JPS5826821B2 - Molecular beam epitaxial growth equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in molecular beam epitaxial growth equipment.

FIG. 1 shows a schematic diagram of an example of a conventional molecular beam epitaxial growth apparatus.

In the figure, 1 is an ultra-high vacuum chamber, 2 and 3 are ejection cells that contain the evaporation source material consisting of the elements constituting the grown film and eject these elements, and 4 is a liquid nitrogen gas chamber surrounding the ejection cells 2 and 3. A container to be cooled; 5 and 6 are molecular beams ejected from the ejection cells 2 and 3, respectively; 7 is a substrate on which a grown film is formed; 8 is a heater for heating the substrate 7; 9 is an ionized beam; 10 is a filament for electron emission, 11 is an electron collector, 12 is an electrode for ion acceleration, 13, 14, 15 and 16 are for applying voltage to each part. It is a power source.

Next, the operation of the above conventional device will be explained.

After evacuating the ultra-high vacuum chamber 1 to an ultra-high vacuum, the molecular beams 5 and 6 generated by heating the ejection cells 2 and 3 are transferred to the heater 8.
The heated substrate 7 is irradiated with irradiation 1, and the elements constituting the molecular beams 5 and 6 are deposited on the substrate 7, thereby performing molecular beam epitaxial growth.

Gallium arsenide (GaAs), a ■-■ group compound semiconductor
In this case, the ejection cell 2 contains metal gallium (Ga) and the ejection cell 3 contains metal arsenic (As), and the molecular beams 5 and 6 containing Ga and As as constituent elements, respectively, are
By irradiating the substrate 7 made of GaAs, GaAs is deposited on the substrate 7.
s is epitaxially grown.

In molecular beam epitaxial growth, some dopant substances do not adhere to the substrate 7 even if they are irradiated as molecular beams to the substrate 7, but are immediately reflected and are not incorporated into the crystal.

For example, in molecular beam epitaxial growth of GaAs, tin (Sn), which is an n-type dopant, and silicon (Si)
), germanium (Ge), etc. are incorporated into the crystal, but sulfur (S) is reflected and is not incorporated into the crystal.

Further, for the same reason, it is impossible to dope zinc (Zn) and cadmium (Cd), which are P-type dopants, in the form of a neutral molecular beam.

Therefore, a method has been proposed in which the above-mentioned S, Zn, Cd, etc. are ionized and doped by shallowly implanting them during crystal growth.

Therefore, for example, Zn is put in the ejection cell 9,
By heating this, a Zn molecular beam is generated.

Electrons emitted from the filament 10 heated by the power source 14 are accelerated toward the electron collector 11 by the power source 13 .

These accelerated electrons collide with Zn molecules to generate Zn ions.

These Zn ions are directed toward the ion accelerating electrode 12, pass through it, impact the substrate 7, and are mixed into the crystal growing on the substrate 7 as a P-type impurity.

A conventional molecular beam epitaxial growth apparatus for ion doping is configured as described above, in which ions are generated along the traveling direction of electrons from the filament 10 toward the electron collector 11, and the ions are generated after passing through the ion acceleration electrode 12. Since the spatial distribution takes a long distribution in a direction parallel to the traveling direction of electrons, it is difficult to uniformly dope the entire surface of the crystal on the substrate 7.

In addition, since the ion yield is low, as a result of ion doping by evaporating a large amount of molecules from the ejection cell 9, a large amount of neutral molecules also reach the substrate 7 and droplets are likely to be formed, resulting in a flat crystal surface. This results in disadvantages that are difficult to obtain.

This invention was made in order to eliminate the drawbacks of the conventional device as described above, and by housing the ejection cell and the ion generating section in a container cooled with liquid nitrogen, excess neutral molecules can be removed. The purpose of the present invention is to provide a molecular beam epitaxial growth apparatus that prevents ions from reaching a substrate, and at the same time makes the spatial distribution of ions uniform and increases the ion yield by arranging a filament around the molecular beam and providing an electron reflecting electrode. That is.

The present invention will be explained below based on examples.

FIG. 2 is a schematic diagram of an embodiment of the molecular beam epitaxial growth apparatus according to the present invention, and FIG. 3 is an enlarged explanatory diagram of the ion generator of the apparatus shown in FIG.

In FIGS. 2 and 3, numerals 1 to 8 represent the same components as shown in FIG. 1.

Reference numeral 17 denotes an ion generator according to the present invention, which is used for ion doping.

18 is an ejection cell for molecular beam evaporation source material, 19 is a D heater for heating the ejection cell 18, 20 is a molecular beam ejected from the ejection cell 18, 21 is a filament for electron beam emission, and 22 is a cylindrical , 23 is a cylindrical electron reflecting electrode, 24 to 27 are power sources for applying voltage to each part, and 28 is a metal structure that houses the filament 21, the grid 22, and the electron reflecting electrode 23, and is cooled with liquid nitrogen. The container 29 is an ion beam.

Here, the filament 21 is placed in the space between the cylindrical grid 22 and the cylindrical electron reflecting electrode 23.
are arranged around.

Next, the operation of the above embodiment device will be explained.

The operation of growing the host crystal by molecular beam epitaxial growth is the same as that of the conventional apparatus, so we will not explain it again. explain.

Zn is used as an evaporation source material in the ejection cell 18 shown in FIG.
The ejection cell 18 is heated by the heater 19.
heat up.

A molecular beam 20 made of Zn is generated from the heated ejection cell 18 .

With respect to the electron reflecting electrode 23, the filament 21 is set to about +50V and the grid 22 is set to about +200V by the power supply 25.26.
When the electric potential is set to , electrons emitted from the filament 21 heated by the power supply 24 collide with the molecular beam 20 made of Zn while repeating reciprocating motion in the electron reflecting electrode 23 and ionize the Zn.

The ionized Zn is pulled out by the potential of the container 28 (earth potential), becomes an ion beam 29, is accelerated by the ion acceleration electrode 12, and is irradiated onto the base 7, where it is incorporated into the host crystal and doped as a P-type impurity. be done.

In the above operation, since the electrons from the filament 21 are reciprocating within the electron reflecting electrode 23, the traveling distance of the electrons becomes longer and the ion yield increases.

Moreover, since the filament 21 is arranged surrounding the cylindrical grid 22, it is uniformly ionized within the space surrounded by the grid 22, so that the ion generator 17
The spatial distribution of the ion beam 29 pulled out from the ion beam becomes axially symmetrical and uniform around the ion beam, and the host crystal on the substrate 7 is uniformly doped.

In the above embodiment, the case where the host crystal on the substrate is doped with the ion beam pulled out from the ion generator is explained, but the ion generator according to the present invention can also be used to create the host crystal with the ion beam. Needless to say, the device can be used.

As detailed above, in the molecular beam epitaxial growth apparatus according to the present invention, by housing the ejection cell, filament, grid, and electron reflecting electrode in a container cooled with liquid nitrogen, excess neutral molecular beams can be removed. Since it is possible to prevent the molecular beam from reaching the epitaxial growth substrate, it is possible to create a molecular beam epitaxial growth layer with a mirror surface.

Furthermore, since the filament is placed between the grid and the electron reflecting electrode, both of which are cylindrical, so as to surround the grid, the yield of ions is increased and the spatial distribution of ions in the ion beam is uniform.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an example of a conventional molecular beam epitaxial growth apparatus, Fig. 2 is a schematic diagram of an embodiment of a molecular beam epitaxial growth apparatus according to the present invention, and Fig. 3 is an enlarged explanatory diagram of an ion generator of the embodiment apparatus. It is. In the figure, 18 is an ejection cell, 20 is a molecular beam, 21 is a filament, 22 is a grid, 23 is an electron reflecting electrode, 2
8 is a container, and 29 is an ion beam. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An ejection cell that accommodates an element of the evaporation source material and ejects a molecular beam made of this element, a cylindrical grid arranged so as to surround the molecular beam, and an electron emitting cell arranged surrounding the grid. A filament, a cylindrical electron reflecting electrode surrounding the filament, the ejection cell, the grid, the filament, and the electron reflecting electrode, and is formed by ionizing constituent elements of the molecular beam. A molecular beam epitaxial growth apparatus comprising an ion generating apparatus including a container having an ion beam injection port and cooled with liquid nitrogen.