JPH0437909Y2 - - Google Patents

Description

[Detailed description of the invention] [Summary] This invention relates to molecular beam crystal growth devices, and in particular, to improving the monitoring mechanism for growing crystals, with the aim of correctly imaging the diffraction image of a reflection-type high-energy electron beam diffraction device. In a molecular beam crystal growth apparatus incorporating a reflection-type high-energy electron beam diffraction device, anti-static charge is provided at least around a passage near a liquid nitrogen shroud through which the emitted electron beam and reflected electron beam from the reflection-type high-energy electron beam diffraction device pass. The antistatic plate is surrounded by a plate, and the antistatic plate and the liquid nitrogen shroud are not in contact with each other.

[Industrial Field of Application] The present invention relates to a molecular beam crystal growth apparatus, and particularly to an improvement in a mechanism for monitoring growing crystals.

The epitaxy method of epitaxially growing a semiconductor film along a crystal substrate is known as a basic technology in semiconductor manufacturing. Molecular beam epitaxy has been developed as a notable technology for this epitaxy method, and this is a method of growing crystals of compound semiconductors by irradiating a metal source or metal compound source under ultra-high vacuum (10 Torr or less). It is used for.

In molecular beam crystal growth equipment that uses such molecular beam epitaxy, a method is adopted in which a crystal layer is grown while checking the crystallinity during crystal growth, and this checking must of course be performed accurately. Must be.

[Prior art] Figure 3 shows a reflective high energy electron diffraction device (RHEED).
This figure shows an overview of a molecular beam crystal growth (MBE) system incorporating a Diffraction system, in which 1 is a high vacuum growth chamber, 2 is a wafer (substrate to be grown), 3 is a substrate holder, 4 is a molecular beam source cell, and 5 is a The liquid nitrogen shroud 6 is a gate valve leading to the substrate preparation chamber. Further, 8 is an electron beam emitting unit, 9 is a fluorescent screen, and a viewing port 10 is provided behind the fluorescent screen 9.

With this configuration, a crystal layer is grown on the wafer surface by heating the wafer 2 and irradiating molecular beams from a plurality of molecular beam source cells provided at positions facing the wafer. For example, if the wafer is a GaAs substrate, it is heated to 600 to 700℃, and the surface of the substrate is
When growing a GaAs crystal layer, an As molecular beam source cell, a Ga molecular beam source cell, and other dopant molecular beam source cells are placed facing the wafer. Further, the liquid nitrogen shroud 5 is a cooling body for adsorbing impurities in the growth chamber and maintaining the growth region at an ultra-high vacuum.

When molecular beam epitaxial growth is performed on the wafer 2 using this crystal growth apparatus, RHEED is usually incorporated in order to continuously observe the crystallinity and growth rate of the grown layer. It consists of an electron beam emitting section 8 consisting of an extraction electrode and an electromagnetic coil, a fluorescent screen 9, and an observation section including a viewing window 10. The pattern is observed by irradiating the surface of the wafer with an electron beam emitted from an electron beam emitter 8, projecting a diffraction image of scattered electrons on a fluorescent screen 9, and observing the diffraction image through a viewing window 10 behind it. The quality of crystallinity is determined by this. In addition, the growth rate can be detected by observing the number of repetitions of brightness and darkness at the specular reflection point.

[Problems to be solved by the invention] Since the RHEED described above emits an electron beam onto the wafer surface and then reflects it from the wafer surface, there are electron beam emitters and fluorescent screens on both sides of the wafer. A hole is provided in the liquid nitrogen shroud 5 through which the electron beam passes.

However, the liquid nitrogen shroud 5 is cooled to an extremely low temperature called liquid nitrogen temperature, and its surface is covered with impurities such as As, which are cooled and become an insulator.

The insulator on the surface of the liquid nitrogen shroud 5 is
During RHEED operation, the electron beam is charged up, and this charge up affects and distorts the electron beam, causing a problem in which the diffraction image is distorted. In addition, if it is severe, an image may not appear on the fluorescent screen.

Conventionally, in order to reduce the distortion of this diffraction image, a method has been adopted to reduce the effect by increasing the hole diameter r provided in the liquid nitrogen shroud, but this conversely reduces the adsorption effect of the liquid nitrogen shroud. This is not very preferable from the viewpoint of crystal quality, as it lowers the degree of vacuum.

The present invention eliminates such distortion of the diffraction image,
This paper proposes a molecular beam crystal growth device that aims to produce accurate diffraction images.

[Means for Solving the Problems] The purpose is to provide a molecular beam crystal growth apparatus incorporating a reflection-type high-energy electron beam diffraction apparatus, in which emitted electron beams and reflected electron beams from the reflection-type high-energy electron beam diffraction apparatus are This is achieved by a molecular beam crystal growth apparatus in which an antistatic plate surrounds at least a passage near the liquid nitrogen shroud through which the antistatic plate passes, and the antistatic plate and the liquid nitrogen shroud are not in contact with each other.

[Function] That is, in order to avoid the influence of the insulator on the surface of the liquid nitrogen shroud, the present invention surrounds the electron beam path in the vicinity with an antistatic plate, and arranges it without contacting the liquid nitrogen shroud. Set up In this way, the electron beam will not be affected by charge up, and a distortion-free diffraction image can be imaged and observed.

[Examples] Hereinafter, examples will be described in detail with reference to the drawings.

Figure 1 shows a cross-sectional view of the molecular beam crystal growth apparatus according to the present invention, where e ₁ is an emitted electron beam, e ₂ is a reflected electron beam, 11 is an antistatic plate, and other tertiary elements.
Components that are the same as those in the figures are given the same symbols. That is,
An antistatic plate 11 surrounds the electron beam path, and is installed and grounded so as not to come into contact with the liquid nitrogen shroud. For example, the antistatic plate is made of a high melting point metal such as tantalum or molybdenum and is formed into a cylindrical shape and is screwed to a flange so as to be separated from the liquid nitrogen shroud. As such, if the antistatic plate is kept away from the liquid nitrogen shroud, the cooling heat will not be transferred by conduction, nor will it be transferred by radiation because it is in a vacuum. Even if impurities adhere to it, it will not become an insulator. Moreover, if this plate is grounded,
It is held at ground potential and does not charge up. It should be noted that since impurities are similarly deposited on the surface of this antistatic plate, there is a risk that the surface will become insulated over a long period of time.Therefore, it is desirable that the antistatic plate be installed in a way that it can be replaced.

Fig. 2 is a partial sectional view showing an example of the mounting method, in which 12 is a flange, 13 is a gasket, 14 is a screw, and the symbols of other parts are the same as in Fig. 1, but in this example, the screw 14 is used. It is attached to a flange that is grounded. If you do this,
Grounding is easy and plates can be easily replaced.

[Effects of the invention] As is clear from the description of the embodiments above, the molecular beam crystal growth apparatus equipped with the antistatic plate according to the invention allows diffraction images to be correctly imaged and observed. Correspondingly, a high quality crystal layer can be stably obtained. In addition, if the antistatic plate is precisely placed with respect to the emitted and reflected electron beams, the holes in the liquid nitrogen shroud do not need to be large, and the high vacuum growth chamber can be maintained at high vacuum, allowing the crystal layer to grow. This will further contribute to improving the quality of the products.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a molecular beam crystal growth apparatus according to the present invention, FIG. 2 is a partial sectional view of the attachment of an antistatic plate, and FIG. 3 is a sectional view of a conventional molecular beam crystal growth apparatus. In the figure, 1 is a high vacuum growth chamber, 2 is a wafer, 3 is a substrate holder, 4 is a molecular beam source cell, 5 is a liquid nitrogen shroud, 6 is a gate valve, 8 is an electron beam emitter, 9 is a fluorescent screen, 10 is a viewing window, 11 is an antistatic plate, 12 is a flange,
13 indicates a gasket, and 14 indicates a screw.

Claims (1)

[Scope of utility model registration request] In a molecular beam crystal growth apparatus incorporating a reflection-type high-energy electron beam diffraction device, anti-static charge is provided at least around a passage near a liquid nitrogen shroud through which the emitted electron beam and reflected electron beam from the reflection-type high-energy electron beam diffraction device pass. A molecular beam crystal growth apparatus characterized in that the antistatic plate is surrounded by a plate, and the antistatic plate and a liquid nitrogen shroud are not in contact with each other.