Coating processes – Coating by vapor – gas – or smoke
Patent
1996-06-17
1999-08-31
Lusignan, Michael
Coating processes
Coating by vapor, gas, or smoke
4272551, 118725, C23C 1600
Patent
active
059451629
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a device for depositing thin layers by chemical vapor deposition (CVD), possibly by low pressure chemical vapor deposition (LPCVD).
2. Discussion of the Related Art
According to a so-called CVD method, the chemical elements to be deposited are conveyed directly or in the form of gas compounds (precursors) to a deposition chamber where is placed a substrate on which deposition must be achieved. The mixture is introduced into an area where the reaction occurs, activated by an energy input (temperature increase, plasma, photons, and so on), the reaction generally provides only a single solid compound. Gas residues are evacuated outside of the reactor. ##STR1##
The method generally uses as many sources as elements present in the compound to synthesize. One or more carrier gases, which may be neutral or may participate to the reaction, convey the precursor vapors up to the deposition area.
In the CVD method, one of the problems encountered is the introduction of precursors into the deposition chamber.
FIG. 1 schematically illustrates the problem to solve. A chamber 1 is maintained at a temperature and at a pressure adapted to the deposition on a substrate 2, which is generally heated. One or more pipes 3 lead into the airtight chamber for introducing diluent or reactive carrier gases and pipes 4, 5, 6 for introducing gaseous precursors into the airtight chamber.
If precursors are initially gaseous at room temperature, there are few problems. If the precursors are in liquid or solid phase, it is necessary to heat them in tanks 7, 8, 9 to volatilize them and therefore to obtain a sufficient vapor pressure in order to convey the material by a carrier gas.
In the particular case where one or more solid or liquid sources are used, it is necessary to perfectly stabilize the temperature and the flow of the carrier gas of each source to set the composition of the deposition. Thus, for a compound including n elements, the temperature and the flow of each source must be controlled, i.e., 2n parameters. In addition, when a solid in the form of a powder is heated to be vaporized, its evaporation surface may often be blocked by impurities or by oxidation by humidity traces in the carrier gas, which causes the surface to change and the performance to be unsteady. This surface also varies while the solid source is consumed. Furthermore, in the case of solids having very high sublimation temperatures, this temperature must be maintained in the whole pipe between the source and the chamber. This raises several problems, i.e., basic problems as regards the possible decomposition of unsteady precursors in the source or in the path between the source and the deposition chamber, and technical problems for the fabrication of valves adapted to withstand high temperatures.
Several solutions have been proposed in the prior art to overcome these problems.
A first solution consists of regularly taking small amounts of precursor powder in the solid phase and introducing them directly into the evaporator where they are immediately evaporated. This method enables one to obtain a controlled vapor flow even with thermally unsteady precursors because only the small amount of precursor is heated at high temperature in the deposition chamber after introduction into this chamber. However it is clear that the method has the following drawbacks.
It is difficult to accurately measure the injection of regular powder amounts. This requires a perfect control of the granulometry and the fabrication of a device capable of injecting micro amounts of powders (some 10.sup.-6 grams of powder per injection).
The devices for measuring powders are not accurate enough to allow the use of several solid injectors in parallel to synthesize compounds comprising several elements. In order to simultaneously inject several precursors, it is necessary to use mixtures comprising perfectly homogeneous powders (both for the composition and for the particle size distribution
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Abrutis Adulfas
Madar Roland
Senateur Jean-Pierre
Thomas Olivier
Weiss Francois
Centre National de la Recherche Scientifique
Chen Bret
Lusignan Michael
Plevy Arthur L.
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