JP3418384B2 - Vapor growth method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vapor phase growth method for vapor phase growing a gallium nitride compound semiconductor crystal on a sapphire substrate.

[0002]

2. Description of the Related Art Conventionally, a gallium nitride-based compound semiconductor (Al _X Ga _1-X N; including X = 0) thin film has been formed on a sapphire substrate by using a metal organic chemical vapor deposition method (hereinafter referred to as "MOVPE"). A light emitting device has been researched by vapor-depositing it on top and using the gallium nitride compound semiconductor thin film as a light emitting layer. Since a gallium nitride compound semiconductor single crystal wafer cannot be easily obtained, a gallium nitride compound semiconductor is epitaxially grown on a sapphire substrate having a lattice constant close to that of the gallium nitride compound semiconductor.

[0003]

However, since the lattice mismatch between sapphire and the gallium nitride compound semiconductor as the light emitting layer and the vapor pressures of gallium and nitrogen are greatly different, a good gallium nitride compound semiconductor crystal is obtained. However, there is a problem in that it is impossible to obtain a light emitting device having high emission efficiency for blue light emission.

Accordingly, it is an object of the present invention to provide a vapor phase growth method capable of vapor-depositing a good quality gallium nitride compound semiconductor crystal with little site dependence on a sapphire substrate.

In order to achieve the above object, the present invention supplies a reaction gas having at least a gallium source and a nitrogen source to a crystal growth surface of a sapphire substrate to vapor-phase a gallium nitride compound semiconductor crystal on the sapphire substrate. In the vapor phase growth method for growing, a step of heating the temperature of the sapphire substrate to a crystal growth temperature of a gallium nitride-based compound semiconductor, and the reaction gas through the flat-shaped space formed on the reaction gas upstream side of the sapphire substrate. And a step of supplying the sapphire substrate while pressing the sapphire substrate while flowing the sapphire substrate. The step of supplying the reaction gas while pressing it against the sapphire substrate while flowing it over the sapphire substrate is through a flat-shaped space formed from the reaction gas upstream side to the downstream side of the crystal growth surface of the sapphire substrate. May be done.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on specific embodiments. FIG. 1 is a sectional view showing the structure of a vapor phase growth apparatus for carrying out the present invention. The quartz tube 10 is sealed with an O-ring 15 at the left end thereof and abuts the flange 14, and a shock absorbing material 38 and a fixing tool 39 are used to attach the bolts 46, 4 to the quartz tube 10.
7 and nuts 48, 49, etc. at several places for flange 14
It is fixed to. The right end of the quartz tube 10 is an O-ring 4.
0 and sealed to the flange 27 with screw fastening fixtures 41, 4
It is fixed by 2.

A liner tube 12 for guiding a reaction gas is arranged in an inner chamber 11 surrounded by a quartz tube 10. One end 13 of the liner tube 12 is held by a holding plate 17 fixed to the flange 14, and the bottom portion 18 of the other end 16 is held by the quartz tube 10 by holding legs 19. The cross section of the liner tube 12 perpendicular to the X-axis direction of the quartz tube 10 is shown in FIGS.
As shown in, it depends on the position in the X-axis direction. That is, the reaction gas flows in the X-axis direction, but has a circular shape on the upstream side of the gas flow, and as it proceeds to the downstream side (X-axis positive direction),
The direction perpendicular to the paper surface (Y-axis direction) is the major axis, the major axis direction is enlarged, and the minor axis direction is reduced to form an elliptical shape. At a position A on the upstream side where the susceptor 20 is placed, the vertical direction (Z It has a flat elliptical shape that is thin in the (axis) direction and long in the Y-axis direction. In the sectional view taken along the line IV-IV at the position A, the length of the opening in the Y-axis direction is 7.0 cm and the length in the Z-axis direction is 1.2 cm.

A susceptor 2 is provided downstream of the liner tube 12.
A sample mounting chamber 21 having a rectangular cross section perpendicular to the X-axis for mounting 0 is integrally connected. The sample placing chamber 21
The susceptor 20 is placed on the bottom 22 of the. The susceptor 20 has a rectangular cross section perpendicular to the X-axis, but its upper surface 2
3 is gently inclined with respect to the X axis in the positive direction of the Z axis.
A sample, that is, a rectangular sapphire substrate 50 is placed on the upper surface 23 of the susceptor 20, and the gap between the sapphire substrate 50 and the upper tube wall 24 of the liner tube 12 facing the sapphire substrate 50 is 12 mm on the upstream side, and the downstream side is 12 mm. 4mm on the side.

An operating rod 26 is connected to the susceptor 20. The flange 27 is removed and the operating rod 26 is used to set the susceptor 20 on which the sapphire substrate 50 is placed in the sample placing chamber 21 or to grow crystals. When finished, the susceptor 20 can be taken out from the sample mounting chamber 21. In addition, a first gas pipe 28 is opened on the upstream side of the liner pipe 12, and a second gas pipe 29 is sealed at an end portion to form a first gas pipe.
It covers the gas pipe 28. And both of these tubes 28,
Reference numeral 29 has a coaxial double tube structure. First gas pipe 28
A large number of holes 30 are formed in the portion protruding from the second gas pipe 29 and the side peripheral portion of the second gas pipe 29, and the reaction gas introduced by the first gas pipe 28 and the second gas pipe 29 is Is
Each is blown out into the liner tube 12 through a number of holes 30. And inside the liner tube 12,
Both reaction gases are mixed for the first time.

The first gas pipe 28 is the first manifold 3
1, the second gas pipe 29 is connected to the second manifold 32.
It is connected to the. And in the first manifold 31,
NH ₃ Supply system H and carrier gas supply system I and birds
Methyl gallium (hereinafter referred to as "TMG") supply system J
And trimethylaluminum (hereinafter referred to as "TMA")
The supply system K is connected, and the second manifold 32 is connected to the key.
Carrier gas supply system I and diethyl zinc (hereinafter "DE
Z ”) supply system L is connected.

Further, a cooling pipe 33 for circulating cooling water is formed on the outer peripheral portion of the quartz tube 10, and a high frequency coil 34 for applying a high frequency electric field is arranged on the outer peripheral portion thereof. The liner pipe 12 is connected to an outer pipe 35 via a flange 14, and a carrier gas is introduced from the outer pipe 35. In addition, the sample placement chamber 2
In FIG. 1, an introduction pipe 36 extends from the outside through the flange 14 from the side, and a thermocouple 43 for measuring the temperature of the sample and its lead wires 44, 45 are arranged in the introduction pipe 36. The sample temperature can be externally measured. With such a device configuration, a mixed gas of NH ₃ , TMG, TMA, and H ₂ introduced through the first gas pipe 28,
The mixed gas of DEZ and H ₂ introduced through the second gas pipe 29 is mixed in the vicinity of the outlets of those pipes, and the mixed reaction gas is introduced into the sample mounting chamber 21 through the liner pipe 12 and the sapphire substrate 50. It passes through the gap formed between the liner tube 12 and the upper tube wall 24. At this time, the sapphire substrate 5
The flow of the reaction gas above 0 becomes uniform, and a good quality crystal with little location dependence grows.

When forming an N _- type Al _X Ga _1-X N thin film, it is sufficient to let the mixed gas flow out only from the first gas pipe 28 to form an I-type Al _X Ga _1-X N thin film. In that case, the mixed gas may be discharged from the first gas pipe 28 and the second gas pipe 29. I type Al _X Ga _1-X N
When forming a thin film, the dopant gas DEZ
Will be mixed with the reaction gas flowing out of the first gas pipe 28 for the first time inside the liner gap 12 near the sapphire substrate 50. Then, DEZ is sprayed on the sapphire substrate 50 and thermally decomposed, and the dopant element grows Al.
I-type Al _X Ga _1-X doped with _X Ga _1-X N
N is obtained. In this case, the first gas pipe 28 and the second gas pipe 29 are separated from each other, and the reaction gas and the dopant gas are guided to the vicinity of the sapphire substrate 50, so that good doping is performed.

Next, using this apparatus, a sapphire substrate 50
Crystal growth was carried out as follows. First, a single crystal sapphire substrate 50 having a (0001) plane as a main surface washed by organic washing and heat treatment is mounted on the susceptor 20.
Next, the sapphire substrate 50 was vapor-phase etched at a temperature of 1100 ° C. while flowing H ₂ at 0.3 liter / min into the liner pipe 12 through the first gas pipe 28, the second gas pipe 29, and the outer pipe 35. Next, the temperature is lowered to 650 ° C and the first
H ₂ 3 liter / min, NH ₃ 2 liter from gas pipe 28
/ Min, TMA at 15 ° C was supplied at 50 cc / min for 2 minutes.

In this growth step, as shown in FIG.
The N buffer layer 51 was formed to a thickness of about 300 Å. The RHEED image of this buffer layer was measured. The result is shown in FIG. 7. From the RHEED image of FIG. 7, it is understood that the crystal structure is non-single crystal, that is, amorphous, microcrystalline, or polycrystalline.

Further, various AlN buffer layers were formed on another sapphire substrate by using the above-mentioned apparatus at a growth temperature of 650 ° C. and changing the film thickness in the range of 50 to 1000Å. The RHEED image of the surface at that time was measured. The results are shown in FIGS. 8 (a) and 8 (b). When the film thickness is 100 Å or less, the single crystallinity is strong and the film thickness is 500
If it is Å or higher, the polycrystallinity becomes stronger. Further, in each of the above various samples in which the film thickness of the AlN buffer layer is in the range of 50 to 1000 Å, the sample temperature is maintained at 970 ° C., and H ₂ is 2.5 liter / min and NH ₃ is 1.5 liter from the first gas pipe 28. / Min,-
TMG at 15 ° C. was supplied at 100 cc / min for 60 minutes, and as shown in FIG.
2 were each formed. Then, the SEM image and the RHEED image of the N layer 52 were measured. The results are shown in Fig. 10 (a), (b),
This is shown in FIGS. 11 (a) and 11 (b). The SEM image magnification is 4100 times.
When the film thickness of the buffer layer 51 is 100 Å or less, pits are generated in the N layer 52, and the film thickness of the buffer layer 51 is 500
Even above Å, the N layer 52 is in the same state as below 100 Å. Therefore, in order to obtain an N layer having good crystallinity, the film thickness of the AlN buffer layer 51 is preferably in the range of 100 to 500 Å.

As another sample, a 300 Å-thick AlN buffer layer was grown on a sapphire substrate at a growth temperature of 300.
Various growth was performed by changing the temperature within a range of up to 1200 ° C. Then, similarly, the RHEED image of the AlN buffer layer was measured.
The results are shown in Figures 12 (a) and (b). Therefore, if the growth temperature is 300 ° C. or lower, the desired film thickness of the AlN buffer layer cannot be obtained, and if the growth temperature is 900 ° C. or higher, the crystallization of AlN proceeds and the desired film quality cannot be obtained. I understand.

Further, with respect to various samples in which the AlN buffer layer having the above-mentioned film thickness of 300 Å was grown in the growth temperature range of 300 to 1200 ° C., the film thickness was further formed on the AlN buffer layer under the same conditions as described above. An N layer of about 7 μm N-type GaN was grown. Then, the SEM image and the RHEED image of this N layer were measured. The results are shown in FIGS. 13 (a) and 13 (b) and FIGS. 14 (a) and 14 (b). The magnification of the SEM image is 3700 times. When the growth temperature of the AlN buffer layer is lower than 400 ° C., the N layer made of N-type GaN becomes a crystal with pits formed, and when the growth temperature of the AlN buffer layer is 900 ° C. or higher, it has a hexagonal morphology. It becomes a crystal. From the result, the growth temperature of the AlN buffer layer is 40 in order to obtain an N layer with good crystallinity.
It turns out that 0 to 900 ° C is desirable.

According to the above experiment, when the crystal structure of the AlN buffer layer is the wurtzite structure in which polycrystalline or microcrystals are mixed in the amorphous structure, the crystal of the GaN layer grown thereon is obtained. It turned out that the sex improved. It was also found that the existence ratio of the polycrystal or the microcrystal is preferably 1 to 90%, and the size thereof is preferably 0.1 μm or less. In the formation of the AlN buffer layer having such a crystal structure, the film thickness and the growth temperature are not limited to the above conditions,
TMA of 15 ℃ as a reaction gas flow rate is 0.1 to 1000cc /
Min, NH ₃ is 100cc ~10liter / min, H ₂ is 1 liter to 50
Although it was performed in the range of liter / minute, the wurtzite structure was obtained in each case.

Next, a method of manufacturing the light emitting diode will be described. Next, using this apparatus, the configuration shown in FIG.
Crystal growth was performed on the sapphire substrate 60 as follows. In the same manner as above, single crystal sapphire substrate 6
At a growth temperature of 650 ° C., from the first gas pipe 28, H ₂ at ₃ liter / min, NH ₃ at 2 liter / min, and TMA at 15 ° C.
Was supplied at 500 cc / min for 1 minute to form a 350 Å AlN buffer layer 61. Next, when one minute has passed, TMA
Supply is stopped and the temperature of the sapphire substrate 60 is set to 970 ° C.
Held in the H ₂ 2.5liter / min through the first gas pipe 28,
The NH ₃ 1.5liter / minute, the TMG of -15 ℃ 100cc /
For 60 minutes to form an N layer 62 of N-type GaN having a film thickness of about 7 μm. The sapphire substrate 60 on which the N layer 62 is formed is taken out from the vapor phase growth apparatus, and the N layer 62
A photoresist having a predetermined pattern was obtained by applying a photoresist to the main surface of the substrate, exposing it using a mask having a predetermined pattern, and then performing etching.

Next, using this photoresist as a mask, a SiO ₂ film 63 having a film thickness of about 100 Å was patterned. After that, the photoresist was removed, and the sapphire substrate 60 on which only the SiO ₂ film 63 was patterned was washed, and then mounted on the susceptor 20 again and vapor-phase etched. Then, the temperature of the sapphire substrate 60 is maintained at 970 ° C., and the first gas pipe 2
From 8, the H ₂ 2.5liter / min, 1.5Liter the NH ₃
/ Min, TCC at −15 ° C. is supplied at 100 cc / min, and DEZ at 30 ° C. is supplied at 500 cc / min for 5 minutes from the second gas pipe 29 to form the I layer 64 made of I-type GaN. 1.0 μm
Formed.

At this time, in the exposed portion of GaN, single crystal I-type GaN is grown to obtain the I layer 64.
A conductive layer 65 made of polycrystalline GaN is formed on the iO ₂ film 63. After that, the sapphire substrate 60 is taken out of the reaction chamber 20, aluminum electrodes 66 and 67 are vapor-deposited on the I layer 64 and the conductive layer 65, and the sapphire substrate 60 is formed.
Was cut into a predetermined size to form a light emitting diode. In this case, the electrode 66 becomes the electrode of the I layer 64,
The electrode 67 becomes an electrode of the N layer 62 via the conductive layer 65 and the extremely thin SiO ₂ film 63. Then, the I layer 64 is replaced with the N layer 6
By setting a positive potential with respect to 2, light is emitted from the joint surface. The light emitting diode thus obtained had an emission wavelength of 485 nm and a luminous intensity of 10 mcd. The luminous intensity is 1 compared to the AlN buffer layer formed of a single crystal.
A 0-fold improvement was seen.

As described above, according to the vapor phase growth method of the present invention, the reaction gas is flowed onto the sapphire substrate through the flat-shaped space formed on the upstream side of the reaction gas from the sapphire substrate. Since the crystals are supplied while being pressed against each other, even in the gallium nitride system, which is a combination of elements whose vapor pressures greatly differ at the growth temperature, crystal growth is performed uniformly, and a high-quality compound semiconductor crystal with little site dependence is obtained. You can Further, by supplying the reaction gas through the flat-shaped space formed from the reaction gas upstream side to the downstream side of the crystal growth surface of the sapphire substrate, a higher quality gallium nitride compound semiconductor crystal can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of a vapor phase growth apparatus used to carry out the present invention.

FIG. 2 is a sectional view of the liner pipe of the same embodiment.

FIG. 3 is a sectional view of the liner pipe of the same embodiment.

FIG. 4 is a sectional view of the liner pipe of the same embodiment.

FIG. 5 is a sectional view of the liner pipe of the same embodiment.

FIG. 6 is a cross-sectional view showing the structure of a crystal-grown semiconductor.

FIG. 7 is a photograph showing a RHEED crystal structure of an AlN buffer layer.

FIG. 8 is a photograph showing the RHEED crystal structure of the AlN buffer layer when the thickness of the AlN buffer layer is changed.

FIG. 9 is a sectional view showing a structure of a semiconductor in which an N-type GaN layer is grown.

FIG. 10 is a photograph showing a crystal structure of a GaN layer grown on an AlN buffer layer with the thickness thereof changed by a microscope (SEM).

FIG. 11 is a photograph showing a RHEED crystal structure of a GaN layer grown on an AlN buffer layer with the film thickness varied.

FIG. 12 is a photograph showing a RHEED crystal structure of an AlN buffer layer grown by changing the growth temperature.

FIG. 13: Various Al grown by changing the growth temperature
Photograph showing the crystal structure of the GaN layer grown on the N buffer layer under a microscope (SEM)

FIG. 14: Various Al grown by changing the growth temperature
A photograph showing the RHEED crystal structure of the GaN layer grown on the N buffer layer.

FIG. 15 is a cross-sectional view showing a crystal structure for manufacturing a light emitting diode.

[Explanation of symbols]

10-quartz tube 12-liner tube 20-susceptor 21-Sample Placement Room 28-First gas pipe 29-Second gas pipe 50, 60-sapphire substrate 51, 61-AlN buffer layer 52, 62-N layer 53, 63-I layer 64-conducting layer 65, 66-electrode H-NH3 supply system I-Carrier gas supply system J-TMG supply system K-TMA supply system L-DEZ supply system

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhide Masabe 1 Ochiai, Nagachi, Kasuga-cho, Nishikasugai-gun, Aichi Prefecture Toyota Gosei Co., Ltd. (72) Inventor Kuki Kato, Kasuga-cho, Nishi-Kasugai, Aichi 1 Nagachiata, Ochiai Address: Toyoda Gosei Co., Ltd. (72) Inventor Yu Akasaki Furomachi, Chikusa-ku, Nagoya-shi, Aichi (No house number) Inside Nagoya University (72) Inventor Hamamatsu, Kazumasa Furo-cho, Chikusa-ku, Nagoya city, Aichi prefecture (No. Nagoya University (72) Inventor Hiroshi Amano Furo-cho, Chikusa-ku, Nagoya, Aichi (No house number) Nagoya University (56) Reference JP 61-186289 (JP, A) JP 63-188934 (JP) , A) JP 63-188935 (JP, A) JP 63-176395 (JP, A) JP 64-27225 (JP, A) JP 61-77696 (JP, A) JP 55-1 10031 (JP, A) JP 63-188937 (JP, A) JP 63-188977 (JP, A) JP 64-82614 (JP, A) JP 2-81482 (JP, A) JP-A-2-211620 (JP, A) JP-A-2-229476 (JP, A) JP-A-2-257679 (JP, A) JP-A-4-164895 (JP, A) JP-A-11-121801 (JP, A) Kazumasa Hiramatsu et al., Effect of buffer layer on GaN crystal growth on sapphire substrate by MOVPE method, Journal of Japanese Society for Crystal Growth, 1988, Vol. 15, No. 3 & 4, pp. 74-82 (58) Fields investigated (Int.Cl. ⁷ , DB name) C30B 1/00-35/00 H01L 21/205 H01L 33/00 JISST file (JOIS)

Claims (2)

(57) [Claims] 1. A vapor phase growth method in which a reaction gas having at least a gallium source and a nitrogen source is supplied to a crystal growth surface of a sapphire substrate to vapor grow a gallium nitride compound semiconductor crystal on the sapphire substrate. Heating the temperature of the sapphire substrate to the crystal growth temperature of the gallium nitride-based compound semiconductor; the sapphire while flowing the reaction gas on the sapphire substrate through a flat-shaped space formed on the reaction gas upstream side of the sapphire substrate. And a step of supplying while pressing against the substrate. 2. The step of supplying the reaction gas while pressing it against the sapphire substrate while flowing the reaction gas onto the sapphire substrate is formed from a reaction gas upstream side to a downstream side of the crystal growth surface of the sapphire substrate. The vapor phase growth method according to claim 1, wherein the vapor phase growth is performed through a flat space.