JPS63215590A - Device for diffracting reflecting high-speed electron beam - Google Patents

Abstract

PURPOSE:To observe growth surface in situ in a state of revolving substrate crystal, by strengthening diffraction pattern of electron beam, radiated upon the surface of the substrate crystal, on a second electron intensifying face and forming an image on a fluorescent screen. CONSTITUTION:Substrate crystal 3 is supported on a manipulator 2 set in a growing chamber 6 of a molecular beam epitaxial growth device and DC voltage is impressed to a second electron intensifying face 5 laid on one side wall of the growing chamber 6. Then electron beam is radiated from an electron gun 1 set on another side wall of the growing chamber 6 to the surface of the crystal 3, diffracted on the surface of the crystal 3, introduced as an incident ray into the second intensifying face 5, strengthened by a factor of 10<7>-10<8> and a diffraction pattern is formed on a rear fluorescent screen 4. Then a DC high- voltage pulse is impressed to the second electron intensifying face 5 while being accurately synchronized with pattern from an arbitrary and accurately same position on the substrate 3 is intermittently formed on the screen 4 at each revolution of the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a reflection high-speed electron beam diffraction apparatus installed in a growth chamber of a molecular beam epitaxial growth apparatus for epitaxially growing thin film crystals.

[Prior Art] In order to evaluate a thin film crystal being grown in a molecular beam epitaxial (hereinafter referred to as MBE) growth apparatus, a reflective high-speed electron beam diffraction bag rI1. (hereinafter referred to as RHEED device) is used. FIG. 2 shows an example.

As shown in the figure, an electron beam emitted from an electron gun 1 is diffracted by the surface of a substrate crystal 3 held by a manipulator 2, producing a diffraction pattern on a fluorescent screen 4 reflecting the surface structure. Note that 6 is a growth chamber.

Since MBE growth is performed in an ultra-high vacuum, it has the excellent feature that the growing surface structure can be observed in situ by reflection electron diffraction during crystal growth.

On the other hand, recently, MBE growth apparatuses have come to be used not only for research purposes but also for preparation purposes. Therefore, it is necessary to increase the diameter of the substrate crystal and to make the epitaxial thin film highly uniform. Therefore, during crystal growth, in order to obtain uniform temperature distribution and uniform molecular beam intensity within the plane of the substrate, a method is usually adopted in which the substrate crystal is rotated.

However, in conventional RHEED devices, when the substrate crystal is rotated, the location on the substrate irradiated with the electron beam changes over time, so the electron beam diffraction pattern imaged on the screen changes continuously. Resulting in. Therefore, the conventional apparatus has the problem that the structure of the growth surface cannot be observed in situ by backscattered electron diffraction while the substrate is being rotated during crystal growth.

[Problems to be Solved] The present invention solves the drawbacks of the conventional RHEED lif,
Provides a means for continuously obtaining an electron beam diffraction pattern from any location on the substrate surface while the l&plate crystal is rotated,
This allows in-situ observation of the growing surface structure during growth.

The present invention will be explained below with reference to an embodiment shown in FIG. The same parts as in FIG. 2 are indicated by the same reference numerals.

In the growth chamber θ, a manipulator 2 is held by a rotating shaft (not shown), and a molecular beam source is placed below the manipulator 2 (not shown).

An electron gun 1 is attached to the side wall surface of the growth chamber 6.

The electron gun 1 is attached so that the electron beam emitted from the electron gun 1 is incident on the surface of a substrate crystal 3 held on the surface of a manipulator 2 at a slight angle of about 1 degree.

A secondary electron multiplier 5 is held at a position where the diffracted electron beam from the substrate crystal 3 reaches the side wall of the growth chamber 6, and a fluorescent screen 4 is placed behind it. A DC high voltage or a DC high voltage pulse is applied to the secondary electron multiplier 5 from a power source outside the growth chamber.

[Operation] The device of the present invention has the above-described configuration, and when a high DC voltage is applied to the secondary electron multiplier surface 5, electrons are emitted from the electron gun 1 and diffracted at the substrate crystal surface. When the emitted electron beam enters the secondary electron multiplier surface 5, the incident electrons are multiplied in a mouse formula by repeated secondary electron emission, and the number of electrons increases by 10' to 10@ times compared to a single electron. The number is multiplied. Therefore, a very bright electron diffraction pattern is imaged on the fluorescent screen 4 behind the secondary electron multiplier 5.

Such an image amplification effect occurs only when a DC high voltage is applied to the secondary electron multiplier 5.

Therefore, when a DC high voltage pulse is applied to the secondary electron multiplier 5 in precise synchronization with the rotation of the substrate crystal, only the electron beam diffraction pattern from exactly the same location for a given Δ on the substrate 3 becomes 1. Obtained intermittently with each rotation. Here, the time required for one rotation of the substrate 3 is about 2 seconds, and the diffraction pattern obtained on the fluorescent screen 4 by using the secondary electron multiplier surface 5 is so bright that it is visible to the naked eye due to afterimage development. , the diffraction patterns from the same location can be observed almost continuously.

[Example] GaAs (100
) A GaAs thin film with a thickness of 1 μm was grown on a substrate by molecular beam epitaxy, and the structure of the grown surface was observed for about 5 minutes after the start of growth using reflection high-speed electron diffraction according to the present invention. The substrate was rotated at 30 rpm during growth.

The electron accelerating voltage was 15 kV, and the secondary electron multiplier used was a chevron type multiplier consisting of two independent multiplier surfaces with a diameter of 3 inches (7, G2c)' stacked one on top of the other. Accurately synchronize with the rotation of the substrate during growth, and apply 900V to the secondary electron multiplier in the first stage.
A DC high voltage pulse of 1500 V was repeatedly applied at exactly 2 second intervals to the secondary electron multiplier in the second stage. DC high voltage pulses are applied to each secondary electron multiplier so that the front side, where the electron beam is incident, has a negative potential with respect to the rear side, and the rear side of the former stage and the front side of the latter stage are at the same potential. potential.

The degree of vacuum near the secondary electron multiplier during growth is approximately 1 × heavy o”
torr. By doing this, it was possible to continuously observe an electron beam diffraction pattern that reflected the structure of the growth surface during growth. By continuously observing the diffraction patterns from the [1103 direction and the [TIO] direction of the substrate, it was confirmed that the surface structure during growth was a C(2×8) superstructure.

Furthermore, the diffraction pattern during growth was that of a sliver tx, and the surface was two-dimensionally very flat, confirming that layer growth was occurring.

Furthermore, GaAs grown by rotating the manipulator
The uniformity of the thickness of the thin film within the substrate surface was ±1.2%.

On the other hand, without rotating the manipulator, GaAs
When the thin film was grown under the same conditions as above, it was confirmed that the uniformity within the substrate was ±18.6%.

[Effects of the Invention] As explained above, according to the apparatus of the present invention, during crystal growth, the structure of the growing surface can be observed in-situ using reflective high-speed electron diffraction while the substrate crystal is being rotated. It becomes possible. Therefore, a highly uniform epitaxial thin film can be grown on a large diameter substrate crystal while monitoring the structure of the growth surface.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the invention in cross-section. FIG. 2 shows a cross-sectional view of an example of a conventional device. DESCRIPTION OF SYMBOLS 1... Electron gun, 2... Manipulator, 3... Crystal substrate, 4... Fluorescent screen, 5... Secondary electron multiplier, 6... Growth chamber. Dice 1 Calculation 2 Diagram

Claims (1)

[Claims] (1) In a reflection high-speed electron diffraction device installed in the growth chamber of a molecular beam epitaxial growth device, an electron gun emits an electron beam onto the substrate crystal surface and images the diffraction pattern of the electron beam diffracted by the substrate crystal surface. and a secondary electron multiplication surface having a function of enhancing the brightness of the diffraction pattern and a gate function of limiting the time during which the diffraction pattern is obtained on the fluorescent screen. Electron beam diffraction device.