JP2010180114A - METHOD FOR GROWING GaN-BASED COMPOUND SEMICONDUCTOR AND SUBSTRATE WITH GROWTH LAYER - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing a GaN-based compound semiconductor, by which a crystal growth layer can be easily separated from a sapphire substrate without causing damage to the crystal growth layer, and to provide a substrate with the growth layer. <P>SOLUTION: The method for growing a GaN-based compound semiconductor includes: a process for growing a column-like crystal layer 11 on a sapphire substrate 10; a process for growing a buffer layer 12 on the column-like crystal layer 11; and a process for growing a GaN-based compound crystal 13 on the buffer layer 12. After crystal growth, when the temperature is reduced, a large strain occurs in the interface between the sapphire substrate 10 and the ZrB<SB>2</SB>layer 11 in a nano-column state, and thereby, the crystal growth layer 18 is easily separated from the sapphire substrate 10. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for growing a GaN-based compound semiconductor and a substrate with a growth layer, and in particular, a crystal growth method capable of separating a GaN-based compound semiconductor crystal layer grown on a sapphire substrate from the substrate, and the substrate with a growth layer About.

  Gallium nitride compound semiconductors (hereinafter simply referred to as GaN compound semiconductors or GaN semiconductors) are direct transition semiconductors with large band gap energy, and are actively researched and developed as materials for optical devices in the blue or ultraviolet region. Has been made. Further, since it has various characteristics such as a high saturation drift speed and a large dielectric breakdown electric field, it can be widely applied to high-frequency devices and high-power devices.

  For crystal growth of a GaN-based compound semiconductor, sapphire is generally used as a substrate. For example, a GaN-based compound semiconductor is grown on a sapphire substrate, and the GaN-based crystal layer is peeled off from the substrate to produce a GaN substrate or a so-called thin-film type light emitting diode (LED). Has been done.

  For example, there is a method in which zinc oxide (ZnO) is grown as an intermediate layer on a sapphire substrate, a nitride semiconductor crystal layer is grown on the ZnO intermediate layer, and then the nitride semiconductor crystal layer is separated by etching the intermediate layer. (For example, patent document 1).

  Also, there is a method for producing a thin film LED by obtaining a GaN-based crystal layer by a laser lift-off (LLO) technique in which a GaN-based crystal grown on a sapphire substrate is irradiated with laser light from the sapphire side to separate the GaN-based crystal. It is shown (for example, patent document 2).

  In addition, a method is shown in which a GaN-based crystal is grown on a sapphire substrate using CrN as an intermediate layer, separated into a chip state, and then etched to obtain a GaN-based crystal to produce a thin film LED (for example, Non-Patent Document 1).

  However, the method of separating the semiconductor crystal growth layer by etching the intermediate layer has a problem that the removal of the semiconductor crystal growth layer takes a long time because the intermediate layer to be removed is thin and etching proceeds from the periphery of the wafer. .

  Further, an expensive laser device (an excimer laser device, a YAG laser device, etc.) is necessary to perform laser lift-off. Furthermore, when the crystal growth layer is peeled off from the sapphire substrate by laser lift-off technology, cracks in the crystal growth layer due to thermal damage to the crystal growth layer due to laser light and physical impact due to nitrogen gas generated during laser lift-off, etc. There was danger.

JP-A-7-202265 US Pat. No. 6,420,242

IEEE Photon. Technol. Lett. Vol.20, No.3, 175 (2008) JJAP (Japanese Journal of Applied Physics) vol.38, L492 (1999)

  The present invention has been made in view of the above points, and its purpose is to grow a GaN-based compound semiconductor that can easily separate a crystal growth layer from a sapphire substrate without damaging the crystal growth layer. It is to provide a method and a substrate with a growth layer. Also, the growth of GaN-based compound semiconductors that do not require expensive equipment such as laser lift-off technology and can easily separate the crystal growth layer from the substrate without causing thermal damage and cracking due to physical shock. It is to provide a method and a substrate with a growth layer.

The present invention relates to a method for crystal growth of a GaN-based compound semiconductor on a sapphire (Al ₂ O ₃ ) substrate, a step of growing a columnar crystal layer on the sapphire substrate, and a buffer layer on the columnar crystal layer And a step of growing a GaN-based compound crystal on the buffer layer.

  The step of growing the buffer layer includes a step of partially removing the columnar crystal layer and covering the removed region with a selective growth coating material, and a step of buffering the buffer layer on the non-removed region of the columnar crystal layer. The step of growing the GaN-based compound crystal may include a lateral growth step of growing the GaN-based compound crystal by lateral growth (ELO).

  The substrate with a crystal growth layer of the present invention includes a columnar crystal layer formed on a sapphire substrate, a buffer layer grown on the columnar crystal layer by MOCVD, and a GaN-based layer grown on the buffer layer. And a compound crystal layer.

  More preferably, the buffer layer is formed so as to be in an island-like growth state or a network-like growth state.

The columnar crystal layer may be a hexagonal crystal layer, and is particularly characterized by being a zirconium diboride (ZrB ₂ ) crystal layer. The thickness of the columnar crystal layer is preferably in the range of 50 nm to 500 nm.

  Further, the buffer layer may be a low temperature grown nitride crystal layer, particularly a low temperature grown aluminum nitride (AlN) crystal layer.

2 is a cross-sectional view schematically showing a crystal growth step of Example 1. FIG. ZrB a ₂ shoot growth top the scanning electron microscope (SEM) images. The state of separation at the interface of the sapphire substrate and ZrB ₂ layers is a cross-sectional view schematically showing. It is a graph which shows the EDX analysis result of the surface of the sapphire substrate after isolate | separating a crystal growth layer from a board | substrate. 6 is a cross-sectional view schematically showing a crystal growth step that is Embodiment 2. FIG. 6 is a cross-sectional view schematically showing a crystal growth step that is Embodiment 2. FIG. It is a top view after lift-off (FIG. 6, STEP15) and shows the patterning shape of the ZrB ₂ crystal layer. It is sectional drawing which shows the case where an element operation | movement layer is formed on a buffer layer.

Hereinafter, a method for crystal growth of a GaN-based compound semiconductor layer on a sapphire (Al ₂ O ₃ ) substrate by MOCVD (Metal Organic Chemical Vapor Deposition) method will be described. A case where gallium nitride (GaN) is grown as an example of a GaN-based compound semiconductor will be described in detail with reference to the drawings.

  In the drawings described below, substantially the same or equivalent components or parts are denoted by the same reference numerals.

First, an Al ₂ O ₃ single crystal sapphire substrate having a corundum structure was used as the substrate 10. In this example, crystal growth was performed on the sapphire C surface using the sapphire C surface ({0001} surface) as a crystal growth surface. Hereinafter, a substrate having a sapphire C plane ({0001} plane) as a main surface (crystal growth plane) is also referred to as a C-plane sapphire substrate. Here, the Miller index {} indicates a representative value of an equivalent surface.

FIG. 1 is a cross-sectional view schematically showing a crystal growth process in the first embodiment. As shown in FIG. 1, a GaN crystal was grown on a sapphire substrate 10 with zirconium diboride (ZrB ₂ ) as an intermediate layer.

First, crystal growth of zirconium diboride (ZrB ₂ ) was performed on the sapphire substrate 10 by MOCVD. ZrB ₂ has a hexagonal crystal structure. More specifically, zirconium borohalide (Zr (BH ₄ ) ₄ ) is used as a raw material, the {0001} plane of the sapphire substrate is the main plane (crystal growth plane), the growth temperature is 1190 ° C., and the growth pressure is 40 Torr. It was grown ZrB ₂ crystal nano column shape (Fig. 1, STEP1). Further, hydrogen (H ₂ ) gas was used as the carrier gas and the atmospheric gas. The raw material supply amount was 2.4 μmol / min, and the growth rate was 2 nm / min. The thickness of the nanocolumn-shaped ZrB ₂ crystal (nanocolumn crystal) layer 11 (the height of the ZrB ₂ nanocolumn crystal) was about 50 nm, but is not limited thereto. The thickness of the ZrB ₂ crystal is preferably 50 nm to 500 nm.

  Next, a low temperature growth (LT-AlN) buffer layer 12 of aluminum nitride (AlN) was formed by MOCVD (hereinafter simply referred to as AlN low temperature buffer layer 12).

  In this specification, the low temperature growth is generally a temperature lower than a growth temperature (“high growth temperature”) for growing a nitride crystal (GaAlInN-based crystal) by MOCVD. It is called “temperature”). Specifically, the growth temperature (low growth temperature) of the AlN low-temperature buffer layer is preferably in the range of 400 ° C to 600 ° C.

More specifically, the AlN low-temperature buffer layer 12 was grown at a growth temperature of 600 ° C. and a growth pressure of 760 Torr (FIG. 1, STEP 2). The layer thickness of the AlN low-temperature buffer layer 12 was 100 nm. As raw materials, trimethylaluminum (TMA) was supplied at a flow rate of 22.4 μmol / min and ammonia (NH ₃ ) at a flow rate of 6,120 μmol / min. At this time, the V / III ratio was 2,735. The layer thickness of the AlN low-temperature buffer layer 12 is not particularly limited, but it is preferable that the AlN low-temperature buffer layer 12 is not grown so as to cover the entire surface of the ZrB ₂ crystal layer 11 as will be described later.

More specifically, as the growth process of the AlN crystal, the growth region is expanded from the island-like growth state, and the whole area of the ZrB ₂ crystal layer 11 is passed through the state where the island-like growth portions are connected (network growth state). In the present invention, the AlN low-temperature buffer layer 12 is formed so as to be in an island-like growth state or a network-like growth state before covering the entire surface of the ZrB ₂ crystal layer 11. Is preferred. Hereinafter, the growth state (island growth and network growth) before the AlN crystal covers the entire surface of the ZrB ₂ crystal layer 11 is also collectively referred to as an island growth state.

  In this example, the growth was performed so that the AlN low-temperature buffer layer 12 was in an island-like growth state (including a network-like growth state). That is, the AlN low-temperature buffer layer 12 was grown so as to have an opening (opening) 12A.

After the growth of the AlN low-temperature buffer layer 12, crystal growth of the GaN crystal layer 13 was performed using trimethyl gallium (TMG) and ammonia (NH ₃ ) as raw materials (FIG. 1, STEP 3). The growth temperature was 1100 ° C., the growth pressure was 80 Torr, the TMG supply rate was 44.7 μmol / min, and the NH ₃ supply rate was 6,120 μmol / min. The growth time was about 20 min, and the growth layer thickness after growth was 1.7 μm. At this time, the growth rate was 5 μm / min, and the V / III ratio was 1,370.

After the growth under such growth conditions, a GaN crystal was grown under growth conditions that further promote the lateral growth (ELO: epiaxial lateral overgrowth). For example, the growth temperature is 1150 ° C., the growth pressure is 90 Torr, the TMG supply rate is 134 μmol / min, the NH ₃ supply rate is 101560 μmol / min, the growth layer thickness is 10 μm, the growth rate is 15 μm / min, and the V / III ratio is 758. The GaN crystal layer 13 was formed by performing growth under such lateral growth promotion conditions (FIG. 1, STEP 3). In addition, after the growth of the AlN low-temperature buffer layer 12, the growth conditions were changed (in two stages) to grow the GaN crystal layer. However, after the growth of the AlN low-temperature buffer layer 12, the lateral growth (ELO) is performed. The GaN crystal layer may be grown under the above-described growth condition that promotes further.

FIG. 2 is an SEM image obtained by taking out the substrate with the growth layer after the ZrB ₂ growth from the MOCVD apparatus and photographing the upper surface of the ZrB ₂ growth with a scanning electron microscope (SEM). It can be seen that on the {0001} plane of the sapphire substrate 10, a ZrB ₂ crystal having a c-axis orientation is grown in a column shape (columnar shape), and a gap is formed between the columnar crystals. It can also be seen that columnar crystals having a hexagonal cross section are formed reflecting the C-plane crystal structure of the ZrB ₂ crystal. The outer diameter of the columnar crystal was about 50 nm to 100 nm. A gap 15 is formed between the columnar crystals.

In the above, ZrB ₂ takes out the grown layer-provided substrate from the MOCVD apparatus after growth has been described a case where the growth of the AlN low temperature buffer layer 12 and the GaN crystal layer 13 in the MOCVD apparatus after SEM observation. However, without removing the growth layer with the substrate from the MOCVD apparatus after the growth of the ZrB ₂ layer 11 may be grown AlN low temperature buffer layer 12 and the GaN crystal layer 13 in succession to the growth of the ZrB ₂ layers 11. Alternatively, a low temperature buffer layer 12 and a GaN crystal layer 13 may be grown by MOCVD using a wafer in which the columnar crystal layer 11 is formed on the sapphire substrate 10 by a method other than the MOCVD method.

In the substrate with a crystal growth layer (wafer) on which the columnar ZrB ₂ layer 11, the low-temperature buffer layer 12 and the GaN crystal layer 13 (hereinafter referred to collectively as the crystal growth layer 18) are grown. The crystal growth layer 18 can be separated (peeled) from the sapphire substrate 10 very easily. This point will be described in detail below.

The lattice constants in the a-axis direction of sapphire, ZrB ₂ , and GaN are 0.275 nm, 0.317 nm, and 0.320 nm, respectively. That is, the lattice constants of ZrB ₂ and GaN are very close, but there is a large difference between sapphire and ZrB ₂ . The thermal expansion coefficients of sapphire, ZrB ₂ , and GaN are 7.5E-6 / K, 5.9E-6 / K, and 5.6E-6 / K, respectively (where “E-6” is × 10 ^-6 ), like the lattice constant, the thermal expansion coefficients of ZrB ₂ and GaN are very close, but there is a large difference between sapphire and ZrB ₂ . For this reason, a large strain (stress) occurs at the interface between the sapphire substrate 10 and the ZrB ₂ layer 11 due to the temperature drop after crystal growth. On the other hand, the strain at the interface between the ZrB ₂ layer 11 and the crystal growth layer 18 (that is, the low-temperature buffer layer 12 and the GaN crystal layer 13) is small. Further, the ZrB ₂ layer 11 as the intermediate layer is in a nanocolumn state and mechanically weak. Therefore, when the temperature is lowered after the crystal growth, a large strain is generated at the interface between the sapphire substrate 10 and the nanocolumn ZrB ₂ layer 11, so that the crystal growth layer 18 is easily separated from the sapphire substrate 10.

More specifically, as schematically shown in FIG. 3, for large strain at the interface between the sapphire substrate 10 and ZrB ₂ layers 11, easily separated at the interface between the sapphire substrate 10 and the ZrB ₂ layer 11 ( In the figure, the arrows indicate the separation of the sapphire substrate 10 and the crystal growth layer 18). In FIG. 3, the interfaces on the sapphire substrate 10 side after separation are schematically shown as S1A and S2A, and the corresponding interfaces on the ZrB ₂ layer 11 side are shown as S1B and S2B, respectively.

Furthermore, since the AlN low-temperature buffer layer 12 is grown so as to be in an island-like growth state (including a network growth state) having an opening 12A, the crystal growth layer 18 can be easily separated from the sapphire substrate 10. Can do. More specifically, in the growth of the GaN crystal layer 13, the AlN low-temperature buffer layer 12 is covered by the lateral growth of the GaN crystal with the AlN crystal layer as a nucleus. However, the GaN crystal is not directly grown on the ZrB ₂ layer 11 in the portion where there is no AlN crystal layer on the ZrB ₂ layer 11, that is, in the opening 12A of the AlN low-temperature buffer layer 12. Therefore, the crystal growth layer 18 can be easily separated from the sapphire substrate 10 between the ZrB ₂ layer 11 and the GaN crystal layer 13 in the opening 12A. In FIG. 3, the interfaces on the sapphire substrate 10 side after separation (namely, the upper surface of the ZrB ₂ layer) are E1A, E2A, and E3A, and the corresponding interfaces on the GaN crystal layer 13 side (namely, GaN crystal layers). The lower surface is schematically shown as E1B, E2B, and E3B, respectively.

The surface of the sapphire substrate 10 after separating the crystal growth layer 18 from the sapphire substrate 10 was analyzed by an energy dispersive X-ray analyzer (EDX). FIG. 4 is a graph showing the EDX analysis results. In the EDX analysis, Zr was detected from the surface of the sapphire substrate 10 in addition to the substrate composition Al and O, although the strength was weak. Therefore, as described above, it was verified that the ZrB ₂ layer 11 and the GaN crystal layer 13 were easily separated in the opening 12A, and the columnar ZrB ₂ layer remained on the sapphire substrate 10 side.

As described above, the crystal growth layer 18 can be separated (peeled) from the sapphire substrate 10 very easily. For example, the crystal growth layer 18 is separated from the sapphire substrate 10 due to a large strain generated at the interface between the sapphire substrate 10 and the nanocolumnar ZrB ₂ layer 11 due to the temperature drop after crystal growth. As described above, even when the temperature is not separated only by the temperature drop after the crystal growth, the crystal growth layer 18 is easily separated from the sapphire substrate 10 by applying a slight force from the outside to the sapphire substrate 10 (growth wafer) on which the crystal is grown. (Peeling). For example, the crystal growth layer 18 can be separated from the sapphire substrate by giving a light impact to the sapphire substrate 10. Further, the crystal growth layer 18 can be easily separated by applying vibration to the growth wafer using ultrasonic waves or the like. Alternatively, separation may be performed using an LLO (laser lift-off) method. In this case, it can be separated by laser irradiation with a lower energy density than the prior art, and damage to the crystal growth layer 18 can be reduced. Thus, the crystal growth layer 18 can be easily separated from the sapphire substrate 10 without damaging the crystal growth layer 18.

ZrB ₂ is easily dissolved by a mixed solution of hydrofluoric acid and nitric acid. Therefore, a process of etching the ZrB ₂ layer may be applied to make separation easier. Further, ZrB ₂ intermediate layer is nanocolumns state, easily etchant permeates may be short etching. Moreover, there is little damage to a sapphire substrate.

As described above, according to the present invention, the crystal growth layer can be easily separated from the sapphire substrate without damaging the crystal growth layer. Further, by applying chemical etching, the crystal growth layer can be more reliably and easily separated from the substrate. For this reason, it is not necessary to immerse in etching liquid for a long time. Furthermore, since the ZrB ₂ intermediate layer is in the nanocolumn state, distortion is reduced as compared with the case where the GaN-based crystal layer is directly grown on the sapphire substrate, so that the warpage of the wafer can be reduced.

In this embodiment, the case where the AlN low-temperature buffer layer 12 is grown so as to be in an island-like growth state (including a network-like growth state) has been described. However, as AlN low temperature buffer layer 12 covers the entire surface of the ZrB ₂ crystal layer 11, i.e., it may be performed grown so as not to have an opening 12A. Even in this case, the crystal growth layer 18 is easily separated from the sapphire substrate 10 due to a large strain generated at the interface between the sapphire substrate 10 and the nanocolumn-shaped ZrB ₂ layer 11.

5 and 6 are cross-sectional views schematically showing a crystal growth step that is Embodiment 2. FIG. In the first embodiment described above, and grown as an intermediate layer of two zirconium boride (ZrB ₂₎ on the sapphire substrate 10 has been described for the case of growing AlN low temperature buffer layer and GaN layer ZrB ₂ intermediate layer. In this embodiment, a case where an AlN low-temperature buffer layer and a GaN layer are selectively grown after growing a ZrB ₂ intermediate layer on the sapphire substrate 10 will be described.

First, the ZrB ₂ layer 11 is grown by MOCVD using the C plane ({0001} plane) of the sapphire substrate 10 as the main plane (crystal growth plane) (FIG. 5, STEP11). Zr (BH ₄ ) ₄ is used as a raw material, a growth temperature is 1190 ° C., a growth pressure is 40 Torr, and a ZrB ₂ crystal is grown in a nanocolumn shape. Further, hydrogen (H ₂ ) gas is used as the carrier gas and the atmospheric gas, and for example, the raw material supply rate is 2.4 μmol / min and the growth rate is 2 nm / min. The thickness of the nanocolumn-shaped ZrB ₂ crystal (nanocolumn crystal) layer 11 is, for example, about 100 nm, but is not limited thereto. The thickness of the ZrB ₂ crystal is preferably 50 nm to 500 nm.

Next, a resist pattern is formed by a general photolithography method. Specifically, for example, a photoresist (thickness 2 μm) 21 is formed on the nanocolumn-shaped ZrB ₂ crystal layer 11 and patterned, for example, in a lattice shape (FIG. 5, STEP 12). The patterning shape and the like will be described later. Using the resist 21 as a mask, the ZrB ₂ crystal layer 11 is etched and removed (FIG. 5, STEP 13). The ZrB ₂ crystal layer 11 can be etched with a nitric acid-hydrofluoric acid etchant. For example, a mixed solution of hydrofluoric acid (HF): nitric acid (HNO ₃ ): water (H ₂ O) = 1: 2: 1 can be used as an etchant.

Next, SiO ₂ is deposited by an electron beam (EB) deposition method or the like to form a film so that the thickness of the SiO ₂ layer 22 is about 100 nm (FIG. 5, STEP 14).

Next, by using the lift-off method, the SiO ₂ layer 22 remains in the portion where the ZrB ₂ layer 11 is removed on the sapphire substrate 10 (FIG. 6, STEP 15). That is, by removing the resist 21, the SiO ₂ layer 22 on the resist 21 is removed.

FIG. 7 shows a top view after lift-off (FIG. 6, STEP 15). By the patterning process, the ZrB ₂ crystal layer 11 is patterned in a lattice shape, for example. More specifically, ZrB ₂ crystal layer 11 in the crystal growth surface (c plane), for example, a-axis direction ([2-1-10] direction) and the m-axis direction orthogonal thereto ([01-10] (Direction) is removed in a lattice shape composed of stripes parallel to each other. The width of the ZrB ₂ crystal layer 11 to be removed is, for example, several μm to 20 μm in the m-axis direction (width S1) and the a-axis direction (width S2), respectively. The length of one side of the rectangular ZrB ₂ crystal layer 11 left without being removed is in the m-axis direction (length Z1) and a-axis direction (length Z2), for example, about 200 to 300 μm, respectively. It is.

  Next, an AlN low temperature buffer layer 23 was grown. More specifically, the AlN low-temperature buffer layer 23 is grown at a growth temperature of 600 ° C. and a growth pressure of 760 Torr (FIG. 6, STEP 16). The layer thickness of the AlN low-temperature buffer layer 23 is 100 nm. As in the case of Example 1, the AlN low-temperature buffer layer 23 is preferably formed so as to be in an island-like growth state or a network-like growth state. The raw materials and their flow rates are the same as in the first embodiment.

After the growth of the AlN low-temperature buffer layer 23, the GaN crystal layer 24 is grown (FIG. 6, STEP 17). Using TMG and NH ₃ , the growth temperature is 1100 ° C., the growth pressure is 80 Torr, the supply amount of TMG is 44.7 μmol / min, and the supply amount of NH ₃ is 6,120 μmol / min. The growth layer thickness is 1.7 μm, the growth rate is 5 μm / min, and the V / III ratio is 1,370.

After the GaN crystal layer 24 is selectively grown, the GaN crystal is grown under growth conditions that further promote lateral growth (ELO: epiaxial lateral overgrowth). For example, the growth temperature is 1150 ° C., the growth pressure is 90 Torr, the TMG supply rate is 134 μmol / min, the NH ₃ supply rate is 101560 μmol / min, the growth layer thickness is 10 μm, the growth rate is 15 μm / min, and the V / III ratio is 758. A GaN crystal layer 25 is formed by growth under such lateral growth promoting conditions (FIG. 6, STEP18). Therefore, the width of the SiO ₂ layer 22 on the sapphire substrate 10 in the patterning process, that is, the width of the ZrB ₂ crystal layer 11 to be removed may be set so as to be buried by lateral growth of GaN. The patterning direction is not limited to the m-axis direction or the a-axis direction, and may be appropriately selected according to the growth conditions of the GaN crystal that is the buried layer. The shape of the ZrB ₂ crystal layer 11 to be left without being removed even not limited to the rectangular shape. In short, the columnar ZrB ₂ crystal layer 11 is partially removed, and the removed region is covered with a selective growth coating material made of, for example, SiO ₂ , and then on the non-removed region of the columnar ZrB ₂ crystal layer 11. In addition, the buffer layer may be selectively grown.

In the GaN crystal growth described above, no GaN crystal grows on the SiO ₂ layer 22, but the GaN crystal grown on the ZrB ₂ crystal layer 11 grows in the lateral direction so as to cover the top of the SiO ₂ layer 22. A GaN crystal is formed. Then, the substrate side of the SiO ₂ layer 22 and the GaN crystal layer 25 by a gap 27 formed between the SiO ₂ layer 22 and the GaN crystal layer 25 of the upper are separated.

Furthermore, as in the case of Example 1, due to the temperature drop after crystal growth, a large strain is generated at the interface between the sapphire substrate 10 and each of the ZrB ₂ crystal layers 11 that are patterned rectangular nanocolumn crystal layers. As a result, the crystal growth layer 18 is easily separated from the sapphire substrate 10.

Therefore, according to the present embodiment, the crystal growth layer 28 is easily separated from the sapphire substrate 10 due to a large strain generated at the interface with the ZrB ₂ crystal layer 11, and the SiO ₂ layer 22 is further formed. It is easy to separate the sapphire substrate 10 and the GaN crystal layer 25 in the existing region. Therefore, compared with the case of Example 1, it is easier to separate the sapphire substrate 10 and the crystal growth layer 28 on the substrate. Further, by applying chemical etching, it becomes more reliable and easy to separate the crystal growth layer from the substrate.

As described above, according to the present invention, the crystal growth layer can be easily separated from the sapphire substrate without damaging the crystal growth layer. Further, by applying chemical etching, the crystal growth layer can be more reliably and easily separated from the substrate. For this reason, it is not necessary to immerse in etching liquid for a long time. Furthermore, since the ZrB ₂ intermediate layer is in the nanocolumn state, distortion is reduced as compared with the case where the GaN-based crystal layer is directly grown on the sapphire substrate, so that the warpage of the wafer can be reduced.

  In the first and second embodiments described above, the case where the GaN-based crystal layers 13, 24, and 25 are grown on the buffer layers 12 and 23 has been described. However, a crystal layer is further grown on the GaN-based crystal layer. May be. For example, a light emitting layer (active layer), an LED light emitting operation layer, a cladding layer in a semiconductor laser element, or an element operation layer such as an electronic device can be grown on the GaN-based crystal layers 13, 24, and 25. Alternatively, the GaN-based crystal layers 13, 24, and 25 grown under the above growth conditions may be grown as part of the LED light emitting operation layer, the cladding layer, and the element operation layer.

  Here, in this specification, an operation layer or an element operation layer refers to a layer composed of a semiconductor to be included in order for a semiconductor element to perform its function. For example, a simple transistor includes a structural layer formed by a pn junction of an n-type semiconductor, a p-type semiconductor, and an n-type semiconductor (or a p-type semiconductor, an n-type semiconductor, and a p-type semiconductor). Note that a semiconductor layer that includes a p-type semiconductor layer, a light-emitting layer, and an n-type semiconductor layer (or a p-type semiconductor layer and an n-type semiconductor layer) and emits light by recombination of injected carriers, particularly, emits light. This is called the operation layer.

  For example, as shown in FIG. 8, an n-type GaN-based cladding layer 31, a light emitting layer 32, and a p-type cladding layer 33 are sequentially grown on the buffer layer 12 in Example 1 and FIG. An operation layer (light emitting operation layer) 30 may be formed. Note that the crystal layer grown on the buffer layer 12 may be a GaN-based crystal layer, and the crystal layer grown on the GaN-based crystal layer is not limited to the GaN-based crystal layer, and aluminum containing no Ga (Al). And a nitride-based semiconductor crystal layer made of indium (In) or the like. Further, although the case where the element operation layer 30 is a light emitting operation layer has been described as an example, it is needless to say that the element operation layer 30 may be an element operation layer such as an electronic device. Further, the element operation layer 30 similar to that described above may be grown on the buffer layer 23 (FIG. 6) in the second embodiment.

  Then, after such an element operation layer 30 is grown, the crystal growth layer 18 including the element operation layer 30 can be separated from the sapphire substrate 10 and removed. Thus, after separating the crystal growth layer 18 including the element operation layer 30 from the substrate, electrodes can be formed and diced to form an electronic device, a light emitting element such as an LED or a semiconductor laser. In this case, by providing a support (UV peeling tape or the like) on the crystal growth layer side before separation from the sapphire substrate 10, handling in the steps of electrode formation and dicing (including dicing street formation by dry etching, etc.) is performed. Can be easily and reliably performed.

  The crystal growth layer separated and removed from the sapphire substrate can be used as a substrate for further growing the crystal layer.

Note that ZrB ₂ remaining in the crystal growth layer after separating and peeling the crystal growth layer from the sapphire substrate can be removed by etching, polishing, or the like.

  In the above-described embodiments, the case where the GaN crystal is grown on the sapphire substrate via the buffer layer has been described. However, the present invention is not limited to this. The present invention is not limited to the GaN crystal, and can be similarly applied to the case of growing a GaN-based compound semiconductor containing aluminum (Al), indium (In), etc. in addition to Ga. The composition of the buffer layer is not limited to AlN, and may be a III-V group compound semiconductor buffer layer containing Ga or In.

Moreover, although the case where a ZrB ₂ crystal is used as the columnar crystal has been described, this is merely an example. Other diboride (TiB ₂ ) may be used.

  Furthermore, in the above-described embodiments, the case where the crystal growth is performed by the MOCVD method has been described as an example, but other crystal growth methods such as a hydride VPE (H-VPE: Hydride Vapor Phase Epitaxy) method can also be applied. . For example, the H-VPE method may be applied to the growth of GaN crystals.

DESCRIPTION OF SYMBOLS 10 Sapphire substrate 11 Columnar crystal layer 12A Opening 12 Buffer layer 13 GaN crystal layer 18 Crystal growth layer 22 SiO ₂ layer 23 Low temperature buffer layer 24 GaN crystal layer 25 GaN crystal layer 27 Gap 28 Crystal growth layer 30 Element operation layer

Claims (15)

A sapphire (Al ₂ O ₃₎ a method of crystal growing a GaN-based compound semiconductor on a substrate,
Growing a columnar crystal layer on the sapphire substrate;
Growing a buffer layer on the columnar crystal layer;
And growing a GaN-based compound crystal on the buffer layer.   The method of claim 1, wherein the buffer layer is formed to have an island-like growth state or a mesh-like growth state.   The method according to claim 1, wherein the columnar crystal layer is a hexagonal crystal layer. The method according to claim 1, wherein the hexagonal crystal layer is a zirconium diboride (ZrB ₂ ) crystal layer.   The method of claim 1, wherein the buffer layer is an aluminum nitride (AlN) based crystal layer.   The method according to claim 1, wherein the crystal growth surface of the sapphire substrate is a {0001} plane. The step of growing the buffer layer includes a step of partially removing the columnar crystal layer and covering the removed region with a selective growth coating material, and a buffer layer on the non-removed region of the columnar crystal layer. And a selective growth process for growing,
The method according to claim 1, wherein the step of growing the GaN-based compound crystal includes a lateral growth step of growing the GaN-based compound crystal by lateral growth (ELO). A columnar crystal layer formed on a sapphire substrate;
A buffer layer grown by MOCVD on the columnar crystal layer;
A substrate with a crystal growth layer, comprising: a GaN-based compound crystal layer grown on the buffer layer.   9. The substrate with a crystal growth layer according to claim 8, wherein the buffer layer is formed so as to be in an island-like growth state or a network-like growth state.   9. The substrate with a crystal growth layer according to claim 8, wherein the columnar crystal layer is a hexagonal crystal layer. 11. The substrate with a crystal growth layer according to claim 8, wherein the hexagonal crystal layer is a zirconium diboride (ZrB ₂ ) crystal layer.   9. The substrate with a crystal growth layer according to claim 8, wherein the buffer layer is an aluminum nitride (AlN) based crystal layer. A method for producing a GaN-based compound crystal growth layer,
Growing a columnar crystal layer on the sapphire substrate;
Growing a buffer layer on the columnar crystal layer;
Growing a GaN-based compound crystal on the buffer layer;
And a step of removing the sapphire substrate after the step of growing the GaN-based compound crystal layer.   The manufacturing method according to claim 14, wherein the buffer layer is an island-like growth or a network-like growth buffer layer.   The step of growing the GaN-based compound crystal layer includes a step of growing a GaN-based crystal and growing an element operation layer made of a nitride crystal layer on the GaN-based crystal. Manufacturing method.