JP2020125230A - Annealing method of nitride semiconductor substrate - Google Patents

Abstract

To provide an annealing method of a nitride semiconductor substrate capable of reducing as much as possible generation of warp, when annealing the nitride semiconductor substrate.SOLUTION: When a semiconductor nitride substrate 13 formed by growing a nitride semiconductor thin film 12 on the surface of a substrate 11 is installed on an anneal holder 14, and the nitride semiconductor thin film is annealed by heating the anneal holder and the semiconductor nitride substrate at specific temperature and time in a specific gas atmosphere, a dummy substrate 15 is installed on the outer surface of the semiconductor nitride substrate.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method of annealing a nitride semiconductor substrate, and more particularly, to a method of placing a nitride semiconductor substrate having a nitride semiconductor thin film grown on the surface of the substrate in an annealing holder and performing annealing.

Ultraviolet light emitting devices have been widely noticed as next-generation light sources such as alternatives to fluorescent lamps, high-density DVDs, biochemical lasers, decomposition of pollutants by photocatalysts, He-Cd lasers, alternatives to mercury lamps. This ultraviolet light emitting element is made of an AlGaN-based nitride semiconductor called a wide gap semiconductor, and is laminated on a heterogeneous substrate such as sapphire. However, since sapphire has a large lattice mismatch with AlGaN, a large number of threading dislocations are present and serve as non-radiative recombination centers, which significantly reduces the internal quantum efficiency.

On the other hand, since AlN has a lattice constant close to that of AlGaN and is transparent up to the ultraviolet region of 200 nm, it is possible to efficiently extract the ultraviolet light to the outside without absorbing the emitted ultraviolet light. However, a bulk single crystal AlN crystal is very expensive even if it has a size of 1 inch and cannot be easily obtained. Therefore, when considering cost and mass productivity, it is unsuitable as a substrate material for an ultraviolet light emitting device. On the other hand, sapphire is available in a 4 to 6 inch size at low cost. From this, if a high-quality AlN single crystal film can be formed on a sapphire substrate, an AlGaN-based light emitting device is used as a substrate for quasi-homoepitaxial growth to obtain an ultraviolet ray having a low crystal defect density. The light emitting element can be manufactured at low cost.

However, since AlN has a large lattice mismatch with sapphire, many threading dislocations are present in the AlN film grown on sapphire. Therefore, it is not suitable as a substrate for an AlGaN light emitting device. Therefore, as a method for obtaining a high-quality layer (thin film) in which the defect density of an AlN crystal is suppressed low, a method for producing a high-quality AlN film having a flat surface is disclosed (for example, see Patent Document 1). ..). Further, on each surface, at least a pair of single crystal silicon carbide substrates ion-implanted with atoms, the step of heat treatment by placing in close contact or close to each other so that the ion-implanted surfaces face each other is disclosed. (For example, see Patent Document 2).

It seems that a nitride semiconductor substrate can be obtained by combining the two. However, if the nitride semiconductor substrate comes into contact with the closed container or the outside air during annealing, it will be inert gas in a high temperature atmosphere. There is a possibility that one surface (sapphire substrate portion) of the nitride semiconductor substrate may be deteriorated by being exposed to, and as a result, the nitride semiconductor substrate may be largely warped. Further, even when the carbon member comes in contact with the annealing holder, the contact may cause a large warp. Therefore, a method for preventing deterioration of the sapphire substrate by adding carbon monoxide has been disclosed (for example, refer to Patent Document 3).

JP, 2017-55116, A JP, 2006-339396, A JP, 2005-042598, A

However, even if the methods described in each patent document are combined, it is difficult to control the warp of the substrate in a stable manner, and the substrate that is largely warped loses the uniformity of the film thickness distribution in the subsequent film forming process. However, there is a problem in that the device does not enter the device that performs each subsequent process.

Therefore, an object of the present invention is to provide a method for annealing a nitride semiconductor substrate, which can minimize the occurrence of warpage when annealing the nitride semiconductor substrate.

In order to achieve the above object, a method for annealing a nitride semiconductor substrate according to the present invention is a method in which a nitride semiconductor substrate having a nitride semiconductor thin film grown on a surface of the substrate is placed in an annealing holder, and the annealing holder and the nitride semiconductor are provided. In the method of annealing the nitride semiconductor thin film by heating the substrate together with a gas, a dummy substrate is provided on the outer surface of the nitride semiconductor substrate.

Further, the method for annealing a nitride semiconductor substrate of the present invention is characterized in that the dummy substrate is formed of the same material as the substrate of the nitride semiconductor substrate, and in particular, the substrate has an Al element ratio of 40% or more. It is characterized by being formed from the aluminum compound of. Further, when a plurality of the nitride semiconductor substrates are stacked and installed in the annealing holder, the nitride semiconductor thin films are alternately stacked with the directions of the surfaces of the nitride semiconductor thin films in the nitride semiconductor substrates reversed. ..

In addition, the nitride semiconductor thin _{film, Al x Ga y In (1} -x-y) N (0 ≦ x ≦ 1,0 ≦ y ≦ 1, (x + y) ≦ 1) that is, the gas, It is characterized in that it is any one gas of nitrogen, argon, helium, krypton, neon, carbon monoxide, and ammonia, or a mixed gas thereof.

According to the method for annealing a nitride semiconductor substrate of the present invention, warpage of the nitride semiconductor thin film substrate during annealing can be reduced.

It is a schematic diagram which shows the 1st form example of the processing state of the annealing method of the nitride semiconductor substrate of this invention. It is a figure which shows the result of having measured the curvature amount of the nitride semiconductor substrate after the process in a 1st form example. It is a schematic diagram which shows the 2nd example of a process state of the annealing method of the nitride semiconductor substrate of this invention. It is a figure which shows the result of having measured the curvature amount of the nitride semiconductor substrate after the process in the example of a 2nd form. It is a figure which shows the result of having measured the curvature amount of the nitride semiconductor substrate annealed, without using a dummy substrate. It is a schematic diagram which shows the 3rd example of a processing state of the annealing method of the nitride semiconductor substrate of this invention.

1 and 2 show a first embodiment of the present invention. In the method for annealing a nitride semiconductor substrate shown in the present embodiment, a nitride semiconductor substrate 13 having a nitride semiconductor thin film 12 grown on a surface (one surface) of a substrate (wafer) 11 is placed in an annealing holder 14, and the annealing holder 14 is used. When the nitride semiconductor substrate 13 is annealed by heating 14 and the nitride semiconductor substrate 13 together in a gas, dummy substrates are formed on both outer surfaces (both the front surface and the back surface) of the nitride semiconductor substrate 13. 15 is installed.

The substrate 11 may be made of a material depending on the application and the type of thin film to be formed, and the thickness and the outer shape are arbitrary, but it is generally preferable to use a disc-shaped substrate made of sapphire, and the dummy substrate 15 May have any adverse effect on the nitride semiconductor thin film 12 and may have any thickness and shape, but normally it is preferable to use the substrate 11 on which the nitride semiconductor thin film 12 is not formed as it is. .. For example, a sapphire substrate having a thickness of 900 μm and a diameter of 100 mm can be used. In this case, the material of the substrate 11 may be an aluminum compound such as sapphire (Al ₂ O ₃ ) having an Al element ratio of 40% or more.

Nitride semiconductor thin film 12, using, for example, well-known MOCVD method _{Al x Ga y In (1-} x-y) N (0 ≦ x ≦ 1,0 ≦ y ≦ 1 is a nitride semiconductor thin film, (x + y) ≦1) is formed, and for example, AlN in which x=1 in the above chemical formula can be mentioned.

The anneal holder 14 on which the nitride semiconductor substrate 13 is installed is, for example, a cylinder of carbon and is formed so that the nitride semiconductor substrate 13 installed therein can be heated uniformly. The inner diameter of the anneal holder 14 is equal to or larger than the diameter of the substrate 11, and the height (depth) in the cylinder is a height obtained by stacking at least one nitride semiconductor substrate 13 and two dummy substrates 15 in total of three layers. The nitride semiconductor substrate 13 is formed to have a size larger than that, and is usually formed to a height capable of accommodating a plurality of nitride semiconductor substrates 13 at the same time.

The gas used as the atmosphere during annealing may be any gas that does not adversely affect the substrate 11, the nitride semiconductor thin film 12, and the annealing holder 14, and is usually nitrogen, argon, helium, krypton, neon, It is preferable to use any one gas of carbon monoxide and ammonia or a mixed gas in which a plurality of gases are mixed.

As shown in FIG. 1, when annealing one nitride semiconductor substrate 13, the nitride semiconductor substrate 13 is sandwiched between two dummy substrates 15 and stacked in the annealing holder 14. The annealing holder 14 with the nitride semiconductor substrate 13 installed therein is placed in a well-known annealing device (not shown). Then, the inside of the annealing device is filled with a preset gas atmosphere, for example, a nitrogen atmosphere, and is kept at a preset temperature, for example, 1700° C. for a preset time, for example, 3 hours, thereby performing nitriding. The semiconductor substrate 13 is annealed.

FIG. 2 shows a nitride semiconductor substrate 13 in which a sapphire substrate having a thickness of 900 μm and a diameter of 100 mm is used as the substrate 11, and AlN is deposited on the surface as a nitride semiconductor thin film 12 to a thickness of 300 nm by the MOCVD method. The results are shown in FIG. Showing. From this measurement result, it can be seen that the amount of warpage of the nitride semiconductor substrate 13 is suppressed to 15 μm or less.

Further, the dummy substrate 15 superposed on the nitride semiconductor thin film 12 side (front surface side) of the substrate 11 is also used for evaporation prevention in order to prevent the nitride semiconductor thin film 12 from evaporating during heating in the annealing device. It functions and prevents the nitride semiconductor thin film 12 from being deteriorated by heating.

3 and 4 show a second embodiment of the present invention. The present embodiment shows a state in which two or more even-numbered nitride semiconductor substrates 13 are simultaneously annealed. When annealing an even number, six in FIG. 3, of the nitride semiconductor substrates 13, the nitride semiconductor thin films 12 on each of the nitride semiconductor substrates 13 are alternately stacked with the directions of the faces of the nitride semiconductor thin films 12 reversed, and the nitride semiconductors are stacked. The thin films 12 are made to face each other so that the nitride semiconductor thin film 12 does not face the outermost surface. When installed in the annealing holder 14, the even number of nitride semiconductor substrates 13 with the nitride semiconductor thin films 12 facing each other are placed on the first dummy substrate 15 placed on the bottom surface of the annealing holder 14. Are placed on top of each other, and the second dummy substrate 15 is placed on the uppermost surface.

By arranging the annealing holder 14 in the annealing apparatus in this state and performing annealing, it is possible to perform effective annealing while suppressing the warp of the substrate 11 and the evaporation of the nitride semiconductor thin film 12.

FIG. 4 shows the amount of warpage in each nitride semiconductor substrate 13 when six nitride semiconductor substrates 13 and two dummy substrates 15 are installed and annealed under the same processing conditions as shown in FIG. The measurement results are shown. As a result, it can be seen that the warpage amount of all six nitride semiconductor substrates 13 is suppressed to 15 μm or less.

Similar to FIG. 3, FIG. 5 shows the amount of warpage in each nitride semiconductor substrate 13 when the six nitride semiconductor substrates 13 are simultaneously annealed without using the upper and lower dummy substrates 15. The result is shown. From this result, it can be seen that a large warp of 40 to 50 μm occurs in the uppermost and lowermost nitride semiconductor substrates. Therefore, it is understood that the warp during the annealing can be prevented by disposing the dummy substrates 15 on the upper and lower sides, respectively.

FIG. 6 shows a state in which three or more odd-numbered nitride semiconductor substrates 13 are simultaneously annealed. When annealing the odd-numbered nitride semiconductor substrates 13 (7 in FIG. 5), the nitride semiconductor thin films for 6 nitride semiconductor substrates 13 are the same as in the second embodiment (FIG. 3). 12 are made to face each other, and the remaining one is made to cover the nitride semiconductor thin film 12 with the dummy substrate 15 as in the first embodiment (FIG. 1). It is possible to suppress the occurrence of warpage while suppressing deterioration due to evaporation of the.

Thus, when the nitride semiconductor substrate 13 is annealed, the dummy substrate 15 is annealed between the bottom surface of the annealing holder 14 and the nitride semiconductor substrate 13 and on the outer surface portion of the nitride semiconductor substrate 13. By doing so, warpage of the nitride semiconductor substrate 13 can be reduced, each subsequent process can be reliably performed, and productivity can be improved. This can reduce the manufacturing cost of the ultraviolet light emitting device.

In particular, by using the same substrate as the substrate 11 for forming the nitride semiconductor substrate 13 as the dummy substrate 15, compared with the case where a dummy substrate formed of a material and a thickness different from that of the substrate 11 is prepared, The substrate can be easily prepared, and the cost required for the dummy substrate can be reduced.

The material of the substrate, the shape of the thickness and diameter is optional, the nitride semiconductor thin films, can be any of the thin film according to the _{purpose, Al x Ga y In (1} -x-y) N ( The numerical values of x and y in 0≦x≦1, 0≦y≦1, (x+y)≦1) are also arbitrary. Further, the type of atmosphere gas at the time of annealing is also arbitrary, and carbon monoxide or ammonia can be used, including an inert gas such as nitrogen, argon, helium, krypton, or neon, and any one of them can be used. A gas may be used, or a mixed gas obtained by mixing a plurality of gas species may be used. Further, the annealing conditions can be appropriately set to the temperature and the time depending on the conditions such as the material of the substrate, the type of the nitride semiconductor thin film, the type of the atmospheric gas, and the like.

11... Substrate, 12... Nitride semiconductor thin film, 13... Nitride semiconductor substrate, 14... Annealing holder, 15... Dummy substrate

Claims (6)

A nitride semiconductor substrate having a nitride semiconductor thin film grown on the surface of the substrate is placed in an anneal holder, and the anneal holder and the nitride semiconductor substrate are heated together in a gas to anneal the nitride semiconductor thin film. The method for annealing a nitride semiconductor substrate according to claim 1, wherein a dummy substrate is provided on the outer surface of the nitride semiconductor substrate. The method for annealing a nitride semiconductor substrate according to claim 1, wherein the dummy substrate is formed of the same material as the substrate of the nitride semiconductor substrate. The method for annealing a nitride semiconductor substrate according to claim 1, wherein the substrate is formed of an aluminum compound having an Al element ratio of 40% or more. When stacking a plurality of the nitride semiconductor substrates on each other and placing them on the annealing holder, the nitride semiconductor thin films are alternately stacked with the directions of the surfaces of the nitride semiconductor thin films on the nitride semiconductor substrates reversed. 4. The method for annealing a nitride semiconductor substrate according to any one of 1 to 3. The nitride semiconductor thin _{film, Al x Ga y In (1} -x-y) N (0 ≦ x ≦ 1,0 ≦ y ≦ 1, (x + y) ≦ 1) 1 to claim characterized in that it is a 5. The method for annealing a nitride semiconductor substrate according to any one of 4 above. The said gas is any one kind of gas of nitrogen, argon, helium, krypton, neon, carbon monoxide, and ammonia, or the gas which mixed two or more, The gas of any one of Claim 1 thru|or 5 characterized by the above-mentioned. Annealing method for nitride semiconductor substrate.

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