JP4756418B2 - Method for manufacturing single crystal gallium nitride substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a single crystal gallium nitride substrate. More specifically, the present invention relates to a method for manufacturing a single crystal gallium nitride substrate supported by a polycrystalline silicon carbide layer that can realize a blue light emitting element.

  Gallium nitride is widely used as a material for blue light-emitting elements typified by LEDs and laser diodes. This gallium nitride is obtained by growing a single crystal on a sapphire substrate by MOCVD (organic chemical vapor deposition) or the like (for example, see JP-A-8-78728 (Patent Document 1)). Sapphire is relatively close to the lattice constant of gallium nitride (mismatch ratio of about 15%) and is used as a growth substrate for gallium nitride.

However, sapphire has drawbacks that it has low electrical conductivity, cannot be enlarged (larger diameter) like a silicon substrate, and has a high manufacturing cost.
Therefore, silicon carbide has been proposed that is closer to the lattice constant of gallium nitride than sapphire (mismatch ratio is about 5%) and has good heat resistance (for example, Japanese Patent Laid-Open No. 10-106949 (Patent Document 2)). reference).

JP-A-8-78728 Japanese Patent Laid-Open No. 10-106949

However, there is a need for a substrate for a blue light-emitting element that has higher crystal matching with gallium nitride, higher electrical conductivity, can be increased in size (larger diameter), and is low in cost.
An object of the present invention is to provide a method for manufacturing a single crystal gallium nitride substrate supported by a polycrystalline silicon carbide layer, which can realize a blue light emitting device.

Thus, according to the present invention,
A method for producing a single crystal gallium nitride substrate supported by a polycrystalline silicon carbide layer,
(A) An SOI substrate having a structure in which a single crystal silicon layer having a plane orientation (111), a buried oxide film layer, and a silicon substrate are sequentially stacked is heat-treated in a hydrocarbon-based gas atmosphere, and the single crystal silicon layer To a single crystal silicon carbide layer having a plane orientation (111) and a step of thickening the single crystal silicon carbide layer by an epitaxial growth method,
(B) forming a single crystal gallium nitride layer having a thickness sufficient to constitute the single crystal gallium nitride substrate on the single crystal silicon carbide layer;
(C) a step of forming a polycrystalline silicon carbide layer having a thickness sufficient to support the single crystal gallium nitride substrate on the single crystal gallium nitride layer by a high-frequency plasma method; and (D) the obtained laminate To the silicon substrate, the buried oxide film layer, and the single crystal silicon carbide layer are sequentially removed under different conditions.
Moreover, according to this invention, the single crystal gallium nitride substrate obtained by said manufacturing method is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the single crystal gallium nitride substrate supported by the polycrystalline silicon carbide layer which can implement | achieve a blue-type light emitting element can be provided.

The single crystal gallium nitride substrate of the present invention is supported by a polycrystalline silicon carbide layer.
FIG. 1 is a schematic cross-sectional view showing the configuration, where 1 is a single crystal gallium nitride layer and 2 is a polycrystalline silicon carbide layer.

The method for producing a single crystal gallium nitride substrate of the present invention includes the steps (A) to (D) described above.
FIG. 2 is a schematic sectional view showing the manufacturing method, which will be described in detail.
However, the following description is one embodiment of the present invention, and the present invention is not limited thereby.

Process (A)
First, an SOI substrate 6 having a structure in which a single crystal silicon layer 3 having a plane orientation (111), a buried oxide film layer 4 and a silicon substrate 5 are sequentially stacked is heat-treated in a hydrocarbon gas atmosphere, and the single crystal silicon layer 3 is buried. The crystalline silicon layer 3 is transformed into a single crystal silicon carbide layer 7 having a plane orientation (111), and then the single crystal silicon carbide layer 7 is thickened by epitaxial growth.

An SOI (Silicon-on-Insulator) substrate 6 is a substrate having a laminated structure of single crystal silicon layer 3 / buried oxide film layer 4 / silicon substrate 5 (see FIG. 2A), and a known one is used. Can do. The thickness and thickness of each layer and substrate are about 3 to 15 nm / about 90 to 400 nm / about 600 to 900 μm in the above order.
In order to easily epitaxially grow the single crystal gallium nitride layer 1 in the step (C), a single crystal silicon carbide layer 7 having a plane orientation (111) is required as its substrate, and the single crystal silicon layer 3 before the transformation is It preferably has a plane orientation (111).
In addition, from the viewpoint of production efficiency when producing a blue light-emitting device using the single crystal gallium nitride substrate of the present invention, the SOI substrate 6 is preferably larger, for example, having a diameter of 200 mm.

  The hydrocarbon-based gas is not particularly limited as long as it is a gas capable of transforming the single crystal silicon layer 3 into the single crystal silicon carbide layer 7, and examples thereof include hydrogen / propane mixed gas, hydrogen / butane mixed gas, hydrogen / butane mixed gas, Examples thereof include an ethylene mixed gas, a hydrogen / propylene mixed gas, and a hydrogen / benzene mixed gas. Among these, a hydrogen / propane mixed gas is particularly preferable because it is inexpensive and highly versatile. What is necessary is just to set the mixture ratio of mixed gas suitably.

What is necessary is just to set heat processing conditions suitably, for example, heating temperature is about 1100-1405 degreeC, and heating time is about 5 minutes-about 1 hour.
The film thickness of the modified single crystal silicon carbide layer is about 10 nm to the thickness of the single crystal silicon layer. If the film thickness is less than 3 nm, the crystallinity of the single crystal gallium nitride layer formed in the next step (B) may be lowered, which is not preferable.

The reactive gas in the epitaxial growth method is not particularly limited as long as it is a gas capable of epitaxially growing the single crystal silicon carbide layer 7, but monomethylsilane is particularly preferable in that it is inexpensive and highly safe.
The substrate temperature, that is, the temperature of the SOI substrate 6 is preferably 1000 to 1100 ° C.
The growth time may be appropriately set depending on the film thickness of the single crystal silicon carbide layer 7 to be formed, and is, for example, about 30 to 45 minutes.
The film thickness of the single crystal silicon carbide layer 7 after thickening is about 50 to 100 nm.

  Specifically, the SOI substrate 6 is installed in a processing chamber, and the SOI substrate 6 is heat-treated while flowing a hydrocarbon-based gas in the processing chamber, thereby transforming the single crystal silicon layer 3 to obtain a plane orientation ( 111) is obtained, and subsequently, the single crystal silicon carbide layer 7 is thickened by an epitaxial growth method. (See FIG. 2 (b)).

Process (B)
Next, the single crystal gallium nitride layer 1 having a thickness sufficient to form a single crystal gallium nitride substrate is formed on the single crystal silicon carbide layer 7.
Specifically, single crystal gallium nitride layer 1 is epitaxially grown on single crystal silicon carbide layer 7.
The reaction gas is not particularly limited as long as it is a gas capable of epitaxially growing the single crystal gallium nitride layer 1, but a trimethyl gallium / ammonia mixed gas is preferable because it is versatile and has a high use record. What is necessary is just to set the mixture ratio of mixed gas suitably.

As substrate temperature, ie, the temperature of the single-crystal silicon carbide layer 7, 700-1200 degreeC is preferable and 1000-1150 degreeC is especially preferable.
The growth time may be set as appropriate depending on the thickness of the single crystal gallium nitride layer 1 to be formed, and is, for example, about 15 to 50 minutes.
The film thickness of the single crystal gallium nitride layer 1 to be formed is about 0.5 to 10 μm. If the film thickness is less than 20 nm, it may not function as a single crystal gallium nitride substrate, which is not preferable.

  Specifically, the obtained stacked body is heated while circulating the reaction gas in the processing chamber to epitaxially grow the single crystal gallium nitride 1 on the single crystal silicon carbide layer 7 (see FIG. 2C). .

Process (C)
Next, a polycrystalline silicon carbide layer 2 having a thickness sufficient to support the single crystal gallium nitride substrate is formed on the single crystal gallium nitride layer 1 by a high frequency plasma method (also referred to as “high frequency plasma deposition method”).
If the high-frequency plasma method is used, the polycrystalline silicon carbide layer 2 is formed on the single-crystal gallium nitride layer 1 without being decomposed at a relatively low temperature, specifically, at a substrate temperature range of 850 to 1150 ° C. be able to.
On the other hand, MOCVD (organic chemical vapor deposition) is not suitable for forming the polycrystalline silicon carbide layer 2 of the present invention because the substrate temperature needs to be heated to 1400 ° C. or higher and at least 1200 ° C. or higher.

The high-frequency plasma apparatus (also referred to as “high-frequency plasma deposition apparatus”) is not particularly limited as long as the substrate temperature can be controlled from room temperature to about 1150 ° C.
The frequency of the high frequency to be applied is preferably 13.56 MHz in terms of legal and general versatility.
The reaction gas is not particularly limited as long as it is a gas that can form the polycrystalline silicon carbide layer 2, but monomethylsilane is particularly preferable in terms of low cost and high safety.

The substrate temperature, that is, the temperature of the single crystal gallium nitride layer 1 is preferably 850 to 1150 ° C., and particularly preferably 850 to 1000 ° C.
Moreover, what is necessary is just to set suitably the time to hold | maintain a plasma state with the film thickness of the polycrystalline silicon carbide layer 2 to deposit.
The film thickness of the polycrystalline silicon carbide layer 2 to be formed is about 100 to 1000 μm. If the film thickness is less than 500 nm, it may not function as a support substrate for the single crystal gallium nitride substrate, which is not preferable.

  Specifically, the obtained laminate is placed in a high-frequency plasma apparatus, and the obtained laminate is heated to 1000 ° C. while circulating a reaction gas, and high frequency is applied to generate high-frequency plasma. While maintaining this state, a decomposition product of monomethylsilane is deposited on single crystal gallium nitride 1 to obtain polycrystalline silicon carbide layer 2 (see FIG. 2D).

Process (D)
Next, the silicon substrate 5, the buried oxide film layer 4 and the single crystal silicon carbide layer 7 are sequentially removed under different conditions from the obtained laminate.
The silicon substrate 5 is selectively removed by a known method, for example, by immersing the obtained laminate in a mixed solution of nitric acid / hydrofluoric acid (see FIG. 2 (e)).

Next, the buried oxide film layer 4 is selectively removed by a known method, for example, by immersing the obtained laminate in a dilute hydrofluoric acid solution (see FIG. 2F).
Next, the single crystal silicon carbide layer 7 is removed from the obtained laminate by a known method, for example, mechanical polishing using alumina toner, and the single crystal gallium nitride substrate of the present invention, that is, polycrystalline silicon carbide. A single crystal gallium nitride substrate supported by the layer is obtained (see FIG. 2G).

The thus obtained single crystal gallium nitride substrate of the present invention can realize a blue light emitting element. That is, the present invention does not refer to an element (transistor) but can provide a substrate for realizing the element.
As described above, the film thickness of the single crystal gallium nitride is about 0.5 to 10 μm, and the film thickness of the polycrystalline silicon carbide is about 100 to 1000 μm.

(Example)
The present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples.

Example 1
Based on the manufacturing method of FIGS. 2A to 2G, the single crystal gallium nitride substrate of FIG. 1 was produced.
An SOI substrate 6 having a diameter of 200 mm having a laminated structure of single crystal silicon layer 3 (7 nm) / buried oxide film layer 4 (110 nm) / silicon substrate 5 (750 μm) having a plane orientation (111) was prepared (FIG. 2 ( a)).
The SOI substrate 6 is set in a processing chamber, and a mixed gas of 1 slm hydrogen (H ₂ ) gas and 10 sccm propane (C ₃ H ₈ ) is circulated in the processing chamber at 1550 ° C. The single crystal silicon layer 3 was transformed by heat treatment for 5 minutes to obtain a single crystal silicon carbide layer 7 having a plane orientation (111) with a film thickness of 5 nm.
Subsequently, while flowing 1 sccm of monomethylsilane gas through the processing chamber, the SOI substrate 6 is heated at 1100 ° C. for 45 minutes to epitaxially grow single crystal silicon carbide on the single crystal silicon carbide layer 7, thereby producing single crystal carbonization. The film thickness of the silicon layer 7 was increased to 100 nm (see FIG. 2B).

  Next, while the mixed gas of 5 sccm of trimethyl gallium and 2 slm ammonia was circulated in the processing chamber, the obtained laminate was heated at 1100 ° C. for 15 minutes to form a single crystal of 500 nm on the single crystal silicon carbide layer 7. Gallium nitride 1 was epitaxially grown (see FIG. 2C). Next, the obtained laminate was once cooled to room temperature and taken out from the processing chamber.

  Next, the obtained laminate is placed in a high-frequency plasma apparatus, and the obtained laminate is heated to 1000 ° C. while supplying 50 sccm of monomethylsilane gas, and a high frequency of 13.56 MHz is applied. High frequency plasma was generated. This state was maintained for 2 hours, and a decomposition product of monomethylsilane was deposited on the single crystal gallium nitride 1 to obtain a 500 μm polycrystalline silicon carbide layer 2 (see FIG. 2D). Next, the obtained laminate was once cooled to room temperature and taken out from the high-frequency plasma apparatus.

Next, the obtained laminate was immersed in a mixed solution of nitric acid / hydrofluoric acid to selectively remove the silicon substrate 5 (see FIG. 2E).
Next, the obtained laminate was immersed in dilute hydrofluoric acid solution to selectively remove the buried oxide film layer 4 (see FIG. 2F).

  Next, the single crystal silicon carbide layer 7 was mechanically polished using an alumina toner to obtain a single crystal gallium nitride substrate supported by the polycrystalline silicon carbide layer (see FIG. 2G).

  When the diffraction pattern of the obtained single crystal gallium nitride substrate was measured using an X-ray diffractometer, it was confirmed that a single crystal gallium nitride layer having a desired crystal orientation (0001) was formed.

It is a schematic sectional drawing which shows the structure of the single crystal gallium nitride substrate of this invention. It is a schematic sectional drawing which shows the manufacturing method of the single crystal gallium nitride substrate of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Single crystal gallium nitride layer 2 Polycrystalline silicon carbide layer 3 Single crystal silicon layer 4 Embedded oxide film layer 5 Silicon substrate 6 SOI substrate 7 Single crystal silicon carbide layer

Claims (9)

A method for producing a single crystal gallium nitride substrate supported by a polycrystalline silicon carbide layer,
(A) An SOI substrate having a structure in which a single crystal silicon layer having a plane orientation (111), a buried oxide film layer, and a silicon substrate are sequentially stacked is heat-treated in a hydrocarbon-based gas atmosphere, and the single crystal silicon layer To a single crystal silicon carbide layer having a plane orientation (111) and a step of thickening the single crystal silicon carbide layer by an epitaxial growth method,
(B) forming a single crystal gallium nitride layer having a thickness sufficient to constitute the single crystal gallium nitride substrate on the single crystal silicon carbide layer;
(C) a step of forming a polycrystalline silicon carbide layer having a thickness sufficient to support the single crystal gallium nitride substrate on the single crystal gallium nitride layer by a high-frequency plasma method; and (D) the obtained laminate A step of removing the silicon substrate, the buried oxide film layer and the single crystal silicon carbide layer sequentially under different conditions.   2. The single crystal nitriding according to claim 1, wherein the hydrocarbon gas in the heat treatment in the step (A) is a hydrogen / propane mixed gas, the heating temperature is 1100 to 1405 ° C., and the heating time is 5 minutes to 1 hour. A method for manufacturing a gallium substrate.   The step (B) is an epitaxial growth of a single crystal gallium nitride layer, a reaction gas in the epitaxial growth is a trimethylgallium / ammonia mixed gas, and the temperature of the single crystal silicon carbide layer as a substrate is 700 to 1200 ° C. 3. A method for producing a single crystal gallium nitride substrate according to 2.   The method for producing a single-crystal gallium nitride substrate according to any one of claims 1 to 3, wherein the reactive gas in the high-frequency plasma method in step (C) is monomethylsilane.   The method for producing a single crystal gallium nitride substrate according to any one of claims 1 to 4, wherein the temperature of the single crystal gallium nitride layer as the substrate in the high-frequency plasma method of step (C) is 850 to 1150 ° C.   The method for producing a single-crystal gallium nitride substrate according to any one of claims 1 to 5, wherein a frequency of a high frequency applied in the high frequency plasma method in step (C) is 13.56 MHz.   The single-crystal gallium nitride substrate according to any one of claims 1 to 6, wherein the single-crystal gallium nitride layer has a thickness of 0.5 to 10 µm, and the polycrystalline silicon carbide layer has a thickness of 100 to 1000 µm. Production method.   The step (D) is removal of the silicon substrate with a mixed solution of nitric acid / hydrofluoric acid, removal of the buried oxide film layer with hydrofluoric acid solution, and removal of the single crystal silicon carbide layer by mechanical polishing. The manufacturing method of the single-crystal gallium nitride substrate as described in any one.   A single crystal gallium nitride substrate obtained by the manufacturing method according to claim 1.

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