JPH0574710A - Semiconductor thin film growth method - Google Patents

Abstract

PURPOSE:To obtain a GaN semiconductor thin film which is optimum for the photo-element of an ultraviolet-blue color region. CONSTITUTION:Using a plasma gas cell provided in vacuum, a GaN semiconductor thin film is formed by a film forming method using the vacuum device such as a gas source MBE and the like using activated nitrogen as the source of nitrogen. As a result, a flat thin film, having excellent crystallizability, can be obtained. Also, as the carrier density can be controlled easily, this method is considered optimum as the manufacturing method for semiconductor thin film to be used for photo element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a gallium nitride based semiconductor thin film which can be used particularly for displays, ultraviolet-blue light emitting diodes, laser diodes and the like which are optimal for optical communication.

[0002]

2. Description of the Related Art Semiconductor devices, particularly visible light emitting diodes (LEDs), are used as display devices in a wide range of fields, but ultraviolet to blue light emitting diodes and laser diodes have not been put into practical use. Development is urgently needed for displays that require three primary colors. Ultraviolet to blue light emitting diodes and laser diodes include ZnSe, ZnS, GaN and SiC.
It has been reported that using such.

Most gallium nitride (GaN) is deposited on the C-plane of sapphire by MOCVD or VPE [Journal of Applied].
Physics, 56 (1984) 2367-236.
8], it is necessary to raise the reaction temperature, which is not only difficult to manufacture, but also the carrier density becomes extremely large due to lack of nitrogen, and good semiconductor characteristics cannot be obtained.

In order to realize low temperature film formation, there is an attempt to activate a nitrogen source by an electron shower [Jap.
J. Appl. Phys. , 20, L545 (198
1)] is said to be insufficient for improving the film quality even by this method. Further, it is considered to form a film by using a highly active nitrogen source so as not to cause a shortage of nitrogen. Atomic nitrogen and nitrogen ions are available as highly active nitrogen sources, but conventional techniques using plasma [J.
Vac. Sci. Technol. , A7 P.A. 701
(1989)] etc., it is difficult to efficiently generate them.

[0005]

In order to produce a GaN thin film having good characteristics as a semiconductor thin film, it is necessary but not realized to generate highly active nitrogen with high efficiency and form a film at low temperature. is the current situation. The present invention solves this problem and provides GaN having good characteristics as a semiconductor.
It is intended to produce a system thin film.

[0006]

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a GaN-based thin film having good characteristics by a film forming method using a plasma gas cell in a high vacuum. The inventors have found that manufacturing is possible and have completed the present invention. That is, the present invention is a method for growing a gallium nitride based semiconductor thin film, characterized in that, when a gallium nitride based semiconductor thin film is manufactured in a high vacuum, activated nitrogen generated by a plasma gas cell is supplied to the substrate surface.

The high vacuum in the present invention means 10 ^-5 Torr
The pressure below is a pressure of 10 ^-5 Torr or less and a large mean free path in order that the gases and metal vapors necessary for GaN thin film deposition reach the substrate without colliding with each other. Will be preferred. In the present invention, by using a plasma gas cell, the surface of the substrate is prevented from directly touching the plasma, and the active nitrogen in the plasma generated inside the gas cell is drawn into a high vacuum to reach the substrate surface. By supplying it, active nitrogen and gallium atoms react with each other on the surface of the substrate, thereby making it possible to manufacture a target semiconductor thin film. When the plasma directly contacts the surface of the substrate, the surface of the thin film is sputtered, resulting in poor flatness and depletion of nitrogen, so that only a semiconductor thin film having low characteristics can be obtained.

The structure of the plasma gas cell 8 of the present invention is characterized in that it comprises a gas introduction tube 12 for supplying a gas to be turned into plasma to the plasma gas cell, an orifice 10, and electrodes and coils for generating plasma. In order to stably generate plasma in the plasma gas cell, it is necessary to maintain the inside of the cell at an appropriate pressure. The pressure cannot be uniquely determined because it varies depending on the type of gas that generates plasma, the structure and size of the plasma gas cell, the frequency of the applied high frequency, and the applied voltage, but at least for maintaining stable plasma It is preferably 10 ^-4 Torr or more, more preferably 10 ^-3 Torr or more.

The structure of the plasma gas cell must be changed depending on the frequency of the applied high frequency, the applied voltage and the pressure inside the cell. The distance between the electrodes, the volume of the plasma gas cell, the number of plasma gas outlets installed in the cell, and the like. The shape may be designed to have an appropriate value. It is important that the pressure in the plasma gas cell be higher than the pressure in the growth chamber, so that the plasma is held stable, and the plasma is pulled out from the cell due to the pressure difference between the growth chamber and the cell to grow crystals. It is possible to supply to the surface. The pressure in the plasma gas cell can be maintained by providing a suitable orifice, nozzle, or slit at the plasma outlet of the cell. The opening area and shape are the amount of gas to be introduced,
It may be changed depending on the size of the crystal growth chamber and the pumping speed of the pump.

In order to generate plasma, a capacitance type in which an appropriate electrode is provided in the cell is used, or an inductive coupling type in which an appropriate coil is provided is selected, and an appropriate voltage is applied to the electrode or coil. It can be performed by applying a high frequency. Further, in order to draw the plasma from the cell into the growth chamber, the pressure difference is used as described above, and further, necessary active species are selectively supplied from the plasma to the substrate surface, A suitable DC or AC electric field may be applied between the cell and the crystal growth surface to energize the plasma.

As the nitrogen source in the present invention, nitrogen, ammonia, or nitrogen trifluoride may be used alone or a mixed gas containing them as a main component. As the gas mixed with nitrogen, ammonia or nitrogen trifluoride, an inert gas such as argon or helium can be used. As a method of supplying these gases, a valve, a flow rate control device, and a pressure control device are connected in the middle of a pipe leading to the cell to control the mixing ratio and supply amount of these gases,
It is preferable to use one that can start and stop the supply.

In the present invention, a gallium nitride based semiconductor thin film
Substrates used to grow Si, Al₂
O₃, ZnO, MgO, SiC, or GaAs, I
III-V group compound semiconductors such as nAs, ZnSe and the like
II-VI group compound semiconductor single crystal substrates, quartz glass,
A glass substrate such as MESA glass is used. Also with the substrate
Amorphous state as a buffer layer between GaN thin film
, Such as AlN, GaN, Si, SiC, etc.
Or as a single crystal substance, for example, AlN, ZnO, SiC
Etc. can be provided. Among these boards, the
Fire (Al ₂O₃) Use an R-side substrate
Is preferable, and the off angle is preferably 0.8 degrees or less.
Good. Furthermore, the sapphire R surface is
Use a surface rotated by 9.2 degrees around the R-plane projection
Highly oriented GaN-based semiconductor thin film
Can be obtained. The substrate is 2 by the substrate heating device.
Heat in the range of 00 to 900 ° C.

The GaN-based semiconductor thin film in the present invention is
For example, in addition to GaN, Ga _1-x Al _x N, Ga _1-x In _x
It refers to a mixed crystal compound semiconductor thin film mainly composed of GaN such as N and Ga _1-x B _x N. Furthermore, when a GaN-based semiconductor thin film is manufactured, impurities can be doped to perform carrier density control and p-type or n-type control.
Examples of impurities to be doped are Mg, Zn, Be,
There are Sb, Si, Ge, C, Sn, Hg, As, P and the like. The type of carrier and the carrier density can be changed by changing the type and doping amount of these dopants.

In the case of actually manufacturing a light emitting device (LED) or a laser diode using a GaN-based semiconductor thin film, a GaN-based semiconductor thin film of a mixed crystal system or a doped GaN-based semiconductor thin film is combined to form a pn. A device having a junction, a single hetero structure, a double hetero structure, a quantum well structure, a superlattice structure, or the like is manufactured.

A method of manufacturing a GaN-based semiconductor thin film using the gas source MBE method will be described below as an example, but the method is not particularly limited to this. As the apparatus, a gas source MBE apparatus provided with an evaporation crucible (Knudsen cell) 2, 3 and 4, a plasma gas cell 8 and a substrate heating holder 5 in a vacuum container 1 as shown in FIG. 1 was used.

Ga metal is put in the evaporation crucible 2 to form a substrate.
Ga vapor is 10¹³-10 ¹⁹/ Cm²・ Sec
It was heated to a temperature of. Gas introduction pipe 12 for introducing nitrogen
Is used to convert nitrogen into plasma in the plasma gas cell 8 and
So that it sprays directly onto the substrate 6 through the refill 10.
It was The amount of nitrogen introduced is such that the amount of active nitrogen is Ga on the substrate surface.
It was supplied so as to be at least 10 times as much as steam or more. Steaming
Place In, Al, As, Sb, etc. in the crucible 3
To obtain a mixed crystal compound semiconductor with a constant composition, the temperature and
And the time are controlled to form the film. M for evaporation crucible 4
g, Zn, Be, Sb, Si, Ge, C, Sn, Hg,
Put As, P, etc., and adjust the temperature and
And doping is controlled by controlling the supply time.

A sapphire R surface is used for the substrate 6, and 20
Heated to 0-900 ° C. The sapphire R-plane substrate preferably has an off angle of 0.8 degrees or less, and more preferably uses a plane obtained by rotating the sapphire R-plane by 9.2 degrees around the R-plane projection of the sapphire c-axis. First, after heating the substrate 6 in the vacuum chamber 1 at 900 ° C., a predetermined growth temperature is set and a GaN-based semiconductor thin film having a thickness of 0.4 to 10 μm is produced at a growth rate of 0.1 to 30 Å / sec. To do.

When the carrier density of this GaN-based semiconductor thin film was measured by the Van der Pauw method, it was 10 ¹⁷ /
It was cm ³ to 10 ²⁰ / cm ³ . Further, when cathodoluminescence (CL) was measured at 200 K, a spectrum having a peak near 3.5 eV was obtained as shown in FIG.

[0019]

EXAMPLES The present invention will be described in more detail below with reference to examples.

[0020]

Example 1 Gas source MBE using nitrogen plasma
An example of forming a GaN thin film by the method will be described.
In a vacuum container 1 as shown in FIG. 1, an evaporation crucible 2, a plasma gas cell 8 and a substrate heating holder 5, a gas introduction pipe 12 for supplying a gas to the plasma gas cell 8, a gas flow rate control valve 13 and a high frequency wave. A gas source MBE equipped with a power supply 14 was used.

Ga metal was put in the evaporation crucible 2 and 10
Heated to 20 ° C. Nitrogen is used as the gas, and 5 cc / min is applied to the plasma gas cell 8 through the gas introduction pipe 12.
Was fed at a rate of. The plasma gas cell 8 is made of quartz glass having an internal volume of 80 cc, and the plasma gas outlet of the gas cell is made of a quartz glass orifice 1 having a diameter of 1 mm.
0 is set. A silver plate was used as the electrode 9 and was wired with a high frequency power source 14 and a silver wire. The pressure in the gas cell was maintained at about 10 ⁻³ Torr, and the electrode 9 was 13.56.
A nitrogen plasma was generated by applying a high frequency power of 300 watts at MHz. The generated active nitrogen passed through the orifice 10 and was supplied to the substrate 6 provided 5 cm away from the orifice.

As the substrate 6, a sapphire R surface having an off angle of 0.5 degrees is used. The pressure in the vacuum container was 2 × 10 ⁻⁶ Torr during film formation. First, the substrate 6 is set to 9
A film is formed by heating at 00 ° C. for 30 minutes and then maintaining the temperature at 750 ° C. The film formation was performed by opening the shutter of the Ga crucible while supplying nitrogen from the plasma gas cell 8.
Film thickness 0.8 at 1.2 Angstrom / sec deposition rate
A μm GaN thin film was prepared.

In the example of measuring the X-ray diffraction spectrum of this GaN thin film, it is understood that highly oriented GaN is produced as shown in FIG. Moreover, when the carrier density was measured by the Van der Pauw method, it was 8 × 10 ¹⁷ / cm 2.
^{Was 3} . Further, when cathodoluminescence (CL) was measured at 200 K, a spectrum having a peak near 3.5 eV was obtained as shown in FIG.

[0024]

Example 2 Ga _1-x In _x N by gas source MBE method
An example of producing a mixed crystal thin film will be described. As the apparatus, the same apparatus as in Example 1 was used. Ga metal was placed in the evaporation crucible 2 and heated to 1020 ° C., and In was placed in the evaporation crucible 3 and heated to 660 ° C. The gas was introduced by the same method as in Example 1 with nitrogen at 6 cc / mi.
This was done by feeding at a rate of n.

As the substrate 6, a sapphire R surface having an off angle of 0.5 degrees is used. The pressure in the vacuum container was 3 × 10 ⁻⁶ Torr during film formation. First, the substrate 6 is set to 900
A film was formed by heating at 30 ° C. for 30 minutes and then maintaining the temperature at 730 ° C. The film formation was performed by opening the crucible shutter of Ga and In while supplying nitrogen from the plasma gas cell 8, and the Ga _1-x In _x N mixed crystal having a film thickness of 0.8 μm was formed at the film formation rate of 1.0 angstrom / sec. Thin film (x = 0.2)
Was produced.

When the carrier density of this mixed crystal thin film was measured by the Van der Pauw method, it was 2 × 10 ¹⁸ / cm ^3.
Met. Further, when the cathodoluminescence (CL) was measured at 200 K, as shown in FIG.
A spectrum having a peak near 9 eV was obtained.

[0027]

Example 3 An example of forming a GaN thin film by a gas source MBE method using ammonia will be described. As the device, the same device as in Example 1 was used to produce a GaN thin film. Ga metal is put in the evaporation crucible 2 and 10
Heated to 20 ° C. Ammonia is used as gas,
5 cc / in the plasma gas cell 8 through the gas introduction pipe 12.
It was supplied at a rate of min. A high frequency power of 300 watts at 13.56 MHz was applied to the electrode 9 of the plasma gas cell to generate plasma. An orifice 10 having a hole diameter of 1 mm was provided at the gas outlet of the gas cell so that the activated nitrogen species could be directly supplied to the substrate 6.

As the substrate 6, a sapphire R surface having an off angle of 0.5 degrees is used. The pressure in the vacuum container was 2 × 10 ⁻⁶ Torr during film formation. First, the substrate 6 is set to 900
The film is formed by heating at 30 ° C. for 30 minutes and then maintaining the temperature at 750 ° C. The film was formed by opening the shutter of the Ga crucible while supplying nitrogen from the plasma gas cell 8, and
0.8 μm film thickness at film forming rate of Angstrom / sec
A GaN thin film was prepared.

When the carrier density of this GaN thin film was measured by the Van der Pauw method, it was 5 × 10 ¹⁷ / cm 2.
^{Was 3} . Further, when the cathodoluminescence (CL) was measured at 300 K, a spectrum having a peak near 3.4 eV was obtained as shown in FIG.

[0030]

Example 4 An example of producing a GaN thin film for producing a mis type structure by a gas source MBE method will be described. A GaN thin film was prepared using the same device as in Example 1. Ga metal is put in the evaporation crucible 2 and 102
Heated to 0 ° C. Ammonia is used as the gas, and 5 cc / m is supplied to the plasma gas cell 8 through the gas introduction pipe 12.
Supplied at a rate of in. A high frequency power of 300 watts at 13.56 MHz was applied to the electrode 9 of the plasma gas cell to generate plasma. An orifice 10 having a diameter of 1 mm was provided at the gas outlet of the gas cell so that the activated nitrogen species could be directly supplied to the substrate 6.

As the substrate 6, a sapphire R surface having an off angle of 0.5 degree is used. The pressure in the vacuum container was 5 × 10 ⁻⁶ Torr during film formation. First, the substrate 7
A film is formed by heating at 00 ° C. for 30 minutes and then maintaining the temperature at 750 ° C. The film formation is performed by opening the shutter of the Ga crucible while supplying active nitrogen from the plasma gas cell 8 to form a GaN thin film with a thickness of 0.7 μm at a film formation rate of 1.2 Å / sec. Subsequently, the shutter for the magnesium crucible and the shutter for the magnesium crucible were simultaneously opened to form a doping layer having a thickness of 500 Å.

When the cathode luminescence (CL) of this GaN laminated thin film at 200K was measured, FIG.
A spectrum having a peak near 3.5 eV was obtained as shown in FIG. Further, when a mis type structure was prepared and current-voltage characteristics were measured, diode characteristics as shown in FIG. 7 were obtained.

[0033]

According to the method for producing a GaN-based thin film of the present invention, since it is possible to form a film at a low temperature, it is easy to control the carrier density, and the semiconductor light emission has good surface flatness and crystallinity. A GaN-based thin film for devices can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view of a gas source MBE apparatus used for thin film production.

FIG. 2 is a spectrum diagram showing the measurement result of cathodoluminescence of the GaN thin film produced in Example 1.

FIG. 3 is an X-ray diffraction spectrum diagram of the GaN thin film produced in Example 1.

FIG. 4 is a spectrum diagram showing the measurement result of cathode luminescence of the GaN thin film manufactured in Example 2.

FIG. 5 is a spectrum diagram showing the measurement result of cathode luminescence of the GaN thin film manufactured in Example 3.

FIG. 6 is a spectrum diagram showing the measurement result of cathode luminescence of the GaN thin film manufactured in Example 4.

FIG. 7 is a graph showing a current-voltage measurement result of a GaN mis type structure element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Evaporating crucible 3 Evaporating crucible 4 Evaporating crucible 5 Substrate heating holder 6 Substrate 7 Quadrupole mass spectrometer 8 Plasma gas cell 9 Electrode 10 Orifice 11 Wiring 12 Gas introduction pipe 13 Flow control valve 14 High frequency power supply 15 Cryo Panel 16 Valve 17 Cold trap 18 Oil diffusion pump 19 Oil rotary pump 20 Shutter 21 Shutter 22 Shutter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01L 33/00 C 8934-4M

Claims (1)

[Claims] 1. A method for growing a gallium nitride based semiconductor thin film, which comprises supplying active nitrogen generated by a plasma gas cell to the surface of a substrate when the gallium nitride based semiconductor thin film is manufactured in a high vacuum.