applications, and features fast switching speeds, excellent voltage resistance, and excellent reliability.

[0082] Figure 4 The HEMT 400 is an example of the HEMT of the present invention. The HEMT 400 includes a wide-bandgap n-type semiconductor layer 401 , a narrow-bandgap n-type semiconductor layer 402 , an n+-type semiconductor layer 403 , a semi-insulator layer 404 , a buffer layer 405 , a gate electrode 406 , a source electrode 407 , and a drain electrode 408 .

[0083] Figure 5 MOSFET 500 is an example of a MOSFET of the present invention. MOSFET 500 includes an n-type semiconductor layer 501 , n+ type semiconductor layers 502 and 503 , a gate insulating film 504 , a gate electrode 505 , a source electrode 506 , and a drain electrode 507 .

[0084] Figure 6 The IGBT 600 is an example of an IGBT of the present invention and includes an n-type semiconductor layer 601 , an n-type semiconductor layer 602 , an n+ type semiconductor layer 603 , a p-type semiconductor layer 604 , a gate insulating film 605 , a gate electrode 606 , an emitter electrode 607 , and a collector electrode 608 .

[0085] Figure 7 The LED 700 is an example of an LED of the present invention. The LED 700 includes a first electrode 701 , an n-type semiconductor layer 702 , a light-emitting layer 703 , a p-type semiconductor layer 704 , a light-transmitting electrode 705 , and a second electrode 706 .

[0086] Materials for the translucent electrode include conductive materials containing indium or titanium oxides. More specifically, examples include In2O3, ZnO, SnO2, Ga2O3, TiO2, CeO2, mixed crystals of two or more thereof, or materials doped with these. The translucent electrode can be formed by depositing these materials using known methods such as sputtering. Furthermore, after forming the translucent electrode, thermal annealing may be performed to render it transparent.

[0087] Examples of materials for the first electrode 701 and the second electrode 706 include metals such as aluminum, molybdenum, cobalt, zirconium, tin, niobium, iron, chromium, tantalum, titanium, gold, platinum, vanadium, manganese, nickel, copper, hafnium, tungsten, iridium, zinc, indium, palladium, neodymium, or silver, or alloys thereof; conductive metal oxide films such as tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO), or indium zinc oxide (IZO); organic conductive compounds such as polyaniline, polythiophene, or polypyrrole; or mixtures thereof. The electrode film formation method is not particularly limited, and the electrodes can be formed on the substrate using a method appropriately selected from wet methods such as printing, spraying, and coating, physical methods such as vacuum evaporation, sputtering, and ion plating, and chemical methods such as CVD and plasma CVD, taking into account the compatibility of the material.

[0088] Example

[0089] Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

[0090] (Example 1)

[0091] A semiconductor stack was produced using a spray CVD apparatus as follows: Two sprayers (sprayer A and sprayer B) and a quartz tubular reactor were prepared, the two sprayers were connected with a quartz tube, and a quartz tube branched from the tube was connected to the reactor.

[0092] Next, 34% hydrochloric acid was added to a 0.04 mol / L aqueous solution of gallium acetylacetonate at a concentration of 1% by volume, and the mixture was stirred for 60 minutes using a stirrer to obtain a precursor. This precursor was then filled into a sprayer A. Next, 34% hydrochloric acid was added to a 0.06 mol / L aqueous solution of aluminum acetylacetonate at a concentration of 1% by volume, and the mixture was stirred for 60 minutes using a stirrer to obtain a precursor.

[0093] The precursor was filled into nebulizer B.

[0094] Next, a 4-inch c-plane sapphire substrate with a thickness of 0.6 mm was placed upright on a quartz susceptor in a reactor and heated to a temperature of 450°C. A 2.4 MHz ultrasonic vibrator then transmitted ultrasonic vibrations through water to the precursors in sprayers A and B, thereby atomizing the precursors.

[0095] Next, nitrogen gas was supplied from both sprayers A and B at a total flow rate of 20 L / min, and a mixture of the spray and nitrogen was supplied to the reactor, forming a 400 nm thick buffer film on the substrate. The second to fourth buffer films were stacked by reducing the nitrogen flow rate from sprayer B, thereby lowering the Al ratio in the mixed gas. The Al / Ga ratios in the buffer films were 0.60, 0.30, 0.15, and 0.05, respectively, for the first to fourth layers. The nitrogen supply to sprayer B was then stopped, and the nitrogen flow rate from sprayer A was reduced to 20 L / min. The mixture of the spray and nitrogen was supplied to the reactor for 180 minutes, resulting in a semiconductor film approximately 7 μm thick.

[0096] Then, the nitrogen supply and heating of the substrate were stopped, and the substrate was removed from the reactor after cooling to near room temperature. X-ray diffraction analysis confirmed that the obtained semiconductor film was α-Ga2O3.

[0097] The produced films were then evaluated for crack, warpage, and dislocation density. Cracks were evaluated as linear defects with a length of 1 mm or greater observed in the bright field of an optical microscope across the entire substrate surface. Warpage was evaluated as the shortest distance between a straight line connecting the two ends of the substrate and a concave or convex vertex. Furthermore, dislocation density was quantified by TEM using a sample thinned to a 100 nm thickness in a longitudinal section of the laminate.

[0098] (Examples 2 and 3)

[0099] A semiconductor stack was produced in the same manner as in Example 1, except that the thickness of each buffer film was set to 200 nm (Example 2) and 650 nm (Example 3). X-ray diffraction analysis confirmed that the produced semiconductor film was α-Ga2O3. The same evaluation as in Example 1 was then performed.

[0100] (Comparative Examples 1 and 2)

[0101] A semiconductor stack was produced in the same manner as in Example 1, except that the thickness of each buffer film was set to 150 nm (Comparative Example 1) and 700 nm (Comparative Example 2). X-ray diffraction analysis confirmed that the produced semiconductor film was α-Ga2O3. The same evaluation as in Example 1 was then performed.

[0102] (Example 4)

[0103] A semiconductor stack was produced in the same manner as in Example 1, except that the thickness of the first and second buffer films was set to 150 nm. X-ray diffraction analysis confirmed that the produced semiconductor film was α-Ga2O3. The same evaluation as in Example 1 was then performed.

[0104] (Comparative Example 3)

[0105] A semiconductor stack was produced in the same manner as in Example 1, except that the thickness of the first, second, and third buffer films was set to 150 nm. X-ray diffraction analysis confirmed that the produced semiconductor film was α-Ga2O3. The same evaluation as in Example 1 was then performed.

[0106] The evaluation results of cracks, warpage, and dislocation density of Examples 1, 2, and 3 and Comparative Examples 1 and 2 are shown in Table 1. In addition, the evaluation results of cracks, warpage, and dislocation density of Example 4 and Comparative Example 3 are shown in Table 2.

[0107] [Table 1]

[0108] Buffer film thickness crack Warpage [mm] <![CDATA[Dislocation density [cm -2 > 150nm have 1.31 <![CDATA[8×10 10 ]]> 200nm none 0.08 <![CDATA[2×10 9 ]]> 400nm none 0.01 <![CDATA[2×10 9 ]]> 650nm none 0.01 <![CDATA[1×10 9 ]]> 700nm have 2.20 <![CDATA[3×10 10 ]]>

[0109] [Table 2]

[0110]

[0111] As shown in the results of the examples shown in Tables 1 and 2, the semiconductor stack of the present invention is a high-quality film with suppressed cracking and warping and a reduced dislocation density. On the other hand, the semiconductor stack obtained in the comparative example of the prior art exhibited cracking and significant warping, and also had a high dislocation density.

[0112] The present invention is not limited to the above embodiments, which are merely examples, and any technical solution having substantially the same structure and effect as the technical concept described in the claims of the present invention is within the scope of protection of the present invention.

Claims

1. A semiconductor stack comprising at least a substrate, a buffer layer, and a crystalline metal oxide semiconductor film having a corundum structure containing at least one metal element, The semiconductor stack has the buffer layer directly on the main surface of the substrate, and the crystalline metal oxide semiconductor film on the buffer layer and in contact with the buffer layer. The semiconductor stack is characterized in that The buffer layer is a stacked structure of multiple buffer films having different compositions. At least two buffer films in the multi-layer buffer film have a thickness of not less than 200 nm and not more than 650 nm. The buffer film includes the main component metal element that is most abundant among the metal elements contained in the crystalline metal oxide semiconductor film and the main component metal element that is most abundant among the metal elements contained in the substrate of the buffer layer. The buffer layer is a stacked structure formed by stacking the multiple buffer films in a manner that the composition ratio of the main component metal element of the crystalline metal oxide semiconductor film increases as it moves from the base side of the buffer layer toward the crystalline metal oxide semiconductor film side, and is a stacked structure formed by stacking the multiple buffer films in a manner that the composition ratio of the main component metal element of the substrate of the buffer layer decreases.

2. A semiconductor stack comprising at least a substrate, a buffer layer, and a crystalline metal oxide semiconductor film having a corundum structure containing at least one metal element, The semiconductor stack has the buffer layer directly on the main surface of the substrate, and the crystalline metal oxide semiconductor film on the buffer layer and in contact with the buffer layer. The semiconductor stack is characterized in that The buffer layer is a stacked structure of multiple buffer films having different compositions. The thickness of the multilayer buffer film is not less than 200 nm and not more than 650 nm. The buffer film includes the main component metal element that is most abundant among the metal elements contained in the crystalline metal oxide semiconductor film and the main component metal element that is most abundant among the metal elements contained in the substrate of the buffer layer. The buffer layer is a stacked structure formed by stacking the multiple buffer films in a manner that the composition ratio of the main component metal element of the crystalline metal oxide semiconductor film increases as it moves from the base side of the buffer layer toward the crystalline metal oxide semiconductor film side, and is a stacked structure formed by stacking the multiple buffer films in a manner that the composition ratio of the main component metal element of the substrate of the buffer layer decreases.

3. The semiconductor stack according to claim 1, wherein The substrate of the buffer layer is the matrix, and the main component metal element of the matrix is ​​aluminum.

4. The semiconductor stack according to claim 2, wherein: The substrate of the buffer layer is the matrix, and the main component metal element of the matrix is ​​aluminum.

5. The semiconductor stack according to claim 1, wherein The main component metal element of the crystalline metal oxide semiconductor film is gallium. The semiconductor stack according to claim 2 , wherein: The main component metal element of the crystalline metal oxide semiconductor film is gallium.

7. The semiconductor stack according to claim 1, wherein The crystalline metal oxide semiconductor film has a thickness of 1 μm or more.

8. The semiconductor stack according to claim 2, wherein: The crystalline metal oxide semiconductor film has a thickness of 1 μm or more.

9. The semiconductor stack according to any one of claims 1 to 8, wherein The area of ​​the main surface of the substrate is 10 cm 2 above.

10. A semiconductor element, characterized in that: The semiconductor stack according to any one of claims 1 to 9 comprises at least the buffer layer and the crystalline metal oxide semiconductor film.

11. A method for manufacturing a semiconductor device comprising at least a crystalline metal oxide semiconductor film and an electrode, characterized in that: have: forming a multilayer buffer film including two or more buffer films having different compositions and a thickness of 200 nm to 650 nm on the main surface of the substrate as a buffer layer; forming a crystalline metal oxide semiconductor film having a corundum structure on the buffer layer so as to be in contact with the buffer layer; and a step of forming an electrode on at least the crystalline metal oxide semiconductor film, The buffer film includes the main component metal element that is most abundant among the metal elements contained in the crystalline metal oxide semiconductor film and the main component metal element that is most abundant among the metal elements contained in the substrate of the buffer layer. The buffer layer is a stacked structure formed by stacking the multiple buffer films in a manner that the composition ratio of the main component metal element of the crystalline metal oxide semiconductor film increases as it moves from the base side of the buffer layer toward the crystalline metal oxide semiconductor film side, and is a stacked structure formed by stacking the multiple buffer films in a manner that the composition ratio of the main component metal element of the substrate of the buffer layer decreases.

12. A method for manufacturing a semiconductor device comprising at least a crystalline metal oxide semiconductor film and an electrode, characterized in that: have: forming a plurality of buffer films having different compositions and a thickness of not less than 200 nm and not more than 650 nm as a buffer layer on the main surface of the substrate; forming a crystalline metal oxide semiconductor film having a corundum structure on the buffer layer so as to be in contact with the buffer layer; and a step of forming an electrode on at least the crystalline metal oxide semiconductor film, The buffer film includes the main component metal element that is most abundant among the metal elements contained in the crystalline metal oxide semiconductor film and the main component metal element that is most abundant among the metal elements contained in the substrate of the buffer layer. The buffer layer is a stacked structure formed by stacking the multiple buffer films in a manner that the composition ratio of the main component metal element of the crystalline metal oxide semiconductor film increases as it moves from the base side of the buffer layer toward the crystalline metal oxide semiconductor film side, and is a stacked structure formed by stacking the multiple buffer films in a manner that the composition ratio of the main component metal element of the substrate of the buffer layer decreases.

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