JP2002053399A - Method for manufacturing nitride semiconductor substrate and nitride semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate made of a nitride semiconductor good in crystallinity. SOLUTION: The substrate is produced by providing a first wafer obtained by growing the nitride semiconductor on a first substrate and a second wafer obtained by growing the nitride semiconductor on a second substrate, then adhering the first wafer and the second wafer so that the nitride semiconductor are closely adhered to each other and removing the first substrate and the second substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (In _{XA).
l Y Ga 1-XY N,} 0 ≦ X, 0 ≦ Y, a method of manufacturing a substrate made of X + Y ≦ 1).

[0002]

2. Description of the Related Art Generally, when a semiconductor is grown on a substrate,
It is known that using a substrate lattice-matched with the semiconductor to be grown reduces crystal defects of the semiconductor and improves crystallinity. However, nitride semiconductors are generally grown on substrates that do not lattice match with nitride semiconductors, such as sapphire, spinel, and silicon carbide, because there are no substrates that lattice match in the world.

Attempts to produce a GaN bulk crystal have been made by various research institutions, but only reports of a few millimeters have been obtained, and it is far from practical use.

As a technique for manufacturing a GaN substrate, for example, Japanese Patent Application Laid-Open No. 7-202265 and Japanese Patent Application Laid-Open
No. 8 discloses a technique of forming a buffer layer made of ZnO on a sapphire substrate, growing a nitride semiconductor on the buffer layer, and then dissolving and removing the buffer layer.

However, the crystallinity of a ZnO buffer layer grown on a sapphire substrate is poor, and it is difficult to obtain a good quality nitride semiconductor even if a nitride semiconductor is grown on the buffer layer. Furthermore, it takes a very long time to dissolve and remove the thin-film buffer layer made of ZnO, and it is practically difficult.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object of the present invention is to provide a nitride semiconductor device having high luminous efficiency and high light receiving efficiency. It is an object of the present invention to provide a substrate made of a nitride semiconductor having a good quality.

[0007]

The nitride semiconductor substrate of the present invention is a substrate made of a nitride semiconductor having at least a two-layer structure, wherein the nitride semiconductor layers have different carrier concentrations.

Further, the nitride semiconductor substrate of the present invention is characterized in that the nitride semiconductor layer is non-doped or doped with an n-type impurity at 1 × 10 ¹⁹ / cm ³ or less.

Further, in the nitride semiconductor substrate of the present invention,
The n-type impurity is at least one selected from Si, Ge, Sn, and S. further,
The nitride semiconductor layer is characterized in that a half width of an X-ray rocking curve by a biaxial crystal method is 15 minutes or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the manufacturing method of the present invention, a first substrate on which a nitride semiconductor is grown and a second substrate on which a conventionally proposed nitride semiconductor can be grown are provided. Any substrate may be used as long as it is a substrate other than a substrate made of a semiconductor. For example, sapphire, spinel, SiC, etc. are frequently used.
There are GaAs, Si, GaP and the like.
An oxide substrate lattice-matched to a nitride semiconductor described in 9475 can be used.

In order to grow a nitride semiconductor, for example, M
Conventionally known vapor deposition methods such as OVPE (metal organic chemical vapor deposition), MBE (molecular beam vapor deposition), and HVPE (halide vapor deposition) can be used.

In order to grow a nitride semiconductor on a substrate,
First, in contact with the substrate, GaN, A
It is desirable to grow a buffer layer such as 1N or AlGaN. The buffer layer is described in detail in, for example, Japanese Patent Application Laid-Open No. H4-297023.

Next, the nitride semiconductor to be grown on the substrate is most preferably non-doped, or 1 × 1
GaN doped at 0 ¹⁹ / cm ³ or less is grown. As the n-type impurity, at least one of Group 4 elements such as Si, Ge, Sn, and S is selected, and Si and Ge are particularly preferably used. The nitride semiconductor is grown with a thickness of 50 μm or more, more preferably 80 μm or more, and most preferably 100 μm or more. The upper limit is not particularly limited, but is 200 μm.
m or less is desirable. Further, the doping amount of the n-type impurity is 1 × 1
If it exceeds 0 ¹⁹ / cm ³ , it is difficult to grow a nitride semiconductor having good crystallinity as a substrate. It is to be noted that good crystallinity means that the half width of the X-ray rocking curve by the biaxial crystallization method is 15%, for example.
Min. Or less.

Next, in order to bond the nitride semiconductors respectively grown on the two substrates, it is desirable to use, for example, a wafer bonding method. Wafer bonding is a technology in which the surface of a grown nitride semiconductor is mirror-finished and flattened by a technique such as etching or polishing, and then the flat surfaces are bonded to each other and bonded by pressing and heating. is there. Pressing can be achieved by fixing using a suitable jig.
When the wafers are bonded in this manner, no other substance is present at the interface between the nitride semiconductor layer and the opposing nitride semiconductor layer, so that both nitride semiconductors have the same carrier concentration, mobility, resistivity, and the like. Thus, it is easy to obtain a substrate having uniform characteristics. Further, as described later, substrates having different carrier concentrations or the like may be intentionally manufactured.

Particularly preferably, in the bonding step, it is desirable to heat the wafer in a nitrogen atmosphere pressurized to a pressure higher than the decomposition pressure of the nitride semiconductor. Heating temperature is over 600 ° C,
More preferably, the heating is performed at 800 ° C. or higher. In the case of GaN, the decomposition pressure of GaN is about 0.01 atm at 800 ° C.,
The pressure is about 1 atm at 00 ° C and about 10 atm at 1100 ° C. Therefore, when heating is performed in a nitrogen atmosphere while applying a pressure equal to or higher than the decomposition pressure of GaN, N can be prevented from falling out of GaN, and a substrate with a good adhesion can be provided.

[0016]

The present invention will be described in detail with reference to the following examples. FIGS. 1 to 3 are schematic cross-sectional views showing the structure of a wafer for explaining the method of the present invention, and illustrate the steps of the present invention in Examples.

[Embodiment 1] As shown in FIG. 1, buffer layers 2 and 2 'made of GaN are grown on a sapphire substrate 1 and 1' to a thickness of 200 angstroms, and a nitride semiconductor layer 3 and A first wafer (a) and a second wafer (b) on which 3 ′ has been grown are prepared. The nitride semiconductor was grown by MOVPE as follows.

A substrate 1 made of sapphire (C plane) having a diameter of 2 inches and a thickness of 400 μm is set in a reaction vessel, and the inside of the vessel is sufficiently replaced with hydrogen. Then, the temperature of the substrate is raised to 1050 ° C. while flowing hydrogen. Then, the substrate is cleaned.

Subsequently, the temperature is lowered to 510 ° C., and a buffer layer 2 made of GaN is grown to a thickness of 200 Å on the substrate using hydrogen as a carrier gas, ammonia and TMG (trimethylgallium) as a source gas. .

Subsequently, the temperature is increased to 1050 ° C.
When the temperature reaches 050 ° C., a nitride semiconductor layer 3 made of non-doped GaN having a carrier concentration of 1 × 10 ¹⁸ / cm ³ is grown to a thickness of 150 μm using TMG and ammonia gas as source gases. After the growth, the temperature is returned to room temperature, the wafer is taken out of the reaction vessel, and this is used as a first wafer (a). Next, the same operation is performed on the sapphire substrate 1 ′, and the carrier concentration is 5 × by Si doping.
At 10 ¹⁸ / cm ³ , the film thickness is 120 μm. This is referred to as a second wafer (b).

Next, the first wafer (a) and the second wafer (b) are transferred to a polishing apparatus, and the surface of GaN is polished to a mirror surface by several hundred angstroms.

After polishing, the GaN layer 3 of the first wafer and the GaN layer 3 'of the second wafer are bonded to each other as shown in FIG. 2 and transferred to an annealing apparatus while being strongly fixed by a heat-resistant jig. I do. And 20 atmospheres in a nitrogen atmosphere,
Anneal at 1100 ° C. for 10 minutes.

After the GaN layers 3 and 3 'are bonded and annealed, the GaN layer 3' having a small thickness is formed.
Is first polished and removed. In the case where nitride semiconductor layers having different thicknesses are thus grown, it is preferable to polish the substrate side having the thin nitride semiconductor first because the wafer is less likely to break during polishing. FIG. 3 shows the structure of the nitride semiconductor layer after the removal. Since the buffer layer 2 is a layer including a polycrystalline layer grown at a low temperature, the buffer layer 2 is removed by lapping during polishing in the same manner as the sapphire substrate. After removal, both exposed substrate surfaces are polished to mirror surfaces.

Further, substrates having different carrier concentrations may be intentionally produced by growing nitride semiconductor layers having different thicknesses. When substrates having different carrier concentrations can be manufactured, for example, an n + layer having a high carrier concentration is used as an n-electrode formation surface.
When the low n− layer is used as the cladding layer, a nitride semiconductor device having high light emitting efficiency and high light receiving efficiency can be manufactured.

[0025]

As described above, according to the method of the present invention, a GaN substrate having good crystallinity can be obtained by a very simple operation. A GaN substrate is obtained, and p
-Stacking a nitride semiconductor layer having an -n junction, for example, L
When a light emitting element such as an ED or LD is realized, it is not necessary to take out a p-electrode and an n-electrode from the same surface side from the same surface side as in the conventional case. Since the electrodes can be taken out, the chip size can be reduced. Further, since the substrate is lattice-matched with the nitride semiconductor, a nitride semiconductor having few lattice defects and good crystallinity can be easily grown, so that the lifetime of the LD is improved. Further, conventionally, a buffer layer was grown to alleviate lattice mismatch between the insulating substrate and the nitride semiconductor. However, if a GaN substrate is formed, there is a possibility that the buffer layer does not need to be grown. By manufacturing substrates having different carrier concentrations, for example, n + having a high carrier concentration can be obtained.
When the layer is used as an n-electrode forming surface and the low n− layer is used as a cladding layer, a substrate made of a nitride semiconductor having good crystallinity, which can produce a nitride semiconductor element having high light emission efficiency and high light reception efficiency, can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a wafer obtained in one step of the method of the present invention.

FIG. 2 is a schematic sectional view showing the structure of a wafer obtained in one step of the method of the present invention.

FIG. 3 is a schematic sectional view showing the structure of a wafer obtained in one step of the method of the present invention.

[Explanation of symbols]

 1, 1 '... substrate 2, 2' ... buffer layer 3, 3 '... GaN layer

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 4G077 AA03 AB01 AB08 BE15 DB01 EB01 FF07 FJ03 TB03 TB05 TC14 TC15 TC16 5F041 AA40 CA40 CA46 CA49 CA56 CA57 CA65 CA77 5F045 AA04 AB14 AC08 AC12 AD09 AD14 AF09 BB12 BB16 CA10 CA12 DA12 CA02 CA07 CB05 CB19 DA05 DA16 DA35 EA29

Claims (4)

[Claims] 1. A nitride semiconductor substrate comprising a nitride semiconductor having at least a two-layer structure, wherein the nitride semiconductor layers have different carrier concentrations. 2. The nitride semiconductor substrate according to claim 1, wherein the nitride semiconductor layer is non-doped or doped with an n-type impurity at 1 × 10 ¹⁹ / cm ³ or less. 3. The method according to claim 1, wherein the n-type impurities are Si, Ge, Sn, S
The nitride semiconductor substrate according to claim 2, wherein the nitride semiconductor substrate is at least one selected from the group consisting of: 4. The nitride semiconductor substrate according to claim 1, wherein the nitride semiconductor layer has a half-width of an X-ray rocking curve by a biaxial crystal method of 15 minutes or less.