Coating apparatus – Gas or vapor deposition
Patent
1989-02-24
1991-02-12
Morgenstern, Norman
Coating apparatus
Gas or vapor deposition
118719, 118728, 118733, C23C 1600
Patent
active
049915401
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Background of the Invention
The present invention relates to a reactor for MOCVD (metal oxide vapor deposition) systems having a reaction vessel, through which the reactant gas or gases flow and in which the substrates are arranged in such a manner that a main surface is approximately parallel to the flow direction.
State of the Art
The problem, in general, with the known reactors hereto is that a diffusion boundary layer forms between the reactant gas flow and the substrates, the distance of which increases from the substrate surface with increasing distance from the entrance side end of the reaction vessel. By this means the uniformity of the produced layers is diminished.
In accordance with the present invention, it was discovered that the problem with the diffusion boundary layer, the distance of which increases in the flow direction, can be solved by having the reactant gases flow past the substrates with high flow velocity. A boundary layer is yielded by this means that runs practically parallel to and at a little distance from the main surface of the substrates.
Furthermore, low pressure in the range between 10 and 1000 mbar should be worked with in order to keep the material use at a minimum.
However, an inventive element is that it was discovered that raising the flow velocity and, if required, lowering the overall pressure does not suffice in the prior art reactors having a round cross-section as vortices, etc., occur in the known reactors which hinder the formation of uniform mixed crystal layers.
DESCRIPTION OF THE INVENTION
The object of the present invention is to improve a reactor for MOCVD systems having a reaction vessel, through which the reactant gas or gases flow in which the substrates area is arranged in such manner that a main surface is approximately parallel to the flow direction, in such a way that uniform flow conditions are obtained with high flow velocities and, if required, low pressure without demanding complicated and elaborate equipment.
An inventive feature is that the reaction vessel is made of quartz-glass in an as such known manner and has a rectangular cross-section at least in that region where the reactant gases flow in. By this means, the same flow conditions are obtained over the cross-sectional dimensions of the substrates.
As rectangular tubes made of quartz-glass are not very sturdy under pressure diffences like those occuring during tube evacuation, a protective tube surrounding the reaction vessel is provided. This protective tube has a face-end reactant gas inlet which is connected to a flange element to which a flange element attached to the reaction vessel can be flanged. By this means, there is a smooth flow channel from the flange of the protective tube into the interior of the reaction vessel, in which, if required, the adaption of the round cross-section of the flange to the rectangular cross-section of the reaction vessel in the substrates can take place without dead volume occuring which would prevent rapid "switching" of different reactant gases.
In order to facilitate handling as well as production and, in particular, also to reduce the danger of glass breakage due to differences in temperature, the reaction vessel is firmly connected with the protective tube only on one side. To prevent reactant gases from escaping in such a construction from the reaction vessel and precipitating on the (colder) wall of the protective tube, a purging of the intermediate space reaction vessel/protective tube is provided. For this purpose, there is a protective gas inlet at the superficies, which permits purging the space between the reaction vessel and the protective tube, and a reactant gas outlet. The reactant gases are deflected in the reaction vessel and exit via an opening in the reactant vessel corresponding to the reactant gas outlet. The diffusion barrier provided at the end of the reaction vessel opposite the gas-entrance-side end prevents the reactant gases from escaping into the protective tube. In an embodiment of the invention a su
REFERENCES:
patent: 3750620 (1973-07-01), Eversteijn et al.
patent: 4081313 (1978-03-01), McNeilly et al.
patent: 4266507 (1981-05-01), Satoh
Heyen Meino
Jurgensen Holger
Aixtron GmbH
Morgenstern Norman
Owens Terry J.
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