JP2008273768A - Group III nitride crystal growth method and group III nitride crystal substrate - Google Patents

Abstract

A method for growing a group III nitride crystal and a group III nitride crystal substrate capable of reducing the dislocation density are provided.
The Group III nitride crystal growth method is a method of growing a Group III nitride crystal 20 on a main surface 10m of a base substrate 10 by a liquid phase method, and the base substrate 10 is at least a main surface. Including a group III nitride crystal layer 10a on the side, and a normal line 10mv of the principal surface 10m has an inclination angle of 0.5 ° to 10 ° with respect to the <0001> direction 10cv of the group III nitride crystal layer 10a. When the group III nitride crystal 20 is grown, at least a part of the dislocations remaining in the group III nitride crystal 20 is propagated in a direction substantially parallel to the {0001} plane 20c, thereby causing the group III nitride. Drain to the outer periphery of the crystal.
[Selection] Figure 1

Description

  The present invention relates to a method for growing a group III nitride crystal having a low dislocation density and a group III nitride crystal substrate, which are preferably used as substrates for various semiconductor devices such as light-emitting elements, electronic elements, and semiconductor sensors.

Group III nitride crystals such as Al _x Ga _y In _1-xy N crystal (0 ≦ x, 0 ≦ y, x + y ≦ 1, and so on) are substrates for various semiconductor devices such as light emitting elements, electronic elements, and semiconductor sensors. It is very useful as a material for forming. Here, in order to improve the characteristics of various semiconductor devices, a group III nitride crystal substrate having a low dislocation density and good crystallinity is required.

  Here, the liquid phase methods such as the ultra-high temperature ultra-high pressure solution method and the flux method have a dislocation density higher than the vapor phase methods such as the HVPE (hydride vapor phase epitaxy) method and the MOCVD (metal organic chemical vapor deposition) method. It is expected that low group III nitride crystal growth is possible.

For example, Japanese Unexamined Patent Application Publication No. 2004-244307 (hereinafter referred to as Patent Document 1) includes a substrate, a semiconductor layer formed on the substrate, and a group III nitride crystal formed above the semiconductor layer. A group III nitride substrate, wherein the semiconductor layer is made of a semiconductor represented by a composition formula Al _u Ga _v In _1-uv N (0 ≦ u ≦ 1, 0 ≦ v ≦ 1), The surface is a (0001) plane step inclined in one direction arranged stepwise, the angle between the inclined plane and the (0001) plane is 0.05 ° or more, and A group III nitride substrate is disclosed in which the in-plane variation of the carrier concentration of the group III nitride crystal formed on the semiconductor layer is 1/5 or more and 5 times or less of the average value of the carrier concentration.

Further, Patent Document 1 discloses a method for producing such a group III nitride crystal substrate, which is represented by a composition formula Al _u Ga _v In _{1 -uv} N (0 ≦ u ≦ 1, 0 ≦ v ≦ 1) on the substrate. Forming a semiconductor layer having a (0001) plane on the surface thereof, and treating the surface of the semiconductor layer so as to be inclined with respect to the (0001) plane of the semiconductor layer At least one group III element by bringing the surface of the semiconductor layer into contact with a melt containing at least one group III element selected from gallium, aluminum and indium and a solvent in an atmosphere containing nitrogen And a step of reacting nitrogen with nitrogen to grow a group III nitride crystal on the semiconductor layer.

  In the method of Patent Document 1, the surface of the semiconductor layer is processed into a stepped shape with the (0001) plane exposed. Therefore, abnormal growth during crystal growth can be prevented. In addition, a crystal having high surface flatness can be obtained as compared with the case where a normal seed crystal substrate is used. In particular, by using a tilted substrate in the liquid phase growth, it is possible to improve the growth rate and the uniformity of the concentration of impurities incorporated into the crystal as compared with the case where the tilted substrate is not used.

  Here, when a group III nitride crystal is grown on a group III nitride substrate whose principal surface is the (0001) plane by the liquid phase method, the dislocation of the group III nitride substrate is the growth direction of the group III nitride crystal. In the <0001> direction, and reaches the growth surface of the group III nitride crystal. When a group III nitride crystal is grown thickly, dislocations having different Burgers vector directions are combined by attraction and disappear, thereby reducing the dislocation density of the group III nitride crystal.

However, when the dislocation density of the crystal is less than 1 × 10 ⁷ cm ⁻² , the distance between the dislocations is increased, so that the possibility of the above-described dislocation coalescence is extremely reduced. That is, when a group III nitride crystal is grown on a group III nitride crystal substrate having a dislocation density of less than 1 × 10 ⁷ cm ⁻² by a liquid phase method, the dislocation density is higher than that of the group III nitride crystal substrate that is the base substrate. It was difficult to grow a group III nitride crystal having a low A.
JP 2004-244307 A

  An object of the present invention is to provide a group III nitride crystal growth method and a group III nitride crystal substrate capable of reducing the dislocation density.

  The present invention is a method of growing a group III nitride crystal on a main surface of a base substrate by a liquid phase method, and at least of the dislocations remaining in the group III nitride crystal during the growth of the group III nitride crystal. A method for growing a group III nitride crystal, characterized in that a part thereof is propagated in a direction substantially parallel to the {0001} plane and discharged to the outer periphery of the group III nitride crystal.

  In the group III nitride crystal growth method according to the present invention, the base substrate includes at least a group III nitride crystal layer on the main surface side, and a normal line of the main surface is in a <0001> direction of the group III nitride crystal layer. And an inclination angle of 0.5 ° to 10 °.

Further, in the method for growing a group III nitride crystal according to the present invention, the dislocation density on the main surface of the base substrate is less than 1 × 10 ⁷ cm ⁻² , and the growth surface after crystal growth of the group III nitride crystal is The dislocation density can be 1/10 or less of the dislocation density in the main surface. Moreover, nitrogen-containing gas can be supplied in the melt containing a group III element as a liquid phase method.

  In addition, the present invention is a group III nitride crystal substrate obtained by cutting out from a group III nitride crystal obtained by the above growth method.

  According to the present invention, it is possible to provide a group III nitride crystal growth method and a group III nitride crystal substrate capable of reducing the dislocation density.

(Embodiment 1)
One embodiment of a method for growing a group III nitride crystal according to the present invention is a method for growing a group III nitride crystal 20 on a main surface 10 m of a base substrate 10 by a liquid phase method with reference to FIG. The base substrate 10 includes at least the group III nitride crystal region 10a on the main surface side, and the normal line of the main surface 10m is 0.5 ° or more to the <0001> direction of the group III nitride crystal region 10a. When the group III nitride crystal 20 is grown, at least a part of the dislocations remaining in the group III nitride crystal 20 is substantially parallel to the {0001} plane 20c. It is characterized by being propagated in the direction and discharged to the outer peripheral portion of the group III nitride crystal 20.

  Here, the liquid phase method is not particularly limited, but from the viewpoint of efficiently growing a crystal having a low dislocation density, a base substrate is disposed in the melt 32 containing a group III element with reference to FIG. A method of growing a group III nitride crystal 20 on the main surface 10 m of the base substrate 10 by supplying a nitrogen-containing gas 34 into the melt 32 is preferable. If it is the melt 32 containing group III nitride, there will be no restriction | limiting in particular, The metal element (Na, Li which becomes a group III element melt (self-flux method), a group III element, and a solvent (flux) of a group III element For example, a melt (flux method) with an alkali metal element such as Ca, an alkaline earth metal element such as Ca, or a transition metal element such as Cu, Ti, Fe, Mn, or Cr is used. In particular, from the viewpoint of reducing the concentration of intrinsic defects contained in the crystal and / or controlling electrical characteristics such as carrier concentration, a melt having a high purity of the group III element is preferable. For example, the purity of the group III element is 99 mol% or more. Is preferable, more preferably 99.99 mol% or more, and still more preferably 99.9999 mol% or more.

  The base substrate 10 used in the present embodiment includes at least the group III nitride crystal region 10a on the main surface side, and the normal line 10mv of the main surface 10m is relative to the <0001> direction 10cv of the group III nitride crystal region 10a. It has an inclination angle θ of 0.5 ° or more and 10 ° or less. When the group III nitride crystal 20 is grown on such a main surface 10m, at least a part of the dislocation inherited from the base substrate 10 or generated during crystal growth and remaining in the group III nitride crystal 20 is obtained. Can be propagated in a direction substantially parallel to the {0001} plane 20c and discharged to the outer periphery of the group III nitride crystal 20, and the dislocation density of the group III nitride crystal 20 can be reduced. . The {0001} plane and <0001> direction of the crystal can be specified by X-ray diffraction of the crystal. The state of dislocation propagation (dislocation propagation line 20d) in the crystal can be observed by a light scattering tomography method. The <0001> direction is a generic name including the [0001] direction and the [000-1] direction that are geometrically equivalent. The {0001} plane is a generic name including a geometrically equivalent (0001) plane and (000-1) plane.

Such a reduction method is different from the reduction of dislocation density in which dislocations having different Burgers vector directions are combined and disappeared by attractive force, and even if the dislocation density of the crystal is less than 1 × 10 ⁷ cm ^−2. The dislocation density can be further reduced. The dislocation density on the surface of the crystal can be measured by a cathodoluminescence method.

  Referring to FIG. 2, main surface 10m of base substrate 10 includes a plurality of {0001} surfaces 10mc and a plurality of step surfaces 10t having an angle with respect to each of {0001} surfaces 10mc. Are step-like uneven surfaces each having a plurality of steps 10s. In addition, the normal line of the main surface 10m shall mean the normal line about the plane which looked at the main surface 10m macroscopically.

  When the group III nitride crystal 20 is grown on such a main surface 10m, the group III nitride crystal 20 is formed on the step surface 10t of the main surface 10m and the direction perpendicular to the {0001} surface 10c of the main surface 10m. Grows in a vertical direction. Therefore, the crystal growth surfaces 20a and 20b during the growth of the group III nitride crystal 20 have an angle with respect to each of the plurality of {0001} surfaces 20ac and 20bc and the {0001} surfaces 20ac and 20bc. A plurality of steps 20as and 20bs each formed by a plurality of step surfaces 20at and 20bt are formed. Here, the crystal growth in the direction perpendicular to the step faces 20at and 20bt is superior to the crystal growth in the direction perpendicular to the {0001} faces 20ac and 20bc. Dislocations propagate in the crystal growth direction. For this reason, dislocations inherited from the main surface of the base substrate 10 or generated during crystal growth and remaining in the crystal are propagated substantially parallel to the {0001} direction (FIG. 1 (b) and It is considered that the dislocation propagation line 20d in FIG. 2B can be discharged to the outer periphery of the crystal. Here, the dislocation propagation line 20 refers to a line indicating a trajectory of dislocation propagation.

  Here, the direction substantially parallel to the {0001} plane, which is the direction in which dislocations remaining in the crystal propagate, is the crystal growth rate in the direction perpendicular to the step surfaces 20at and 20bt in the flux method or the self-flux method. Since the crystal growth rate in the direction perpendicular to the {0001} planes 20ac and 20bc is about twice or more, the tilt angle φ with respect to the {0001} plane (this is the dislocation propagation line 20d and the {0001} plane 20c Is a direction in which the dislocation propagation angle φ is about 26 ° or less.

  As the group III nitride crystal 20 grows, the step surfaces 20at and 20bt move to the outer periphery of the crystal together with dislocations, and the step surface disappears at a certain crystal growth surface 20e. Furthermore, the group III nitride crystal 20 having the crystal growth surface 20s is obtained by growing the crystal in the direction perpendicular to the {0001} plane. In this way, a group III nitride crystal having a reduced dislocation density at the crystal growth surface 20s is obtained.

  In the base substrate 10, the normal line 10 mv of the main surface 10 m with respect to the <0001> direction 10 cv of the group III nitride crystal region 10 a exists on the main surface 10 m of the base substrate 10 when the inclination angle θ is smaller than 0.5 °. Since the number of 10s is small, dislocations cannot be efficiently propagated in a direction substantially parallel to the {0001} plane, and if it is larger than 10 °, the number of steps 10s existing on the main surface 10m increases, and crystal growth occurs. Steps 20as and 20bs are combined into a macro step (not shown). When the macro step occurs, the melt is caught in the macro step and a vacuole is easily generated in the crystal. From this viewpoint, the inclination angle θ is more preferably 0.5 ° or more and 5 ° or less.

  Further, the direction 6h of the inclination of the normal line 10mv of the main surface 10m is not particularly limited, but from the viewpoint of crystal symmetry, it is inclined from the <0001> direction to the <1-100> direction or the <11-20> direction. It is preferable.

In the group III nitride crystal growth method of this embodiment, in addition to the tilt angle θ described above, crystal growth occurs on the main surface 10m of the base substrate having a dislocation density of less than 1 × 10 ⁷ cm ⁻² on the main surface 10m. A group III nitride crystal in which the dislocation density on the subsequent growth surface 20 s is 1/10 or less of the dislocation density on the main surface 10 m of the base substrate 10 can be grown. In the present embodiment, unlike the reduction of dislocation density caused by dislocations with different Burgers vector directions combined by attraction, the dislocation density of the base substrate is less than 1 × 10 ⁷ cm ^−2. However, the dislocation density of the crystal to be grown can be further reduced, and the dislocation density on the growth surface 20 s after the crystal growth can be reduced to 1/10 or less of the dislocation density on the main surface 10 m of the base substrate 10.

(Embodiment 2)
One embodiment of a group III nitride crystal substrate according to the present invention is obtained by cutting out from a group III nitride crystal 20 obtained by the growth method of embodiment 1 with reference to FIG. Such a group III nitride crystal substrate has a reduced dislocation density on its main surface.

  Here, the method of cutting out the substrate from the group III nitride crystal 20 is not particularly limited, and a wire saw, an inner peripheral blade, an outer peripheral blade, laser light, or the like is used. Moreover, it is preferable that the cut main surfaces 20q and 20r of the group III nitride crystal substrate 20p are mirror-finished by polishing and / or grinding.

Example 1
Referring to FIG. 1A, first, a wurtzite GaN crystal substrate having a size of 10 mm × 10 mm × 350 μm in thickness was prepared as a base substrate 10. The base substrate (GaN substrate) 10 has a main surface 10m of (0001) surface, and the normal of the main surface 10m has an inclination angle θ of 1 ° from the [0001] direction to the [1-100] direction. The main surface 10m is made into a mirror surface by polishing. When the dislocation density on the main surface of the base substrate was detected and measured as a dark spot by the cathodoluminescence method, the in-plane average dislocation density was 5 × 10 ⁶ cm ⁻² .

  Referring to FIG. 1B, next, a GaN crystal was grown to 500 μm on the main surface 10 m of the base substrate 10 by a liquid phase method using high-purity Ga as a solvent. Specifically, referring to FIG. 3, a high-purity metal having a purity of 7N (99.99999 mol%) is placed in the bottom surface of the crucible with the main surface 10m facing upward in an alumina crucible 30. 50 g of Ga was weighed and put together in a crucible and heated to 950 ° C. to form a high-purity Ga melt (melt 32 containing a group III element) in contact with the base substrate 10. Nitrogen gas (nitrogen-containing gas 34) having a pressure of 8 MPa was supplied to this high-purity Ga melt (melt 32) for 5000 hours to grow a GaN crystal (Group III nitride crystal 20) to an average growth thickness of 500 μm. . The plane orientation of the growth surface of the GaN crystal after crystal growth was (0001).

Next, the grown GaN crystal was taken out of the crucible, and its surface was polished to make a mirror surface. When the in-plane average dislocation density of the mirror-finished GaN crystal surface was examined by the cathodoluminescence method in the same manner as the base substrate, the dislocation density was 7 × 10 ⁴ cm ⁻² . The dislocation propagation of the GaN crystal was observed by light scattering tomography. As a result, the dislocation propagated in a direction substantially parallel to the (0001) plane and reached the outer peripheral side of the crystal in the early growth stage near the base substrate. It was confirmed that Further, when the inside of the crystal was observed with a fluorescence microscope, no vacuole was observed.

(Example 2)
A GaN crystal is grown in the same manner as in Example 1 except that the inclination angle from the [0001] direction to the [1-100] direction of the normal line of the main surface 10 m is 3 °, and the surface is mirror-finished did. For this GaN crystal, the average dislocation density on the surface is 5.5 × 10 ⁴ cm ⁻² , and the dislocation propagates in a direction substantially parallel to the (0001) plane in the early growth stage close to the base substrate. It was confirmed that it reached the outer peripheral side surface, and no vacuoles were observed inside the crystal.

(Example 3)
A GaN crystal is grown in the same manner as in Example 1 except that the inclination angle from the [0001] direction to the [1-100] direction of the normal of the main surface 10 m is 5 °, and the surface is mirror-finished did. With respect to this GaN crystal, the average dislocation density on the surface is 4.8 × 10 ⁴ cm ⁻² , and the dislocation propagates in a direction substantially parallel to the (0001) plane in the early growth stage close to the base substrate. It was confirmed that it reached the outer peripheral side surface, and no vacuoles were observed inside the crystal.

Example 4
A GaN crystal is grown in the same manner as in Example 1 except that the inclination angle from the [0001] direction to the [1-100] direction of the normal line of the main surface 10 m is 8 °, and the surface is mirror-finished did. With respect to this GaN crystal, the average dislocation density on the surface is 4.3 × 10 ⁴ cm ⁻² , and the dislocation propagates in a direction substantially parallel to the (0001) plane in the initial stage of growth close to the base substrate. It was confirmed that it reached the outer peripheral side surface, and no vacuoles were observed inside the crystal. Virtually no problem was observed, but a very small amount of vacuoles were observed inside the crystal.

(Comparative Example 1)
A GaN crystal was grown in the same manner as in Example 1 except that the normal of the main surface of the base substrate was in the [0001] direction (inclination angle θ was 0 °), and the surface thereof was mirror-finished. For this GaN crystal, the average dislocation density at the surface was 5.1 × 10 ⁶ cm ⁻² , and it was confirmed that the dislocations propagated in a direction substantially perpendicular to the (0001) plane. No vacuoles were observed.

(Comparative Example 2)
A GaN crystal is grown in the same manner as in Example 1 except that the inclination angle from the [0001] direction to the [1-100] direction of the normal line of the main surface 10 m is 11 °, and the surface is mirror-finished did. For this GaN crystal, the average dislocation density on the surface is 6.0 × 10 ⁴ cm ⁻² , and dislocations propagate in a direction substantially parallel to the (0001) plane in the early growth stage close to the base substrate. Although it was confirmed that it reached the outer peripheral side surface, vacuoles were observed inside the crystal.

  From Examples 1 to 4 and Comparative Examples 1 and 2, a group III nitride crystal is formed on a base substrate whose normal to the main surface has an inclination angle of 0.5 ° to 10 ° with respect to the <0001> direction. By growing, at least some of the dislocations remaining in the group III nitride crystal are propagated in a direction substantially parallel to the {0001} plane and discharged to the outer periphery of the group III nitride crystal. It was found that a group III nitride crystal having a reduced dislocation density on the crystal growth surface after growth was obtained. However, from the viewpoint of eliminating the presence of vacuoles in the crystal, it is more preferable that the tilt angle be 0.5 ° or more and 5 ° or less.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every 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.

It is a schematic sectional drawing which shows one Embodiment of the growth method of the group III nitride crystal concerning this invention. Here, (a) shows a base substrate, and (b) shows a state in which a group III nitride crystal is grown on the base substrate. It is a general | schematic fragmentary expanded sectional view which shows one Embodiment of the growth method of the group III nitride crystal concerning this invention. Here, (a) shows what expanded the IIA part in Fig.1 (a), (b) shows what expanded the IIB part in FIG.1 (b). It is a schematic sectional drawing which shows an example which grows a group III nitride crystal by a liquid phase method. It is a schematic sectional drawing which shows one Embodiment of the group III nitride crystal substrate concerning this invention.

Explanation of symbols

  10 base substrate, 10c, 10mc, 20c, 20ac, 20bc {0001} plane, 10cv <0001> direction, 10h direction of inclination of normal of main surface, 10m, 20q, 20r main surface, 10mv normal, 10s, 20as , 20bs step, 10t, 20at, 20bt step plane, 20 group III nitride crystal, 20a, 20b, 20e, 20s crystal growth plane, 20d dislocation propagation line, 20p group III nitride crystal substrate, 30 crucible, 32 melt, 34 Nitrogen-containing gas.

Claims (5)

A method of growing a group III nitride crystal on a main surface of a base substrate by a liquid phase method,
During the growth of the group III nitride crystal, at least some of the dislocations remaining in the group III nitride crystal are propagated in a direction substantially parallel to the {0001} plane, thereby causing the group III nitride crystal. A method for growing a group III nitride crystal, characterized in that it is discharged to the outer periphery of the substrate. The base substrate includes a group III nitride crystal layer on at least the main surface side,
2. The method for growing a group III nitride crystal according to claim 1, wherein the normal line of the main surface has an inclination angle of 0.5 ° or more and 10 ° or less with respect to a <0001> direction of the group III nitride crystal layer. . A dislocation density in the main surface of the base substrate is less than 1 × 10 ⁷ cm ⁻² ;
The method for growing a group III nitride crystal according to claim 1 or 2, wherein a dislocation density on a growth surface of the group III nitride crystal after crystal growth is 1/10 or less of a dislocation density on the main surface.   The method for growing a group III nitride crystal according to any one of claims 1 to 3, wherein a nitrogen-containing gas is supplied into the melt containing a group III element as the liquid phase method.   A group III nitride crystal substrate obtained by cutting out from a group III nitride crystal obtained by the growth method according to any one of claims 1 to 4.

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