JPS61242991A - Particle beam source for particle beam epitaxial apparatus - Google Patents

Abstract

PURPOSE:To obtain sharp particle beam by using a particle beam source composed of a crucible containing a solid raw material and heated with a heater, and a thin tantalum tube having spiral intermediate part, a base end inserted into the opening of the crucible and a tip end designed to get desired particle beam angle distribution. CONSTITUTION:The objective particle beam source is composed of a crucible 2 containing a solid raw material 4 and heated with the heater 8, and a thin tantalum tube 16 having spiral intermediate part, a base end 18 inserted into the opening of the crucible 2 and a tip end 20 designed to get a particle beam having desired angular distribution. When the heater is electrified, the crucible 2 is heated, and at the same time, an electrical current passes through the heater 8 and the thin tantalum tube 16 to generate heat in the thin tantalum tube 16. Particles generated by the evaporation of the solid raw material 4 in the crucible 2 are introduced through the base end 18 into the thin tantalum tube 16 and ejected from its tip end 20.

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 III element in an apparatus for epitaxially growing a compound semiconductor such as a group III-v 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), the newly proposed so-called particle beam epitaxial device (Japanese Patent Application No. 59-37660, described below), and other devices that perform epitaxial growth by irradiating a substrate with a particle beam as described above. used in meaning.

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

(Prior Art) A Knudsen cell equipped with a cracking furnace is known as a particle beam source for secondary elements using solid raw materials. According to the particle source, 97% of the evaporated particles in the A s a state generated in the Knudsen cell are decomposed in the cracking furnace, of which about 70% become the A s 2 state and about 30% into the A s a state. It has been reported that the state of

■The next element has been tetrama (Ag3.P4゜5ba)
Since these particles were used in the form of particle beams such as P2 and Dimer (AS2I P2, 5b2), there is no means to directly measure the intensity of these particle beams, and strict control of the particle beam intensity has not been carried out.

(The problem that an invention attempts to solve.

If a continuous element particle beam in a monoatomic state can be obtained by providing a cracking furnace, it will be possible to detect and control the particle beam intensity using an atomic absorption detector. However, in order to detect particle beam intensity, conventional particle beam sources have a small proportion of monatomic particles, and it is necessary to decompose most of the evaporated particles into monatomic particles.

In addition, when a cracking furnace is added to a Knudsen cell, if the structure is such that mounting wiring for the cracking furnace's heater and thermocouple, and lead-throughs for the flange are added, failures such as lead wire contact may easily occur. .

Furthermore, in conventional particle beam sources, the angular distribution of the particle beam is generally large, resulting in a large loss of raw material and a heavy burden on the exhaust system.

The present invention provides a particle beam source equipped with a cell that uses solid raw materials, such as a Knudsen cell, and a cracking furnace. By simplifying the physical connection and sharpening the angular distribution of the particle beam, we aim to improve the efficiency of raw materials, reduce the burden on the exhaust system, and reduce the negative effects caused by contamination of the particle beam epitaxial equipment by continuation elements. The purpose is to reduce the

(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 proximal end 1 is formed into a spiral shape.
8 is inserted into the opening of the crucible 2, and the tantalum capillary tube 16 has an inner diameter and length set so that the tip portion 20 obtains a desired particle beam angle distribution.
The tantalum tube 16 is made to generate heat by passing a current through itself, and the tantalum tube 16 and the crucible 2 are
The heater 8 is connected to the heater 8.

(Function) When the heater 8 of the crucible 2 is energized, the crucible 2 is heated, and the current also flows through the heater 8 to the tantalum tube 16, causing the tantalum tube 16 to generate heat. In the crucible 2, the solid raw material 4 is heated and evaporated, and in the case of a continuous element, it generally evaporates in the form of polyatomic particles. These evaporated particles enter the tantalum thin tube 16 from the crucible 2, and while passing through a spiral portion, are decomposed by the catalytic action of the heated tantalum surface, becoming particles in a diatomic state or a monoatomic state.

The particle beam ejected from the tip of the tantalum tube 16 is as follows.

It is ejected with an angular distribution defined by the inner diameter and length of the tip 20 of the tantalum thin tube 16.

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

2 is a crucible constituting a Knudsen cell, in which a solid raw material 4 of a V-group element is accommodated.

Crucible 2 is pyrolytic boron nitride (hereinafter referred to as PBN) that has been well degassed in a high vacuum.
At the upper opening, the upper fixing plate 6
Supported by The upper fixing plate 6 is also made of PBN. A tantalum plate heater 8 is arranged around the side of the crucible 2. The tantalum plate heater 8, as shown in FIG. 2 when unfolded, is made by punching out a single tantalum plate in a meandering shape, and has protrusions 10 at the bends along a pair of opposing sides. ..., 12...
is provided. The tantalum plate heater 8 is bent so as to surround the side of the crucible 2, and has protrusions 10...
. . , 12 . . . are inserted into holes provided in the upper fixing plate 6 and the lower fixing plate 14, respectively, and are fixed. The lower fixing plate 14 is also made of PBN.

Reference numeral 16 denotes a tantalum thin tube, the proximal end 18 of which is formed in a linear shape, and is inserted into the opening of the crucible 2 through the fixing plate 6. Thereby, the opening of the crucible 2 and the tantalum thin tube 16 are connected, and the other part of the opening of the crucible 2 is closed by the upper fixing plate 6 or the like. The middle portion of the tantalum thin tube 16 is formed into a spiral shape to increase the efficiency of particle beam decomposition. In addition, the tip portion 2 of the tantalum thin tube 16
0 is formed in a straight line, and the ratio of its inner diameter to length is set so as to obtain a desired particle beam angle distribution.

Reference numeral 22 denotes a fixture that is fixed to the upper fixing plate 6 and also serves as a heater connection terminal; the base end 18 of the tantalum thin tube 16 is fixed to and supported by the fixture 22; It is fixed to and supported by a fixing rod 26 by a fixing metal fitting 24. 28 is a fixing metal fitting that is fixed to the upper fixing plate 6 and also serves as a heater connection terminal, and the fixing rod 2
6 is fixed and supported by its fixture 28.

The fixing fittings 22, 24, 28 and the fixing rod 26 are made of tantalum. The fixing fittings 22 and 28 are each connected to a tantalum plate heater 8, so that a current is passed through the tantalum plate heater 8 and into the tantalum capillary tube 16.

30.32 is a support rod fixed to the flange 34;
A support stand 36 is fixed to their tips. Two tantalum leads 38.40 are fixed through the support base 36, and the proximal ends of the leads 38.40 become lead throughs 42.44 that pass through the flange 34, and the leads 38 A lower fixing plate 14 is fixed to the tip of the .40.

46 is a thermocouple, which is brought into contact with the bottom of the crucible 2 and taken out to the outside through a lead through 47 of the flange 34.

48 is a heat shield surrounding the sides of the tantalum tube 16;
50 is a heat shield that surrounds the sides of the Knudsen cell consisting of the crucible 2 and the heater 8, and is constructed by stacking tantalum thin plates in multiple layers with gaps between them. Furthermore, a heat shield 52 is also provided between the lower fixing plate 14 and the support base 36, and this heat shield 52 is also constructed by stacking tantalum thin plates in multiple layers with gaps between them.

When voltage is applied to lead throughs 42, 44, leads 38, 40 . A current flows through the heater 8 through the path of the fixture 22, the tantalum thin tube 16, the fixture 24, the fixture rod 26, and the fixture 28.

The intensity of the particle beam can be determined by changing the amount of electricity applied to the heater 8.
This is done by changing the temperature of the cell, but the heater 8 and the tantalum tube 16 are connected so that even if the amount of current applied to the heater 8 is changed, a current flows through the tantalum tube 16 at a temperature that provides a predetermined decomposition rate. When the resistance value is set 6, that is, when an arsenic particle beam is generated according to this embodiment, the cracking rate by the tantalum thin tube 16 is as shown in FIG. Therefore, even when the amount of current applied to the heater 8 is changed, the temperature of the tantalum thin tube 16 is set so as to fall within the shaded area.

In this embodiment, a plate-shaped heater 8 is used as a heater for the crucible 2.
This eliminates the need for supporting members like in the case of conventional coil heaters, suppresses the generation of unnecessary gas, allows for high-quality crystal growth, and reduces the risk of failure compared to coil heaters. rate decreases.

FIG. 4 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, 90C, . . . from the 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...
Particle beams 82 a, 82 b, 82 c... from one particle beam source 72, 74, 76...
A shutter 78 for selecting a particle beam and an exhaust port 80 connected to a high vacuum pump are provided.
.

82b, 82c, . . . are reflected by the liquid nitrogen shroud 64 or the shutter 78, resulting in an unnecessary reflected particle beam 84. .

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. On the surface of the substrate 86, elementary groups 70a and 70b of the liquid nitrogen shroud 64 are formed.
, 70c... and then the particle beam sources 72, 74, 76
Useful particle beams 90a, 90c... from...
. . is incident, but it is reflected by the surface of the substrate 86, resulting in an unnecessary particle beam 92. The fixing angle of the substrate 86 is set so that... is reflected toward the exhaust port 88 and effectively discharged.

The particle beam sources 72, 74, 76, . . . are configured such that the intensity of the generated particle beams can be controlled. Examples of such a particle beam source include the particle beam source of the present invention, a Knudsen cell without a cracking furnace that uses solid raw materials, and one that uses a particle beam shaped by a particle beam generation aperture. Electron ionization source where the beam is ionized as it passes through the ionization chamber, accelerated and focused by an electrode, unneeded ions are separated by a magnetic field, and only useful ions are emitted as a particle beam, ionized in the photoionization chamber Alternatively, a photoionization source in which unnecessary ions of the radicalized particle beam are separated by a quadrupole mass filter and only useful ion and radical particle beams are emitted as a particle beam, or a source gas is heated. These include those that use gaseous raw materials, such as those that are decomposed.

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 six 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, epitaxial growth is performed on the substrate 86 by useful particle beams 90a, 90c, etc., which have passed through elementary groups 70a, 70b, 70c, etc. . . . Among them, unnecessary particle beams not used for epitaxial growth are reflected particle beams 92.・
...and is discharged to the exhaust port 88 or adsorbed by the liquid nitrogen shroud 64, thereby leaving the growth chamber 68.
A high vacuum is maintained. Then, in the growth chamber 68, the prime group 7
The amount of particle beams 90a, 90c..., which are incident on the radiation source chamber 66 through the particle beams 82a, 82b, 82c... The growth chamber 68 and the radiation source chamber 66 are connected by six groups 70a, 70b, 70c... Since the diameter of . is maintained at a high vacuum of, for example, 10 −1 Torr.

(Effects of the Invention) According to the present invention, it is possible to obtain a highly practical solid raw material particle radiation source having the following effects.

(1) By energizing the tantalum tube itself to generate heat and connecting the tantalum tube to the heater of the crucible, the number of heater members and heater lead wires can be reduced. This simplifies the electrical wiring, reduces the need for flange lead-through, and reduces the occurrence of failures due to lead wire contact.

(2) High decomposition efficiency.

FIG. 3 shows an example of the temperature of the tantalum tube 16 and the rate of thermal decomposition of the arsenic particle beam.

The arsenic particle beam is efficiently decomposed by the catalytic action of the heated tantalum surface, and most of the generated particle beams are monoatomic As.
It becomes a + state.

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.

(3) The particle beam is injected from the tip of the tantalum tube 16,
The shape of the tip 20 is set to reduce the angular distribution of the ejected particle beam.

FIG. 5 shows the results of comparing the angular distribution of peak intensity between the particle beam source of this example and the conventional particle beam source, with the particle doses being made equal.

55 is for this example, 56 is for the conventional case. 0 In this example, the peak intensity distribution of the particle beam is sharp due to the shape effect of the thin tube, whereas in the conventional particle beam source, the nozzle diameter is thicker. Therefore, the spread angle when the particle beam is ejected from the nozzle tip increases. In the case of a particle beam epitaxial apparatus as shown in FIG. 4, if the particle beam source has a small peak intensity distribution of the particle beam as in this example, it is possible to introduce more particle beams into the growth chamber. This is advantageous in terms of increasing the efficiency of raw materials, reducing the burden on the exhaust system, and reducing contamination of the particle beam epitaxial apparatus.

(4) Since a tantalum tube is used as the pyrolysis pipe, it is mechanically stronger than the conventional one using a quartz pipe, and moreover, there is less contamination of impurities into the growing crystal.

(5) Since the tantalum thin tube itself is heated by electricity, fewer parts are required compared to the conventional method of heating a quartz pipe from the outside, which reduces the number of sources of bad gas and improves the quality of the grown crystal. will improve.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the present invention, Fig. 2 is a plan view showing the crucible heater used in the embodiment in an expanded state, and Fig. 3 is the temperature of the tantalum thin tube in the embodiment. FIG. 4 is a schematic cross-sectional view showing an example of a particle beam epitaxial device to which the present invention is applied, and FIG. Or it is a figure which shows the angular distribution of the particle beam injected from a nozzle. 2... Crucible, 4... Solid raw material, 8... Heater, 16... Tantalum tubule, 18... Base of tantalum tubule. End, 20...
...The tip of a tantalum tube.

Claims (1)

[Claims] (1) A crucible that accommodates a solid raw material and is heated by a heater; an intermediate portion is formed in a spiral shape, a base end is inserted into the opening of the crucible, and a tip end is configured to obtain a desired particle beam angle distribution. A tantalum tube whose inner diameter and length are set to
A particle beam source for a particle beam epitaxial apparatus, comprising: causing the tantalum thin tube to generate heat by passing a current through the tantalum thin tube, and connecting the tantalum thin tube to a heater of the crucible.