JP6706705B2 - Ga2O3-based single crystal substrate - Google Patents

Description

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

There has been proposed a β-Ga ₂ O ₃ -based substrate whose main surface is a surface rotated by 50° or more and 90° or less from a (100) plane (see, for example, Patent Document 1).

Further, in Patent Document 1, (010), (001), (-201), (101), and (310) planes can be cited as the planes rotated from this (100) plane by 50° or more and 90° or less. 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 growing a Ga ₂ O ₃ -based crystal film having a small surface roughness.

The inventors of the present invention conducted extensive studies on a method of growing a Ga ₂ O ₃ -based crystal film on a Ga ₂ O ₃ -based single crystal substrate, and found that a specific plane orientation was set as the main surface and The inventors have found that the above object can be achieved by epitaxially growing a Ga ₂ O ₃ -based crystal film, and completed the present invention.

That is, the above object is achieved by each invention described in [1] below.

When the rotation direction from the (100) plane to the (001) plane through the (101) plane with the [1] and [010] axes as the rotation axis is defined as plus, 90° or more and 110° or more from the (100) plane A Ga ₂ O ₃ -based single crystal substrate having a rotated surface as a growth surface.

According to the present invention, it is possible to provide a Ga ₂ O ₃ -based single crystal substrate on which a Ga ₂ O ₃ -based crystal film having a small surface roughness can be grown.

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) .. 1 is a surface optical micrograph of a Ga ₂ O ₃ single crystal substrate whose main surface is a surface rotated by 160° from a (100) surface with a [010] axis as a rotation axis after CMP treatment (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). ₃ is a photograph showing an RHEED image of the surface of an epitaxial film grown on a surface of a Ga ₂ O ₃ single crystal substrate rotated about the [010] axis as a rotation axis (Example 3). 4 is a photograph showing an RHEED image of an epitaxial film surface grown on a surface rotated with the [001] axis of the main surface of a Ga ₂ O ₃ single crystal substrate as a rotation axis (Example 3). 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. It is a figure which shows the relationship of (Example 4). 5 is a photograph showing a 5 μm square AFM image of an epitaxial film surface grown on a surface rotated with the [010] axis of the main surface of a Ga ₂ O ₃ single crystal substrate as a rotation axis (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). ₃ is a photograph showing a 1 μm square AFM image of an epitaxial film surface grown on a surface rotated with the [001] axis of the main surface of a Ga ₂ O ₃ single crystal substrate as a rotation axis (Example 4).

Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings with reference to 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 a strong cleavage property on the (100) plane, and when the Ga ₂ O ₃ -based single crystal substrate is processed, peeling or cracks caused by the cleavage occur. It's easy to do. It is difficult to obtain a large-scale Ga ₂ O ₃ -based single crystal substrate because peeling and cracks are likely to occur during substrate processing.

(2) Since the (100) plane has a strong cleavage property, the closer the (100) plane becomes perpendicular to the substrate surface (main surface), the more the angle formed by the (100) plane with the main surface becomes 45. If the temperature is higher than 0°, there is a problem that the Ga ₂ O ₃ -based single crystal substrate is easily cracked during device manufacturing.

Therefore, in the present example, in order to obtain a Ga ₂ O ₃ -based single crystal substrate in which cracks and breakage are unlikely to occur, a plurality of Ga ₂ O ₃ single crystal substrates having different principal surface plane orientations were manufactured, and The relationship between the orientation and the amount of cracks generated was evaluated.

The Ga ₂ O ₃ -based single crystal substrate is a β-(Ga _x In _y Al _z ) ₂ O ₃ single crystal (0<x≦1, 0≦y<1, 0≦, such as a β-Ga ₂ O ₃ single crystal. The substrate is made of z<1, x+y+z=1).

(Production of Ga ₂ O ₃ Single Crystal Substrate)
A Ga ₂ O ₃ single crystal substrate whose main surface is a plane rotated by 0 to 170° from the (100) plane with the [010] axis as the rotation axis, and from the (100) plane with the [001] axis as the rotation axis. Each of the Ga ₂ O ₃ single crystal substrates having the surface rotated by 90° as the main surface was cut out from the Ga ₂ O ₃ single crystal, and then processed into a plate shape having a 10 mm square and a thickness of 1 mm. 20 Ga ₂ O ₃ single crystal substrates were prepared for each rotation angle. One side of a 10 mm square Ga ₂ O ₃ single crystal substrate having the [010] axis as a rotation axis is parallel to the [010] direction. The angle of rotation about the [010] axis as a rotation axis is positive in the direction from the (100) plane to the (001) plane via the (101) plane. Further, one side of a Ga ₂ O ₃ single crystal substrate of 10 mm square with the [001] axis as a rotation axis is parallel to the [001] direction.

Next, the thickness of the Ga ₂ O ₃ single crystal substrate was reduced to about 0.8 mm by using a grinder having a grindstone roughness of No. 1000. The grinding speed is about 6 μm/min. After this grinding, the surface was polished with a shaving amount of about 20 μm while spraying abrasive grains made of diamond.

Finally, surface polishing of about 10 μm was performed by CMP (Chemical mechanical planarization). After the CMP treatment, organic cleaning using an organic solvent (acetone, methanol, IPA, ethanol) was performed, HF immersion cleaning was performed, and 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 with nitrogen blow were performed.

(Evaluation of crack density of Ga ₂ O ₃ single crystal substrate)
Referring to FIGS. 1 and 2, FIG. 1 shows a rotation angle of a main surface of a Ga ₂ O ₃ single crystal substrate from a (100) surface having a [010] axis as a rotation axis and a main surface after CMP treatment. The relationship with the crack density on the plane is shown in FIG. 2, and 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 densities of the Ga ₂ O ₃ single crystal substrates at the respective rotation angles shown in FIGS. 1 and 2 are the average values of the crack densities of the 20 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 a direction perpendicular to the [010] direction on the main surface of the Ga ₂ O ₃ single crystal substrate. Of these, when the longest straight line is the reference straight line, the number of cracks along the [010] direction intersecting with the reference straight line is defined as a value divided by the length of the reference straight line. For example, when the Ga ₂ O ₃ single crystal substrate has a circular shape, this reference straight line is a straight line passing through the center and perpendicular to the [010] direction, and the reference straight line has a circular Ga ₂ O ₃ length. 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 with the [001] axis as the axis of rotation is the straight line in the direction perpendicular to the [001] direction on the main surface of the Ga ₂ O ₃ single crystal substrate. , Where the longest straight line is the reference straight line, the number of cracks along the [001] direction that intersects this reference straight line is defined as the value divided by the length of this reference straight line. For example, when the Ga ₂ O ₃ single crystal substrate has a circular shape, this reference straight line is a straight line in a direction perpendicular to the [001] direction passing through the center of the Ga ₂ O ₃ single crystal substrate, and the reference straight line has a circular Ga ₂ O ₃ length. Corresponds to the diameter of a single crystal substrate.

As shown in FIGS. 1 and 2, a [010]-axis rotating 10-150° substrate having a main surface that is a surface rotated by 10 to 150° from a (100) plane with the [010] axis as a rotation axis, No cracks were generated on the [001]-axis rotated 10-90° substrate whose main surface is a surface rotated by 10-90° from the (100) plane with the (001) axis as the rotation axis.

It can be said that no cracks are generated on a 10 mm×200 mm rectangular substrate whose one side is parallel to the [010] direction because no crack is generated on a 10 mm square substrate whose one side is parallel to the [010] direction. . It can be said that the crack density is less than 0.05/cm since the number of cracks generated in the 10 mm×200 mm rectangular substrate parallel to the [010] direction is less than one.

Similarly, since no cracks are generated on a 10 mm square substrate whose one side is parallel to the [001] direction, cracks are not generated on a 10 mm×200 mm rectangular substrate whose short direction is parallel to the [001] direction. I can say that. It can be said that the crack density is less than 0.05/cm because the number of cracks generated in the 10 mm×200 mm rectangular substrate whose short direction is parallel to the [001] direction is less than one.

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

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

FIG. 3 shows a Ga ₂ O ₃ single crystal substrate having a main surface that is a surface rotated from the (100) surface by 160° about the [010] 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 portion in the photograph is the deep groove caused by the crack, and the white portion 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 lines/cm for the [010] axis rotation 160° substrate and 79 lines/cm for the [010] axis rotation 170° substrate. When the crack density was 53/cm, the width of the crack-free region in the direction perpendicular to the [010] direction was about 189 μm.

By the way, even if the flatness of the substrate is obtained by observation with an optical microscope after surface polishing and an AFM (atomic force microscope), polishing damage may remain on the substrate in some cases. Those residual polishing damages (latent scratches) emerge as surface defects by growing a homoepitaxial film on the latent scratches.

To evaluate the presence or absence of latent scratches, homoepitaxial growth was performed using MBE. 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 latent scratches (polishing damage). There is.

As is clear from FIG. 4, the homoepitaxial film on the [010]-axis rotated 90° substrate had a mirror surface on one half and the other surface covered with scratches and hillocks derived from polishing damage. The entire surface of the homoepitaxial film on the [010] axis rotation 80° substrate was covered with the same hillock. The homoepitaxial film on the [010] axis rotation 76.3° substrate was mirror-polished only in a small part, and was almost entirely covered with the same hillock. Therefore, it was found that the range where the [010] axis rotation was 76.3 to 90° was the surface where polishing damage was likely to remain.

In the case of a [001]-axis rotated 10-90° substrate whose main surface is a surface rotated by 10-90° from the (100) plane with the [001] axis as a rotation axis, surface defects due to latent scratches are caused over the entire substrate. Not confirmed.

Therefore, in order to suppress the occurrence of cracks and the occurrence of latent scratches during surface polishing, the [010] axis rotation is 10 to 70° surface, the [010] axis rotation is 100 to 150° surface, and the [001] axis rotation is. It can be seen 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 The same evaluation result as the evaluation result is obtained.

As is clear from the above description, the following Ga ₂ O ₃ -based single crystal substrate is obtained.

When the rotation direction from the (100) plane to the (001) plane through the (101) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, a plane rotated from the (100) plane by 10 to 150° Ga ₂ O ₃ -based single crystal substrate having a main surface of 4 and a crack density of less than 0.05 cracks/cm.

When the rotation direction from the (100) plane to the (001) plane through the (101) plane with the [010] axis as the rotation axis is defined as plus, 10 to 70° from the (100) plane, 100 to 150 A Ga ₂ O ₃ -based single crystal substrate whose main surface is a surface rotated by °, crack density is less than 0.05 lines/cm, and which has no latent scratches.

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

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

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

It becomes possible to significantly suppress cracks, latent scratches, and peeling during substrate processing, and it is possible to improve the production yield of a large-area Ga ₂ O ₃ -based single crystal substrate. Specifically, a surface rotated by 10 to 150° from the (100) plane with the [010] axis as the rotation axis or a surface rotated from 10 to 90° from the (100) plane by using the [001] axis as the rotation axis. By using it as the main surface, it becomes possible to manufacture a large 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 the (100) plane, the raw material supplied when growing the Ga ₂ O ₃ crystal film on the main surface is likely to be re-evaporated, so that the Ga ₂ O ₃ crystal is grown. There is a problem that the growth rate of the film is very slow and mass productivity is low.

Therefore, in this 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 is high, a plurality of Ga ₂ O having different main surface orientations are used. _A Ga ₂ O ₃ crystal film was grown on each of the ₃ 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.

(Production 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 via the (101) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, a 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 I 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 ground and polished, and after the grinding and polishing step, CMP treatment was performed. After the CMP treatment, organic cleaning using an organic solvent (acetone, methanol, IPA, ethanol) was performed, HF immersion cleaning was performed, and 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 with nitrogen blow were performed to prepare a substrate in which epitaxial growth is possible. 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)
FIGS. 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 having the [010] axis of the main surface of the Ga ₂ O ₃ single crystal substrate as the rotation axis. The results and the evaluation results of the growth rate of the Ga ₂ O ₃ crystal film on the plane rotated from the (100) plane having 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 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 growth rate (nm/h) of the Ga ₂ O ₃ crystal film. ) Is shown. FIG. 6 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 the growth rate (nm/h) of the Ga ₂ O ₃ crystal film. ) Is shown.

In FIG. 5, the growth rate of the [010]-axis rotated 10° plane, which is a plane rotated by 10° from the (100) plane with the [010] axis as the rotation axis, is about 500 nm/h, while the (100 Since the growth rate of the () plane is 10 nm/h or less (below the measurement lower limit), the growth rate of the Ga ₂ O ₃ crystal film can be increased by rotating 10° from the (100) plane with the [010] axis as the rotation axis. It has been found that can be improved at least 50 times or more.

Further, in FIG. 5, when the surface rotated from the (100) surface in the range of 10° to 150° with the [010] axis as the rotation axis is the main surface, the (100) surface is the main surface. This shows that the growth rate of the Ga ₂ O ₃ crystal film can be significantly increased as compared with the case.

FIG. 6 shows that when the main surface is a surface rotated from the (100) surface in the range of 10° to 90° with the [001] axis as the rotation axis, Also shows that the growth rate of the Ga ₂ O ₃ crystal film can be significantly increased.

On the other hand, the (100) plane has a strong cleavage property, and if the angle formed by the (100) plane and the principal plane is 45° or more, substrate cracking tends to occur during device manufacturing. Therefore, it is preferable to use as the main surface a surface rotated by less than 45° from the (100) surface.

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

Further, when the rotation direction from the (100) plane through the (101) plane to the (001) plane with the [010] axis as the rotation axis is defined as plus, 10° or more and less than 45° from the (100) plane are defined. By rotating the surface or the surface rotated more than 135° and 150° or less, or the surface rotated by 10° or more and less than 45° from the (100) plane with the [001] axis as the rotation axis, It is possible to increase the growth rate of the Ga ₂ O ₃ crystal film, suppress substrate cracking during device manufacturing, and further reduce the crack density on the main surface to less than 0.05 cracks/cm.

Note that this study was conducted using a substrate whose principal surface is a plane having two rotation axes of the [010] axis and the [001] axis as orthogonal rotation axes, and similar results were obtained between the two orthogonal axes. ing. Therefore, it can be easily inferred that similar results can be obtained even in the middle of these rotation axes. That is, when the main surface is a plane rotated from the (100) plane and the rotation angle is 10° or more and less than 45° regardless of the direction of the rotation axis, the Ga ₂ O ₃ crystal film is more than the (100) plane. The growth rate of Ga ₂ O ₃ can be increased. Therefore, the growth rate of the Ga ₂ O ₃ crystal film can be increased and the substrate cracking at the time of device manufacturing can be achieved by using the plane rotated by 10° or more and less than 45° from the (100) plane as the main surface. It can be said that

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

FIG. 7 shows the relationship between the inclination angle (off angle) from the [010] axis rotation 126.2°=(−201) plane to the [010] direction and the growth rate of the epitaxial film. As is clear from FIG. 7, the growth rate increases as the tilt angle from the (−201) plane to the [010] direction of the Ga ₂ O ₃ single crystal substrate increases, and the growth rate is saturated at an off angle of 7°. Do you get it.

From this result, it can be said that it is effective to have 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. Further, since the increase in the growth rate is saturated at 7°, tilting the growth rate by 7° or more eliminates the dependence of the growth rate on the off angle, and suppresses the growth rate variation due to the variation in the substrate off angle, thus improving the manufacturing stability. The effect is obtained. Therefore, the off angle is more preferably 7° or more. Similar results are also obtained when the [010] axis rotation plane other than the [010] axis rotation (−201) plane is tilted 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, the same evaluation result as the above evaluation result is obtained. Further, instead of the Ga ₂ O ₃ crystal film, 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) is grown. Even in the case of performing the same, the same evaluation result can be obtained.

As is clear from the above description, the following Ga ₂ O ₃ -based single crystal substrate is obtained.

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

When the rotation direction from the (100) plane to the (001) plane via the (101) plane to the (001) plane is defined as a positive axis with the [010] axis as the rotation axis, rotation from the (100) plane to 10° or more and less than 45° A Ga ₂ O ₃ -based single crystal substrate having a grown surface or a surface rotated by more than 135° and not more than 150° from the (100) surface as a growth surface.

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

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

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

[Example 3]
When forming a Ga ₂ O ₃ crystal film on a Ga ₂ O ₃ -based single crystal substrate, there are problems listed in (1) and (2) below.

(1) When a Ga ₂ O ₃ crystal film is grown on a Ga ₂ O ₃ single crystal substrate having (010) plane, (001) plane, and (−201) plane as main planes, there is no problem in the growth rate. However, the uniformity of the in-plane crystallinity distribution of the Ga ₂ O ₃ crystal film is low, and some portions are not single crystals. [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 has not been clarified. When a device is formed on a portion that is not a single crystal, the crystal grain boundaries serve as paths for leakage current, which may reduce the off performance of the device.

(2) When a Ga ₂ O ₃ crystal film is grown on a Ga ₂ O ₃ single crystal substrate whose main surface is the (001) plane, there is no problem with the growth rate and a flatter Ga ₂ O ₃ crystal film is used. Although it is easy to obtain, the (001) plane has a strong cleavage property like the (100) plane, it is difficult to polish the substrate surface, and peeling due to the cleavage may occur during device manufacturing.

Therefore, in the present embodiment, in order to obtain a Ga ₂ O ₃ -based single crystal substrate on which a Ga ₂ O ₃ crystal film having a high uniformity of in-plane crystallinity distribution can be obtained, the plane orientation of the main surface is changed. A plurality of 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.

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 below with reference to FIGS. The details will be described.

(Production 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 via the (101) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, a 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 I 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 ground and polished, and after the grinding and polishing step, CMP treatment was performed. After the CMP treatment, organic cleaning using an organic solvent (acetone, methanol, IPA, ethanol) was performed, HF immersion cleaning was performed, and 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 with nitrogen blow were performed to prepare a substrate in which epitaxial growth is possible. 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.

(Suppression of inclusion of crystals with different orientation from the substrate)
FIG. 8A shows an X-ray diffraction spectrum obtained by an X-ray diffraction measurement ((001) asymmetric 2θ-ω scan} of an XRD (X-Ray-Diffractometer). FIG. 8B is an enlarged view showing the vicinity of (002) diffraction of the X-ray diffraction spectrum of FIG.

The horizontal axis in the drawing represents the angle 2θ (°) formed by the X-ray incident azimuth and the reflection azimuth, and the left vertical axis in the drawing represents the X-ray diffraction intensity (arbitrary unit). The numerical value on the right side of the X-ray diffraction spectrum shows 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.

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

In the Ga ₂ O ₃ crystal film on the [010] axis rotation plane of 50 to 80°, it was confirmed that the (001) plane-oriented crystals were mixed. On the other hand, from the Ga ₂ O ₃ crystal film on the [010] axis rotation 120 to 140° plane, it was confirmed that the (400) oriented crystal was mixed on the (001) plane.

FIG. 9 shows typical [010] axis rotations 40°, 50°, 70°, 90°, 100°, 126.2°, 140°, and 150° on the Ga ₂ O ₃ crystal film surface RHEED ( Reflective High-Energy Electron Diffraction: High-energy electron diffraction image.

As is clear from FIG. 9, mixing of crystals having different orientations from the substrate was confirmed in XRD evaluation. Ga ₂ O ₃ crystal film on [010] axis rotation 50°, 70°, 126.2°, 140° planes RHEED image showed a spotty pattern. It is considered that when the Ga ₂ O ₃ crystal film was mixed with crystals having different orientations from the substrate, the atomic arrangement was disturbed and a spotty pattern was formed.

On the other hand, the RHEED image of the Ga ₂ O ₃ crystal film on the [010] axis rotations of 40°, 90°, 100°, and 150° planes in which crystals having different orientations from the substrate were not mixed showed a streak pattern. .. The streak pattern indicates that a Ga ₂ O ₃ single crystal film is obtained.

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

As is clear from FIG. 10, all RHEED images showed a streak pattern on the surface of the Ga ₂ O ₃ crystal film on the [001] axis rotation 10 to 90° plane. Therefore, a Ga ₂ O ₃ single crystal film in which crystals having different orientations from the substrate are not mixed can be obtained.

It is known that the inclusion of crystals having different orientations from those of the substrate 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, the same evaluation result as the above evaluation result is obtained. Further, instead of the Ga ₂ O ₃ crystal film, 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) is grown. Even in the case of performing the same, the same evaluation result can be obtained.

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

When the rotation direction from the (100) plane to the (001) plane through the (101) 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. A Ga ₂ O ₃ -based single crystal substrate having a surface rotated by 90°, 90° to 110°, and 150° as a growth surface.

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

When the rotation direction from the (100) plane to the (001) plane through the (101) 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 A method of growing a Ga ₂ O ₃ -based single crystal film, which comprises a step of forming.

A 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 a surface rotated from the (100) plane by 10 to 90° with the [001] axis as a 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 above, a Ga ₂ O ₃ -based crystal film containing no crystal having a different orientation from the substrate can be grown on the main surface of the Ga ₂ O ₃ -based single crystal substrate, and the device leakage current can be reduced. 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, when a transistor is manufactured 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 non-uniform, which may cause the breakdown voltage of the device to decrease. Therefore, the higher the surface flatness of the crystal film, the more preferable.

Therefore, in this example, 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 high, a plurality of Ga ₂ O having different main surface orientations are used. _A Ga ₂ O ₃ crystal film was grown on each of the ₃ 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.

(Production 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 through the (101) plane to the (001) plane is defined as positive with the [010] axis as the rotation axis, the rotation is performed from 0 to 150° from the (100) plane. A Ga ₂ O ₃ single crystal substrate having a plane as a main surface, and a Ga ₂ O ₃ single crystal substrate having a plane rotated by 10 to 90° from a (100) plane with a [001] axis as a rotation axis. 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 after the grinding and polishing step, CMP treatment was performed. After the CMP treatment, organic cleaning using an organic solvent (acetone, methanol, IPA, ethanol) was performed, HF immersion cleaning was performed, and 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 with nitrogen blow were performed to prepare a substrate in which epitaxial growth is possible. 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 the relationship with roughness (RMS) (nm). The surface roughness (RMS) was estimated from a 5 μm square AFM image of the surface of the Ga ₂ O ₃ crystal film.

As is clear from FIG. 11, Ga ₂ O ₃ crystals grown on the plane rotated by 30°, 76.3°, 90° to 110°, 150° from the (100) plane with the [010] axis as the rotation axis. It was confirmed that the surface roughness of the film was significantly reduced.

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

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

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

As is clear from FIG. 13, a flat Ga ₂ O ₃ crystal film was obtained over the entire angular range on the surface 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 epitaxial film surface grown on the surface of the Ga ₂ O ₃ single crystal substrate rotated about the [001] axis. ing.

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

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

As is clear from FIG. 15, a flat surface that two-dimensionally grew around 60° was observed. It was confirmed that the step bunching increased as the distance from the vicinity of 60° increased, and the surface became rough.

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, the same evaluation result as the above evaluation result is obtained. Further, instead of the Ga ₂ O ₃ crystal film, 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) is grown. Even in the case of performing the same, the same evaluation result can be obtained.

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

When the rotation direction from the (100) plane to the (001) plane through the (101) plane with the [010] axis as the rotation axis is defined as plus, 30°, 76.3° from the (100) plane, A Ga ₂ O ₃ -based single crystal substrate having a surface rotated by 90° to 110° and 150° as a growth surface.

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

When the rotation direction from the (100) plane to the (001) plane through the (101) plane with the [010] axis as the rotation axis is defined as plus, 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 for growing a Ga ₂ O ₃ single crystal film, comprising the step of forming a film.

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

(Effect of Example 4)
According to the fourth embodiment, in addition to the effect similar to that of the third embodiment, a Ga ₂ O ₃ crystal film having high flatness can be obtained, and the breakdown voltage of the device can be prevented from lowering.

[Other embodiments]
Although a typical configuration example of the Ga ₂ O ₃ -based single crystal substrate in the present invention has been described with reference to the above-described embodiments and illustrated examples, other embodiments as shown below are also possible.

As is clear 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, (401) plane, (201) plane, (-102) plane, (- A Ga ₂ O ₃ -based single crystal substrate having a (101) plane, a (−401) plane, a (210) plane, or the like as a main surface may be used. These Ga ₂ O ₃ -based single crystal substrates can also be used as Ga ₂ O ₃ -based single crystal substrates with low polishing crack density for high-speed growth of Ga ₂ O ₃ -based single crystal films with high flatness. .. 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 planes as main surfaces, a leak current is increased because there is no part that is not a single crystal. Does not occur, and the flatness of the crystal film surface is high, so that the electric field at the interface between the electrode and the Ga ₂ O ₃ -based crystal film becomes uniform, and a decrease in breakdown voltage can be suppressed.

In each of the above-described examples, the angular range of [010] axis rotation from the (100) plane of the main surface of the Ga ₂ O ₃ -based single crystal substrate that can obtain the effect is [010] within the substrate plane. Even if there is an angle deviation about the rotation axis in the direction orthogonal to the axis, if the magnitude of the angle deviation is within about ±5 degrees, it is hardly affected.

Further, in each of the above-described examples, the angular range of [001] axis rotation from the (100) plane of the main surface of the Ga ₂ O ₃ -based single crystal substrate that can obtain the effect is [001] within the substrate plane. Even if there is an angular deviation about the rotation axis in the direction orthogonal to the axis, if the magnitude of the angular deviation is within about ±5 degrees, it is hardly affected.

As is clear from the above description, the representative examples and the illustrated examples according to the present invention are illustrated, but the above-described examples and the illustrated examples do not limit the invention according to the claims. Absent. Therefore, it should be noted that not all of the combinations of the features described in the above embodiments and illustrated examples are essential to the means for solving the problems of the invention.

Claims (1)

When the rotation direction from the (100) plane to the (001) plane through the (101) plane to the (001) plane is defined as plus with the [010] axis as the rotation axis, the rotation direction is 90° or more and 110° or less from the (100) plane. Has a growth surface as
Ga ₂ O ₃ -based single crystal substrate.