JP5163045B2 - Epitaxial growth substrate manufacturing method and nitride compound semiconductor device manufacturing method - Google Patents

Description

  The present invention relates to an epitaxial growth substrate and a nitride-based compound semiconductor device, and more particularly to a method for manufacturing an epitaxial growth substrate, which suppresses the occurrence of warpage and cracks in an epitaxial growth layer on a support substrate and relatively shortens the manufacturing lead time, and nitride The present invention relates to a method for manufacturing a compound semiconductor device, an epitaxial growth substrate, and a nitride compound semiconductor device.

  Materials such as power elements (HEMT, Schottky barrier diode, etc.), light emitting diodes (LED), gallium nitride (GaN), indium nitride (InN), aluminum nitride (AlN), indium gallium nitride (InGaN) In general, a nitride compound semiconductor such as aluminum gallium nitride (AlGaN) is used. These nitride-based compound semiconductors use substrates of dissimilar materials such as sapphire substrates, silicon carbide (SiC) substrates, silicon (Si) substrates, etc., metal organic chemical vapor deposition (MOVPE) method, molecular beam crystal growth (MBE). For example, vapor phase epitaxy such as hydride vapor phase epitaxy (HVPE).

  However, there is a large difference in lattice constant and thermal expansion coefficient between a nitride-based semiconductor layer such as GaN formed by epitaxial growth or the like and a supporting substrate such as a Si substrate or sapphire substrate serving as the foundation. For example, when a nitride-based semiconductor layer is epitaxially grown on a silicon substrate and then the temperature of the reaction furnace is lowered to take it out of the reaction furnace, a large compressive stress acts on the support substrate, and a tensile stress acts on the epitaxial growth layer. As a result, cracks may occur in the epitaxial growth layer.

  Therefore, as shown in FIG. 4, a trapezoidal groove is formed on the upper surface of the silicon substrate using a silicon nitride (SiN) mask, and a semiconductor film (silicon oxide film) is selectively grown on the surface of the trapezoidal groove, thereby forming a semiconductor. After the AlN buffer layer is not formed on the film surface, the AlN buffer layer is selectively formed on the upper surface of the silicon substrate, and the GaN layer formed on the AlN buffer layer is formed so as to cover the trapezoidal groove. There have been proposals for suppressing warpage and cracking of an epitaxial growth substrate (see, for example, Patent Document 1). In the case of a sapphire substrate, a large tensile stress acts on the support substrate when the temperature is lowered after the nitride-based semiconductor layer is epitaxially grown on the support substrate. As a result, the warpage of the nitride-based compound semiconductor layer increases, and a crack is generated at the interface between the nitride-based compound semiconductor layer and the support substrate, which may propagate through the nitride-based compound semiconductor layer. Therefore, as shown in FIG. 5, after an AlN layer having a lower etching rate than the sapphire substrate is formed on the sapphire substrate in a dot shape, an etching solution having a higher solubility in the sapphire substrate than the AlN is formed using this AlN layer as a mask. When the mask is completely etched to form a multi-hard buffer layer, a hole is formed in the surface area of the sapphire substrate where the mask is not formed, and then the GaN layer is formed so as to cover the hole. Proposals have been made to suppress the occurrence of warpage and cracks in the substrate (for example, see Patent Document 2).

However, in the above-described method, it is necessary to perform a film formation (evaporation, sputtering, etc.) step, a photolithography step, an etching step, etc. in addition to the step of epitaxially growing GaN or the like on the support substrate. It will cause.
Japanese Patent Laid-Open No. 2002-11069 JP 2006-191074 A

  The present invention relates to an epitaxial growth substrate manufacturing method, a nitride-based compound semiconductor device manufacturing method, an epitaxial growth substrate, and a nitride-based manufacturing method capable of suppressing warpage and cracking of the epitaxial growth substrate and relatively shortening the manufacturing lead time. An object is to provide a compound semiconductor device.

According to one aspect of the present invention, the first nitridation has a thickness in which holes and hole spaces are closed by meltback etching on the upper surface of a silicon substrate that reacts with gallium to form holes in the surface and does not contain gallium. A step of forming a first layer made of a physical compound semiconductor, and a step of vapor phase epitaxially growing a layer made of a second nitride based compound semiconductor containing gallium on the support substrate on which the first layer is formed. The gist of the present invention is a method for manufacturing an epitaxial growth substrate.

According to another aspect of the present invention, the first surface of the silicon substrate , which reacts with gallium to form a hole in the surface, has a thickness in which a hole and a hole space are closed by meltback etching and does not contain gallium. Forming a first layer made of a nitride-based compound semiconductor; and vapor-phase epitaxially growing a second layer made of a nitride-based compound semiconductor containing gallium on the support substrate on which the first layer is formed. And a method of manufacturing a nitride-based compound semiconductor element including a step of forming an element formation region made of a nitride-based compound semiconductor on a support substrate via a second layer.

  According to the present invention, a method of manufacturing an epitaxial growth substrate, a method of manufacturing a nitride-based compound semiconductor device, a method of manufacturing a nitride compound semiconductor device, an epitaxial growth substrate, and a nitride A physical compound semiconductor device can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in light of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

(Embodiment)
An epitaxial growth substrate and a nitride compound semiconductor device manufacturing method according to an embodiment of the present invention will be described with reference to FIG.

(A) First, as shown in FIG. 1A, for example, a silicon (Si) substrate is used as a support substrate 10 made of a material that reacts with gallium (Ga) to generate a meltback and form holes in the surface. Can be adopted. When a Si substrate or the like is adopted as the support substrate 10, when the support substrate 10 reacts with gallium (Ga), an alloy is formed on the surface of the support substrate 10 and is strong enough to open a hole in the surface of the support substrate 10. An etching reaction (meltback etching) occurs.

Incidentally, the support substrate 10 has a thickness of 350 to 1000 μm, for example, and a lattice constant larger than the buffer layer 22 and the element formation region 30 (see FIGS. 2 and 3) (for example, 0.543 nm in the case of a silicon substrate). And having a linear expansion coefficient (for example, 4.70 × 10 ₋₆ / K) smaller than that of the buffer layer 22 (for example, 5.59 × 10 ₋₆ / K). Thus, the buffer layer 22 and the element formation region 30 have a function for epitaxial growth and a function as a mechanical support substrate.

(B) Next, after removing the oxide film on the surface of the support substrate, a plurality of buffer layer growth nuclei 20 are formed on the support substrate 10 as shown in FIG. The buffer layer growth nucleus 20 is a stage before the first layer 22a made of a nitride-based compound semiconductor described later is uniformly grown. Therefore, the support substrate 10 is exposed in the region of the support substrate 10 where the buffer layer growth nucleus 20 is not provided. The buffer layer growth nucleus 20 is a first nitride compound semiconductor having a lattice constant close to that of the support substrate 10 and smaller than that of GaN. As the first nitride compound semiconductor, a three-dimensionally grown crystal such as AlN is formed on the (111) plane of the support substrate 10. The temperature of the support substrate 10 is increased to 1000 to 1300 ° C. by a vapor phase epitaxial growth method such as a metal organic chemical vapor deposition (MOCVD) method so that the thin single crystal has a thickness of about 1 to 50 nm. Here, when the buffer layer growth nucleus 20 is polycrystalline, a reaction between Ga and the upper surface of the support substrate 10 provided with the buffer layer growth nucleus 20 is likely to occur, and the support substrate provided with the buffer layer growth nucleus 20 is provided. This is because the holes 12 are also easily formed on the upper surface of 10. In this step, the buffer layer growth nuclei 20 are also grown in a dot shape or further in the lateral direction from the dot shape, the mutual buffer layer growth nuclei 20 are connected, and the portion where the mutual buffer layer growth nuclei 20 are connected is the buffer. It may be formed thinner than other portions of the layer growth nucleus 20. In other words, the buffer layer growth nuclei 20 made of a nitride compound semiconductor formed in a dot shape are further crystal-grown, and the buffer layer growth nuclei 20 are joined to each other. It may be an initial layer (in particular, having pits on the upper surface where the buffer layer growth nuclei 20 are connected to each other).

(C) Next, as shown in FIG. 1C, trimethylgallium (TMG) containing Ga and having a methyl group or ethyl group containing Ga at a temperature of 800 ° C. or higher, for example, 1000 ° C. to 1300 ° C. Preflow is performed using triethylgallium (TEG) or the like and ammonia (NH ₃ ) having hydrogen (H ₂ ) or nitrogen (N ₂ ) as a carrier gas. Note that, if the temperature is raised too much, Ga does not react with the support substrate 10, so it is desirable that the temperature be 1300 degrees or less. In addition, AlN constituting the buffer layer growth nucleus 20 has a stronger binding energy than the Si substrate, and AlN hardly causes meltback on the surface of the Si substrate on which AlN is provided. Accordingly, as shown in FIG. 1 (d), the buffer substrate growth nucleus 20 is not provided, and the support substrate 10 reacts with Ga contained in trimethylgallium (TMG) at the place where the support substrate 10 is exposed. 10 is melt-back etched, and an anisotropic hole longer in the lateral direction than in the depth direction is formed on the surface of the support substrate 10 where the buffer layer growth nuclei 20 are not provided. A hole 12 is provided on the upper surface side of the plate 10. On the other hand, on the upper surface of the support substrate 10 provided with the buffer layer growth nuclei 20, meltback etching due to the reaction between the surface of the support substrate 10 and Ga is less likely to occur, and the upper surface of the support substrate 10 provided with the buffer layer growth nuclei 20 is provided. The hole 12 centering on this portion is not formed. Therefore, it is necessary to form the buffer layer growth nucleus 20 in contact with the portion of the upper surface of the support substrate 10 where the hole 12 is not desired to be formed to a thickness that does not cause meltback etching. The width of the hole 12 is about 1 to 100 nm, and the depth is about 1 to 100 nm. At this time, at least a part of the buffer layer growth nucleus 20 may react with Ga and the etched residue of the support substrate 10 to form a polycrystalline film containing the first nitride-based compound semiconductor. On the other hand, when the initial layer is formed in the step (b), the support substrate 10 reacts with Ga contained in trimethylgallium (TMG) at the place of the support substrate 10 where the initial layer is formed thin. An anisotropic hole that is longer in the lateral direction than the depth direction is formed on the surface of the support substrate 10 in which the meltback etching occurs and the initial layer is formed thin, for example, and the hole is formed on the upper surface side of the support substrate 10. 12 is provided. On the other hand, on the upper surface of the support substrate 10 in which the initial layer is formed thin, meltback etching due to the reaction between the surface of the support substrate 10 and Ga is less likely to occur, and the upper surface portion of the support substrate 10 in which the initial layer is formed thin is the center. The hole 12 is not formed. Therefore, the thickness of the initial layer in contact with the upper surface portion of the support substrate 10 where the holes 12 are not desired to be formed needs to be greater than the thickness at which meltback etching does not occur.

(D) Next, after removing only the multilayer film produced by meltback etching by injecting only hydrogen (H ₂ ), the temperature of the support substrate 10 is set to 1000 to 1300 ° C. as shown in FIG. The buffer layer growth nucleus 20 or the above-mentioned initial layer including the above-mentioned initial layer has a thickness enough to cover the hole 12 of the support substrate 10 by a vapor phase epitaxial growth method such as MOCVD, for example, about 10 to 500 nm. A first layer 22a made of, for example, AlN containing the same or the same constituent element as that of one nitride-based compound semiconductor is stacked. Therefore, the hole 12 provided in the support substrate 10 is closed by the first layer 22a.

(E) Next, as shown in FIG. 1F, for example, GaN is stacked on the first layer 22a as a second nitride compound semiconductor having a lattice constant different from that of the first nitride compound semiconductor. Thus, the second layer 22b is provided. Further, the first layer 22a is provided by laminating an AlN layer of the first nitride-based compound semiconductor on the second layer 22b. Thus, the multilayer buffer layer (buffer layer) 22 is formed by sequentially laminating the first layer 22a and the second layer 22b. The number of pairs of the first layer 22a and the second layer 22b in the multilayer buffer layer 22 can be determined as appropriate, but the crystallinity deteriorates even when the number of pairs is too small or too large. The number is preferably about 2 to 100. Further, when a plurality of the first layers 22a and the second layers 22b are formed, the first layer 22a and the second layer 22b are formed in order to suppress warping and cracks of the epitaxial growth layer on the support substrate 10. The thickness of each of the first layer 22a and the second layer 22b such that one or a plurality of the thicknesses of the first layer 22a and the second layer 22b are sequentially different from each other. May be appropriately changed according to the thickness of the buffer layer 22. Further, an impurity such as Si may be added to at least one of the first layer 22a and the second layer 22b in order to reduce the resistance value of at least one of the first layer 22a and the second layer 22b.

  By the above process, it is provided as an epitaxial growth substrate.

  Next, an element formation region 30 made of a nitride compound semiconductor, an electrode, and the like are appropriately formed on the buffer layer 22 in accordance with each application, and provided as a nitride compound semiconductor element.

  Even if the buffer layer 22 made of GaN or the like having a lattice constant and a linear expansion coefficient different from those of the support substrate 10 is provided on the support substrate 10 through the above steps, the holes 12 are provided at the interface between the support substrate 10 and the buffer layer 22. Therefore, warpage in the epitaxial growth layers such as the buffer layer 22 and the element formation region 30 becomes large when the temperature after the epitaxial growth of the buffer layer 22 and the like is reduced, and the occurrence of cracks in the epitaxial growth layer can be suppressed. In addition, since there is no need to perform a film formation (evaporation, sputtering, etc.) process, a photolithography process, an etching process, etc. other than the epitaxial growth process, the manufacturing lead time can be made relatively short. Furthermore, since the width of the hole 12 can be made smaller than that in the case of forming a general mask, the provision of the hole 12 can suppress abnormal defects and the like that occur during the buffer layer 22 forming process.

  Examples of nitride-based compound semiconductor devices using the epitaxial growth substrate manufactured by the above manufacturing method will be described below.

(First embodiment)
As shown in FIG. 2, in the first example of the nitride-based compound semiconductor device according to the embodiment of the present invention, the hole 12 is formed by the above-described melt-back etching with Ga, and the support substrate is made of Si. 10 and a first nitride-based compound semiconductor made of, for example, AlN, a first layer 22a provided on the support substrate 10 so as to close a lid in the hole of the support substrate 10, and a second nitride The physical compound semiconductor is made of, for example, GaN, and the second layer 22b formed on the first layer 22a and the first layer 22a and the second layer 22b are repeatedly formed thereon. The buffer layer 22 provided on the support substrate 10 and the second nitride-based compound semiconductor made of, for example, GaN, the channel layer 31 provided on the buffer layer 22, and the channel layer 31 are provided. The band gap energy is wider than that of the channel layer 31, a two-dimensional electron gas layer is formed in the vicinity of the interface with the channel layer 31, and a barrier layer 32 made of, for example, AlGaN as the third nitride compound semiconductor, This is a heterojunction field effect transistor (HFET) comprising a source electrode 40a, a gate electrode 40b, and a drain electrode 40c. Here, the element formation region 30 in the claims corresponds to the channel layer 31 and the barrier layer 32.

  According to the nitride compound semiconductor device formed by the method for manufacturing a nitride compound semiconductor device according to the embodiment of the present invention, the buffer layer 22 and the device formation region 30 are formed by forming the holes 12 in the support substrate 10. It is possible to suppress warping and cracks occurring in the epitaxial growth layer made of and to relieve stress. Thereby, the epitaxial growth layer can be formed thick, and a high quality epitaxial growth substrate can be obtained. Further, by obtaining a high-quality epitaxial growth substrate, it contributes to an increase in wafer diameter. By forming the epitaxial growth layer thick, the breakdown voltage in the vertical direction of the nitride-based compound semiconductor element can be improved.

  In addition, since the holes 12 are formed in the support substrate 10 during the epitaxial growth process, it is not necessary to perform a film formation (evaporation, sputtering, etc.) process, a photolithography process, an etching process, etc. Lead time can be shortened.

(Second embodiment)
As shown in FIG. 3, the second example of the nitride-based compound semiconductor device according to the embodiment of the present invention includes a support substrate 10 in which holes 12 are formed, and a buffer layer 22 provided on the support substrate 10. A first semiconductor layer 34 provided on the buffer layer 22, an active layer 36 provided on the first semiconductor layer 34, a second semiconductor layer 38 provided on the active layer 36, and a second semiconductor A second electrode 44 provided on the second semiconductor layer 38 in low resistance (ohmic) contact with the layer 38, and a first electrode 42 formed on the support substrate 10 in low resistance (ohmic) contact with the support substrate 10. It is a light emitting diode (LED) provided. Here, the first semiconductor layer 34 is, for example, a GaN P-type cladding layer to which a p-type dopant is added. The active layer 36 is, for example, non-doped indium gallium nitride (InGaN). The second semiconductor layer 38 is, for example, a GaN N-type cladding layer to which an n-type dopant is added. As shown in FIG. 3, a contact layer 50 sandwiched between the second semiconductor layer 38 and the second electrode 44 may be provided, or the first semiconductor layer may be provided from the support substrate 10 so as to short-circuit the buffer layer 22. The first electrode 42 may be provided so as to extend to 34. Here, the element formation region 30 in the claims corresponds to the first semiconductor layer 34, the active layer 36, and the second semiconductor layer 38.

  According to the nitride-based compound semiconductor element formed by the method for manufacturing a nitride-based compound semiconductor element according to the embodiment of the present invention, the holes 12 are formed in the support substrate 10, thereby warping or cracking the epitaxial growth substrate. Suppression and stress relaxation. Thereby, crystal defects in the active layer can be further reduced, and a high-quality and high-brightness nitride-based compound semiconductor element can be obtained. Further, by obtaining a high-quality epitaxial growth substrate, it is possible to contribute to an increase in the wafer diameter and increase the number of nitride-based compound semiconductor elements.

  In addition, by forming the holes 12 in the support substrate 10 during the epitaxial growth process, it is not necessary to perform a film formation (evaporation, sputtering, etc.) process, a photolithography process, an etching process, etc. Manufacturing lead time can be shortened.

  Further, the support substrate 10 made of Si absorbs light emitted from the active layer 36 (light having a wavelength of about 470 nm). Here, the refractive index of AlN is about 1.98, the refractive index of air is 1.0, and the refractive index of the support substrate 10 made of Si is about 4.5. In the second embodiment of the present invention, the hole 12 is provided between the first layer 22a and the support substrate 10, and the light emitted from the active layer 36 is the first layer (AlN) 22a / hole. In the case of reaching the interface of (air) 10 and in the case of reaching the interface of first layer (AlN) 22a / support substrate (Si) 10, the first layer 22a / hole 12 is the first. Reflection is more likely to occur than the interface of the layer 22a / support substrate 10. Therefore, light is refracted at the interface between the first layer 22a and the hole 12 and can be easily taken out of the nitride-based compound semiconductor device, and the luminous efficiency of the nitride-based compound semiconductor device can be increased.

(Other embodiments)
As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques should be apparent to those skilled in the art.

  For example, in the embodiments, the heterojunction field effect transistor and the semiconductor light emitting device are shown. However, the present invention is not limited to a structure in which a Schottky diode is formed on the element formation region 30 made of a nitride compound semiconductor having a heterojunction, Embodiments of the invention may be adapted.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

It is process sectional drawing for demonstrating the manufacturing method of the epitaxial growth board | substrate which concerns on embodiment of this invention. It is 1st Example of the nitride type compound semiconductor element by the manufacturing method of the nitride type compound semiconductor element which concerns on embodiment of this invention. It is 2nd Example of the nitride type compound semiconductor element by the manufacturing method of the nitride type compound semiconductor element which concerns on embodiment of this invention. It is a specific example (the 1) of the conventional epitaxial growth board | substrate which has a nitride type compound semiconductor layer. It is a specific example (the 2) of the conventional epitaxial growth board | substrate which has a nitride type compound semiconductor layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Support substrate 12 ... Hole 20 ... Buffer layer growth nucleus 22 ... Buffer layer 22a ... 1st layer 22b ... 2nd layer 30 ... Element formation area 31 ... Channel layer 32 ... Barrier layer 34 ... 1st semiconductor layer 36 ... Active layer 38 ... second semiconductor layer 40a ... source electrode 40b ... gate electrode 40c ... drain electrode 42 ... first electrode 44 ... second electrode 50 ... contact layer

Claims (4)

A first nitride-based compound semiconductor made of a first nitride-based compound semiconductor which has a hole closed by a melt-back etching and a space closed by the hole on the upper surface of a silicon substrate which reacts with gallium to form a hole in the surface and does not contain gallium. Forming a layer of
Vapor phase epitaxial growth of a layer made of a second nitride compound semiconductor containing gallium on the support substrate on which the first layer is formed. Forming the hole and the first layer comprises:
Disposing a buffer layer growth nucleus having a non-uniform thickness and comprising a first nitride-based compound semiconductor on the support substrate;
The method for producing an epitaxial growth substrate according to claim 1, further comprising: supplying a gas phase containing gallium to the support substrate on which the buffer layer growth nuclei are arranged.   3. The first layer according to claim 1, wherein a plurality of buffer layer growth nuclei made of the first nitride-based compound semiconductor are bonded to each other, and the first layer has a non-uniform thickness. Epitaxial growth substrate manufacturing method. A first nitride-based compound semiconductor comprising a hole formed by melt-back etching on a top surface of a silicon substrate that reacts with gallium to form a hole in the surface and a space in which the hole is closed and does not contain gallium. Forming a layer of
Vapor phase epitaxially growing a second layer made of a nitride compound semiconductor containing gallium on the support substrate on which the first layer is formed;
Forming a device forming region made of a nitride compound semiconductor on the support substrate through the second layer. A method for manufacturing a nitride compound semiconductor device, comprising:

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