JP6505995B2 - Ga2O3-based single crystal substrate - Google Patents

Description

The present invention relates to a Ga ₂ O ₃ -based single crystal substrate.

(100) _β-Ga 2 _{O 3} based substrate whose principal plane is rotated 50 ° to 90 ° from the surface has been proposed (e.g., see Patent Document 1.).

  Moreover, in patent document 1, (010), (001), (-201), (101), and (310) planes are mentioned as a plane rotated 50 degrees or more and 90 degrees or less from this (100) plane. ing.

International Publication No. 2013/035464

An object of the present invention is to provide a Ga ₂ O ₃ -based single crystal substrate capable of rapidly growing a Ga ₂ O ₃ -based crystal film.

The inventors of the present invention conducted intensive studies on a method of growing a Ga ₂ O ₃ -based crystal film on a Ga ₂ O ₃ -based single crystal substrate. The inventors have found that the above object can be achieved by epitaxially growing a Ga ₂ O ₃ -based crystal film, resulting in the present invention.

  That is, the said objective is achieved by each invention described in following [1]-[4].

[1] When the rotation direction from the (100) plane to the (001) plane is defined as positive, with the [010] axis as the rotation axis, 10 ° or more 45 ° from the (100) plane A Ga ₂ O ₃ -based single crystal substrate having, as a growth surface, a surface rotated less than (but excluding the (201) surface) or a surface rotated by more than 135 ° and 150 ° or less from the (100) surface .

[2] A Ga ₂ O ₃ -based single crystal substrate having, as a growth surface, a plane rotated by 10 ° or more and less than 45 ° from the (100) plane with the [001] axis as the rotation axis .

According to the present invention, a Ga ₂ O ₃ based crystal film can be grown at high speed.

Of Ga ₂ O ₃ single crystal substrate main surface is a diagram showing a rotation angle from that (100) plane and the rotation axis [010] axis, the relationship between crack density over the main surface (Example 1) . Of Ga ₂ O ₃ single crystal substrate main surface is a diagram showing the angle of rotation from the [001] axis as a rotation axis (100) plane, a relationship between crack density over the main surface (Example 1) . It is a surface optical microscope picture after CMP processing of the principal surface of a Ga ₂ O ₃ single crystal substrate whose principal surface is the surface rotated by 160 ° from the (100) surface with the axis as the rotation axis [010] (Example 1) ). Ga ₂ O ₃ is a diagram showing the relationship between the rotation angle and the latent scratches (polishing damage) from (100) plane to the rotational axis [010] axis of the main surface of the single crystal substrate (Example 1). Ga ₂ O ₃ as a rotation axis [010] axis of the main surface of the single crystal substrate and the rotation angle from the (100) plane is a diagram showing the relationship between the growth rate of the epitaxial film (Example 2). Ga ₂ O ₃ as a rotation axis [001] axis of the main surface of the single crystal substrate and the rotation angle from the (100) plane is a diagram showing the relationship between the growth rate of the epitaxial film (Example 2). And the inclination angle of the Ga ₂ O ₃ to the [010] direction of the (-201) plane of the single crystal substrate is a diagram showing the relationship between the growth rate of the epitaxial film (Example 2). Ga ₂ O ₃ is a diagram showing an X-ray diffraction measurement results after epitaxial growth on the single crystal substrate (a), a diagram showing an enlarged vicinity of (002) plane of FIG. (A) (b) (Example 3). Is a photograph showing the RHEED image of Ga ₂ O ₃ [010] epitaxial film surface grown axis plane is rotated as the rotation axis of the single crystal substrate (Example 3). FIG. 16 is a photograph showing a RHEED image on the surface of an epitaxial film grown on a surface rotated about the [001] axis of the main surface of the Ga ₂ O ₃ single crystal substrate (Example 3). FIG. The rotation angle from the (100) plane with the [010] axis of the main surface of the Ga ₂ O ₃ single crystal substrate as the rotation axis, and the surface roughness (RMS) of the epitaxial film grown on the main surface of each substrate (Example 4) which shows the relationship of. Of Ga ₂ O ₃ [010] were grown axis plane is rotated as the rotation shaft of the epitaxial film surface of the main surface of the single crystal substrate is a photograph showing an AFM image of 5μm angle (Example 4). Is a diagram illustrating Ga ₂ O ₃ of the main surface of the single crystal substrate [001] surface roughness estimate an axis from AFM images of 5μm angle of the grown epitaxial film surface is rotated plane as the rotation axis (RMS) (Example 4). Is a diagram illustrating Ga ₂ O ₃ of the main surface of the single crystal substrate [001] surface roughness estimate an axis from AFM images of 1μm square of the grown epitaxial film surface is rotated plane as the rotation axis (RMS) (Example 4). FIG. 16 is a photograph showing an AFM image of a 1 μm square of an epitaxial film surface grown on a surface rotated with the [001] axis of the main surface of the Ga ₂ O ₃ single crystal substrate as a rotational axis (Example 4).

  Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings, using examples.

Example 1
The Ga ₂ O ₃ -based single crystal substrate has the following problems (1) and (2).

(1) The Ga ₂ O ₃ -based single crystal substrate has strong cleavage in the (100) plane, and when processing a Ga ₂ O ₃ -based single crystal substrate, peeling or cracking due to cleavage occurs. It's easy to do. It is difficult to obtain a large-sized Ga ₂ O ₃ -based single crystal substrate because peeling and cracking easily occur during substrate processing.

(2) Since the (100) plane has strong cleavage, the angle between the (100) plane and the main surface is particularly 45 as the (100) plane approaches perpendicular to the substrate surface (main surface). If the temperature is more than °, there is a problem that the Ga ₂ O ₃ -based single crystal substrate is easily broken at the time of device manufacture.

Therefore, in the present embodiment, in order to obtain a Ga ₂ O ₃ -based single crystal substrate which is less likely to cause cracking or cracking, a plurality of Ga ₂ O ₃ single crystal substrates having different plane orientations of the main surface are manufactured. The relationship between the orientation and the amount of cracks was evaluated.

Ga ₂ O ₃ system single crystal substrate, _β-Ga 2 _{O 3} single crystal such as _{β- (Ga x In y Al z} ) 2 O 3 single crystal (0 <x ≦ 1,0 ≦ y <1,0 ≦ It is a substrate which consists of z <1, x + y + z = 1).

(Preparation of Ga ₂ O ₃ single crystal substrate)
A Ga ₂ O ₃ single crystal substrate whose main surface is a plane rotated from 0 ° to 170 ° from the (100) plane with the [010] axis as the rotation axis, and 10 to 10 from the (100) plane with the [001] axis as the rotation axis. Each of a Ga ₂ O ₃ single crystal substrate having a principal surface rotated by 90 ° was cut out of a Ga ₂ O ₃ single crystal, and then processed into a plate of 10 mm square with a thickness of 1 mm. Twenty of these Ga ₂ O ₃ single crystal substrates were prepared for each rotation angle. One side of the 10 mm square Ga ₂ O ₃ single crystal substrate whose rotation axis is this [010] axis is parallel to the [010] direction. The rotation angle with the [010] axis as the rotation axis is positive in the direction from the (100) plane to the (001) plane via the (101) plane. Further, one side of a 10 mm square Ga ₂ O ₃ single crystal substrate whose rotation axis is the [001] axis is parallel to the [001] direction.

Next, the thickness of the Ga ₂ O ₃ single crystal substrate was ground to about 0.8 mm using a grinding apparatus having a grinding wheel roughness of 1000. The grinding speed is about 6 μm / min. After this grinding, while the abrasive grains made of diamond were sprayed, the surface was polished about 20 μm.

Finally, surface polishing of about 10 μm was performed by CMP (Chemical mechanical planarization: chemical mechanical polishing). After CMP treatment, organic cleaning was performed using an organic solvent (acetone, methanol, IPA, ethanol), HF immersion cleaning, H ₂ SO ₄ , H ₂ O ₂ and H ₂ O were mixed at 4: 1: 1. Immersion cleaning in acid, rinsing with ultrapure water, and drying by nitrogen blow were performed.

(Evaluation of crack density of Ga ₂ O ₃ single crystal substrate)
1 and 2, in FIG. 1, the rotation angle from the (100) plane with the [010] axis as the rotation axis of the main surface of the Ga ₂ O ₃ single crystal substrate, and the main after CMP processing The relationship with the crack density on the surface is shown. FIG. 2 shows the rotation angle from the (100) plane with the [001] axis of the main surface of the Ga ₂ O ₃ single crystal substrate as the rotation axis, and CMP. The relationship with the crack density on the main surface after treatment is shown. The crack density of the Ga ₂ O ₃ single crystal substrate at each rotation angle shown in FIGS. 1 and 2 is an average value of the crack densities of 20 sheets of Ga ₂ O ₃ single crystal substrates.

Here, the crack density on the main surface of the Ga ₂ O ₃ single crystal substrate having the [010] axis as the rotation axis is a straight line in the direction perpendicular to the [010] direction on the main surface of the Ga ₂ O ₃ single crystal substrate. Among them, when the longest straight line is a reference straight line, the number of cracks along the [010] direction intersecting the reference straight line is defined as a value obtained by dividing by the length of the reference straight line. This reference straight line is, for example, a straight line in the direction perpendicular to the [010] direction passing through the center of the Ga ₂ O ₃ single crystal substrate, and the length of the reference straight line is circular Ga ₂ O _3. It corresponds to the diameter of a single crystal substrate.

In addition, the crack density on the main surface of the Ga ₂ O ₃ single crystal substrate having the [001] axis as the rotation axis is a straight line in the direction perpendicular to the [001] direction on the main surface of the Ga ₂ O ₃ single crystal substrate. When the longest straight line is a reference straight line, the number of cracks along the [001] direction intersecting the reference straight line is defined as a value obtained by dividing by the length of the reference straight line. This reference straight line is, for example, a straight line in the direction perpendicular to the [001] direction passing through the center of the Ga ₂ O ₃ single crystal substrate, and the length of the reference straight line is circular Ga ₂ O _3. It corresponds to the diameter of a single crystal substrate.

  As shown in FIG. 1 and FIG. 2, a [010] axis rotation 10 to 150 ° substrate, whose main surface is a plane rotated 10 to 150 ° from the (100) plane with the [010] axis as the rotation axis, Cracks were not generated in the [001] axis rotation 10 to 90 ° substrate whose main surface is a plane rotated 10 to 90 ° from the (100) plane with the 001] axis as the rotation axis.

  Since no crack is generated on a 10 mm square substrate in which one side of 20 sheets is parallel to the [010] direction, it can be said that no crack is generated on a 10 mm × 200 mm rectangular substrate parallel to the [010] direction in the short direction. . Since less than one crack is generated in a 10 mm × 200 mm rectangular substrate in which the short direction is parallel to the [010] direction, it can be said that the crack density is less than 0.05 / cm.

  Similarly, no crack is generated in a 10 mm × 200 mm rectangular substrate in which the short side direction is parallel to the [001] direction because no crack is generated in a 10 mm square substrate in which one side of 20 sheets is parallel to the [001] direction. It can be said. Since less than one crack is generated in a 10 mm × 200 mm rectangular substrate in which the short direction is parallel to the [001] direction, it can be said that the crack density is less than 0.05 / cm.

  That is, it can be said that the crack density of the [010] axis rotation 10 to 150 ° substrate and the [001] axis rotation 10 to 90 ° substrate is less than 0.05 / cm.

  On the other hand, in the [010] axis rotation 160 to 180 ° substrate whose main surface is the plane rotated from 160 ° to 180 ° from the (100) plane with the [010] axis as the rotation axis, a stripe shape deep in the [010] direction A lot of defects (cracks) occurred. These cracks were generated in the polishing process using diamond abrasive grains and did not disappear in the subsequent CMP process.

FIG. 3 is a Ga ₂ O ₃ single crystal substrate whose main surface is the surface rotated by 160 ° from the (100) plane with the [010] axis as the rotation axis (the surface related to the measurement point of arrow III in FIG. 1) It is a surface optical microscope photograph after CMP processing of the main surface. The black part in the photograph is the deep groove created by the crack, and the white part in the photograph is the polished surface. The arrow in FIG. 3 indicates a direction perpendicular to the [010] direction.

  The crack density was 53 pieces / cm for the [010] axis rotation 160 ° substrate and 79 pieces / cm for the [010] axis rotation 170 ° substrate. When the crack density was 53 pieces / cm, the width in the direction perpendicular to the [010] direction of the area without cracks was about 189 μm.

  By the way, even if the flatness of the substrate was obtained by observation of the optical microscope after surface polishing and AFM (atomic force microscope), there were cases where polishing damage remained on the substrate. The residual polishing damage (latent flaw) comes to the surface as surface defects by growing a homoepitaxial film on the latent scratch.

Homoepitaxial growth was performed using MBE to evaluate the presence or absence of latent damage. The growth temperature was 750 ° C., and the growth time was 30 minutes. FIG. 4 shows the relationship between the rotation angle from the (100) plane whose rotation axis is the [010] axis of the main surface of the Ga ₂ O ₃ single crystal substrate and the presence or absence of a latent flaw (abrasive damage). There is.

  As apparent from FIG. 4, the homoepitaxial film on the [010] -axis-rotated 90 ° substrate had a mirror surface on one side, and the remaining surface was covered with scratches and hillocks derived from polishing damage. [010] Axial rotation The homoepitaxial film on the 80 ° substrate was covered with the same hillock on the entire surface. [010] Axis rotation 76.3 ° The homoepitaxial film on the substrate was only a part of mirror surface, and almost the entire surface was covered with the same hillock. Therefore, it turned out that the range of [710] axis rotation 76.3-90 degrees is a field which polish damage tends to remain.

  In the case of a [001] axis rotation 10 to 90 ° substrate whose main surface is a plane rotated 10 to 90 ° from the (100) plane with the [001] axis as the rotation axis, surface defects due to latent scratches across the entire substrate It was not confirmed.

  Therefore, in order to suppress the generation of cracks and surface scratches during surface polishing, the [010] axis rotation of 10 to 70 °, the [010] axis rotation of 100 to 150 °, and the [001] axis rotation It can be understood that a 10-90 ° plane may be used.

Evaluation of the above embodiment are those conducted on Ga ₂ O ₃ single crystal substrate, but when evaluated the Ga ₂ O ₃ system single crystal substrate other than Ga ₂ O ₃ single crystal substrate, the An evaluation result similar to the evaluation result is obtained.

As apparent from the above description, the following Ga ₂ O ₃ -based single crystal substrate can be obtained.

When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, the plane rotated 10 to 150 ° from the (100) plane A Ga ₂ O ₃ -based single crystal substrate having a main surface and a crack density of less than 0.05 / cm.

When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, 10 to 70 ° from the (100) plane, 100 to 150 A Ga ₂ O ₃ -based single crystal substrate which has a rotated surface as a main surface, a crack density of less than 0.05 / cm, and no latent flaw.

A Ga ₂ O ₃ -based single crystal substrate having a plane rotated by 10 to 90 ° from the (100) plane with the [001] axis as the axis of rotation as the main surface and having a crack density of less than 0.05 / cm.

A Ga ₂ O ₃ system that has a crack density of less than 0.05 / cm and has no latent flaw, with the [001] axis as the axis of rotation and the plane rotated 10 to 90 ° from the (100) plane as the main plane. Single crystal substrate.

(Effect of Example 1)
According to the first embodiment, in addition to the above-described effects, the following effects can be obtained.

Cracks, latent scratches and peeling during substrate processing can be remarkably suppressed, and the production yield of a large-area Ga ₂ O ₃ -based single crystal substrate can be improved. Specifically, a plane rotated about 10 to 150 degrees from the (100) plane with the [010] axis as a rotation axis, or a plane rotated 10 to 90 degrees from the (100) plane with the [001] axis as the rotation axis By using as a main surface, it becomes possible to manufacture a large-sized Ga ₂ O ₃ -based single crystal substrate having a width of about 0.2 mm or more and a width of 20 cm or less.

Example 2
When the main surface of the Ga ₂ O ₃ -based single crystal substrate is a (100) plane, the raw material supplied when growing the Ga ₂ O ₃ crystal film on the main surface is likely to be reevaporated, so the Ga ₂ O ₃ crystal is There is a problem that the film growth rate is very slow and mass productivity is low.

Therefore, in the present embodiment, in order to obtain a Ga ₂ O ₃ -based single crystal substrate in which the growth rate of the Ga ₂ O ₃ crystal film grown on the main surface becomes high, a plurality of Ga ₂ O different in plane orientation of the main surface _A Ga ₂ O ₃ crystal film was grown on each of the _three single crystal substrates, and the relationship between the plane orientation of the main surface and the growth rate of the Ga ₂ O ₃ crystal film was evaluated.

(Preparation of Ga ₂ O ₃ Single Crystal Substrate and Ga ₂ O ₃ Crystal Film)
When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, the plane rotated from 0 to 150 ° from the (100) plane and _Ga 2 _{O 3} single crystal substrate having a major surface and a rotation axis [001] axis, and a _Ga 2 _{O 3} single crystal substrate whose principal plane is rotated 10 to 90 ° from the (100) plane Prepared. Note that the _Ga 2 _{O 3} single crystal substrate Sn are added, _Ga 2 _{O 3} single crystal substrate is n-type conductivity.

The surface of the Ga ₂ O ₃ single crystal substrate was subjected to grinding and polishing, and after the grinding and polishing process, was subjected to CMP treatment. After CMP treatment, organic cleaning was performed using an organic solvent (acetone, methanol, IPA, ethanol), HF immersion cleaning, H ₂ SO ₄ , H ₂ O ₂ and H ₂ O were mixed at 4: 1: 1. Immersion cleaning in acid, rinsing with ultrapure water, and drying by nitrogen blow were performed to obtain a substrate capable of epitaxial growth. A Ga ₂ O ₃ crystal film was epitaxially grown on the substrate using MBE. The growth temperature was 750 ° C., and the growth time was 30 minutes.

(Evaluation of growth rate of Ga ₂ O ₃ single crystal film)
5 and 6 show the evaluation of the growth rate of the Ga ₂ O ₃ crystal film on the plane rotated from the (100) plane with the [010] axis of the main surface of the Ga ₂ O ₃ single crystal substrate as the rotation axis. The result and the evaluation result of the growth rate of the Ga ₂ O ₃ crystal film on the plane rotated from the (100) plane with the [001] axis of the main surface of the Ga ₂ O ₃ single crystal substrate as the rotation axis are shown. ing.

FIG. 5 shows the growth rate (nm / h) of the Ga ₂ O ₃ crystal film when the rotation angle (°) from the (100) plane with the [010] axis of the main surface of the Ga ₂ O ₃ single crystal substrate as the rotation axis. Shows the relationship with). FIG. 6 shows the growth rate (nm / h) of the Ga ₂ O ₃ crystal film as the rotation angle (°) from the (100) plane with the [001] axis of the main surface of the Ga ₂ O ₃ single crystal substrate as the rotation axis. Shows the relationship with).

In FIG. 5, the growth rate of the [010] axis rotation 10 ° plane, which is a plane rotated from the (100) plane by 10 ° with the [010] axis as the rotation axis, is approximately 500 nm / h. Because the growth rate of the surface is 10 nm / h or less (less than the measurement lower limit), the growth rate of the Ga ₂ O ₃ crystal film can be obtained by rotating 10 ° from the (100) plane with the [010] axis as the rotation axis. Can be improved by at least 50 times or more.

Further, in FIG. 5, when the plane rotated from the (100) plane in the range of 10 ° or more and 150 ° or less with the [010] axis as the rotation axis is the main plane, the (100) plane is the main plane. It shows that the growth rate of the Ga ₂ O ₃ crystal film can be made much larger than that in the case.

FIG. 6 is a case where the (100) plane is the main surface when the plane rotated from the (100) plane in the range of 10 ° or more and 90 ° or less with the [001] axis as the rotation axis is the main surface. Also indicates that the growth rate of the Ga ₂ O ₃ crystal film can be significantly increased.

  On the other hand, the (100) plane has strong cleavage, and when the angle between the (100) plane and the main surface is 45 ° or more, substrate cracking is likely to occur during device manufacture. For this reason, it is preferable to use a plane rotated less than 45 ° from the (100) plane as the main surface.

Therefore, in order to increase the growth rate of the Ga ₂ O ₃ crystal film and to suppress substrate cracking during device manufacture, the [010] axis is a rotation axis, and rotation is 10 ° or more and less than 45 ° from the (100) plane. It can be said that the main surface may be a surface rotated by 10 ° or more and less than 45 ° from the (100) plane, with the surface thus made or the [001] axis as the rotation axis.

When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, 10 ° or more and less than 45 ° from the (100) plane By using a rotated surface or a surface rotated by 150 ° or less by more than 135 °, or a surface rotated by 10 ° or more and less than 45 ° from the (100) plane, with the [001] axis as the rotation axis, The growth rate of the Ga ₂ O ₃ crystal film can be increased, and substrate cracking during device manufacture can be suppressed, and the crack density on the main surface can be made less than 0.05 / cm.

In addition, this examination is performed using a substrate whose main surface is a plane whose rotation axis is two orthogonal axes of [010] axis and [001] axis, and similar results are obtained between the two orthogonal axes. ing. Therefore, it can be easily estimated that the same result can be obtained even in the middle of these rotation axes. That is, when the main surface is a surface rotated from the (100) plane, the Ga ₂ O ₃ crystal film is more than the (100) plane if the rotation angle is 10 ° or more and less than 45 ° regardless of the direction of the rotation axis. since the growth rate can be increased, (100) by a principal surface which is rotated smaller than 10 ° or 45 ° from the surface, increasing the growth rate of the Ga ₂ O ₃ crystal film, and substrate crack during device manufacture Can be suppressed.

  Comparing FIG. 5 and FIG. 6, with the [001] axis as the rotation axis, the [001] axis rotational surface, which is a surface rotated from the (100) plane, has the [010] axis as the rotation axis (100 2.) The growth rate is generally higher than that of the [010] axis rotation plane, which is a plane rotated from the plane. For example, while the growth rate of the [010] axis rotation 10 ° surface is about 500 nm / h, the growth rate of the [001] axis rotation 10 ° surface is about 730 nm / h, and it is about 1.5 times It has become. This suggests that the growth rate is increased when the (010) plane component appears on the main surface. Therefore, it is expected that the growth rate may be increased by inclining the [010] axis rotational surface in the [010] direction and taking out the (010) surface component on the main surface.

FIG. 7 shows the relationship between the tilt angle (off angle) in the [010] direction from the [010] axis rotation 126.2 ° = (− 201) plane and the growth rate of the epitaxial film. As apparent from FIG. 7, as the inclination angle from the (-201) plane to the [010] direction of the Ga ₂ O ₃ single crystal substrate increases, the growth rate increases and saturates at an off angle of 7 °. I understood.

  From this result, it can be said that it is effective to provide an off angle in the [010] direction in order to improve the growth rate (raw material use efficiency) on the [010] axis rotation (-201) plane. In addition, since the growth rate is saturated at 7 °, the off-angle dependence of the growth rate disappears by tilting 7 ° or more, the fluctuation of the growth rate due to the substrate off-angle variation can be suppressed, and the manufacturing stability is improved. The effect is obtained. Therefore, the off angle is more preferably 7 ° or more. The same result can be obtained also when the [010] axis rotational plane other than the [010] axis rotation (-201) plane is inclined in the [010] direction.

If the evaluation of the above embodiment are those conducted with Ga ₂ O ₃ single crystal substrate, which was evaluated by using a Ga ₂ O ₃ system single crystal substrate other than Ga ₂ O ₃ single crystal substrate Also, evaluation results similar to the above evaluation results can be obtained. Also, instead of _Ga 2 _{O 3} crystal _film, growing a _{(Ga x In y Al z)} 2 O 3 crystal film (0 <x ≦ 1,0 ≦ y <1,0 ≦ z <1, x + y + z = 1) Similar evaluation results can be obtained even in the case of

As apparent from the above description, the following Ga ₂ O ₃ -based single crystal substrate can be obtained.

A Ga ₂ O ₃ -based single crystal substrate having, as a growth surface, a plane rotated by 10 ° or more and less than 45 ° from a (100) plane.

A Ga ₂ O ₃ -based single crystal substrate having, as a growth plane, a plane rotated by 10 ° or more and less than 45 ° from the (100) plane with the [010] axis as the rotation axis.

When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, it is rotated by 10 ° or more and less than 45 ° from the (100) plane. A Ga ₂ O ₃ -based single crystal substrate having, as a growth surface, a growth surface or a surface obtained by rotating a growth surface or a surface rotated by 150 ° or less by 135 ° or more from a (100) surface.

A Ga ₂ O ₃ -based single crystal substrate having, as a growth surface, a plane rotated by 10 ° or more and less than 45 ° from the (100) plane with the [001] axis as the rotation axis.

(Effect of Example 2)
According to the second embodiment, in addition to the same effect as that of the first embodiment, the following effect can be obtained.

  Re-evaporation of the supplied raw material can be suppressed, and the raw material supply efficiency at the time of epitaxial growth can be improved. Furthermore, it is possible to suppress a decrease in device manufacturing yield. It is also possible to suppress substrate cracking and the like during device manufacture.

[Example 3]
In the case of forming a Ga ₂ O ₃ crystal film on a Ga ₂ O ₃ -based single crystal substrate, the following problems (1) and (2) occur.

(1) When growing a Ga ₂ O ₃ crystal film on a Ga ₂ O ₃ single crystal substrate having a (010) plane, a (001) plane, and a (-201) plane as its main surface, there is no problem in the growth rate However, the uniformity of the distribution of crystallinity in the plane of the Ga ₂ O ₃ crystal film is low, and a portion which is not a single crystal is formed in part. [001] axis plane rotated from (100) plane as a rotation axis to the _Ga 2 _{O 3} single crystal substrate having a major surface of a case of growing a _Ga 2 _{O 3} crystal film of _Ga 2 _{O 3} crystal film The in-plane crystallinity is not clear. When the device is manufactured on a portion which is not a single crystal, the grain boundaries of the device become paths of leakage current, which may lower the off performance of the device.

(2) When growing a Ga ₂ O ₃ crystal film on a Ga ₂ O ₃ single crystal substrate having the (001) plane as the main surface, there is no problem in the growth rate, and a flatter Ga ₂ O ₃ crystal film is used. Although it is easy to obtain, the (001) plane is a plane having strong cleavage like the (100) plane, and it is difficult to polish the surface of the substrate, and there is a possibility that peeling or the like due to cleavage may occur during device manufacture.

Therefore, in the present embodiment, in order to obtain a Ga ₂ O ₃ -based single crystal substrate capable of growing a Ga ₂ O ₃ crystal film having high uniformity of in-plane crystallinity distribution, Several different Ga ₂ O ₃ single crystal substrates were manufactured, and the relationship between the plane orientation of the main surface and the quality of the Ga ₂ O ₃ crystal film grown on the main surface was evaluated.

Hereinafter, the relationship between the plane orientation of the main surface of the Ga ₂ O ₃ single crystal substrate and the quality of the Ga ₂ O ₃ crystal film grown on the main surface will be described with reference to FIGS. It will be described in detail.

(Preparation of Ga ₂ O ₃ Single Crystal Substrate and Ga ₂ O ₃ Crystal Film)
When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, the plane rotated from 0 to 150 ° from the (100) plane and _Ga 2 _{O 3} single crystal substrate having a major surface and a rotation axis [001] axis, and a _Ga 2 _{O 3} single crystal substrate whose principal plane is rotated 10 to 90 ° from the (100) plane Prepared. Note that the _Ga 2 _{O 3} single crystal substrate Sn are added, _Ga 2 _{O 3} single crystal substrate is n-type conductivity.

The surface of the Ga ₂ O ₃ single crystal substrate was subjected to grinding and polishing, and after the grinding and polishing process, was subjected to CMP treatment. After CMP treatment, organic cleaning was performed using an organic solvent (acetone, methanol, IPA, ethanol), HF immersion cleaning, H ₂ SO ₄ , H ₂ O ₂ and H ₂ O were mixed at 4: 1: 1. Immersion cleaning in acid, rinsing with ultrapure water, and drying by nitrogen blow were performed to obtain a substrate capable of epitaxial growth. A Ga ₂ O ₃ crystal film was epitaxially grown on the substrate using MBE. The growth temperature was 750 ° C., and the growth time was 30 minutes. The film thickness of the Ga ₂ O ₃ crystal is about 300 nm.

(Control of mixing of crystals different in orientation from substrate)
FIG. 8A shows an X-ray diffraction spectrum obtained by X-ray diffraction measurement of XRD (X-Ray-Diffractometer: X-ray diffraction apparatus) {(001) asymmetric 2θ-ω scan}. FIG. 8 (b) is an enlarged view of the vicinity of (002) diffraction of the X-ray diffraction spectrum of FIG. 8 (a).

The horizontal axis in the drawing represents the angle 2θ (°) formed by the incident direction of the X-ray and the reflection direction, and the vertical axis on the left side in the drawing represents the diffracted intensity (arbitrary unit) of the X-ray. The numerical values on the right side of the X-ray diffraction spectrum indicate the rotation angle from the (100) plane with the [010] axis of the main surface of the Ga ₂ O ₃ single crystal substrate as the rotation axis.

  Referring to FIGS. 8A and 8B, on the lower angle side of the (002) diffraction, a diffraction peak from a crystal different in orientation from the substrate crystal was observed. The diffraction peaks near 2θ = 26 ° and 46.5 ° are attributable to diffraction from the sample stage of the X-ray diffractometer.

[010] Axial rotation In the Ga ₂ O ₃ crystal film on the surface of 50 to 80 °, mixing of (−401) -oriented crystals on the (001) plane was confirmed. On the other hand, from the _Ga 2 _{O 3} crystal film on [010] axis rotation 120 to 140 ° surface contamination of the crystal was confirmed oriented (400) on the (001) plane.

FIG. 9 shows RHEEDs on the surface of a Ga ₂ O ₃ crystal film on a typical [010] axis rotation of 40 °, 50 °, 70 °, 90 °, 100 °, 126.2 °, 140 °, 150 °. Reflective High-Energy Electron Diffraction (high-energy electron diffraction) image is shown.

As apparent from FIG. 9, the mixing of crystals different in orientation from the substrate was confirmed in the XRD evaluation. [010] Axis rotation: 50 °, 70 °, 126.2 °, 140 ° Ga ₂ O ₃ crystal film on the surface The image of RHEED showed a spotty pattern. It is considered that the arrangement of atoms is disturbed and a spotty pattern is formed by the mixing of crystals having different orientations with the substrate into the Ga ₂ O ₃ crystal film.

On the other hand, the RHEED image of the Ga ₂ O ₃ crystal film on the [010] axis rotation 40 °, 90 °, 100 °, 150 ° with no mixing of crystals different in orientation from the substrate showed a streak pattern. . The streak pattern indicates that a Ga ₂ O ₃ single crystal film is obtained.

FIG. 10 shows a RHEED image on the surface of a Ga ₂ O ₃ crystal film grown on a [001] axis rotational plane.

As apparent from FIG. 10, all the RHEED images showed a streak pattern on the surface of the Ga ₂ O ₃ crystal film on the [001] axis rotation of 10 to 90 °. Thus, a Ga ₂ O ₃ single crystal film free of the mixture of crystals different in orientation from the substrate can be obtained.

  It is known that the mixing of crystals different in orientation from these substrates is caused by stacking faults during epitaxial growth.

If the evaluation of the above embodiment are those conducted with Ga ₂ O ₃ single crystal substrate, which was evaluated by using a Ga ₂ O ₃ system single crystal substrate other than Ga ₂ O ₃ single crystal substrate Also, evaluation results similar to the above evaluation results can be obtained. Also, instead of _Ga 2 _{O 3} crystal _film, growing a _{(Ga x In y Al z)} 2 O 3 crystal film (0 <x ≦ 1,0 ≦ y <1,0 ≦ z <1, x + y + z = 1) Similar evaluation results can be obtained even in the case of

As apparent from the above description, the following growth method of a Ga ₂ O ₃ -based single crystal substrate and a Ga ₂ O ₃ -based single crystal film can be obtained.

When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, 10 to 40 ° from the (100) plane, 76.3 °, _Ga 2 _{O 3} system single crystal substrate having 90 ° to 110 °, the surface obtained by rotating 150 ° as a growth surface.

A Ga ₂ O ₃ -based single crystal substrate having, as a growth surface, a plane rotated 10 to 90 ° from the (100) plane with the [001] axis as the rotation axis.

When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, 10 to 40 ° from the (100) plane, 76.3 °, 90 ° to 110 °, is epitaxially grown _Ga 2 _{O 3} system crystal plane rotated 150 ° on the main surface of the _Ga 2 _{O 3} system single crystal substrate having a major surface, a _Ga 2 _{O 3} based crystal film _Ga 2 _{O 3} system method for growing a single crystal film comprising the step of forming.

The Ga ₂ O ₃ -based crystal is epitaxially grown on the main surface of a Ga ₂ O ₃ -based single crystal substrate whose main surface is rotated by 10 to 90 ° from the (100) plane with the [001] axis as the rotation axis. _Ga 2 _{O 3} system method for growing a single-crystal film including a step of forming a Ga ₂ O ₃ based crystal film.

(Effect of Example 3)
According to Example 3 described above, it is possible to grow a Ga ₂ O ₃ based crystal film which does not contain a crystal different in orientation from the substrate on the main surface of the Ga ₂ O ₃ based single crystal substrate, and It can be reduced.

Example 4
When forming a Ga ₂ O ₃ crystal film on a Ga ₂ O ₃ -based single crystal substrate, the relationship between the surface flatness of the crystal film and the plane orientation has not been clarified. For example, in the case of forming a transistor by forming an electrode on a crystal film having a rough surface, the electric field at the interface between the electrode and the Ga ₂ O ₃ crystal film becomes nonuniform, which may cause a reduction in the breakdown voltage of the device. Therefore, the higher the surface flatness of the crystal film, the better.

Therefore, in this embodiment, in order to obtain a Ga ₂ O ₃ -based single crystal substrate in which the flatness of the Ga ₂ O ₃ crystal film grown on the main surface is enhanced, a plurality of Ga ₂ O different in plane orientation of the main surface _A Ga ₂ O ₃ crystal film was grown on each of the _three single crystal substrates, and the relationship between the plane orientation of the main surface and the flatness of the Ga ₂ O ₃ crystal film was evaluated.

(Preparation of Ga ₂ O ₃ Single Crystal Substrate and Ga ₂ O ₃ Crystal Film)
When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, it is rotated by 0 to 150 ° from the (100) plane and _Ga 2 _{O 3} single crystal substrate of a plane as the main surface, [001] as the axis of rotation the axis, and _Ga 2 _{O 3} single crystal substrate whose principal plane is rotated 10 to 90 ° from the (100) plane Prepared. Note that the _Ga 2 _{O 3} single crystal substrate Sn are added, _Ga 2 _{O 3} single crystal substrate is n-type conductivity.

The substrate surface of the Ga ₂ O ₃ single crystal substrate was ground and polished and subjected to a CMP treatment after the grinding and polishing process. After CMP treatment, organic cleaning was performed using an organic solvent (acetone, methanol, IPA, ethanol), HF immersion cleaning, H ₂ SO ₄ , H ₂ O ₂ and H ₂ O were mixed at 4: 1: 1. Immersion cleaning in acid, rinsing with ultrapure water, and drying by nitrogen blow were performed to obtain a substrate capable of epitaxial growth. A Ga ₂ O ₃ crystal film was grown on the substrate using MBE. The growth temperature was 750 ° C., and the growth time was 30 minutes. The film thickness of the Ga ₂ O ₃ crystal is about 300 nm.

(Flatness of Ga ₂ O ₃ crystal film)
FIG. 11 shows the rotation angle (°) from the (100) plane when the [010] axis of the Ga ₂ O ₃ single crystal substrate is the rotation axis, and the surface of the epitaxial film grown on the main surface of each substrate. It is a figure which shows a relationship with roughness (RMS) (nm). The surface roughness (RMS) was estimated from a 5 μm square AFM image of the Ga ₂ O ₃ crystal film surface.

As apparent from FIG. 11, a Ga ₂ O ₃ crystal grown on a plane rotated 30 °, 76.3 °, 90 ° to 110 °, 150 ° from the (100) plane with the axis [010] as the rotation axis. In the film, it was confirmed that the surface roughness tends to be significantly reduced.

FIG. 12 shows a 5 μm square AFM image of the surface of the epitaxial film grown on the surface rotated about the [010] axis of the Ga ₂ O ₃ single crystal substrate.

As apparent from FIG. 12, the Ga ₂ O ₃ crystal film on the surface rotated 30 °, 76.3 °, 90 ° to 110 °, 150 ° from the (100) plane with the [010] axis as the rotation axis. It is considered that clear atomic steps have been observed and that step flow is growing.

FIG. 13 shows the surface roughness (RMS) estimated from the 5 μm square AFM image of the surface of an epitaxial film grown on a plane rotated about the [001] axis of a Ga ₂ O ₃ single crystal substrate. ing.

As apparent from FIG. 13, a flat Ga ₂ O ₃ crystal film was obtained over the entire angle range on the plane rotated by 10 to 90 ° with the [001] axis as the rotation axis.

FIG. 14 shows the surface roughness (RMS) estimated from the 1 μm square AFM image of the surface of the epitaxial film grown on the surface rotated about the [001] axis of the Ga ₂ O ₃ single crystal substrate. ing.

As apparent from FIG. 14, a flat Ga ₂ O ₃ crystal film was obtained over the entire angle range of the plane rotated 10 to 90 ° with the [001] axis as the rotation axis. Among the obtained flat Ga ₂ O ₃ crystal film, it can be seen that the flatness is enhanced particularly at around 60 °.

FIG. 15 shows a 1 μm square AFM image of the surface of an epitaxial film grown on a plane rotated about the [001] axis of a Ga ₂ O ₃ single crystal substrate.

  As apparent from FIG. 15, a flat surface two-dimensionally grown at around 60 ° was observed. It was confirmed that the step bunching became larger and the surface became rougher as it got away from around 60 °.

If the evaluation of the above embodiment are those conducted with Ga ₂ O ₃ single crystal substrate, which was evaluated by using a Ga ₂ O ₃ system single crystal substrate other than Ga ₂ O ₃ single crystal substrate Also, evaluation results similar to the above evaluation results can be obtained. Also, instead of _Ga 2 _{O 3} crystal _film, growing a _{(Ga x In y Al z)} 2 O 3 crystal film (0 <x ≦ 1,0 ≦ y <1,0 ≦ z <1, x + y + z = 1) Similar evaluation results can be obtained even in the case of

As apparent from the above description, the following growth method of a Ga ₂ O ₃ -based single crystal substrate and a Ga ₂ O ₃ -based crystal film can be obtained.

When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, 30 °, 76.3 ° from the (100) plane, A Ga ₂ O ₃ -based single crystal substrate having a plane rotated 90 ° to 110 ° and 150 ° as a growth plane.

A Ga ₂ O ₃ -based single crystal substrate having, as a growth surface, a plane rotated 10 to 90 ° from the (100) plane with the [001] axis as the rotation axis.

When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, 30 °, 76.3 ° from the (100) plane, 90 ° to 110 °, is epitaxially grown _β-Ga 2 _{O 3} system crystal plane rotated 150 ° on the main surface of the _Ga 2 _{O 3} system single crystal substrate having a major surface, _β-Ga 2 _{O 3} based crystals A method of growing a Ga ₂ O ₃ single crystal film comprising the step of forming a film.

A β-Ga ₂ O ₃ -based crystal is epitaxially grown on the main surface of a Ga ₂ O ₃ -based single crystal substrate whose main surface is rotated by 10 to 90 ° from the (100) plane with the [001] axis as the rotation axis. A method of growing a Ga ₂ O ₃ single crystal film, comprising the steps of forming a β-Ga ₂ O ₃ based crystal film.

(Effect of Example 4)
According to this fourth embodiment, in addition to the same effects as in Example 3, high Ga ₂ O ₃ crystal film flatness can be obtained, it is possible to suppress the decrease of breakdown voltage of the device.

[Other embodiments]
Typical configuration example of the above respective embodiments Ga ₂ O ₃ system single crystal substrate in the present invention, and has been described by way of illustrative example, it is capable of other embodiments as shown below.

As apparent from the illustrated example, in order to epitaxially grow a Ga ₂ O ₃ based crystal film on a Ga ₂ O ₃ based single crystal substrate, the (401) plane, the (201) plane, the (-102) plane, (- It may be a Ga ₂ O ₃ -based single crystal substrate whose main surface is a 101) plane, a (-401) plane, a (210) plane or the like. These Ga ₂ O ₃ -based single crystal substrates can also be used as a low polishing crack density Ga ₂ O ₃ -based single crystal substrate for high-speed growth of a highly flat Ga ₂ O ₃ -based single crystal film. . Then, when a device is manufactured using a Ga ₂ O ₃ based crystal film on a Ga ₂ O ₃ based single crystal substrate having these surfaces as main surfaces, a portion which is not a single crystal is not generated, and the leakage current increases. does not occur, because of the high flatness of the crystal film surface, the electric field of the electrode and the Ga ₂ O ₃ based crystal film interface is uniform, the decrease in breakdown voltage can be suppressed.

In each of the above embodiments, the angular range of the [010] axis rotation from the (100) plane of the main surface of the Ga ₂ O ₃ -based single crystal substrate which can obtain effects is [010] in the substrate plane. Even when there is an angular deviation whose rotation axis is in the direction orthogonal to the axis, the influence is hardly affected if the size of the angular deviation is within about ± 5 degrees.

Further, in each of the above embodiments, the angular range of the [001] axis rotation from the (100) plane of the main surface of the Ga ₂ O ₃ -based single crystal substrate which can obtain effects is [001] in the substrate plane. Even when there is an angular deviation whose rotation axis is in the direction orthogonal to the axis, the influence is hardly affected if the size of the angular deviation is within about ± 5 degrees.

  As is apparent from the above description, although typical embodiments and examples of the present invention have been illustrated, the above-described embodiments and examples of the present invention limit the invention according to the claims. Absent. Therefore, it should be noted that not all of the above-described embodiments and combinations of features described in the illustrated examples are necessarily essential to the means for solving the problems of the invention.

Claims (2)

When the rotation direction from the (100) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, it is rotated by 10 ° or more and less than 45 ° from the (100) plane. Have a growth surface that is rotated by more than 135 ° and 150 ° or less from the (100) plane or the (100) plane ,
Ga ₂ O ₃ -based single crystal substrate. Having a plane rotated by 10 ° or more and less than 45 ° from the (100) plane as a growth plane, with the [001] axis as the rotation axis ,
Ga ₂ O ₃ -based single crystal substrate.