The present invention relates to a method for growing group III nitride crystal having a low dislocation density.
Group III nitride crystal such as AlxGa1-xN (0≦x≦1) crystal is suitably used for various types of semiconductor device such as a light emitting device and an electronic device. For improved characteristics of these semiconductor devices, a demand arises in group III nitride crystal having a low dislocation density.
As a method for growing group III nitride crystal having a low dislocation density, an ELO (epitaxial lateral overgrowth) method is disclosed (for example, see International Publication No. WO98/047170 (Patent Document 1)). In the ELO method, a mask layer having an opening is formed on a substrate, and group III nitride crystal is grown laterally from the opening onto the mask layer.
Patent Document 1: International Publication No. WO98/047170
Although the ELO method disclosed in International Publication No. WO98/047170 (Patent Document 1) allows for reduced dislocation density in the group III nitride crystal to be grown, the mask layer having the opening needs to be formed. Hence, processes are complicated. The ELO method is thus disadvantageous in productivity and cost effectiveness.
In view of this, an object of the present invention is to provide a method for growing group III nitride crystal having a low dislocation density readily and efficiently.
The present invention provides a method for growing group III nitride crystal, including the steps of: preparing a substrate including a group III nitride seed crystal constituting one main surface thereof; forming a plurality of facets through vapor phase etching on the main surface of the substrate; and growing group III nitride crystal on the main surface on which the facets are formed.
In the method according to the present invention for growing group III nitride crystal, the main surface may have an off-orientation angle of 10° or smaller relative to a (0001) plane of the group III nitride seed crystal, and the facets include at least one geometrically equivalent crystal plane selected from a group consisting of {11-2m} planes and {10-1n} planes, m being a positive integer, n being a positive integer. In addition, the vapor phase etching may be performed using at least one gas selected from a group consisting of HCl gas, Cl2 gas, and H2 gas. Further, the main surface on which the facets are formed may have an average roughness Ra of 1 μm or greater but 1 mm or smaller. Furthermore, after the vapor phase etching, the substrate may have a thickness of 300 μm or smaller. Moreover, after the step of forming the plurality of facets on the main surface of the substrate, the step of growing group III nitride crystal on the main surface on which the facets are formed is performed uninterruptedly without moving the substrate.
According to the present invention, there can be provided a method for readily and efficiently growing group III nitride crystal having a low dislocation density.
1: HCl gas; 2: group III element raw material; 3: group III element raw material gas; 4: nitride raw material gas; 5, 8: exhaust gas; 7: etching gas; 10: substrate; 10a: group III nitride seed crystal; 10b: underlying substrate; 10m: main surface; 10ms, 10mt, 10mu: facet; 10n: (0001) plane; 20: group III nitride crystal; 100: HYPE apparatus; 110: reaction chamber; 111: first gas introduction pipe; 112: second gas introduction pipe; 113: third gas introduction pipe; 115: gas discharge pipe; 119: substrate holder; 120: group III element raw material gas generation chamber; 121: group III element raw material boat; 131, 132, 133: heater.
Referring to
According to the method for growing group III nitride crystal in the present embodiment, group III nitride crystal 20 is grown on the plurality of facets 10ms, 10mt, 10mu formed on main surface 10m of substrate 10. Here, directions in which the crystal is grown on facets 10ms, 10mt, 10mu and the directions in which dislocations are propagated (directions respectively indicated by arrows S, T, and U in
In the crystal growing on facets facing each other (for example, facet 10mt and facet 10mu), directions in which dislocations are propagated (the directions indicated by arrows T and U) are opposite to each other. Accordingly, the dislocations thus propagated impinge on one another (impinge as indicated by arrows T and U in
Referring to
Here, substrate 10 is not particularly limited as long as it includes group III nitride seed crystal 10a constituting one main surface 10m. Substrate 10 may be a free-standing substrate entirely formed of group III nitride seed crystal 10a. Alternatively, substrate 10 may be a template substrate in which an underlying substrate 10b has a layer of group III nitride seed crystal 10a formed thereon. An exemplary substrate 10 entirely formed of group III nitride seed crystal 10a is a GaN substrate, an AlN substrate, an AlxGa1-xN (0<x<1) substrate, or the like. An exemplary substrate 10 in which underlying substrate 10b has the layer of group III nitride seed crystal 10a formed thereon is a GaN/sapphire substrate (substrate in which a sapphire substrate has GaN seed crystal formed thereon; the same is applied in the description below), a GaN/SiC substrate (substrate in which an SiC substrate has GaN seed crystal formed thereon; the same is applied in the description below); a GaN/Si substrate (substrate in which an Si substrate has GaN seed crystal formed thereon; the same is applied in the description below); a GaN/GaAs substrate (a substrate in which a GaAs substrate has GaN seed crystal formed thereon; the same is applied in the description below); a GaN/GaP substrate (a substrate in which a GaP substrate has GaN seed crystal formed thereon; the same is applied in the description below); a GaN/InP substrate (a substrate in which an InP substrate has GaN seed crystal formed thereon; the same is applied in the description below), or the like.
Next, referring to
Here, group III nitride seed crystal 10a has a wurtzite-type crystal structure in a hexagonal system. Hence, the plurality of facets 10ms, 10mt, 10mu provide an irregular surface having a plurality of projections each shaped in a multi-sided pyramid. Here, the multi-sided pyramid is not particularly limited but one with a six-sided pyramid, a four-sided pyramid, a three-sided pyramid, a twelve-sided pyramid, or the like can be readily formed.
Meanwhile, the plurality of facets 10ms, 10mt, 10mu on main surface 10m of substrate 10 are formed using vapor phase etching. The vapor phase etching provides the facets with surfaces in good condition. The surfaces in good condition herein refer to surfaces having less impurity, which is included due to surface treatment, and exhibiting an intended crystal plane. If polishing processing and liquid phase etching are employed, selectivity in etching is bad and impurity is likely to be included therein, whereby facets with surfaces in good condition cannot be obtained. This makes it difficult to reduce dislocation density in group III nitride crystal to be grown.
The gas used in the vapor phase etching is not particularly limited as long as facets with surfaces in good condition are obtained, but in order to efficiently etch the group III nitride seed crystal, it is preferable to use at least one gas selected from a group consisting of HCl gas, Cl2 gas, and H2 gas. Here, HCl gas and H2 gas are preferable for etching of GaN seed crystal, AlxGa1-xN seed crystal having a low Al composition (for example, 0<x<0.5), or the like. Cl2 gas is preferable for etching of AlN seed crystal, an AlxGa1-xN seed crystal having a high Al composition (for example, 0.5≦x<1), or the like. Alternatively, the above-exemplified etching gases can be used together.
For efficient etching of the group III nitride seed crystal, the partial pressure of the etching gas is preferably 0.1 Pa or greater but 100 kPa or smaller, the etching temperature is preferably 700° C. or higher but 1200° C. or lower, and the etching time is preferably 1 minute or longer but 180 minute or shorter.
Next, referring to
Further, in the crystal growing on facets facing each other (for example, facet 10mt and facet 10mu), the directions in which dislocations are propagated (directions indicated by arrows T and U) are opposite to each other. Hence, the dislocations propagated impinge on one another (impinge as indicated by arrows T and U in
Here, the method for growing group III nitride crystal 20 is not particularly limited. Methods usable therefor are vapor phase methods such as an HVPE (Hydride Vapor Phase Epitaxy) method, an MOCVD (Metal-Organic Chemical Vapor Deposition) method, and a sublimation method; liquid phase methods such as a solution method and a flux method; and the like. Among these methods for growing crystal, the vapor phase methods are preferable because crystal can be grown uninterruptedly after the vapor phase etching. Further, among the vapor phase methods, the HVPE method is more preferable because it allows for fast growth of crystal.
Referring to
Since main surface 10m of substrate 10 has an off-orientation angle θ of 10° or smaller relative to the (0001) plane, which is a stable crystal plane of group III nitride seed crystal 10a, group III nitride crystal 20 having a low dislocation density can be grown stably on such a main surface 10m.
Further, each of facets 10ms, 10mt, 10mu includes at least one geometrically equivalent crystal plane selected from the group consisting of the {11-2 m} planes (m is a positive integer) and the {10-1n} planes (n is a positive integer), which are stable crystal planes of group III nitride seed crystal 10a. Hence, group III nitride crystal 20 having a low dislocation density can be stably grown on facets 10ms, 10mt, 10mu. Here, the {11-2 m} planes refer to a (11-2m) plane and a crystal plane geometrically equivalent to the (11-2m) plane, whereas the 110-1111 planes refer to a (10-1n) plane and a crystal plane geometrically equivalent to the (10-1n) plane.
Here, the (0001) plane of group III nitride seed crystal 10a, the plane orientation of the main surface, and the off-orientation angle relative to the (0001) plane, as well as the plane orientations of the facets can be measured through observation on the substrate with X-ray diffraction, an SEM (scanning electron microscope), and a laser microscope.
Referring to
In the method for growing group III nitride crystal in the present embodiment, the substrate having been through the vapor phase etching preferably has a thickness of 300 μm or smaller. If a substrate having a thickness of more than 300 μm is employed, stress/strain is large between the substrate and the group III nitride crystal due to a difference in thermal expansion coefficient therebetween upon growing the group III nitride crystal on the substrate or cooling it down after the growth thereof. Accordingly, breakage and cracks are likely to occur in the substrate and the group III nitride crystal upon the crystal growth or the cooling after the crystal growth. A substrate with a smaller thickness allows for more relaxation of stress/strain imposed between the substrate and the group III nitride crystal due to the difference in thermal expansion coefficient therebetween upon the growth of group III nitride crystal on the substrate and upon cooling after the growth thereof. In view of this, the substrate having been through the vapor phase etching more preferably has a thickness of 200 μm or smaller, and further preferably has a thickness of 100 μm or smaller.
Referring to
For growth of group III nitride crystal 20 using the HVPE method, for example, an HVPE apparatus 100 shown in
Referring to
Here, etching gas 7 is not particularly limited but is preferably at least one gas selected from a group consisting of HCl gas, Cl2 gas, and H2 gas for efficient etching of group III nitride seed crystal included in at least main surface 10m of substrate 10. Here, in the case where HCl gas is introduced as etching gas 7 via first and second gas introduction pipes 111, 112, the HCl gas needs to be introduced into reaction chamber 110 so that the it does not react with group III element raw material 2. This can be attained when group III element raw material 2 is not placed in group III element raw material gas generation chamber 120 or group III element raw material gas generation chamber 120 is not heated.
Referring to
Then, HCl gas 1 is introduced into group III element raw material gas generation chamber 120 via first gas introduction pipe 111. HCl gas 1 is reacted with group III element raw material 2 (for example, metal Ga melt, metal Al melt, or the like) placed in group III element raw material gas generation chamber 120 and heated by heater 131, so as to generate group III element raw material gas 3 (for example, Ga chloride gas, Al chloride gas, or the like). Group III element raw material gas 3 thus generated is introduced into reaction chamber 110 via second gas introduction pipe 112. Here, the temperature of group III element raw material 2 being heated is not particularly limited, but is preferably 400° C. or higher but 1000° C. or lower for effective generation of group III element raw material gas 3. Meanwhile, as nitride raw material gas 4, NH3 gas is introduced into reaction chamber 110 via third gas introduction pipe 113.
Group III element raw material gas 3 and nitride raw material gas 4 thus introduced into reaction chamber 110 are reacted with each other to grow group III nitride crystal 20 on main surface 10m of substrate 10 that is being heated by heater 133. The temperature of substrate 10 being heated (hereinafter, also referred to as “crystal growth temperature”) is not particularly limited, but is preferably 900° C. or higher but 1600° C. or lower for fast growth of crystal. Meanwhile, the partial pressure (hereinafter, also referred to as PIII) of group III element raw material gas 3 and the partial pressure (hereinafter, also referred to as PN) of nitride raw material gas 4 are not particularly limited, but group III element raw material gas 3 has a partial pressure of 0.1 kPa or greater but 50 kPa or smaller and nitride raw material gas 4 has a partial pressure of 20 kPa or greater but 90 kPa or smaller for fast growth of crystal.
Further, group III element raw material gas 3 and nitride raw material gas 4 are preferably introduced into the reaction chamber together with carrier gas to facilitate adjustment of the partial pressure of group III element raw material gas 3 and the partial pressure of nitride raw material gas 4 as well as control for rate of growth of crystal. Such carrier gas is not particularly limited as long as it is not reacted with group III element raw material gas 3 and nitride raw material gas 4, but is preferably H2 gas, N2 gas, Ar gas, He gas, or the like because such gas is available at low cost with high purity.
GaN bulk crystal was grown by the HVPE method to constitute a main surface substantially corresponding to the (0001) plane and the GaN bulk crystal thus grown had a diameter of 50.8 mm (2 inches) and had a thickness of 10 mm. By slicing it in planes parallel to the (0001) plane, five GaN substrates were obtained each having a main surface having an off-orientation angle of 0.8° or smaller relative to the (0001) plane, having a diameter of 50.8 mm (2 inches), and having a thickness of 400 μm. In this way, 100 GaN substrates were obtained from 20 pieces of GaN bulk crystal. In the main surface of each of such GaN substrates, dislocation density was 1.00×108 cm−2 measured by observation of dark spots using a CL (cathode luminescence) method.
The GaN substrate was placed on a substrate holder in a reaction chamber of an HVPE apparatus. HCl gas having a partial pressure (PHCl) of 4 kPa was introduced into the reaction chamber and the main surface thereof was subjected to vapor phase etching at 950° C. for 60 minutes. After the etching, the substrate had a thickness of 300 μm, and had a plurality of facets formed on the main surface thereof. The main surface had an average roughness Ra of 5 μm, measured using a 3D-SEM in a reference area of 100 μm×100 μm. Further, the plane orientations of the facets formed on the main surface were (11-22) and (10-12) identified by observation using X-ray diffraction, an SEM, and a laser microscope.
On the GaN substrate's main surface having the plurality of facets formed thereon, GaN crystal was grown using the HVPE method. The crystal was grown under the following conditions: the crystal growth temperature was 1050° C., the partial pressure (PGa) of Ga chloride gas, which was group III element raw material gas, was 40.4 kPa, and the partial pressure (PN) of NH3 gas, which was nitride raw material gas, was 10.1 kPa. Under such conditions, crystal was grown for 50 hours to obtain GaN crystal having a diameter of 50.8 mm (2 inches) and a thickness of 10 mm. The crystal growth surface of the GaN crystal had a low dislocation density, 5.00×105 cm−2, which was measured through observation of dark spots using the CL method. The GaN crystal had a curvature radius of 5 m, calculated from distribution of measurements of off-orientation angles using X-ray diffraction, and therefore had a small warpage. In addition, a crack generation ratio in the 100 substrates was 5%. Here, generation of a crack indicates breakage occurring on the surface of the substrate in the form of a line of 2.0 mm or longer in length, breakage occurring thereon in the form of three or more lines of 0.5 mm-2.0 mm in length, or breakage occurring thereon in the form of 21 or more lines of 0.3 mm-0.5 mm in length. A result is shown in Table 1.
Comparative Example 1 is basically the same as in example 1, except that a main surface of each substrate was subjected to liquid phase etching using a phosphoric acid aqueous solution of 85% by mass at 230° C. for 3 minutes. Specifically, GaN substrates were prepared, the main surface of each substrate was etched as such, and GaN crystal was grown on the main surface etched. As a result of the etching, the substrate had a thickness of 370 μm and had a plurality of facets formed on the main surface thereof. The main surface had an average roughness Ra of 1 μm. However, the facets formed on the main surface of the substrate had surfaces in bad condition, and the plane orientations of the facets could not be specified through observation using X-ray diffraction, an SEM, and a laser microscope. With the liquid phase etching in the comparative example, an opposite main surface (rear surface) was preferentially etched as compared with the main surface that should be etched, disadvantageously. In addition, the crystal growth surface of the GaN crystal obtained had a high dislocation density, 7.00×107 cm−2, and the GaN crystal had a curvature radius of 3 m and therefore had a large warpage. A crack generation ratio was 5%. A result is shown in Table 1.
Comparative Example 2 is basically the same as in example 1, except that the main surface of each substrate was subjected to liquid phase etching using a phosphoric acid aqueous solution of 85% by mass at 230° C. for 10 minutes. Specifically, GaN substrates were prepared, the main surface of each substrate was etched as such, and GaN crystal was grown on the main surface etched. As a result of the etching, the substrate had a thickness of 250 μm and had a plurality of facets formed on the main surface thereof. The main surface had an average roughness Ra of 5 μm. However, the facets formed on the main surface of the substrate had surfaces in bad condition, and the plane orientations of the facets could not be specified through observation using X-ray diffraction, an SEM, and a laser microscope. With the liquid phase etching in the comparative example, an opposite main surface (rear surface) was preferentially etched as compared with the main surface that should be etched, disadvantageously. Further, a crack was generated during the crystal growth step. Although the crack was generated, the crystal growth surface of the GaN crystal obtained had a low dislocation density, 1.00×106 cm−2, and the GaN crystal had a curvature radius of 5 m and therefore had a small warpage. A result is shown in Table 1.
Comparative Example 3 is basically the same as in example 1, except that a main surface of each GaN substrate was polished for 120 minutes using a slurry including SiC abrasive grains having an average grain diameter of 15 μm. Specifically, GaN substrates were prepared, the main surface thereof was polished (etched), and GaN crystal was grown on the main surface thus polished (etched). As a result of the polishing (etching), the substrate had a thickness of 340 μm, and had no facet formed on the main surface thereof. The main surface had an average roughness Ra of 1.5 μm. The crystal growth surface of the GaN crystal obtained had a very high dislocation density, 1.00×108 cm−2, and the GaN crystal had a curvature radius of 3m and therefore had a large warpage. A crack generation ratio was 8%. A result is shown in Table 1.
In Table 1, comparative examples 1-3 and example 1 are compared. It is found that a plurality of facets having surfaces in better condition can be formed on a main surface subjected to vapor phase etching as compared with those on the main surface of a substrate subjected to liquid phase etching or polished. In this way, group III nitride crystal having a low dislocation density can be grown on the main surface of the substrate.
Example 2 is basically the same as in example 1 except that etching time was 30 minutes. Specifically, GaN substrates were prepared, a main surface of each substrate was etched, and GaN crystal was grown on the main surface thus etched. As a result of the etching, the substrate had a thickness of 350 μm, and had a plurality of facets formed on the main surface thereof. The main surface thereof had an average roughness Ra of 2.5 μm. The plane orientations of the facets formed on the main surface were (11-23) and (10-13). The crystal growth surface of the GaN crystal obtained had a low dislocation density, 7.00×105 cm−2, and the GaN crystal had a curvature radius of 7m and therefore had a small warpage. A crack generation ratio was 7%. A result is shown in Table 2.
Example 3 is basically the same as in example 1 except that etching time was 120 minutes. Specifically, GaN substrates were prepared, a main surface of each substrate was etched, and GaN crystal was grown on the main surface thus etched. As a result of the etching, the substrate had a thickness of 200 μm, and had a plurality of facets formed on the main surface thereof. The main surface thereof had an average roughness Ra of 13 μm. The plane orientations of the facets formed on the main surface were (11-22) and (10-12). The crystal growth surface of the GaN crystal obtained had a low dislocation density, 6.50×105 cm−2, and the GaN crystal had a curvature radius of 6 m and therefore had a small warpage. A crack generation ratio was 6%. A result is shown in Table 2.
Example 4 is basically the same as in example 1 except that etching time was 180 minutes. Specifically, GaN substrates were prepared, a main surface of each substrate was etched, and GaN crystal was grown on the main surface thus etched. As a result of the etching, the substrate had a thickness of 100 μm, and had a plurality of facets formed on the main surface thereof. The main surface thereof had an average roughness Ra of 17 μm. The plane orientations of the facets formed on the main surface were (11-21), (10-11), and (21-32). The crystal growth surface of the GaN crystal obtained had a low dislocation density, 6.50×105 cm−2, and the GaN crystal had a curvature radius of 6 m and therefore had a small warpage. A crack generation ratio was 4%. A result is shown in Table 2.
Example 5 is basically the same as in example 1 except that etching time was 210 minutes. Specifically, GaN substrates were prepared, a main surface of each substrate was etched, and GaN crystal was grown on the main surface thus etched. As a result of the etching, the substrate had a thickness of 50 μm, and had a plurality of facets formed on the main surface thereof. The main surface thereof had an average roughness Ra of 24 μm. The plane orientations of the facets formed on the main surface were (11-21), (10-11), (21-32), (31-43), and (32-53). The crystal growth surface of the GaN crystal obtained had a low dislocation density, 6.50×105 cm−2, and the GaN crystal had a curvature radius of 6 m and therefore had a small warpage. A crack generation ratio was 3%. A result is shown in Table 2.
Comparing example 1 of Table 1 and examples 2-5 of Table 2 with one another, as vapor phase etching time is longer, the main surface is etched more, resulting in a large average roughness Ra in the main surface. Further, in examples 4 and 5, the crack generation ratio is reduced to 4% or smaller because it is considered that the vapor phase etching provides the substrate with a thickness of 100 μm or smaller to reduce stress/strain between the substrate and the crystal upon the crystal growth on the substrate and cooling after the crystal growth.
Example 6 is basically the same as in example 1 except that etching temperature was 1000° C. Specifically, GaN substrates were prepared, a main surface of each substrate was etched, and GaN crystal was grown on the main surface thus etched. As a result of the etching, the substrate had a thickness of 220 μm and had a plurality of facets formed on the main surface thereof. The main surface thereof had an average roughness Ra of 13 p.m. The plane orientations of the facets formed on the main surface were (11-21) and (10-11). The crystal growth surface of the GaN crystal obtained had a low dislocation density, 5.00×105 cm−2, and the GaN crystal had a curvature radius of 4 m. A crack generation ratio was 6%. A result is shown in Table 3.
Example 7 is basically the same as in example 1 except that AlN substrates were used as the substrate. Specifically, each of the AlN substrates was obtained as follows. MN bulk crystal was grown by the HVPE method to constitute a main surface substantially corresponding to the (0001) plane, having a diameter of 50.8 mm (2 inches), and having a thickness of 10 mm. By slicing it in planes parallel to the (0001) plane, the MN substrates was obtained each of which had a main surface with an off-orientation angle of 0.8° or smaller relative to the (0001) plane, had a diameter of 50.8 mm (2 inches), and had a thickness of 400 μm. The main surface of each MN substrate was etched, and GaN crystal was grown on the main surface thus etched. The main surface of the AlN substrate had a dislocation density of 5.00×109 cm−2. As a result of the etching, the substrate had a thickness of 300 μm and had a plurality of facets formed on the main surface thereof. The main surface thereof had an average roughness Ra of 5 μm. The plane orientations of the facets formed on the main surface were (11-23) and (10-13). The crystal growth surface of the GaN crystal obtained had a low dislocation density, 5.00×105 cm−2, and the GaN crystal had a curvature radius of 5 m and therefore had a small warpage. A crack generation ratio was 5%. A result is shown in Table 3.
Example 8 is basically the same as in example 7 except that employed etching gas for a main surface of each AlN substrate was Cl2 gas having a partial pressure PCl2 of 4 kPa and AlN crystal was grown by the HVPE method on the AlN substrates main surface having a plurality of facets formed thereon. Specifically, MN substrates were prepared, the main surface thereof was etched, and MN crystal was grown on the main surface thus etched.
As a result of the etching, the substrate had a thickness of 350 μm and had the plurality of facets formed on the main surface thereof. The main surface thereof had an average roughness Ra of 4 μm. The plane orientations of the facets formed on the main surface were (11-22) and (10-12).
The AlN crystal was grown under the following conditions: the crystal growth temperature was 1450° C., Al chloride gas, which serves as the group III element raw material gas, had a partial pressure (PAl) of 40.4 kPa, and NH3 gas, which serves as nitride raw material gas, had a partial pressure (PN) of 10.1 kPa. Under such conditions, the crystal was grown for 50 hours to obtain MN crystal having a diameter of 50.8 mm (2 inches) and having a thickness of 10 mm. The crystal growth surface of the MN crystal had a low dislocation density, 5.00×105 cm−2, and the AlN crystal had a curvature radius of 6 m and therefore had a small warpage. A crack generation ratio was 8%. A result is shown in Table 3.
Comparing example 1 of Table 1 and example 6 of Table 3 with each other, it is found that as the etching temperature is higher, the main surface is etched more, resulting in a larger average roughness Ra in the main surface. Meanwhile, comparing example 1 of Table 1 and examples 7 and 8 of Table 3 with one another, it was found that also when an AlN substrate was employed as the substrate instead of a GaN substrate or when AlN crystal was grown instead of GaN crystal as the crystal to be grown, crystal having a low dislocation density can be obtained by forming a plurality of facets on a main surface of a substrate through vapor phase etching and growing crystal on the main surface having the facets thus formed thereon.
Example 9 is basically the same as in example 1 except that GaN/sapphire substrates (template substrates) were used as the substrates and etching time was 30 minutes. In each GaN/sapphire substrate, GaN seed crystal having a thickness of 100 μm was formed on a sapphire underlying substrate having a thickness of 400 μm. Specifically, GaN/sapphire substrates were prepared, a main surface thereof was etched and GaN crystal was grown on the main surface thus etched.
The substrate of the present example was a GaN/sapphire substrate including GaN seed crystal constituting one main surface thereof and obtained by growing the GaN crystal on the (0001) plane of the sapphire substrate by the HYPE method. The main surface had an off-orientation angle of 0.8° or smaller relative to the (0001) plane and had a diameter of 50.8 mm (2 inches). The GaN seed crystal had a thickness of 100 μm, and the sapphire underlying substrate had a thickness of 400 μm. The main surface of GaN/sapphire substrate had a dislocation density of 1.00×108 cm−2. As a result of the etching of the substrate, the GaN seed crystal constituting the one main surface of the substrate had a thickness of 50 μm, and a plurality of facets were formed on the main surface of the substrate. The main surface thereof had an average roughness Ra of 2.5 μm. The plane orientations of the facets formed on the main surface were (11-23) and (10-13). The crystal growth surface of the GaN crystal obtained had a low dislocation density, 7.00×105 cm−2, and the GaN crystal had a curvature radius of 7 m and therefore had a small warpage. A crack generation ratio was 7%. A result is shown in Table 4.
Example 10 is basically the same as in example 9 except that as the substrates, GaN/SiC substrates (template substrates) were employed in each of which GaN seed crystal having a thickness of 100 μm was formed on an SiC underlying substrate having a thickness of 400 μm. Specifically, GaN/SiC substrates were prepared, a main surface of each GaN/SiC substrate was etched, and GaN crystal was grown on the main surface thus etched. The main surface of the GaN/SiC substrate had a dislocation density of 1.00×109 cm2. As a result of the etching of the substrate, the GaN seed crystal constituting the one main surface of the substrate had a thickness of 50 p.m and a plurality of facets were formed on the main surface of the substrate. The main surface thereof had an average roughness Ra of 2.5 μm. The plane orientations of the facets formed on the main surface were (11-23) and (10-13). The crystal growth surface of the GaN crystal obtained had a dislocation density of 7.00×105 cm−2, and the GaN crystal had a curvature radius of 6 m and therefore had a small warpage. A crack generation ratio was 7%. A result is shown in Table 4.
Example 11 is basically the same as in example 9 except that as the substrates, GaN/Si substrates (template substrates) were used in each of which GaN seed crystal having a thickness of 100 μm was formed on an Si underlying substrate having a thickness of 400 μm. Specifically, GaN/Si substrates were prepared, a main surface of each substrate was etched, and GaN crystal was grown on the main surface thus etched. The main surface of the GaN/Si substrate had a dislocation density of 8.00×109 cm−2. As a result of the etching of the substrate, the GaN seed crystal substrate constituting the one main surface of the substrate had a thickness of 50 μm, and a plurality of facets were formed on the main surface of the substrate. The main surface thereof had an average roughness Ra of 2.5 μm. The plane orientations of the facets formed on the main surface were (11-23) and (10-13). Further, the crystal growth surface of the GaN crystal obtained had a low dislocation density, 7.00×105 cm−2, and the GaN crystal had a curvature radius of 6 m and therefore had a small warpage. A crack generation ratio was 7%. A result is shown in Table 4.
Example 12 is basically the same as in example 9 except that as the substrates, GaN/GaAs substrates (template substrates) were used in each of which GaN seed crystal having a thickness of 100 μm was formed on a GaAs underlying substrate having a thickness of 400 p.m. Specifically, GaN/GaAs substrates were prepared, a main surface of each substrate was etched, and GaN crystal was grown on the main surface thus etched. The main surface of the GaN/GaAs substrate had a dislocation density of 1.00×108 cm−2. As a result of the etching of the substrate, the GaN seed crystal constituting the one main surface of the substrate had a thickness of 50 μm, and the plurality of facets were formed on the main surface of the substrate. The main surface thereof had an average roughness Ra of 2.5 μm. The plane orientations of the facets formed on the main surface were (11-23) and (10-13). Further, the crystal growth surface of the GaN crystal obtained had a low dislocation density, 7.00×105 cm−2, and the GaN crystal had a curvature radius of 5 m and therefore had a small warpage. A crack generation ratio was 7%. A result is shown in Table 5.
Example 13 is basically the same as in example 9 except that as the substrates, GaN/GaP substrates (template substrates) were used in each of which GaN seed crystal having a thickness of 100 μm was formed on a GaP underlying substrate having a thickness of 400 μm. Specifically, GaN/GaP substrates were prepared, a main surface of each substrate was etched, and GaN crystal was grown on the main surface thus etched. The main surface of the GaN/GaP substrate had a dislocation density of 1.00×109 cm−2. As a result of the etching of the substrate, the GaN seed crystal constituting the one main surface of the substrate had a thickness of 50 μm, and a plurality of facets were formed on the main surface. The main surface had an average roughness Ra of 2.5 μm. The plane orientations of the facets formed on the main surface were (11-23) and (10-13). Further, the crystal growth surface of the GaN crystal obtained had a dislocation density of 7.00×105 cm−2, and the GaN crystal had a curvature radius of 5 m and therefore had a small warpage. A crack generation ratio was 7%. A result is shown in Table 5.
Example 14 is basically the same as in example 9 except that as substrates, GaN/InP substrates (template substrates) were used in each of which GaN seed crystal having a thickness of 100 μm was formed on an InP underlying substrate having a thickness of 400 μm. Specifically, GaN/InP substrates were prepared, a main surface of each substrate was etched, and GaN crystal was grown on the main surface thus etched. The main surface of the GaN/InP substrate had a dislocation density of 1.00×109 cm−2. As a result of the etching of the substrate, the GaN seed crystal constituting the one main surface of the substrate had a thickness of 50 μm, and a plurality of facets were formed on the main surface. The main surface thereof had an average roughness Ra of 2.5 μm. The plane orientations of the facets formed on the main surface were (11-23) and (10-13). The crystal growth surface of the GaN crystal obtained had a low dislocation density, 7.00×105 cm−2, and the GaN crystal had a curvature radius of 5 m and therefore had a small warpage. A crack generation ratio was 7%. A result is shown in Table 5.
As shown in examples 9-14 of Tables 4 and 5, it is recognized that also when a template substrate including GaN seed crystal on its main surface is employed, crystal having a low dislocation density can be obtained by forming a plurality of facets on the main surface of the substrate through vapor phase etching and growing GaN crystal on the main surface having the facets formed thereon.
Example 15 is basically the same as in example 1 except that crystal to be grown was AlGaN crystal. Specifically, GaN substrates were prepared, a main surface of each substrate was etched, and Al0.25Ga0.75N crystal was grown on the main surface thus etched. The crystal was grown under the following conditions: crystal growth temperature was 1050° C., Al chloride gas and Ga chloride gas, each of which was the group III element raw material gas, had partial pressures of 10.1 kPa (PAl) and 30.3 kPa (PGa) respectively, and NH3 gas, which was the nitride raw material gas, had a partial pressure (PN) of 10.1 kPa. The main surface of the GaN substrate had a dislocation density of 1.00×108 cm−2. As a result of the etching of the substrate, the substrate had a thickness of 300 μm, and had a plurality of facets formed on its main surface. The main surface had an average roughness Ra of 5 p.m. The plane orientations of the facets formed on the main surface were (11-22) and (10-12). Further, the crystal growth surface of the GaN crystal obtained had a low dislocation density, 5.00×105 cm−2, and the GaN crystal had a curvature radius of 5 m and therefore had a small warpage. A crack generation ratio was 5%. A result is shown in Table 6.
Example 16 is basically the same as in example 1 except that employed etching gas for the main surface of the GaN substrate was Cl2 gas. Specifically, GaN substrates were prepared, a main surface of each substrate was etched, and GaN crystal was grown on the main surface thus etched. As a result of the etching of the substrate, the substrate had a thickness of 280 μm and had a plurality of facets formed on its main surface. The main surface thereof had an average roughness Ra of 7 μm. The plane orientations of the facets formed on the main surface were (11-21) and (10-11). Further, the crystal growth surface of the GaN crystal obtained had a low dislocation density, 4.00×105 cm−2, and the GaN crystal had a curvature radius of 6 m and therefore had a small warpage. A crack generation ratio was low, 4%. A result is shown in Table 6.
Example 17 is basically the same as in example 1 except that employed etching gas for the main surface of the GaN substrate was H2 gas. Specifically, GaN substrates were prepared, a main surface of each substrate was etched, and GaN crystal was grown on the main surface thus etched. As a result of the etching of the substrate, the substrate had a thickness of 350 μm, and had a plurality of facets formed on its main surface. The main surface thereof had an average roughness Ra of 4 μm. The plane orientations of the facets formed on the main surface were (11-23) and (10-13). The crystal growth surface of the GaN crystal obtained had a low dislocation density, 8.00×105 cm−2, and the GaN crystal had a curvature radius of 5 m and therefore had a small warpage. A crack generation ratio was 7%. A result is shown in Table 6.
Comparing example 1 of Table 1 and example 15 of Table 6 with each other, it is found that also when crystal to be grown is Al1-xGaxN crystal (0<x<1) instead of GaN crystal, crystal having a low dislocation density can be obtained by forming a plurality of facets on a main surface of a substrate through vapor phase etching and growing crystal on the main surface thus having the facets formed thereon. Comparing example 1 of table 1 and examples 16 and 17 of Table 6 with one another, it is found that also when Cl2 gas or H2 gas is employed as etching gas instead of HCl gas, facets can be formed on the main surface of each substrate.
It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in any respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
Number | Date | Country | Kind |
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2008-006854 | Jan 2008 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2009/050110 | 1/8/2009 | WO | 00 | 7/9/2010 |