JPS61242990A - Particle beam source for particle beam epitaxial apparatus - Google Patents

Abstract

PURPOSE:To obtain sharp particle beam, by using a thin tantalum tube as the furnace to effect the thermal decomposition of gaseous raw material, passing electrical current along the thin tantalum tube to cause generation of heat in the tube, introducing a gaseous raw material from the base end of the tube, and ejecting particle beam through the tip. CONSTITUTION:In a particle beam source furnished with a furnace to heat and decompose gaseous raw material, a thin tantalum tube 2 is used as the furnace. The thin tantalum tube 2 is heated by passing an electric current through a circuit formed by the lead-through 14, the lead 10, the thin tantalum tube 2, the lead 16 and the lead-through 18. A gaseous raw material is supplied to the base end 6 of the thin tantalum tube from the gas transfer pipe 8, and particle beam is ejected from the tip end 4 of the thin tantalum tube.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a particle beam source that generates a particle beam of a group ■ element in an apparatus for epitaxially growing a compound semiconductor such as a group ■-■ group on a substrate. .

Here, the term "particle beam" is used to include molecules, atoms, ions, radicals, etc.

Therefore, the term "particle beam epitaxial apparatus" in the present invention refers to the conventional so-called molecular beam epitaxial apparatus (M
BE) and the newly proposed so-called particle beam epitaxial device (Japanese Patent Application No. 59-37660, described below), as well as other devices that perform epitaxial growth by irradiating the above-mentioned particle beam onto a substrate. used in

The present invention is applied to such a particle beam epitaxial device in a broad sense.

(Prior Art) In a particle beam epitaxial apparatus, a particle beam source for generating a particle beam of a group ■ element during crystal growth of a group ■-■ compound semiconductor is a hydride of a group ■ element (for example, As H3).
) is thermally decomposed.

In such conventional particle beam sources, one particle formed in a spiral
Heat a quartz pipe and apply A s H to the quartz pipe.
3 and other raw material gases are introduced and decomposed.

Additionally, a tantalum wire passed through a quartz pipe has been proposed as a decomposition catalyst for ASH3 (Journal of Vacuum Science and Technology (J, V
ac, Sci.

Technol, Vol. 82, No. 2, pp. 280-284 (1984)).

(Problems to be Solved by the Invention) Conventional particle beam sources using quartz pipes have a problem of being mechanically weak.

There is also the problem that Si in SiO2, which is the material of the quartz pipe, evaporates at high temperatures and becomes an impurity in the epitaxially grown film.

Furthermore, there is the problem that the particle beam source has to be made larger due to the low thermal decomposition efficiency of the raw material gas.

The object of the present invention is to realize a pyrolysis type particle beam source that is small, mechanically strong, has high pyrolysis efficiency, and can generate a group V element particle beam with few impurities. It is.

(Means for Solving the Problems) The particle beam source of the present invention will be described with reference to FIG. 1 showing an embodiment. The tantalum tube 2 is made to generate heat by passing an electric current along the tantalum tube 2 itself, a gaseous raw material is introduced from the base end of the tantalum tube 2, and a particle beam is injected from the tip.

(Function) When the gaseous raw material passes through the tantalum thin tube 2 which has reached a predetermined temperature by applying an electric current, the gaseous raw material is thermally decomposed. At this time, for example, when A s H3 is flowed as a gaseous raw material, ASH3 is efficiently decomposed by the catalytic action of the heated tantalum surface and becomes particles in the atomic Al11 state. The particle beam ejected from the tip of the tantalum tube 2 becomes a sharp beam with a small divergence angle due to the shape effect of the tip 4 of the tantalum tube 2.

(Example) FIG. 1 represents one embodiment of the invention.

Reference numeral 2 designates a tantalum thin tube, the distal end 4 of which is open for injecting a particle beam, and the base end 6 connected to a gas transport pipe 8 formed of the same tantalum thin tube. tantalum tube 2
is formed in a spiral shape at the intermediate portion between the distal end 4 and the proximal end 6 in order to improve the decomposition efficiency of the gaseous raw material.

Reference numeral 10 denotes a lead made of tantalum, which is integrated with a lead through 14 provided on the flange 12, and fixes and supports the tip 4 of the tantalum thin tube 2 at its tip. The lead 16 is also made of tantalum, and is provided on the flange 12 or integrated with the lead through 18, and its distal end fixes and supports the proximal end 6 of the tantalum thin tube 2.

The leads 10 and 16 support the tantalum tube 2 and also serve to flow a current between the tip 4 and the base 6 of the tantalum tube 2 in order to generate heat in the tantalum tube 2.

The base end of the gas transport pipe 8 connected to the base end 6 of the tantalum thin tube 2 is fixed through the flange 2, and a mini flange 2o is provided at the base end, and a flow controller (path shown) is connected to the base end of the gas transport pipe 8. It is connected to the raw material gas cylinder (the path shown) through the inlet. A thermocouple 28 measures the temperature of the tantalum tube 2.

Furnace support rods 30 and 32 are also attached to the flange 12, and a furnace support stand 34 is attached to the tips of the furnace support rods 30 and 32.

A lower heat shield 36 is provided between the tantalum thin tube 2 and the heating furnace support 34, and the lower heat shield 36 has a structure in which a plurality of tantalum thin plates are stacked with gaps between each other. A heat shield 38 is provided having a structure in which thin plates are stacked one on top of the other with a gap between them. A heat shield 40 made of a thin tantalum plate is also provided on the tip side of the tantalum thin tube 2.

The particle beam source of this embodiment is mounted by a flange 12 so that the tantalum thin tube 2 is inside the vacuum chamber of the particle beam epitaxial apparatus. The current for energizing the tantalum thin tube 2 and generating heat is supplied from outside the vacuum chamber to the lead throughs 14 and 18.
o, tantalum tubule 2. Lead 16 and lead through 1
The current flows through the current path formed by 8. The amount of current supplied is controlled such that the temperature of the tantalum tube 2 is measured by a thermocouple 28 so that the temperature of the tantalum tube 2 reaches a predetermined temperature.

FIG. 2 shows the particle beam epitaxial apparatus proposed in Japanese Patent Application No. 59-37660 cited above.

In this particle beam epitaxial apparatus, a vacuum chamber 6
2 is separated into a radiation source chamber 66 and a growth chamber 68 by an inclined liquid nitrogen shroud 64.

The liquid nitrogen shroud 64 is hollow inside and can be filled with a refrigerant such as liquid nitrogen, and includes a refrigerant inlet (not shown) and a gas exhaust port (not shown) for vaporized refrigerant. The liquid nitrogen shroud 64 has elementary groups 7 for passing particle beams 90a, 90b, . . . from the radiation source chamber 66 to the growth chamber 68.
0a, 70b, 70c, etc., and holes for shutter operation are provided as necessary.

The radiation source chamber 66 includes a plurality of particle radiation sources 72, 74° 76...
..., a shutter 78 for selecting particle beams 82a, 82b, 82c, ... from the particle beam sources 72, 74, 76, ... and an exhaust port 80 connected to a high vacuum pump. The exhaust port 80 is connected to each particle beam source 72,
Particle beam 82a from 74.76...

82b, 82c, . . . are reflected by the liquid nitrogen shroud 64 or the shutter 78, resulting in an unnecessary reflected particle beam 84. . . . is provided at a position slanting and facing the liquid nitrogen shroud 64 so that it can effectively discharge the liquid nitrogen shroud 64.

The growth chamber 68 is provided with a substrate 86 fixed to a substrate support (not shown) and an exhaust port 88 connected to a high vacuum pump independent of the vacuum system of the radiation source chamber 66. Board 86
On the surface of the liquid nitrogen shroud 64, elementary groups 70a, 7
0b, 70c... and then the particle beam sources 72, 74,
Useful particle beams 90a, 90c... from 76...
... is incident, but is reflected by the surface of the substrate 86, resulting in unnecessary particle beams 92. The fixing angle of the substrate 86 is set so that... is reflected toward the exhaust port 88 and effectively exhausted.

The particle beam sources 72, 74, 76, . . . are configured such that the intensity of the generated particle beams can be controlled. As such a particle beam source, in addition to the particle beam source of the present invention, for example, a particle beam formed into a beam by a single particle beam generation aperture is ionized as it passes through an ionization chamber, is accelerated and focused by an electrode, and is ionized by a magnetic field. An electron ionization source that separates unnecessary ions and emits only useful ions as a particle beam, and a quadrupole mass filter that removes unnecessary ions from the particle beam that is ionized or radicalized in a photoionization chamber. These include those that use a gaseous raw material such as a photoionization source where only useful ion and radical particle beams are separated and emitted as a particle beam, or those that use a solid source such as a Knudsen cell. be. These particle beam sources can control the amount of particle beam generation by controlling the amount of electricity applied to the heater or the flow rate of the flow controller.

The type and number of particle beam sources provided in such a particle beam epitaxial apparatus can be arbitrarily selected depending on the type of crystal to be grown.

When using a gaseous raw material, a turbo-molecular pump capable of continuous operation as a high-vacuum pump is most preferable.

During operation of this particle beam epitaxial apparatus, the source chamber 66
Now, the elementary groups 70a, 70b of the liquid nitrogen shroud 64,
Unnecessary particle beams that do not pass through the shutter 78 or the liquid nitrogen shroud 64 are discharged to the exhaust port 80, or the liquid nitrogen shroud 64 is cooled to the temperature of liquid nitrogen or other refrigerant. The high vacuum of the radiation source chamber 66 is maintained by being attracted to the radiation source chamber 66 . In the growth chamber 68, the substrate 86 is heated by useful particle beams 90a, 90c (old) that have passed through the elementary groups 70a, 70b, 70c, etc.
Epitaxial growth is performed on the particle beam at 9°a.
, 90c..., unnecessary particle beams not used for epitaxial growth are reflected particle beams 92.・・・・・・
... and is discharged to the exhaust port 88, but the high vacuum of the growth chamber 68 is maintained by being adsorbed by the liquid nitrogen shroud 64. Then, in the growth chamber 68, a large group 70a,
Particle beam 9'0 incident through 70b, 70c, old...
The amount of at90c... is smaller than the amount of particle beams 82a, 82b, 82c... entering the source chamber 66, and the growth chamber 68 and the source chamber 66 are Group 70a
, 70b* 70c... are connected,
Since the diameters of these elementary groups 70a, 70b, 70C, . 68 is a high vacuum', and the periphery of the substrate 86 is maintained at a high vacuum of, for example, 10-111 Torr.

(Effects of the Invention) According to the present invention, it is possible to obtain a highly practical particle beam source for gaseous raw materials having the following effects.

(1) High decomposition efficiency.

FIG. 3 shows an example of the temperature of the tantalum tube 2 and the rate of thermal decomposition of A s H3.

A8HG is efficiently decomposed at a low temperature by the catalytic action of the heated tantalum surface, and most of the generated particle beams are in the state of monoatomic A s l.

Previously, particle beams of group V elements were in a polyatomic state, and there was no easy means to detect their intensity.However, if a particle beam in a monoatomic state is obtained in this way, an atomic absorption detector can be used to measure the particle beam intensity. can now be detected, and the intensity of particle beam generation can be controlled based on the detected values.

(2) The temperature of the heating furnace is low, and since the heating furnace is made only of tantalum, chemical reactions do not occur at the joints of different materials, and impurities are less likely to be mixed into the single particle beam. . Furthermore, since the tantalum thin tube itself is heated by electricity, fewer members are required than in the conventional case where a quartz pipe is heated from the outside, and the number of sources of bad gases is reduced accordingly.

(3) The tip of the tantalum tube can be easily made thinner, and the angular distribution of the ejected particle beam can be made smaller.

Figure 4 shows the results of comparing the angular distribution of peak intensity between the particle beam source of this example and a conventional particle beam source using a single quartz pipe, with the same A s H3 gas flow rate. .

50 is for this example, and 52 is for the conventional case. 6 In this example, the peak intensity distribution of the particle beam is sharp due to the shape effect of the thin tube, that is, the divergence angle when the particle beam is injected from the tip of the tantalum thin tube is small. In contrast, in conventional particle beam sources, the nozzle diameter is large, so the spread angle when the particle beam is ejected from the nozzle tip becomes large. In the case of a particle beam epitaxial device as shown in Fig. 2,
Even if the particle beam source has a small particle beam peak intensity distribution as in this example, more ↓f particle beams can be introduced into the growth chamber, increasing the efficiency of raw materials and reducing the burden on the exhaust system. It is convenient for the above.

(4) Since a tantalum tube is used as the heating furnace, it is mechanically stronger and has a simpler structure than the conventional one using a quartz pipe.

(5) Less gas is released from the constituent materials of the particle beam source. That is, in a conventional heating furnace using a quartz pipe, Si may be generated from the quartz, but in the case of tantalum, such gas generation does not pose a problem.

[Brief explanation of drawings]

FIG. 1 is a front view showing an embodiment of the present invention with the heat shield cut away, FIG. 2 is a schematic sectional view showing an example of a particle beam epitaxial apparatus to which the present invention is applied, and FIG. 3 is the same embodiment. FIG. 4 is a diagram showing the relationship between the heating furnace temperature and the decomposition rate of AsH3, and FIG. 4 is a diagram showing the angular distribution of the particle beam injected from the tip in the same embodiment and the conventional example. 2... Tantalum tube, 4... Tip of tantalum tube, 6...
Proximal end of tantalum tube, 8... Gas transport pipe, 10.16... Lead.

Claims (1)

[Claims] (1) In a particle beam source equipped with a heating furnace for heating and decomposing a gaseous raw material, a tantalum tube is provided as the heating furnace, and an electric current is passed along the tantalum tube to cause the tantalum tube to generate heat; A particle beam source for a particle beam epitaxial device, characterized in that a gaseous raw material is introduced from the base end of a tantalum thin tube, and a particle beam is ejected from the tip.