CN103811611A - Sapphire substrate for growing gallium nitride crystal, manufacturing method of gallium nitride crystal, and gallium nitride crystal - Google Patents

Abstract

The present invention provides a sapphire substrate for growing gallium nitride crystals, a method for manufacturing gallium nitride crystals, and gallium nitride crystals capable of achieving lower dislocation of gallium nitride crystals than conventional ones and higher quality of gallium nitride crystals crystallization. A sapphire substrate (10) for gallium nitride crystal growth, in which a plurality of tiny protrusions (12) are formed on the C-plane of the sapphire substrate (11), so as to face the a-axis direction of the sapphire substrate (11) away from the C-plane The plane with an angle of 43.2 degrees is the reference plane, and the region (13) within ±10 degrees from the reference plane accounts for more than 5% of the surface area of the tiny convex portion (12). A method for manufacturing gallium nitride crystals, comprising growing gallium nitride crystals (14) on the sapphire substrate (10) for growing gallium nitride crystals. A gallium nitride crystal (14) manufactured by the manufacturing method.

Description

Sapphire substrate for growing gallium nitride crystal, manufacturing method of gallium nitride crystal, and gallium nitride crystal

technical field

The present invention relates to a sapphire substrate for growing gallium nitride crystals, a method for manufacturing gallium nitride crystals, and gallium nitride crystals.

Background technique

As a method for improving the light extraction efficiency of gallium nitride-based light-emitting diodes (LEDs), conical or polygonal conical micro-protrusions or micro-concaves are formed on the C-plane of the sapphire substrate, and the A method in which gallium nitride crystals are grown flat and a light emitting layer is formed thereon (for example, Patent Document 1 or 2).

In these methods, when a gallium nitride crystal is grown on a sapphire substrate having uneven portions formed on the surface, dislocations are merged and eliminated by promoting island-like growth at the initial stage of growth. Compared with the case of growing the gallium nitride crystal, it has the effect of obtaining a gallium nitride crystal with less dislocations, and is effective for improving the quality of the gallium nitride crystal.

prior art literature

Patent Document 1: Japanese Patent Laid-Open No. 2004-200523

Patent Document 2: Japanese Unexamined Patent Publication No. 2006-66442

In recent years, gallium nitride crystals have been required to be further improved in quality, and improvement of the above-mentioned method has been desired.

Contents of the invention

Therefore, an object of the present invention is to provide a sapphire substrate for growing a gallium nitride crystal and a production of a gallium nitride crystal capable of achieving lower dislocation of the gallium nitride crystal than conventional ones and higher quality of the gallium nitride crystal. Method and gallium nitride crystallization.

The present invention studied in order to achieve this object is a sapphire substrate for gallium nitride crystal growth, in which a plurality of minute protrusions are formed on the C-plane of the sapphire substrate so as to face the a-axis direction of the above-mentioned sapphire substrate at an angle from the C-plane. The plane at 43.2 degrees is the reference plane, and the region within ±10 degrees from the reference plane accounts for 5% or more of the surface area of the micro-protrusions.

In addition, the present invention is a method for producing a gallium nitride crystal by growing a gallium nitride crystal on the above-mentioned sapphire substrate for growing gallium nitride crystal.

In addition, the present invention is a gallium nitride crystal produced by the above-mentioned production method.

The effects of the present invention are as follows.

According to the present invention, it is possible to provide a sapphire substrate for growing a gallium nitride crystal and a method for producing a gallium nitride crystal, which can achieve lower dislocation of gallium nitride crystals and higher quality of gallium nitride crystals than conventional ones and gallium nitride crystals.

Description of drawings

FIG. 1 is a view showing a sapphire substrate for gallium nitride crystal growth according to one embodiment of the present invention.

FIG. 2 is a diagram showing the crystal structure of gallium nitride.

3( a ) to ( f ) are diagrams illustrating a method of forming a micro-protrusion and a method of adjusting the angle of its inclined surface.

FIG. 4 is a diagram explaining the basis of numerical limitation.

In the picture:

10—sapphire substrate for gallium nitride crystal growth, 11—sapphire substrate, 12—micro convex portion, 13—area, 14—gallium nitride crystal, 15—resist, 16—photoresist pattern.

Detailed ways

Next, preferred embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1 , the sapphire substrate 10 for gallium nitride crystal growth according to this embodiment is characterized in that a plurality of tiny protrusions 12 are formed on the C-plane (including its slightly inclined surface) of the sapphire substrate 11 so as to face the sapphire substrate. The angle between the a-axis direction of 11 and the C plane is 43.2 degrees as a reference, and the region 13 within ±10 degrees from the reference plane accounts for more than 5% of the surface area of the micro-protrusion 12.

The surface facing the sapphire substrate 11 at an angle of 43.2 degrees from the C-plane in the a-axis direction becomes the R-plane (10-12 plane) of the gallium nitride crystal when the gallium nitride crystal is grown thereon. The reason for this is described below.

When joining dissimilar materials, in order to minimize the energy required to form the joint and to ease the lattice deformation between the dissimilar materials, the respective materials are joined in such a manner that the orientations of the crystallographic axes are shifted within the joining plane. Therefore, when the gallium nitride crystal is grown on the sapphire substrate 11 , as shown in FIG.

Thus, the plane facing the a-axis direction of the sapphire substrate 11 at an angle of 43.2 degrees from the C-plane is rotated when the gallium nitride crystal 14 is grown, and as a result, becomes an angle from the C-plane in the m-axis direction of the gallium nitride crystal 14 It is the plane at 43.2 degrees, that is, the R plane of the gallium nitride crystal 14 .

The R plane of the gallium nitride crystal 14 is stable among many crystal planes, and the acquisition efficiency of the raw material during the growth of the gallium nitride crystal 14 is low. Therefore, when there is a region 13 with a certain area close to the R plane on the inclined plane of the minute protrusion 12, the growth on the R plane is slower than that on the other planes. A hexagonal pyramid-shaped structure surrounded by the R plane of the gallium nitride crystal 14 is formed on the top.

The hexagonal pyramid-shaped structure is surrounded by the R surface, so it is more stable than the case where the unevenness formed by the surface other than the R surface is formed, and the hexagonal pyramid-shaped structure is maintained for a long time during the growth of the gallium nitride crystal 14, which is longer than the conventional one. Time continued island growth. In this way, the convergence and elimination of dislocations are promoted compared with conventional ones, and lower dislocations in the obtained gallium nitride crystal 14 are realized.

In order to obtain such a hexagonal pyramid-shaped structure composed of the R plane, as described above, the plane facing the a-axis direction of the sapphire substrate 11 with an angle of 43.2 degrees from the C plane as the reference plane needs to be within ±10 degrees from the reference plane. The area 13 accounts for more than 5% of the surface area of the micro-protrusion 12.

In addition, the area of a minute part of the surface and the angle with respect to the reference plane can be obtained by measuring the surface shape with an AFM (atomic force microscope). Using this AFM, the sum of the areas of the portions satisfying the criterion of the region 13 and the area of the minute convex portion 12 are respectively obtained, and the area ratio is calculated.

Here, a method of forming the minute convex portion 12 and a method of adjusting the angle of the inclined surface will be described.

As shown in FIG. 3 , first, a resist 15 is applied on the surface C of the sapphire substrate 11 ( FIG. 3( a )). Thereafter, in order to evaporate excess organic solvent in the resist 15 , the sapphire substrate 11 coated with the resist 15 was placed on a heat-retaining tray, and preliminary heating was performed for several minutes. The temperature at this time varies depending on the type of the resist 15, but is about 120° C. when a novolak-based resin is used.

Then, pattern exposure, development, cleaning, and the like are performed to form a photoresist pattern 16 ( FIG. 3( b )). At this time, by forming the photoresist pattern 16 of the hexagonal pattern, in the subsequent process, the rounded hexagonal pyramid-shaped minute protrusions 12 shown in FIG. When the plane facing the a-axis direction of the sapphire substrate 11 with an angle of 43.2 degrees from the C plane is used as the reference plane, the ratio of the area 13 within ±10 degrees from the reference plane to the surface area of the micro-protrusion 12 .

Next, the photoresist pattern 16 on the sapphire substrate 11 is irradiated with ultraviolet rays by an ultraviolet irradiation device whose temperature is controlled to be about 100° C. lower than the preliminary heating temperature to bridge and cure the resist resin.

Thereafter, the sapphire substrate 11 was heated to 150° C. higher than the preheating temperature to completely remove the organic solvent in the resist 15 that was not removed by the preheating. As long as the preheating is performed at a high temperature, the organic solvent can be completely removed, but it will have an adverse effect on the subsequent exposure of the pattern, and may not be able to form the desired photoresist pattern 16. Therefore, it is preferable to use two stages. heating.

Next, the sapphire substrate 11 is entered into a plasma etching apparatus, and after supplying Cl ₂ gas, BCl ₃ gas, Ar gas, etc., plasma is generated to etch the sapphire substrate 11 to form minute protrusions 12 ( FIG. 3( c )).

At this time, for example, by prolonging the etching time, an inclined surface is gradually formed on the minute protrusion 12 , and the inclined surface becomes gentle ( FIGS. 3( d ) to ( f )). That is, by adjusting etching conditions such as etching time, it is possible to adjust the angle of the inclined surface of the minute convex portion 12 .

In this way, the surface at an angle of 43.2 degrees from the C plane in the a-axis direction of the sapphire substrate 11 is used as a reference plane, and the region 13 within ±10 degrees from the reference plane accounts for 5% or more of the surface area of the micro-protrusion 12. In this way, the angle of the inclined surface of the minute convex portion 12 is adjusted.

Using these methods, by adjusting the etching time, when the plane facing the a-axis direction of the sapphire substrate 11 with an angle of 43.2 degrees from the C plane is used as the reference plane, the area 13 within ±10 degrees from the reference plane occupies the micro-protrusions 12 The proportion of the surface area was adjusted to 0% to 50%, and gallium nitride crystals were grown on the obtained sapphire substrates for growing gallium nitride crystals. Furthermore, the half widths of the X-ray rocking curves of the R plane and the C plane were measured for each gallium nitride crystal, and the results shown in Table 1 and FIG. 4 were obtained.

[Table 1]

Proportion[%] R side [sec] C side [sec] 0 711 290 2 723 315 3 700 300 5 540 240 7 450 210 10 360 200 15 300 175 25 230 155

30 195 120 40 145 78 50 100 55

As can be seen from Table 1 and FIG. 4, on the basis of the plane facing the a-axis direction of the sapphire substrate 11 at an angle of 43.2 degrees from the C plane, the area 13 within ±10 degrees from the reference plane occupies the surface area of the micro-protrusion 12. When the ratio is less than 5%, the half-width of the X-ray rocking curve is large, and if it is more than 5%, the higher the ratio, the smaller the half-width of the X-ray rocking curve.

When the proportion is less than 5%, its R face disappears in the growth of GaN crystal, and in the early stage of growth, the surface of GaN crystal is flattened, and other faces have advantages over the growth of GaN crystal, so they cannot The above-mentioned effects are obtained.

Therefore, it is adjusted so that the surface facing the a-axis direction of the sapphire substrate 11 at an angle of 43.2 degrees from the C plane is used as a reference plane, and the ratio of the region 13 within ±10 degrees from the reference plane to the surface junction of the micro-protrusion 12 is 5. %above.

When the sapphire substrate 10 for growing a gallium nitride crystal having the above-mentioned structure is used and the gallium nitride crystal 14 is grown thereon, the dislocation of the gallium nitride crystal 14 can be lower than before, and the nitrogen GaN crystal 14 is of higher quality.

Therefore, according to the present invention, it is possible to provide a sapphire substrate for growing a gallium nitride crystal and a gallium nitride crystal capable of achieving lower dislocation of the gallium nitride crystal and higher quality of the gallium nitride crystal than conventional ones. Manufacturing method and gallium nitride crystallization.

In addition, in the present embodiment, the photoresist pattern 16 is made into a hexagonal pattern, but it may be formed in a circular pattern.

Claims (3)

1. A sapphire substrate for gallium nitride crystal growth, which forms a plurality of tiny protrusions on the C face of the sapphire substrate, the sapphire substrate for gallium nitride crystal growth is characterized in that, Taking the plane at an angle of 43.2 degrees from the C plane in the a-axis direction of the sapphire substrate as a reference plane, the area within ±10 degrees from the reference plane accounts for 5% or more of the surface area of the micro-protrusions. 2. A method for manufacturing gallium nitride crystals, characterized in that, A gallium nitride crystal is grown on the sapphire substrate for growing a gallium nitride crystal according to claim 1 . 3. A gallium nitride crystal, characterized in that, Manufactured by the manufacturing method described in claim 2.

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