JP2017218347A - Method for manufacturing free-standing substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a free-standing substrate, capable of easily peeling from a base substrate by a simple process and manufacturing a group III nitride semiconductor free-standing substrate having comparatively excellent crystallinity at a low cost.SOLUTION: The method for manufacturing a free-standing substrate, capable of manufacturing the free-standing substrate consisting of a group III nitride semiconductor comprises: epitaxially growing a low-temperature buffer layer consisting of a group III nitride semiconductor layer at a growth temperature of 400-600°C with a thickness of 80-1000 nm on a substrate; epitaxially growing a group III nitride semiconductor layer at a temperature higher than the growth temperature of the low-temperature buffer layer on the grown low-temperature buffer layer; and manufacturing the free-standing substrate consisting of a group III nitride semiconductor grown at the high temperature by peeling the group III nitride semiconductor layer grown at the high temperature from the substrate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a free-standing substrate.

  Nitride semiconductor materials have a sufficiently large forbidden band width and a direct transition type between band transitions. Therefore, application to a short wavelength light emitting element has been actively studied. In addition, application to electronic devices is also expected due to the high saturation drift velocity of electrons and the use of two-dimensional carrier gas by heterojunction.

  Nitride semiconductor layers constituting these elements are formed by metal-organic vapor phase epitaxy (MOVPE), molecular beam vapor phase epitaxy (MBE), hydride vapor phase epitaxy (HVPE). : Hydride Vapor Phase Epitaxy) or other vapor phase growth method is used to perform epitaxial growth on the base substrate.

  However, since there is no underlying substrate having a lattice constant matching with this nitride semiconductor layer, it is difficult to obtain a high-quality growth layer, and the obtained nitride semiconductor layer contains many crystal defects. . Since this crystal defect becomes a factor that hinders improvement in device characteristics, so far, studies have been actively conducted to reduce the crystal defect in the nitride semiconductor layer.

  As a method for obtaining a group III element nitride-based crystal with relatively few crystal defects, a method of forming a low temperature deposition buffer layer (buffer layer) on a dissimilar substrate such as sapphire and forming an epitaxial growth layer thereon is known. It has been. In the crystal growth method using this low-temperature deposition buffer layer, first, AlN or GaN is deposited on a substrate such as sapphire at around 500 ° C. to form an amorphous film or a continuous film partially including polycrystal. This is heated to around 1000 ° C. to partially evaporate and crystallize to form high-density crystal nuclei. Using this as a growth nucleus, a GaN film with relatively good crystallinity can be obtained.

  However, even when a method for forming a low temperature deposition buffer layer is used, crystal defects such as threading dislocations and vacancies exist, and it is insufficient to obtain a high performance device as currently desired.

  For example, Patent Document 1 proposes that after forming a GaN layer with few dislocations on a sapphire substrate using ELO technology, the sapphire substrate is removed by etching or the like to obtain a GaN free-standing substrate.

  As another technique, Patent Document 2 discloses a technique for obtaining a GaN free-standing substrate using a gap. In this method, after forming a GaN layer on a sapphire C-plane ((0001) plane) substrate, a titanium film is formed thereon. Next, the substrate is heat-treated in an atmosphere containing hydrogen gas or a hydrogen-containing compound gas to form voids in the GaN layer. Thereafter, by forming a new thick GaN layer on the GaN layer, a high-quality GaN free-standing substrate with less warpage can be obtained.

JP-A-11-251253 JP 2003-178984 A

  With the prior art as described above, a free-standing substrate of a group III nitride semiconductor such as GaN having good crystallinity has been obtained. However, a dissimilar substrate such as sapphire can be removed and peeled off, a metal film or a pattern can be formed Therefore, there is a problem in that the manufacturing process becomes high. Therefore, at present, a free-standing substrate of a group III nitride semiconductor, for example, a free-standing substrate of GaN, is used for a GaN-based semiconductor laser diode or the like, and is used only for a device with particularly high added value.

  The present invention has been made in view of the above-mentioned problems, and can be easily peeled off from a base substrate by a simple process, and a group III nitride semiconductor free-standing substrate having relatively good crystallinity is manufactured at low cost. An object of the present invention is to provide a method for manufacturing a free-standing substrate.

  In order to achieve the above object, the present invention provides a self-supporting substrate manufacturing method for manufacturing a self-supporting substrate made of a group III nitride semiconductor, and a group III nitride semiconductor layer at a growth temperature of 400 to 600 ° C. on the substrate. And epitaxially growing a group III nitride semiconductor layer on the grown low-temperature buffer layer at a temperature higher than the growth temperature of the low-temperature buffer layer, after epitaxially growing the low-temperature buffer layer comprising 80 to 1000 nm in thickness, Providing a self-standing substrate manufacturing method characterized by manufacturing a self-standing substrate made of a group III nitride semiconductor grown at a high temperature by peeling the group III nitride semiconductor layer grown at the high temperature from the substrate. To do.

  Thus, by epitaxially growing the low-temperature buffer layer with a thickness of 80 nm or more, the group III nitride semiconductor layer grown at a high temperature can be easily peeled off from the substrate. Further, the epitaxial growth of the low temperature buffer layer with a thickness of 1000 nm or less can prevent the growth time of the low temperature buffer layer from becoming longer than necessary. As a result, peeling from the base substrate can be facilitated by a simple process, and a group III nitride semiconductor free-standing substrate having relatively good crystallinity can be manufactured at low cost.

  At this time, it is preferable that the low-temperature buffer layer and the group III nitride semiconductor layer grown at the high temperature are grown by the HVPE method.

  Thus, by growing the above two layers by the HVPE method, all growth can be performed at high speed without changing the growth apparatus, so that productivity can be improved and cost can be further reduced.

  At this time, it is preferable that the low-temperature buffer layer and the group III nitride semiconductor layer grown at the high temperature are layers made of GaN.

  Thus, GaN can be suitably used as the above two layers.

  As described above, according to the method for manufacturing a self-supporting substrate of the present invention, the group III nitride semiconductor layer grown at a high temperature can be easily peeled off from the substrate by forming the low temperature buffer layer with a thickness of 80 nm to 1000 nm. Can be made. As a result, peeling from the base substrate can be facilitated by a simple process, and a group III nitride semiconductor free-standing substrate having relatively good crystallinity can be manufactured at low cost.

It is process sectional drawing which shows an example of embodiment of the manufacturing method of the self-supporting board | substrate of this invention. It is a figure which shows many cracks and cracks which generate | occur | produce when peeling the group III nitride semiconductor layer grown at high temperature from a base substrate.

  Hereinafter, the present invention will be described in detail as an example of an embodiment with reference to the drawings, but the present invention is not limited thereto.

  As described above, nitride semiconductor materials are expected to be applied to electronic devices, and nitride semiconductor layers constituting these devices can be obtained by epitaxial growth on a base substrate. However, since there is no underlying substrate whose lattice constant matches that of the nitride semiconductor layer, the resulting nitride semiconductor layer contains many crystal defects. Until now, the crystal defects in the nitride semiconductor layer have been included. There have been many studies to reduce this. As described above, it has been proposed to obtain a GaN free-standing substrate by etching a sapphire substrate. In addition, a technique for obtaining a high-quality GaN free-standing substrate with little warpage by utilizing voids is disclosed.

  With the prior art as described above, a free-standing substrate of a group III nitride semiconductor such as GaN having good crystallinity has been obtained. However, a dissimilar substrate such as sapphire can be removed and peeled off, a metal film or a pattern can be formed Therefore, there is a problem in that the manufacturing process becomes high.

  The present inventors diligently studied a manufacturing method of a free-standing substrate that can be easily peeled off from a base substrate by a simple process and can manufacture a group III nitride semiconductor free-standing substrate having relatively good crystallinity at a low cost. did. As a result, by forming a low-temperature buffer layer having a thickness of 80 nm to 1000 nm before forming a group III nitride semiconductor layer grown at a high temperature, a group III nitride semiconductor layer grown at a high temperature thereafter is formed. It was conceived that it can be easily peeled off from the substrate. As a result, it has been found that a group III nitride semiconductor self-supporting substrate having relatively good crystallinity can be easily peeled off from the base substrate by a simple process, and the present invention has been completed.

  First, the manufacturing method of the self-supporting substrate of the present invention will be described with reference to FIG.

  As shown to Fig.1 (a), the board | substrate 1 used as a base material is prepared first. The substrate 1 to be prepared is not particularly limited as long as a low temperature buffer layer can be grown. For example, a sapphire substrate 1 can be prepared.

Next, as shown in FIG. 1B, a low-temperature buffer layer 2 is grown on the prepared substrate 1. As this low-temperature buffer layer 2, for example, GaN, AlN or the like can be grown by the HVPE method or the like. The growth conditions for the low temperature buffer layer 2 are a growth temperature of 400 to 600 ° C. and a thickness of 80 to 1000 nm. Note that the thickness of the low-temperature buffer layer 2 is preferably 300 nm or more, and more preferably 500 nm or more. However, it is not preferable to make it too thick near 1000 nm because crystallinity and peelability are slightly deteriorated.
Thus, by forming the low-temperature buffer layer 2 with a thickness of 80 nm or more, the group III nitride semiconductor layer grown thereon at a high temperature can be easily separated from the substrate 1. Further, by forming the low temperature buffer layer 2 with a thickness of 1000 nm or less, it is possible to prevent the growth time of the low temperature buffer layer 2 from being unnecessarily prolonged.
Conventionally, such a low-temperature buffer layer has been grown only to a thickness of 50 nm or less. This is because not only the problem of cost but also that the thinner buffer layer is considered preferable because it does not cause distortion or the like.

  At this time, the low-temperature buffer layer 2 is preferably a layer made of GaN. GaN can be suitably used as the low temperature buffer layer 2.

  Conventionally, high-temperature cleaning is performed while flowing hydrogen at a temperature of about 1000 ° C. before the growth of the low-temperature buffer layer 2, but the present invention is not limited to this, and it is preferable not to perform this high-temperature cleaning. . By setting it as such conditions, natural peeling becomes easy to occur.

  Next, as shown in FIG. 1C, the group III nitride semiconductor layer 3 is epitaxially grown on the grown low temperature buffer layer 2 at a temperature higher than the growth temperature of the low temperature buffer layer 2. The temperature for this high temperature growth is preferably 600 ° C. to 1100 ° C., more preferably 800 ° C. to 1050 ° C.

  At this time, the group III nitride semiconductor layer 3 grown at a high temperature is not particularly limited and can be a layer made of AlGaN, AlN or the like, but is preferably a layer made of GaN. According to the method for manufacturing a self-supporting substrate of the present invention, a GaN self-supporting substrate that is difficult to manufacture, has high added value, and has relatively high crystallinity can be manufactured at low cost. Is preferred.

  At this time, the method for growing the group III nitride semiconductor layer 3 grown at a high temperature is not particularly limited, but it is preferably grown by the HVPE method. If the HVPE method is used, a thick group III nitride semiconductor layer can be efficiently grown.

  Moreover, it is preferable that both the low temperature buffer layer 2 and the group III nitride semiconductor layer 3 grown at a high temperature are grown by the HVPE method. Thus, by growing the above two layers by the HVPE method, all growth can be performed at high speed without changing the growth apparatus, so that productivity can be improved and cost can be further reduced.

  Next, as shown in FIG. 1 (d), the group III nitride semiconductor layer 3 grown at a high temperature is peeled off from the substrate 1, thereby manufacturing a free-standing substrate 4 made of a group III nitride semiconductor. At this time, the substrate 1 may be naturally separated from the substrate 1 when the temperature is lowered after the growth of the high-temperature group III nitride semiconductor layer, or may be easily separated from the substrate 1 even after the temperature is lowered even if the substrate 1 is not naturally separated from the substrate 1 when the temperature is lowered. it can. FIG. 1D shows the case where a part of the low-temperature buffer layer 2 does not remain on the bottom surface of the free-standing substrate 4 after peeling, but the low-temperature buffer layer 2 on the bottom surface of the free-standing substrate 4 after peeling. Needless to say, some may remain. Even if a part of the low-temperature buffer layer remains on the free-standing substrate, it can be easily removed by a process such as etching or grinding.

  Thus, in the method for manufacturing a self-supporting substrate according to the present invention, the low temperature buffer layer 2 made of a group III nitride semiconductor functions as a release layer by growing the low temperature buffer layer 2 to a relatively large thickness of 80 to 1000 nm. This eliminates the need for complicated processes such as metal film formation and pattern formation as in the past, and easily removes the high-temperature-grown Group III nitride semiconductor layer grown on the single crystal with relatively good crystallinity as described above. Therefore, a high-quality group III nitride semiconductor free-standing substrate can be efficiently obtained by a simple method.

  A group III nitride semiconductor self-supporting substrate manufactured by the method for manufacturing a self-supporting substrate of the present invention as described above is a group III nitride semiconductor self-supporting substrate that is inexpensive and has relatively good crystallinity.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.

Example 1
First, a sapphire substrate was prepared as the substrate 1 and mounted on an HVPE apparatus. High temperature cleaning was performed while raising the temperature to 1000 ° C. and flowing hydrogen. Next, the temperature was set to 500 ° C., and the low temperature buffer layer 2 made of GaN was grown to a thickness of 80 nm. Here, in the HVPE apparatus, GaCl which is a halide of a group III element and NH ₃ as a group V element are used as a raw material gas, and the V / III ratio is set to 10.
Next, the temperature was raised to 1050 ° C., and a GaN layer serving as a self-supporting substrate was grown to a thickness of 400 μm. The wafer on which the GaN layer was grown at a high temperature by lowering the temperature was taken out from the HVPE apparatus. Although there were some portions that did not peel off on the outer periphery of the wafer, the sapphire substrate 1 and the thick GaN layer 3 could be naturally peeled over almost the entire surface of the wafer.

(Example 2)
A GaN free-standing substrate was manufactured by the same method as in Example 1 except that high-temperature cleaning was not performed. As a result, the sapphire substrate 1 and the thick GaN layer 3 could be naturally peeled over the entire surface of the wafer.

(Example 3)
A GaN free-standing substrate was manufactured under the same conditions as in Example 1 except that the low-temperature buffer layer 2 was 500 nm thick. As a result, the sapphire substrate 1 and the thick GaN layer 3 could be naturally peeled over the entire surface of the wafer.

Example 4
A GaN free-standing substrate was manufactured under the same conditions as in Example 1 except that the low-temperature buffer layer 2 had a thickness of 1000 nm. As a result, some portions of the outer periphery of the wafer were not peeled off and there were a few crystal defects (dislocations). However, the sapphire substrate 1 and the thick GaN layer 3 were able to be naturally peeled over almost the entire surface of the wafer.

(Comparative example)
A GaN free-standing substrate was manufactured under the same conditions as in Example 1 except that the low-temperature buffer layer 2 was 50 nm thick. When the sapphire substrate 1 and the thick GaN layer 3 were peeled, as shown in FIG. In addition, many cracks and cracks occurred in the surface with the sapphire substrate.

  Table 1 shows the crystallinity of the GaN free-standing substrate 4 in Examples 1 to 4 and the comparative example, and the ease of peeling of the thick GaN layer 3 from the sapphire substrate 1.

  As can be seen from Table 1, in Examples 1 to 4 in which the film thickness of the low temperature buffer layer 2 is 80 nm to 1000 nm, the thick film GaN layer 3 is different from the comparative example in which the film thickness of the low temperature buffer layer 2 is 50 nm. Peeling from the sapphire substrate 1 is easy.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

1 ... Substrate (sapphire substrate), 2 ... Low temperature buffer layer,
3 ... Group III nitride semiconductor layer (thick GaN layer) grown at high temperature, 4 ... Free-standing substrate.

Claims (3)

A self-supporting substrate manufacturing method for manufacturing a self-supporting substrate made of a group III nitride semiconductor,
A low temperature buffer layer made of a group III nitride semiconductor layer is epitaxially grown to a thickness of 80 to 1000 nm on a substrate at a growth temperature of 400 to 600 ° C., and then the low temperature buffer layer is formed on the grown low temperature buffer layer. A group III nitride semiconductor layer is epitaxially grown at a temperature higher than the growth temperature, and the group III nitride semiconductor layer grown at the high temperature is peeled off from the substrate, thereby forming a group III nitride semiconductor grown at a high temperature. A self-standing substrate manufacturing method, characterized by manufacturing a self-standing substrate.   2. The method for manufacturing a self-supporting substrate according to claim 1, wherein the low-temperature buffer layer and the group III nitride semiconductor layer grown at the high temperature are grown by HVPE.   3. The method for manufacturing a self-supporting substrate according to claim 1, wherein the low-temperature buffer layer and the group III nitride semiconductor layer grown at the high temperature are layers made of GaN.