JPH08264455A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE: To enable the formation of a GaN compound semiconductor layer on a SiC substrate by depositing a GaAlInN layer on the top of the substrate while gradually increasing the temperature of the SiC substrate from a first value to a specified second value, and keeping the substrate at the second temperature and further depositing another GaAlInN layer thereon. CONSTITUTION: A high-frequency coil 3 is wound around the circumference of a processing chamber 1 in such a way that a substrate holder 2 is surrounded therewith. A high-frequency current is passed through the high-frequency coil 3 to heat the substrate holder 2, and a substrate 7 is heated by heat conducted by the substrate holder 2. While the temperature of a SiC substrate 7 is gradually increased from a first value to a second value, 300 deg.C or more higher tan the first value, a Ga1-x-y Alx Iny N layer (0<=x<=0.2, 0<=y<=0.3) is deposited on the top of the SiC substrate 7. Then, while the SiC substrate 7 is kept at the second temperature, a Ga1-i-j Ali Inj N layer (0<=i<=0.2, 0<=j<=0.3) is deposited on the Ga1-x-y Alx Iny N layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a GaN compound semiconductor layer and a semiconductor device having a GaN compound semiconductor layer. GaN-based compound semiconductors are attracting attention as materials that emit light in the blue to ultraviolet region.

[0002]

2. Description of the Related Art Conventionally, a GaN layer is formed by a metal organic chemical vapor deposition method.
Using sapphire (α-Al₂O₃) Formed on the substrate
It was Example of forming a GaN layer on a sapphire substrate
For example, the substrate temperature is 500 ° C., and trimethylgallium is used.
(TMGa) and ammonia (NH ₃) Supply about thickness
Deposit a 30 nm polycrystalline GaN buffer layer. next
The substrate temperature is 1030 ° C., and the same source gas as above is used.
To deposit a GaN layer. In this way, the start of GaN layer deposition
When the substrate temperature is about 500 ° C, a polycrystalline buffer layer
By forming a high quality single crystal on it.
A GaN layer can be formed.

[0003]

A single crystal GaN layer can be formed on a sapphire substrate using conventional techniques. However, since the sapphire substrate is not conductive,
The electrode cannot be taken out from the back surface of the substrate. If the electrodes are drawn out only from the surface of the substrate, it is necessary to secure both positive and negative electrode formation regions, which makes it difficult to reduce the chip area.

Further, the sapphire substrate has no cleavage property.
Since the reflecting surface cannot be formed by cleavage, it is difficult to apply it to a laser diode. The purpose of the present invention is to
It is an object of the present invention to provide a technique for forming a GaN-based compound semiconductor layer on a SiC substrate having electrical conductivity and cleavage.

[0005]

A method of manufacturing a semiconductor device according to the present invention comprises a step of preparing a SiC substrate having an upper surface,
While gradually increasing the temperature of the SiC substrate from the first temperature to the second temperature which is higher than the first temperature by 300 ° C. or more, Ga _1-xy Al _x In is formed on the upper surface of the SiC substrate.
depositing _y N layer (0 ≦ x ≦ 0.2,0 ≦ y ≦ 0.3), while maintaining the temperature of the SiC substrate to the second temperature, the Ga _1-xy Al _x In _On top of the _y N layer, another Ga ₁ -ij Al _i In _j N layer (0 ≦ i ≦ 0.2, 0 ≦ j
≦ 0.3) is deposited.

Another method of manufacturing a semiconductor device according to the present invention comprises the steps of preparing an SiC substrate having an upper surface, and including Al as a group III element on the SiC substrate, wherein the group V element is N, and III Depositing a group III-V compound semiconductor layer in which the composition ratio of Al in the group element is 0.5 or more;
Ga _1-xy A is formed on the III-V group compound semiconductor layer.
and a step of epitaxially growing an l _x In _y N layer (0 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.3).

As the SiC substrate, {0001},
At least one of {10-10} and {11-20} planes
You may use the board | substrate which has the upper surface which the surface perpendicular | vertical to two surfaces was exposed.

A semiconductor device of the present invention is formed on a SiC substrate and the SiC substrate, and is made of Al as a group III element.
A group III-V compound semiconductor layer in which the group V element is N and the composition ratio of Al in the group III element is 0.5 or more; and the group III-V compound semiconductor layer. Ga _1-xy Al _x In _y N layer (0 ≦ x ≦ 0.2, 0 ≦ y
≦ 0.3).

[0009]

[Function] Ga _1-xy A on the surface of the SiC substrate at a relatively low temperature
When a l _x In _y N layer (0 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.3) is formed, a polycrystalline GaAlInN layer is obtained. Furthermore, a high quality GaAlInN layer can be obtained by forming the GaAlInN layer while gradually raising the substrate temperature to the temperature for epitaxial growth and forming the GaAlInN layer at the temperature for epitaxial growth for a certain period of time.

It is considered that this is because the substrate temperature is gradually increased, so that only some specific crystal grains of the polycrystalline GaAlInN layer do not grow significantly, but the respective crystal grains grow on average.

II as a buffer layer on the surface of the SiC substrate
Al is contained as a group I element, a group V element is N, and II
III- where the composition ratio of Al in the group I element is 0.5 or more
A group V compound semiconductor layer is formed, and G is formed on this buffer layer.
When the aAlInN layer is formed, high quality GaAlInN is formed.
Layers can be obtained.

As SiC substrates, {0001}, {10
When a substrate having an upper surface in which a surface perpendicular to at least one of the −10} and {11-20} planes is exposed is used, the cleavage can be performed on the surface perpendicular to the upper surface. Therefore, the fabrication of the laser resonator becomes easy.

[0013]

EXAMPLES First, the results of a preliminary experiment of forming a GaN layer on a SiC substrate by a method similar to the method of growing a GaN layer on a sapphire substrate will be described.

FIG. 1 is a schematic sectional view of a metal organic chemical vapor deposition (MOCVD) apparatus used for forming a GaN layer. From one end of the processing container 1 having an internal space, the raw material gas introduction pipe 4
Also, a purging gas introduction pipe 5 is inserted, and the raw material gas and the purging gas are introduced into the processing container 1. A gas exhaust pipe 6 is connected to the other end of the processing container 1, and the gas in the processing container 1 is exhausted from the gas exhaust pipe 6.

A substrate holder 2 made of carbon is arranged in the internal space of the processing container 1, and the substrate 7 is held on the lower surface of the substrate holder 2 when the GaN layer is formed. A high-frequency coil 3 is wound around the processing container 1 so as to surround the substrate holder 2. By applying a high-frequency current to the high-frequency coil 3, the substrate holder 2 can be heated and the substrate 7 can be heated by heat conduction from the substrate holder 2.

FIG. 6 shows the time change of the substrate temperature during the growth of the GaN layer and the supply timing of the source gas. The horizontal axis represents the time from the start of growth, and the vertical axis represents the substrate temperature. The SiC substrate is held on a substrate holder and the substrate is heated to 500 ° C. About ₃₀ n of trimethylgallium (TMGa) and ammonia (NH ₃ ) were introduced into the processing container using H ₂ gas as a carrier gas.
m GaN buffer layer is formed. The supply of TMGa is stopped, and heating is performed until the substrate temperature reaches 1030 ° C.

When the substrate temperature reaches 1030 ° C., TMG is again generated.
a is supplied to grow a GaN layer. Ga of desired thickness
When the N layer is formed, the supply of TMGa and the heating of the substrate are stopped. When the substrate temperature drops to about 500 ° C., the NH ₃ supply is stopped.

When a sapphire substrate is used, a good GaN layer can be formed under the conditions shown in FIG. However, when the GaN layer formed on the SiC substrate was observed with a microscope, many gaps were seen in the layer. Also, Si
Small crystal grains were observed on the surface of the C substrate.

From the observation result with the microscope, the growth process of the GaN layer by the method shown in FIG. 6 can be inferred as follows. FIG. 7 is a substrate cross-sectional view for explaining the growth process of the GaN layer. When TMGa and NH ₃ are supplied at a substrate temperature of 500 ° C., small crystal grains 8 are deposited on the surface of the SiC substrate 7 as shown in FIG. 7 (A). Substrate temperature is 1030 ℃
As shown in FIG. 7B, when TMGa and NH ₃ are supplied to
Crystal grains grow as shown in FIG. When the growth is further continued, it is considered that only the specific crystal grain 9a grows large, as shown in FIG. 7 (C).

As shown in FIG. 7D, specific crystal grains 9
It is considered that the substrate surface is covered with the GaN lump 9b formed by lateral growth of a. At this time, the gap between the small crystal grains 8 on the substrate surface is not completely filled, and G
It is considered that a gap is formed in the aN layer.

Next, an embodiment of the present invention will be described with reference to FIGS. The MOCVD equipment used is shown in Fig. 1.
It is similar to that shown in. After cleaning and drying the SiC substrate with the exposed (0001) plane, oxidation of the substrate surface and removal of the oxide film are repeatedly performed to expose a clean surface. This SiC substrate is attached to the substrate holder 2 of the MOCVD apparatus shown in FIG. 1, and heat treatment is performed at 1100 ° C. for 10 minutes in a hydrogen atmosphere at a pressure of 40 Torr. Then, the substrate temperature is lowered to 500 ° C. so that GaN does not grow epitaxially.

FIG. 2 shows the time variation of the substrate temperature during the growth of the GaN layer and the supply timing of the source gas. Hydrogen is flown as a carrier gas so that the pressure in the processing container 1 is 200 Torr, and TMG having a flow rate of 0.5 sccm is used as a source gas.
a and NH ₃ with a flow rate of 4 slm are supplied. The substrate temperature is gradually raised to 1030 ° C. while flowing the carrier gas and the raw material gas to a temperature at which GaN is epitaxially grown. The substrate temperature rising rate is about 35 ° C./min. The growth rate of the GaN layer under this condition is about 2 μm / h.

When the substrate temperature reaches 1030 ° C., this temperature is maintained and the GaN layer is grown. GaN of desired thickness
After the layer is formed, the supply of TMGa is stopped and the substrate temperature is gradually lowered. The supply of NH ₃ is stopped when the substrate temperature reaches 500 ° C.

When a GaN layer having a thickness of about 2 μm formed under the conditions shown in FIG. 2 is observed with an interference microscope, it is 10 × 10 m.
No gap was generated over the area of m ² or more, and the surface was a mirror surface. Further, it was found by X-ray diffraction that the GaN layer was c-axis oriented. The growth process of the GaN layer at this time is presumed as follows.

FIG. 3 is a sectional view of the substrate for explaining the growth process of the GaN layer. When TMGa and NH ₃ are supplied at a substrate temperature of 500 ° C., GaN does not grow epitaxially, so that small crystal grains 8 are deposited on the surface of the SiC substrate 7 as shown in FIG. When the substrate temperature is gradually raised, each crystal grain 8 gradually grows as shown in FIG. At this time, since the temperature rise is gradual, it is considered that each crystal grain grows on average without the particular crystal grain growing large.

As the growth progresses further, as shown in FIG. 3C, the crystal grains 8 cover the entire surface and a GaN layer 10 is formed. When the substrate temperature rises to the epitaxial growth temperature of GaN, it is considered that a GaN layer is further epitaxially grown in layers on the GaN layer 10 as shown in FIG. 3 (D). Thus, since the GaN layers are deposited in layers, it is considered that a GaN layer having a mirror surface with no gap can be obtained.

From the above consideration, it is preferable that the substrate temperature at the start of the growth of the GaN layer is a temperature at which a polycrystal is formed without epitaxial growth on the SiC surface, and a temperature at which the GaN layer grows epitaxially when grown in layers. It is considered preferable to set Therefore, it is preferable that the substrate temperature at the start of growth is about 300 ° C. or more lower than the temperature at which the GaN layer is epitaxially grown.

In the growth process of FIGS. 3B to 3C, it is necessary to gradually raise the substrate temperature in order to prevent only specific crystal grains from growing large. Although FIG. 2 shows the case where the temperature rising rate is about 35 ° C./minute, a temperature rising rate of about 20 ° C./minute to 100 ° C./minute may be suitable.

Although FIG. 2 shows the case where the substrate temperature is raised at a substantially constant rate, the temperature rising rate does not necessarily have to be constant. For example, the temperature could be increased along a hyperbola with time so that the rate of change of temperature is constant. Also, the temperature may be increased stepwise.

FIG. 4 shows the time change of the substrate temperature and the supply timing of the source gas when the substrate temperature is raised stepwise. As shown in FIG. 4, the substrate temperature is changed from 500 ° C. to 103 ° C.
The temperature is increased stepwise up to 0 ° C. Note that FIG.
In the above, the case where the supply of TMGa is temporarily stopped during the period in which the temperature is rapidly raised is shown, but TMGa may be supplied continuously.

As described above, by providing at least one step-like portion between the growth start temperature of the GaN layer and the epitaxial growth temperature, it is possible to suppress large growth of only specific crystal grains, and to form a good GaN layer. It seems that you can get it.

In the above embodiment, the case of growing a GaN layer has been described, but the growth method is Ga _{1 -xy} Al _x In.
could also be applied when growing _y N layer (0 ≦ x ≦ 0.2,0 ≦ y ≦ 0.3). A as group III element
The band gap is changed by adding 1 or In. Therefore, when used as a light emitting element, the emission wavelength can be changed.

Next, another embodiment of the present invention will be described. Although a polycrystal layer of GaN is used as the buffer layer in the above-mentioned embodiment, an AlN layer is used in this embodiment. First, S
On the iC substrate, trimethyl aluminum (TMAl) and ammonia (NH ₃ ) are used as source gases, and MOC
An AlN layer having a thickness of about 30 nm is formed by VD. The substrate temperature during growth is about 1150 ° C. Next, the substrate temperature is set to 1030 ° C., and a GaN layer having a thickness of about 2 μm is formed by MOCVD using TMGa and NH ₃ as source gases.

Thus, by using the AlN layer as the buffer layer, it was possible to form a good GaN layer with no gap. It was confirmed by X-ray diffraction that the GaN layer was c-axis oriented. The process of growth of the GaN layer in this case is presumed as follows.

FIG. 5 is a substrate cross-sectional view for explaining a process of growing an AlN layer and then a GaN layer on a SiC substrate. As shown in FIG. 5A, an AlN layer 11 is formed on the SiC substrate 7. It is considered that the AlN layer 11 grows relatively uniformly on the surface of the SiC substrate 7. A
When a GaN layer is deposited on the 1N layer 11 at 1030 ° C.,
First, small crystal grains 12 are formed as shown in FIG. It is considered that when the growth is continued, the crystal grains 12 grow laterally as shown in FIG. 5C and the crystal grains are connected to each other.

When the growth is further continued, as shown in FIG. 5D, most of the crystal grains are connected to form the GaN layer 12a. After that, the growth proceeds in layers on the GaN layer 12a,
As shown in FIG. 5 (E), there is no gap and the surface has a mirror-finished GaN.
It is believed that layer 12b is formed.

In the other embodiments described above, A is used as the buffer layer.
Although the case where the 1N layer is used has been described, Al is contained as the group III element, the group V element is N, and A in the group III element is used.
It is considered that the same effect can be obtained by using a III-V group compound semiconductor layer having a composition ratio of 1 of 0.5 or more as a buffer layer. Further, on the AlN layer, instead of the GaN layer, a Ga _1-xy Al _x In _y N layer (0 ≦ x ≦ 0.2,
The same effect can be expected when 0 ≦ y ≦ 0.3) is formed.

In the laminated structure using the AlN layer as the buffer layer, In is formed on the back surface of the SiC substrate and the front surface of the GaN layer.
Was contacted to form an electrode, and the conductivity in the thickness direction was confirmed. It will be apparent to those skilled in the art that even when a polycrystalline GaN layer is used as the buffer layer, it has conductivity. If SiC is used as the substrate as in the above embodiment, the substrate itself has conductivity, and therefore the electrode can be taken out from the back surface of the substrate.

As the SiC substrate, {0001},
At least one of {10-10} and {11-20} planes
By using the substrate having the upper surface in which the surface perpendicular to the two surfaces is exposed, the cleavage can be achieved in the surface perpendicular to the upper surface.
When the GaN layer is applied to the laser diode, the laser resonator can be easily manufactured by utilizing the cleavage of the substrate.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0041]

As described above, according to the present invention,
A high quality GaAlInN layer can be obtained on the SiC substrate. Since the SiC substrate has conductivity, the electrodes can be taken out from the back surface of the substrate. Therefore, the chip area can be reduced. Moreover, since SiC has a cleavage property, a laser resonator can be easily manufactured by cleavage. The GaAlInN layer can be applied to a laser diode, and it is expected to realize a light emitting element in the blue to ultraviolet region.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an MOCVD apparatus used in an example of the present invention.

FIG. 2 is a graph showing a time change of a substrate temperature and a material supply timing in a GaN layer growth method according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a substrate illustrating a growth process of a GaN layer according to an exemplary embodiment of the present invention.

FIG. 4 is a graph showing a time change of a substrate temperature and a supply time of a raw material when the substrate temperature rises stepwise in the GaN layer growth method according to the embodiment of the present invention.

FIG. 5 is a cross-sectional view of a substrate illustrating a growth process of a GaN layer according to another embodiment of the present invention.

FIG. 6 is a graph showing a time change of a substrate temperature and a material supply timing in a preliminary experiment for growing a GaN layer on a SiC substrate.

FIG. 7 is a cross-sectional view of a substrate for explaining a GaN layer growth process in the preliminary experiment shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Processing container 2 Substrate holding stand 3 High frequency coil 4 Raw material gas introduction pipe 5 Purging gas introduction pipe 6 Gas exhaust pipe 7 SiC substrate 8, 12 Crystal grains 9a, 9b GaN mass 10, 12a, 12b GaN layer 11 AlN layer

Claims (6)

[Claims] 1. A step of preparing a SiC substrate having an upper surface.
And changing the temperature of the SiC substrate from the first temperature to the first temperature.
Gradually increase to a second temperature, which is 300 ° C higher than
On the upper surface of the SiC substrate, Ga_1-xyAl_xIn
_yDeposit N layer (0 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.3)
And, maintaining the temperature of the SiC substrate at the second temperature.
Well, the Ga_1-xyAl _xIn_yOther Ga on N layer
_1-ijAl_iIn_jN layers (0 ≦ i ≦ 0.2, 0 ≦ j ≦
A method of manufacturing a semiconductor device including the step of depositing 0.3).
Law. 2. The SiC substrate comprises {0001}, {1}
The method for manufacturing a semiconductor device according to claim 1, wherein the semiconductor device has an upper surface having a surface perpendicular to at least one of the 0-10} and {11-20} surfaces. 3. A step of preparing a SiC substrate having an upper surface, wherein Al is included as a group III element, the group V element is N, and the composition ratio of Al in the group III element is 0 on the SiC substrate. A step of depositing a III-V group compound semiconductor layer of 0.5 or more; and Ga _1-xy A on the III-V group compound semiconductor layer.
a step of epitaxially growing an l _x In _y N layer (0 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.3). 4. The method for manufacturing a semiconductor device according to claim 3, wherein the composition ratio of Al in the group III element of the compound semiconductor layer is 1. 5. The SiC substrate comprises {0001}, {1}
The surface perpendicular to at least one of the 0-10} and {11-20} planes has an exposed upper surface.
A method of manufacturing a semiconductor device according to item 1. 6. A SiC substrate and A formed as a group III element formed on the SiC substrate.
Al in the group III element containing l, the group V element being N
III-V compound semiconductor layer having a composition ratio of 0.5 or more, and Ga formed on the III-V compound semiconductor layer.
_1-xy Al _x In _y N layer (0 ≦ x ≦ 0.2, 0 ≦ y ≦
0.3).