JPS6065792A - Molecular beam crystal growth apparatus - Google Patents

Abstract

PURPOSE:To enable the stable irradiation with molecular beam at a definite intensity until the irradiation source material is consumed, by using the titled apparatus furnished with a molecular beam source cell encircled with a liquid nitrogen shroud, wherein said source cell is heated at the opening end with a heater. CONSTITUTION:Liquid nitrogen is discharged from the liquid nitrogen shroud 2 to restore the beam source cell 1 to the room temperature. The shutter 3 is opened, the heater 5 is heated e.g. at 350 deg.C, and the state is maintained until e.g. to deposited As is consumed by evaporation. To prevent the contamination of the molecular beam source cell 1 with e.g. the evaporated and readsorbed As, the heater at the beam source cell is heated to e.g. about 250 deg.C. The mounting of the heater 12 at the inner surface of the liquid nitrogen shroud enables the prevention of the thermal adhesion of the beam source cell to the liquid nitrogen shroud by the attached deposit, the elimination of the lowering of the molecular beam intensity, and the irradiation with stable molecular beam having a definite intensity until the irradiation source material is consumed.

Description

Detailed Description of the Invention (a) Technical Field of the Invention The present invention relates to a molecular beam epitaxial growth apparatus for irradiating a semiconductor substrate with a molecular beam to deposit a compound semiconductor thin film, etc.
In particular, the present invention relates to a molecular beam crystal growth apparatus capable of removing molecular beams deposited in a liquid nitrogen sheroud.

(b) Problems with the prior art In this type of molecular beam crystal growth apparatus, a substrate is held in an ultra-high vacuum belljar apparatus, which can be heated to several hundred degrees Celsius, and the molecular beam crystal growth apparatus Place a source cell that generates radiation.

The source cell portion is equipped with a liquid nitrogen shroud to adsorb impurity gas generated from the source cell or residual impurity gas within the bell jar in order to improve the degree of vacuum in the bell jar during film formation.

However, the shroud does not contain impurity gas,
The molecular beam emitted from the source cell is also adsorbed.

For example, when forming a film of GaAs or AlGaAs, a large amount of arsenic As molecular beam is generated (irradiated), so a large amount of As is adsorbed and deposited on the wall of the liquid nitrogen shroud surrounding the source cell. There is no gap around the open end of the shroud wall 9 and the two are in thermal contact.

In particular, in a molecular beam source cell such as As or phosphorus (I) which is operated at a relatively low temperature, irradiated molecular beams tend to accumulate.

However, in the thermal contact state, even if the radiation source cell is heated, heat escapes to the sheroud wall, and the cell temperature does not reach a predetermined temperature, making it difficult to obtain the desired molecular beam intensity. In addition, the work of removing As to repair this is extremely dangerous as As scatters into the surrounding area.

(C) Purpose of the invention An object of the present invention is to solve the above-mentioned problems.

The present invention provides a removal means that heats a localized portion of the liquid nitrogen shroud to evaporate deposits before the source cell and the liquid nitrogen shroud come into thermal contact.

(d) Structure of the Invention The above object provides a molecular beam crystal growth apparatus comprising a molecular beam source cell surrounded by a liquid nitrogen shroud.

This is achieved by providing a heater that heats the open end of the radiation source cell.

(e) Embodiments of the Invention An embodiment of the structure of the radiation source cell of the present invention in a nine-molecular beam crystal growth apparatus will be described in detail below with reference to FIG.

The figures are a simplified cross-sectional view (a) of the molecular beam source cell cut along the cell axis, and a front view (b) seen from the cell opening side in figure (a).

(a) In the figure, 1 is layered boron nitride (PB
A radiation source cell surrounded by N) and containing a built-in irradiation source.

2. A liquid nitrogen shroud surrounding the source cell 1.

3 is a shutter on the open end side of the source cell; 4 is a lead wire of a heater for generating molecular beams led out behind the source cell 1; and a lead wire of a thermocouple for measuring the operating temperature of the heater; and 5 is a source of radiation. This is a heater installation portion of the present invention provided on the inner circumferential surface of the liquid nitrogen shroud on the cell opening end side. The arranged heater section is connected to an external power source through a lead wire 6. Further, the lead wire 7 is a lead of a measuring thermocouple to the heater section 5.

(1) Figure 1 is a front view of the source cell opening, and as shown in Figure 2, the heater arrangement portion of the present invention provided on the inner circumferential surface of the liquid nitrogen shroud is clearly shown.

A method of removing deposits from the opening using the heater 5.

The case of an As irradiation source cell will be explained below as an example.

Extract liquid nitrogen from the liquid nitrogen shroud and return the source cell to room temperature. After opening the shutter, the heater section 5 is heated to 350° C., and this state is maintained until the ^S deposit evaporates and disappears.

However, during this time, the evaporated As is re-adsorbed on the 5-molecular beam source cell side. To avoid this, heat the heater on the radiation source cell side and maintain the temperature at about 250°C.

Re-adsorption contamination of the irradiation source can be prevented (irradiation source not shown).

By installing such a heater on the inner peripheral surface of the liquid nitrogen shroud, it is possible to prevent thermal contact between the radiation source cell and the liquid nitrogen shroud due to attached deposits.

(f) Effects of the invention As described above, if a molecular beam crystal growth apparatus having the radiation source cell structure of the present invention, which is explained in detail with reference to the embodiment drawings, is used, the molecular beam intensity due to contact with the liquid nitrogen sheroud, which has been a problem in the past, can be reduced. Stable molecular beam irradiation can be performed at a predetermined intensity until no deterioration occurs and the irradiation source material is used up.

[Brief explanation of the drawing]

FIG. 1 is a cell sectional view (A) and a front view (B) of the source cell opening side, showing an embodiment of the radiation source cell structure of the present invention. In the figure, l is a radiation source cell and 2 is a liquid nitrogen shroud. 3 is a shutter, 4 is a heater of the radiation source cell 1 and a lead wire for measuring the cell temperature, and 5 is a shield (resistance heating wire) portion of the present invention. Hee! Drunkenness G) 2

Claims (1)

[Claims] What is claimed is: 1. A molecular beam crystal growth apparatus comprising a molecular beam source cell surrounded by a liquid nitrogen shroud, further comprising a heater for heating an open end of the radiation source cell.