JP6085764B2 - Gallium oxide single crystal and gallium oxide single crystal substrate - Google Patents

Description

  The present invention relates to a gallium oxide single crystal and a gallium oxide single crystal substrate.

A Ga ₂ O ₃ substrate made of a gallium oxide (Ga ₂ O ₃ ) single crystal is used, for example, for forming a GaN-based thin film device to form a light emitting element or the like. It has been proposed that such a Ga ₂ O ₃ single crystal is manufactured by various methods. As a crystal growth method for manufacturing a large single crystal substrate, an EFG (Edge Defined Film Fed Growth) method is used. Attention has been paid.

For example, Patent Document 1, Ga ₂ O ₃ with a die having a slit erected in a crucible for receiving the melt, the seed crystal to the Ga ₂ O ₃ melt slits elevated provided in the cross-section of the die It is described that a Ga ₂ O ₃ single crystal having a predetermined size and shape can be obtained by pulling up the seed crystal after bringing it into contact.

JP 2004-56098 A

By the way, in a crystal such as a Ga ₂ O ₃ single crystal used for a growth substrate of a GaN-based thin film device, it is preferable that atoms have an ideal periodic arrangement, but in actual crystal growth, Due to thermal shock when the crystal is brought into contact with the melt and growth at an inappropriate crystal growth rate, the positions of the atoms arranged in a straight line are largely displaced along the crystal growth direction. Such a linear crystal defect is called a dislocation.

In general, in order to obtain high luminous efficiency, it is preferable to use a dislocation-free Ga ₂ O ₃ single crystal substrate, but it is difficult to obtain a dislocation-free single crystal substrate, which is manufactured by the current crystal growth technique by the EFG method. The Ga ₂ O ₃ single crystal contains finite dislocations.

Device in _Ga 2 _{O 3} substrate dislocations present on the surface, for example, the case of manufacturing a GaN-based LED, _Ga 2 _{O 3} dislocations on the substrate, also spread to the grown GaN film, the dislocation density in the light emitting layer Therefore, the dislocation density of the Ga ₂ O ₃ single crystal substrate needs to be as low as possible.

  In order to obtain a crystal with few dislocations, a thin neck is produced at a high temperature and the growth rate of the crystal is generally suppressed. However, the gallium oxide single crystal growth requires caution. Gallium oxide has a high vapor pressure above its melting point, and evaporation of the raw material during crystal growth is a major issue. When crystal growth is performed at a higher temperature to reduce dislocations, the amount of evaporation further increases and a larger amount of raw material is lost. Similarly, slowing the growth rate is not preferable because the longer the crystal growth, the more raw material is lost.

After all, in the current growth of gallium oxide single crystals, the dislocation density is less than 1 × 10 ⁶ pieces / cm ^{2 and} less than 1 inch, while there is a trade-off between suppression of dislocation and reduction of raw material loss. It is difficult to produce a large single crystal, and dislocations of 1 × 10 ⁶ pieces / cm ² or more exist on the surface of a substrate obtained by processing such a single crystal.

  On the other hand, in the process of forming a GaN film on a substrate, there is a technique called a lateral epitaxy on the patterned substrate (LEPS) method for reducing the dislocation density of the GaN film. In this method, unevenness having a width of 2 to 10 μm is formed on the substrate surface, and a GaN film is grown in the lateral direction from the convex portion, so that the dislocation generated at the substrate-GaN interface extends in the lateral direction while extending upward. Since it bends, the dislocation density in the vicinity of the surface of the film can be reduced to about 1/3 compared with the case where unevenness is not formed on the substrate, and the efficiency of the ultraviolet LED can be increased.

By using this method, even from a Ga ₂ O ₃ substrate having a high dislocation density, it becomes possible to reduce the dislocation density on the surface of the GaN film and increase the efficiency of the ultraviolet LED. In order to fabricate a substrate with irregularities on the surface for the LEPS method, a mask is formed on the substrate surface using photolithography technology, and the opening of the mask is processed into a concave shape by wet etching or the like. And the manufacturing cost is high.

The present invention has been made in view of the above problems, and it is possible to produce a high-quality semiconductor device film by actively utilizing dislocations in a single crystal, which is usually not preferable to exist. An object of the present invention is to provide a Ga ₂ O ₃ substrate having unevenness formed on the surface thereof suitable for performing a possible LEPS method at a low cost, and to provide a gallium oxide single crystal containing dislocations necessary for that purpose. To do.

To achieve the above object, a first aspect in accordance gallium oxide single crystal of the present invention are produced by the EFG process, dislocation density Ri 1 × ¹⁰ 6 ~3 × ^{10 7} cells / cm ² der dislocations It exists along the b-axis direction which is a pulling direction .

For example, the neck diameter is preferably 0.4 to 1.3 mm.

The gallium oxide single crystal substrate according to the second aspect of the present invention is:
It consists of a gallium oxide single crystal according to the first aspect, and is subjected to CMP processing.

Dislocations exist along the in-plane direction on the surface of the main surface of the substrate.
Etching is performed on the surface, and a groove-like etch pit is generated at the location where the dislocation exists without using a mask like a photoresist due to the difference in etching rate between the location where the dislocation exists and the location where the dislocation does not exist. The substrate surface is provided with irregularities.
Moreover, it is preferable that it is at least 1 inch size.

  ADVANTAGE OF THE INVENTION According to this invention, the board | substrate with which the unevenness | corrugation suitable for performing a LEPS method was formed in the surface can be produced at low cost.

(A) It is a schematic cross section explaining the growth furnace of an example of the manufacturing method of the gallium oxide single crystal by EFG method. (B) It is the elements on larger scale which show the seed crystal of FIG. 1 (a), the gallium oxide single crystal, and the gallium oxide melt part on a die top. It is the schematic of the gallium oxide single crystal produced by the EFG method. It is the schematic of the gallium oxide single crystal containing the dislocation by EFG method. It is explanatory drawing which shows an example of the gallium oxide single crystal substrate in which the unevenness | corrugation was formed in the surface. It is a perspective view which shows an example of the gallium oxide single crystal substrate in which the unevenness | corrugation was formed in the surface. It is a figure which shows the relationship between a dislocation density, a pit width, and a pit space | interval.

Hereinafter, a gallium oxide (Ga ₂ O ₃ ) single crystal and a gallium oxide single crystal substrate of the present invention will be described with reference to the drawings. In the present embodiment, the present invention will be described by taking as an example a case where a gallium oxide single crystal is manufactured by pulling up a (101) plane crystal in the b-axis direction by an EFG (Edge Defined Film Fed Growth) method.

  In the EFG method, a gallium oxide raw material is put into a crucible containing a die having a slit and heated, and the melt of the gallium oxide raw material overflowing through the slit is brought into contact with the seed crystal to gallium oxide. This is a method for producing (growing) a single crystal. FIG. 1A is a schematic cross-sectional view illustrating a growth furnace as an example of a method for producing a gallium oxide single crystal by the EFG method, and FIG. 1B is a diagram illustrating a seed crystal and a gallium oxide single crystal in FIG. FIG. 2 is a partially enlarged view showing a gallium oxide melt portion on the die top. First, a gallium oxide single crystal manufacturing method using a gallium oxide single crystal manufacturing apparatus will be briefly described.

  As shown in FIG. 1 (a), a crucible 3 for receiving a gallium oxide melt 2 as a raw material for a gallium oxide single crystal is disposed inside a gallium oxide single crystal manufacturing apparatus 1. The crucible 3 is formed in a bottomed cylindrical shape, is placed on a support base 4, and the temperature of the bottom surface thereof is measured by a thermocouple 7. The crucible 3 is formed of a heat-resistant metal material, for example, iridium (Ir), so that the gallium oxide melt 2 can be received, and a necessary amount of raw material is charged into the crucible 3 by a raw material charging portion (not shown). Is done.

  A die 5 is disposed in the crucible 3. The die 5 is formed in a substantially rectangular parallelepiped shape, for example, and is provided with one or a plurality of slits 5A extending from the lower end to the upper end (opening 5B). For example, in FIG. 1A, the die 5 is provided with one slit 5A at the center in the thickness direction. A desired die 5 is used according to the shape, the number, etc. of the gallium oxide single crystal to be produced.

  One slit 5 </ b> A is provided so as to have a slit width of a predetermined interval in the thickness direction of the die 5 over almost the entire width of the die 5. The slit 5A serves to raise the gallium oxide melt 2 from the lower end of the die 5 to the opening 5B of the slit 5A by capillary action.

  A lid 6 is disposed on the upper surface of the crucible 3. The lid 6 is formed in a shape in which the upper surface of the crucible 3 excluding the die 5 is closed. For this reason, the upper surface of the crucible 3 except the opening 5B of the slit 5A is closed in a state where the lid 6 is disposed on the upper surface of the crucible 3. As described above, the lid 6 prevents the high-temperature gallium oxide melt 2 from evaporating from the crucible 3, and further suppresses the vapor of the gallium oxide melt 2 from adhering to other than the upper surface of the slit 5A.

  In addition, around the heat insulating material 8 provided so as to surround the crucible 3, for example, a heater unit 9 made of a high-frequency coil is disposed. The crucible 3 is heated to a predetermined temperature by the heater 9, and the raw material in the crucible 3 is melted to become the gallium oxide melt 2. The melting temperature of the raw material is confirmed, for example, as a temperature at which gallium oxide particles placed on the opening 5B of the die 5 melt (chip melt). The heat insulating material 8 is disposed so as to have a predetermined distance from the crucible 3, and has heat retention properties that suppress a rapid temperature change of the crucible 3 heated by the heater unit 9.

  A seed crystal holder 11 that holds the seed crystal 10 is disposed above the slit 5A. The seed crystal holder 11 is connected to a shaft 12 that supports the seed crystal holder 11 (seed crystal 10) so as to be movable up and down.

  Then, the seed crystal holder 11 is lowered by the shaft 12, is lifted by capillary action, the melt 2A on the die top exposed from the opening 5B is brought into contact with the seed crystal 10 (seed touch), and further the shaft 12 raises the seed crystal holder 11 to form a thin neck portion 13a (necking step) (see FIG. 1B). Thereafter, the single crystal 13 is grown so as to extend in the width direction of the die 5 to grow the spread portion 13b (spreading process) and widen to the width of the die 5 (full spread). A straight body portion 13c having a width is grown (straight body step).

  A schematic view of the gallium oxide single crystal 13 manufactured (grown) by such a gallium oxide single crystal manufacturing apparatus is shown in FIG. As shown in FIG. 2, the gallium oxide single crystal 13 is formed in a substantially sheet shape. The gallium oxide single crystal 13 is formed in a crystal shape corresponding to the growth process, and is formed in a neck part 13a formed in the necking process, a spread part 13b formed in the spreading process, and a straight body process. And a straight body portion 13c. Note that the crystal of the straight body portion 13c is usually used as the gallium oxide single crystal substrate 21.

In the gallium oxide single crystal 13 of the present invention, dislocations exist along the pulling direction of the gallium oxide single crystal, as indicated by reference numeral 14 in FIG. 3, and the dislocation density is 1 × 10 ^{6 to} 3 × 10 ^7. Pieces / cm ² . By setting the dislocation density of the gallium oxide single crystal 13 in such a range, as will be described later, the surface as shown in FIGS. 4 and 5 is suitable for GaN epitaxial film growth by the lateral epitaxy on the patterned substrate (LEPS) method. It is possible to manufacture a gallium oxide single crystal substrate having irregularities formed thereon. When a GaN-based LED device is manufactured by forming a GaN epitaxial film on this substrate by the LEPS method, it is possible to reduce dislocations propagating to the light emitting layer and to suppress loss of light emission efficiency. For this reason, even if it is from the gallium oxide single crystal 13 containing the dislocation | rearrangement 14, it becomes possible to produce a high quality GaN-type LED device.

The dislocation density of the gallium oxide single crystal 13 is preferably 1 × 10 ^{6 to} 3 × 10 ⁷ pieces / cm ² . By setting it as this range, it is because the board | substrate with which the unevenness | corrugation suitable for the said LEPS method was formed on the surface is obtained, and the luminous efficiency of a GaN-type LED device can be improved further.

  The dislocation density of the gallium oxide single crystal in the present case is measured by observing the dislocation as a shading pattern with a transmission electron microscope (TEM) and measuring the number thereof.

Moreover, it is preferable that the neck diameter (diameter of the neck part 13a) of the gallium oxide single crystal 13 is 0.4-1.3 mm. This is because the dislocation density can be easily adjusted to 1 × 10 ^{6 to} 3 × 10 ⁷ pieces / cm ² by setting the neck diameter of the gallium oxide single crystal 13 in such a range.

  A gallium oxide single crystal substrate 21 indicated by a broken line in FIG. 3 is a substrate obtained by cutting a gallium oxide single crystal 13 including dislocations 14 into a predetermined size, for example, 1 inch size. When the gallium oxide single crystal substrate 21 is used as a semiconductor device substrate, it is necessary to flatten the surface at the atomic level. For this purpose, CMP (Chemical Mechanical Polish) processing is applied. The CMP process is a process that combines a chemical etching effect and mechanical processing.

  When the gallium oxide single crystal substrate 21 including the dislocations 14 is subjected to final polishing using CMP processing and then etched by a known method, corrosion proceeds from the location where the dislocations 14 are present, as shown in FIG. A substrate having groove-shaped etch pits 22 as shown in FIG. 1 and having irregularities formed on the surface can be obtained. At this time, the width of the unevenness can be adjusted by appropriately selecting the dislocation density of the single crystal. In addition, a longer etch pit is formed by combining a plurality of etch pits starting from dislocations adjacent to each other in the direction in which the dislocations extend together as etching progresses. As a result, the length of the etch pit is approximately 10 μm to several mm, although it varies depending on the direction in which the dislocation extends. In FIG. 5, the etch pit 22 has a rectangular cross section, but may have a triangular groove shape or a cross-sectional shape with rounded corners of the rectangle.

  When the substrate is etched so that the pit width and the pit interval are about 2 to 10 μm, the corrosion proceeds from the location where dislocations exist on the surface as described above, and the surface is exposed as shown in FIGS. A substrate on which unevenness is formed can be manufactured without a mask. In general, when forming irregularities on the substrate surface, after polishing the substrate, a mask made of photoresist or the like is formed on the substrate surface, and the concave portion is formed by etching the opening of the mask. However, according to the method of the present invention, the steps required for mask formation are completely unnecessary, and a substrate with irregularities formed on the surface can be realized with greatly reduced costs.

When the relationship between the dislocation density of the substrate and the pit width and interval formed by etching, that is, the shape of the unevenness was examined, the result of FIG. 6 was obtained. From FIG. 6, the dislocation density of the gallium oxide single crystal 13 is set to 1 × 10 ^{6 to} 3 × 10 in order to make the width of the concavo-convex portion formed on the gallium oxide single crystal substrate 21 to be 2 to 10 μm suitable for the LEPS method. It can be seen that ⁷ pieces / cm ² is sufficient. For this reason, according to the gallium oxide single crystal 13 of this Embodiment, the width | variety of the uneven | corrugated | grooved part formed in the gallium oxide single crystal substrate 21 can be 2-10 micrometers suitable for a LEPS method.

  Further, when a GaN-based thin film device is formed on a substrate having such irregularities on the surface by the LEPS method, the GaN film grown on the substrate concave portion where many dislocations originally existed is converted into the GaN film grown on the substrate convex portion. Since the film is covered by the lateral growth, dislocations generated at the substrate-GaN interface do not propagate to the device surface, for example, the light emitting layer of the LED element. Also, during this lateral growth, dislocations generated at the substrate-GaN interface bend and propagate in the lateral direction while extending upward, so the dislocation density is reduced at the top of the convex part, and the gallium oxide substrate with many dislocations As a result, a high-quality GaN substrate as shown in FIG. 7 can be produced as a result.

  Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the following examples.

(Examples 1-4)
In order to confirm the effect of this embodiment, as Examples 1 to 4, gallium oxide single crystals having different dislocation densities were produced by controlling the neck diameter in the range of 0.4 to 1.3 mm, and these single crystals were cut out. After obtaining a 1-inch substrate, unevenness was formed on the surface by etching.

(Comparative Examples 1-2)
As a comparative example for confirming the effect of the present embodiment, gallium oxide single crystals having a neck diameter of 0.2 mm and 1.5 mm are manufactured, and after cutting these single crystals to obtain a 1-inch substrate, etching is performed on the surface. Unevenness was formed.

  Table 1 shows the dislocation density of the produced single crystal substrates, the shape of the irregularities formed by etching these substrates, and the neck diameter when each single crystal was produced. The seed touch temperature (the display temperature of the thermocouple 7 at the time of seed touch) was 1930 ° C.

As shown in Table 1, according to the present invention, a gallium oxide single crystal having a dislocation density of 1 × 10 ^{6 to} 3 × 10 ⁷ pieces / cm ² has a neck diameter of 0.4 to 1.3 mm. It was also confirmed that the width of the concavo-convex part was 2 to 10 μm suitable for the LEPS method.

As described above, according to the present embodiment, since the dislocation density of the gallium oxide single crystal is 1 × 10 ^{6 to} 3 × 10 ⁷ pieces / cm ² , the surface processed from the gallium oxide single crystal By using a substrate with irregularities, a high-quality GaN film can be produced.

The present invention is not limited to the above embodiment, and various modifications and applications are possible. For example, in the above embodiment, the present invention has been described by taking as an example the case where a gallium oxide single crystal is manufactured by crystal growth of the (101) plane by the EFG method. However, the method for manufacturing a gallium oxide single crystal is limited to the EFG method. Instead, various methods capable of forming the gallium oxide single crystal 13 having a dislocation density of 1 × 10 ^{6 to} 3 × 10 ⁷ pieces / cm ² can be used. Further, the crystal plane to be grown is not limited to the (101) plane.

  The present invention is useful for the gallium oxide single crystal and the gallium oxide single crystal substrate of the present invention.

DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus of gallium oxide single crystal 2 Gallium oxide melt 3 Crucible 4 Support stand 5 Die 5A Slit 5B Opening 6 Lid 7 Thermocouple 8 Heat insulating material 9 Heater part 10 Seed crystal 11 Seed crystal holder 12 Shaft 13 Gallium oxide single crystal 13a Neck portion of gallium oxide single crystal 13b Spread portion of gallium oxide single crystal 13c Straight body portion of gallium oxide single crystal 21 Gallium oxide single crystal substrate 22 Etch pit

Claims (5)

Manufactured by EFG method, dislocation density of 1 × ¹⁰ 6 ~3 × ^{10 7} pieces / cm are ^two der, dislocations along the b-axis direction is the pulling direction, gallium oxide single crystal, characterized in that . 2. The gallium oxide single crystal according to claim 1, wherein the neck diameter is 0.4 to 1.3 mm. A gallium oxide single crystal substrate comprising the gallium oxide single crystal according to claim 1 or 2 and subjected to CMP processing. 4. The gallium oxide single crystal substrate according to claim 3, wherein the surface is etched, and groove-like etch pits are formed at locations where dislocations exist, whereby irregularities are formed on the substrate surface. 5. . 5. The gallium oxide single crystal substrate according to claim 3, wherein the gallium oxide single crystal substrate has a size of at least 1 inch.