JP3075581B2 - Apparatus for growing nitride-based compound semiconductor films - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for growing a nitride-based compound semiconductor film.

[0002]

2. Description of the Related Art In recent years, wide band gap compound semiconductors have been considered for applications such as high efficiency LEDs and lasers in the blue region. In particular, in order to obtain a higher quality material in the growth of a nitride-based compound semiconductor, a growth method and a growth apparatus have attracted attention.

[0003] As a conventional technique in this field, a halide-based vapor phase epitaxy has been used. For example, Ga
N has been grown by a Ga-HCl-NH ₃ system reaction. As a device for growing a nitride-based compound semiconductor, a sample substrate is set in a quartz reaction tube, the quartz reaction tube is placed in an electric furnace, and a group III element is supplied with chloride and nitrogen is supplied with ammonia (NH ₃ ). There is a halide vapor phase epitaxy apparatus that grows by thermal decomposition on a sample substrate.

Further, Applied Physics Letters, Vol. 48, p. 870 (Applied Physi
cs Letters, Vol. 48, 1986) (Japanese Unexamined Patent Publication (Kokai) No. 61-179527), the substrate is grown on a substrate by using nitrogen molecule ions in a nitrogen ECR plasma and a group 3 organic metal. FIG. 5 shows a schematic view of a nitride-based compound semiconductor growth apparatus using ECR plasma. The basic configuration includes a plasma generation chamber 22 for generating nitrogen molecular ions and a growth chamber 23 for growing a nitride-based compound semiconductor film 19. The plasma generation chamber 22 is supplied with microwaves by the microwave waveguide 20 and is applied with a magnetic field by the electromagnet 10 to generate E.
A CR plasma can be generated, and the growth chamber 23
Is supplied with a group 3 organic metal through an inlet 21. The nitrogen molecular ions generated in the plasma generation chamber 22 are transferred to the growth chamber 2
3 and react with the group 3 organic metal to grow a nitride-based compound semiconductor film on the substrate 5.

[0005]

However, the apparatus and method for growing a nitride-based compound semiconductor according to the above method have the following problems. 1) In the conventional halide-based vapor phase epitaxy method, the substrate temperature must be increased in order to grow a nitride-based compound semiconductor film by reacting a group III element with N. For example, in GaN, the substrate temperature is set to 1
It must be above 500 ° C. At this temperature, the GaN film obtained due to the difference in vapor pressure between Ga and N contains many nitrogen vacancies, and has a problem of poor crystallinity. Further, the GaN film has a low resistance under the influence of the nitrogen vacancies, and it has been difficult to obtain high-resistance GaN without adding an acceptor impurity. A of other nitride-based compound semiconductors
1N and InN also had a similar problem. 2) In the method for growing a nitride-based compound semiconductor film using ECR plasma, the substrate temperature could be reduced by the action of highly excited nitrogen ions. However, highly excited ionic species contained in the ECR plasma are irradiated onto the semiconductor film and the substrate to generate nitrogen vacancies, resulting in poor crystallinity and not being used as a wide band gap semiconductor. This means that the electron temperature in the ECR plasma is about 5
This is considered to be because the ion species is accelerated by the ion sheath formed near the substrate and is incident because it is as high as 10 eV.

Further, in the film growth by a glow discharge method such as the RF sputtering method, there is a problem that only a polycrystalline film is obtained.

The present invention provides a high-quality nitride-based compound semiconductor film having high crystallinity and high resistance by supplying a large amount of nitrogen molecule radicals or nitrogen atom radicals by electron cyclotron resonance plasma and reacting with a group III atom. The purpose is to provide.

[0008]

In order to achieve the above object, the present invention provides an apparatus for growing a nitride-based compound semiconductor film, comprising: means for supplying a group III atom into a vacuum chamber; A device for growing a nitride-based compound semiconductor film comprising at least a means for generating radicals, wherein the means for generating nitrogen molecule radicals or nitrogen atom radicals includes gas electrons containing nitrogen by applying a microwave and a magnetic field. A radical generator for generating cyclotron resonance (ECR) plasma;
As means for removing nitrogen molecular ions or nitrogen atom ions in the plasma, the distribution of the magnetic field strength in the direction of propagation of the microwave is changed from the vicinity of the microwave introduction port of the radical generator to the guide wavelength of the radical generator. A magnetic field strength equal to or higher than the ECR generation condition is maintained in a region up to one wavelength or more, and a magnetic field intensity equal to or lower than the ECR generation condition is set near the exit of the radical generator.

[0009] In the above configuration, the inside of the radical generator
It is preferable to provide a negative potential electrode near the outlet .

[0010] In the above structure, the size of the outlet of the radical generator is set to be smaller than a size capable of blocking microwaves ,
In addition, it is preferable to use one.

[0011]

FIG. 1 is a schematic diagram showing the magnetic field distribution in the radical generator and the movement of ions and radicals. Since the ions 1 in the plasma move along the lines of magnetic force 2, it is possible to reduce the arrival of the ions 1 near the exit of the radical generator as shown in FIG. Since the radical 3 is not a charged particle, the nitrogen molecule radical or the nitrogen atom radical goes straight. Ion species that cause ion damage can be removed, and nitrogen molecular radicals can be transported onto the substrate.

Further, nitrogen gas is introduced into the radical generator.
By carrying out the ECR discharge, a large amount of nitrogen molecule radicals or nitrogen atom radicals in the radical generator can be generated, and the generated radicals can be transported onto the substrate without collision. Thus, one of the highly reactive and long-lived nitrogen molecular radicals is a metastable state (A ³ Σu ⁺ ).
The metastable state (A ³ Σu ⁺ ) has a long life (> 1 sec) and is easily dissociated into nitrogen atoms. Here, in the radical generator
Pressure is 1 × 10 ⁻³ Pa to 1 Pa is nitrogen molecule radical
Is preferred to generate

[0013]

The present invention will be described more specifically with reference to the following examples. FIG. 2 is a schematic configuration diagram of one embodiment of the growth apparatus of the present invention, and FIG. 3 is a schematic configuration diagram of a radical generator. The basic configuration includes a substrate 5, a K cell 6 for supplying a group 3 atom, and a radical generator 7 in a vacuum chamber 4. EC
The radical generator 7 for forming R plasma has a microwave inlet 8 and a nitrogen gas inlet 9, and an electromagnet 10 is arranged around the radical generator 7. The radical generator 7 had an inner diameter of 80 mm and a length of 600 mm. When the microwave frequency is set to 2.45 GHz, the magnetic field intensity that satisfies the ECR generation condition is 0.0875 T. When exciting the cylindrical TE ₁₁ mode to the radical generator 7 having an inner diameter of 80 mm, the guide wavelength of the radical generator 7 Is 277 mm. The intensity distribution of the magnetic field applied in the microwave propagation direction 11 of the radical generator 7 is approximately 0. 0 near the microwave inlet 8.
1T. 0.1T magnetic field intensity at microwave inlet 8
From 300 mm to 300 mm, and this length is at least one wavelength in the guide wavelength (277 mm) of the radical generator 7.
In addition, the magnetic field intensity near the outlet 12 of the radical generator 7 is set to 0.
The magnetic field intensity was reduced to 02T to be equal to or lower than the ECR condition.

The inner diameter D of the outlet 12 of the radical generator 7 is 7
0 mm. This inner diameter D is 2.45 GHz, cylindrical TE
111.8mm inside diameter to block microwaves in ₁₁ mode
The microwave does not propagate into the vacuum chamber 4 because of the following. The microwave power was kept constant at 200W.

The outlet 12 of the radical generator 7 is made a negative potential electrode by a DC power supply 13, and -20 V is applied to the electrode. In order to excite the radical generator 7 in the cylindrical TE ₁₁ mode, microwaves were supplied through the waveguide 14 in the cylindrical TE ₁₁ mode.

FIG. 4 shows the outlet 12 of the radical generator 7 of FIG.
In the vicinity, the emission intensity ratio (I ₃₃₇ / I) of the emission of nitrogen molecule ions ( ₃₉₁ nm: I ₃₉₁ ) and the emission of nitrogen molecule radicals (337 nm: I ₃₃₇ ) obtained by emission spectrometry.
₃₉₁ ) showed pressure dependence. Nitrogen molecular ion (391
nm) and the emission of a nitrogen molecular radical (337 nm) have almost the same lifetime at the upper level of each transition. Therefore, the emission intensity ratio (I ₃₃₇ / I ₃₉₁ ) is equal to the ratio of the amount of the generated nitrogen molecular radical to the amount of the nitrogen molecular ion. Proportional. In addition, the emission (337 nm) of the nitrogen molecule radical shows the transition between electrons of the nitrogen molecule.
Transition between the vibration levels in ^{_{3 Π u -B 3 Π g (}} ν ',
ν ") = (0,0) is a light emission of the excited C ³ [pi _u
State, metastable state through B ³ [pi _g state (A ³ Σ u ⁺⁾
become. Furthermore C ³ Π _u, B ³ of [pi _g state lifetime μse
c or less, emission of nitrogen molecular radicals (337 nm)
Is proportional to the amount of metastable state (A ³ Σu ⁺ ) generated.

The pressure in the radical generator 7 is set to 1 × 10 ⁻³ P
If a is equal to or less than a and equal to or greater than 1 Pa, the amount of generated nitrogen molecular radicals is larger than that of nitrogen molecular ions. Further, by applying the outlet 12 of the radical generator 7 to a negative potential, nitrogen molecular ions can be further removed. When the pressure in the radical generator is less than 1 × 10 ⁻³ Pa, ionic species are generated more than radical species, and the amount of generation is reduced. When the pressure is higher than 1 Pa, the deactivation reaction in the metastable state (A ³ Σu ⁺ ) increases.

Hereinafter, specific embodiments of the present invention will be described. Example 1 (Growth of AlN film) After the pressure in the vacuum chamber 4 was reduced to 10 ⁻⁸ Pa or less, the N ₂ gas was
sccm, and the pressure in the radical generator 7 is set to 10 ⁻³ to
It was set to 1 Pa. Microwave power of 200 to 300 W was applied to generate nitrogen radicals. A sapphire c-plane substrate was used as the substrate, and the substrate temperature was set at 400 to 700 ° C. The cell temperature was set to 700 to 900 ° C. using the K cell 6 as a supply source of Al. 10 ^{-6 in} molecular beam intensity
-10 ^-5 Pa. Thus, sapphire c
An AlN film was grown on the surface substrate. When the crystal was evaluated by the X-ray diffraction method, a diffraction peak from the (002) plane appeared near 2θ = 36 °, indicating that the grown AlN film was c-axis oriented. Evaluation by reflection high energy electron diffraction (RHEED) revealed that a spot-like diffraction pattern was obtained, indicating that the grown AlN film was a single crystal film. In terms of electrical characteristics, the AlN film is considered to be a high-resistance film and a film having few nitrogen vacancies.

In this embodiment, N ₂ gas is used.
Similar results were obtained with NH ₃ gas. Example 2 (Growth of GaN film) The gas pressure in the vacuum chamber 4 and the conditions in the radical generator 7 for generating nitrogen radicals were set the same as in Example 1. A sapphire c-plane substrate was used as the substrate, and the substrate temperature was set at 400 to 600 ° C.
As a source of Ga, trimethylgallium (Ga (CH ₃ ) ₃ ) which is an organic metal of Ga was used. Trimethyl gallium was kept at 35 ° C., and was supplied into the vacuum chamber 4 using a mass flow meter at 0.1 to 0.5 sccm. When the crystal is evaluated by the X-ray diffraction method and RHEED, AlN
A c-axis oriented single crystal film was obtained in the same manner as the film. The electrical characteristics were also high resistance films.

In the first and second embodiments, GaN
Although the film and the AlN film have been described, a single-crystal thin film could be obtained also with other nitride-based compound semiconductors such as GaAlN and InN.

As described above, according to the embodiment of the present invention, there is provided a means for generating a nitrogen molecule radical or a nitrogen atom radical in a vacuum chamber and a means for supplying a group III atom. Alternatively, as a means for generating nitrogen atom radicals, a radical generator for generating a gas containing nitrogen by application of a microwave and a magnetic field is used, and as a means for removing nitrogen molecule ions or nitrogen atom ions in the ECR plasma, The distribution of the magnetic field strength in the propagation direction of the microwave is maintained at a magnetic field strength equal to or higher than the ECR condition in a region of one or more wavelengths in the microwave tube from the vicinity of the inlet in the radical generator of the microwave,
A large amount of highly reactive nitrogen radicals can be generated near the exit of the radical generator under the magnetic field strength below the ECR condition, so that a low substrate temperature and less ion bombardment can be obtained, and a high quality nitride-based compound semiconductor film can be obtained. Has the effect of obtaining

Further, according to the present invention, the pressure P
Is set to 1 × 10 ⁻³ Pa or more and 1 Pa or less,
Since a large amount of radicals can be generated at a low pressure, the effect of easily transporting highly reactive nitrogen radicals to the substrate without colliding with other particles can be exhibited.

As described above, the present invention has excellent effects, and the industrial value of the present invention is high.

[0024]

As described above, according to the present invention, highly excited and high-density ECR plasma can be easily generated in a plasma generator by using a microwave and a magnetic field. A large amount of ionic and radical species can be generated. Furthermore, the distribution of the magnetic field strength in the propagation direction of the microwave in the radical generator is maintained at a magnetic field strength exceeding the ECR generation condition in a region from the vicinity of the inlet of the radical generator to one or more wavelengths in the tube wavelength of the radical generator. ,
By setting the magnetic field intensity below the ECR generation conditions near the exit of the radical generator, nitrogen molecule ions or nitrogen atom ions in the ECR plasma can be removed. In addition, since a region having a magnetic field strength equal to or higher than the ECR generation condition is at least one wavelength in the tube, microwaves can be sufficiently absorbed.

[0025]

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a magnetic field distribution in a radical generator and movement of ions and radicals according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a growth apparatus according to one embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a radical generator according to one embodiment of the present invention.

FIG. 4 shows the emission of nitrogen molecular ions ( ₃₉₁ nm: I ₃₉₁ ) and the emission of nitrogen molecular radicals (337 nm: I ₃₃₇ ) obtained by emission spectroscopy near the exit of the radical generator according to one embodiment of the present invention. Emission intensity ratio (I ₃₃₇ /
It is a figure showing the pressure dependence of _I391 ).

FIG. 5 is a schematic configuration diagram of a conventional nitride-based compound semiconductor film growth apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Ion 2 Magnetic field line 3 Radical 4 Vacuum tank 5 Substrate 6 K cell 7 Radical generator 8 Microwave introduction port 9 Nitrogen gas introduction port 10 Electromagnet 11 Microwave propagation direction 12 Radical generator exit 13 DC power supply 14 TE ₁₁ mode cylinder Waveguide 15 Quartz plate 19 Nitride-based compound semiconductor film 21 Group 3 organic metal inlet 22 Plasma generation chamber 23 Growth chamber

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-179527 (JP, A) JP-A-1-307225 (JP, A) JP-A-61-59821 (JP, A) (58) Investigation Field (Int.Cl. ⁷ , DB name) H01L 21 / 203,21 / 363

Claims (3)

(57) [Claims] An apparatus for growing a nitride-based compound semiconductor film, comprising: a means for supplying a group 3 atom into a vacuum chamber; and a means for generating a nitrogen molecule radical or a nitrogen atom radical. As a means for generating molecular radicals or nitrogen atom radicals, a radical generator for generating electron cyclotron resonance (ECR) plasma of a gas containing nitrogen by applying a microwave and a magnetic field is used, and nitrogen molecule ions or nitrogen in the ECR plasma are used. As means for removing atomic ions, the distribution of the magnetic field strength in the direction of propagation of the microwave is controlled by ECR in a region from the vicinity of the microwave introduction port of the radical generator to one or more wavelengths in the guide tube of the radical generator. ECR generation conditions near the exit of the radical generator were maintained at a magnetic field intensity higher than the generation conditions. Apparatus for growing a nitride-based compound semiconductor film, characterized in that the magnetic field strength below. 2. The apparatus for growing a nitride-based compound semiconductor film according to claim 1, wherein a negative potential electrode is provided near an outlet in the radical generator. 3. An apparatus for growing a nitride-based compound semiconductor film according to claim 1, wherein the number of outlets of the radical generator is less than or equal to a size at which microwaves can be blocked.