JPH034516A - Molecular beam source - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a molecular beam source for a molecular beam epitaxial apparatus for growing crystals of a semiconductor multilayer thin film structure such as a superlattice.

(Prior art) Molecular beam bipitaxial growth method C (hereinafter abbreviated as MBE method) is a technology in which a semiconductor substrate is irradiated with a molecular beam emitted from a molecular g source in a vacuum chamber to grow a semiconductor crystal film6. Semiconductor elements with excellent characteristics can be manufactured by using crystals with a multilayer thin film structure grown by the MBE method (thickness per layer ranges from several layers to several hundred layers).

In order to manufacture such a semiconductor crystal, it is necessary to precisely control the crystal growth rate and film thickness to desired values.

An example of a molecular beam epitaxial growth apparatus (hereinafter abbreviated as HBE apparatus) equipped with a conventional molecular beam source is explained with reference to the cross-sectional view shown in FIG.
For example, Ga and As molecular beam sources 102a, 102
b is installed, and a semiconductor substrate holder 104 holding a semiconductor substrate, for example, a GaAs substrate 103, is provided at a position facing the molecular beam source rib and the rib.

The molecular beam source (c) is the molecular beam material Ga105a.
, each crucible containing As 105b l06a, 10
6b, and each heater 1 for heating the molecular beam material.
07a.

107b, heat reflecting plates 108a and 108b, for example, A0, for improving thermal efficiency, thermocouples 109a and 109b for temperature control, plate-shaped shutters 110a and 110b for blocking molecular beams, and these. Shutter rotation shafts 111a and 111 that rotate the shutter
It is composed of b. The shutter plates 110a, 11
0b is a molecular beam injection port (opening) 116a of each crucible 106a, 106b.

116b is arranged parallel to these molecular beam exit ports (aperture planes).

The growth rate and film thickness are controlled by the following procedure in the above MBE apparatus. First, prior to this growth, experimental crystal growth is performed. After crystal growth, the crystal was removed from the apparatus, separated, and its cross section was etched to make it easier to see the growth layer boundaries, and then subjected to scanning electron microscopy (SEM).
The film thickness is measured using a method, and the growth rate is averaged and determined from the film thickness and growth time. Based on the growth rate, a growth time corresponding to the thickness of the crystal to be grown is calculated, and the crystal of the desired thickness is grown by opening and closing the shirt shirt plate.

FIG. 4 shows an example of the temporal change in the molecular beam intensity immediately after opening the shutter plate in a molecular beam source having the shutter plate as described above. It takes about 30 minutes for the molecular beam intensity to reach a constant value.
It takes minutes. The reason for this is that when the shutter plate is closed, the temperature of the surface of the molecular beam material increases due to the reflection of thermal radiation from the shutter plate, so the molecular beam intensity increases immediately after the shutter is opened, and then the inside of the crucible increases. By having a certain amount of time to reach thermal equilibrium.

Therefore, as explained in the above growth method, when controlling the film thickness based on the average growth rate, an error occurs between the set film thickness and the actually grown film thickness. In particular, when growing crystals with fine structures such as superlattice thin films, it is difficult to precisely control the film thickness.

(Problems to be Solved by the Invention) As mentioned above, the shatter plate is connected to the molecular beam injection port of the crucible (
In an MBE device arranged parallel to the opening plane), the molecular beam intensity fluctuates immediately after the shutter plate is opened, making it difficult to precisely control the film thickness.

The present invention has been made to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a molecular beam source having a shutter structure that allows growth of crystals having a fine structure with good controllability.

[Structure of the invention]

(Means for Solving the Problems) The molecular beam source according to the present invention is capable of intermittent molecular beams ejected from a crucible of the molecular beam source into a vacuum container using a shutter mechanism to irradiate a semiconductor substrate with semiconductor crystals of the semiconductor substrate. In a molecular beam source of a molecular beam epitaxial growth apparatus for growing a film, the shutter is in the shape of a bent tube, and one open end of the shutter rotates around a rotation axis other than the center axis, so that this open end becomes the molecular beam exit of the crucible. It is characterized by facing.

(Function) The present invention provides a molecular beam source in which a shutter for cutting off the molecular beam from the crucible of the molecular beam source to the semiconductor substrate is formed into a bent tube shape, and when the shutter is closed, the molecular beam exit port ( One open end was made to face the open end (opening surface), and the other open end was oriented in a direction different from that of the semiconductor substrate, so that the molecular beam would not be incident on the semiconductor substrate. With this configuration, it is possible to reduce the temperature rise on the surface of the molecular beam material due to thermal radiation caused by the shutter. This makes it possible to suppress fluctuations in the molecular beam intensity immediately after the shutter is opened, which has been a problem in the past.

(Embodiment) Hereinafter, an embodiment of the present invention will be explained with reference to the drawings (described in 2 degrees. In the explanation, parts that are the same as the conventional ones will be indicated with the same reference numerals as in the conventional drawings, and the explanation will be omitted. .

FIG. 1 shows a cross-sectional view of the main parts of a molecular beam epitaxial growth apparatus equipped with a molecular beam source according to the present invention when epitaxially growing GaAs.

As shown in FIG. 1, the improvements to the molecular beam sources 10a and 10b include a luppo 1060 containing the molecular beam material Ga 105a and a crucible 106b containing As 105b.
Immediately before each molecular beam exit port (opening surface) 1i6a, 116b, there is a shutter +1. a, llb is shutter rotation axis 1
2a and 12b. These shutters Ila and Ilb are all made of Mo, for example, and have a bent tube shape, and have shutter rotation axes 12a and 12b at the opening ends 21a and 21b, except for the central axes Xa and Xb. is attached, and one open end 21a is opened by rotation of the rotating shaft.

21b faces each molecular beam exit port (opening surface) of the crucibles 106a and 106b, and the other open ends 31a and 31b are oriented in a direction in which the molecular beam passing through the shutter does not enter the substrate, so that the molecular beam described above is Explain the functions of.

Shutter fla, 11. When b is closed, the evaporated molecules from the molecular beam materials 105a and 105b are transferred to the crucible 10.
Molecular beam injection port (opening) 116a of 6a, 106b
, 1], 6b, enters the interior through the open ends 2La, 21b of the shutters lla, llb, passes through the shutters, and is injected into the vacuum container. At this time, the shutter Ila,
Since Ilb is bent, it does not reach the GaAs substrate 103, and the shutter 1]a.

1] and b are tubular, so the temperature rise on the surface of the molecular beam material due to thermal radiation from the shutter is suppressed.

Therefore, when shutters lla and Ilb are opened,
Since the vapor pressure inside the Ruppo 106a, 106b hardly changes compared to when the Ruppo 106a and 106b are in the closed state, fluctuations in the molecular beam intensity immediately after opening are greatly reduced, as shown in FIG.

Note that the shape of the tube-shaped shutter is not limited to that shown in FIG. It will be clear from the above description that other shapes are possible as long as they are oriented in a direction that prevents them from reaching the substrate.

In addition, although the case of GaAs was described in this example,
It can also be applied to other crystal growths such as AQGaAs.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a molecular beam source that can suppress fluctuations in molecular beam intensity immediately after the shutter is opened and can precisely control the film thickness of a semiconductor crystal having a fine structure.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the main parts of an MBE apparatus for explaining an embodiment of the present invention, and FIG. 2 is a temporal change in molecular beam intensity immediately after the shutter is opened, measured in the embodiment shown in FIG. 1. A line diagram showing an example, FIG. 3 is a cross-sectional view of the main part of a conventional MBE apparatus, and FIG. 4 shows an example of the temporal change in molecular beam intensity immediately after the shutter is opened in the example shown in FIG. FIG. 10a, 10b... molecular beam source 11a, I],
b...Shutters 21a, 21b...One of the shutters G[, Xa, Xb...Central axis of the open end of the shunter +06a, 106b-crucible

Claims (1)

[Claims] In a molecular beam source of a molecular beam epitaxial growth system in which a semiconductor substrate is irradiated with a molecular beam emitted from a crucible of a molecular beam source in a vacuum chamber intermittently by a shutter mechanism to grow a semiconductor crystal film on the semiconductor substrate, the shutter is bent. A molecular beam source characterized in that the open end is rotated about a rotation axis other than the central axis of one open end, and the open end is opposed to the molecular beam injection port of the crucible.