Coating processes – Coating by vapor – gas – or smoke – Mixture of vapors or gases utilized
Patent
1996-09-25
2000-01-18
Beck, Shrive
Coating processes
Coating by vapor, gas, or smoke
Mixture of vapors or gases utilized
42725528, 117 93, 117102, C23C 1600, C30B 2514
Patent
active
060155906
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for growing thin films on substrates placed in a reaction space and subjected to alternately repeated surface reactions of a least two vapor phase reactants.
In the present method, the substrate is typically located in a reaction space, wherein it in accordance with the Atomic Layer Epitaxy (ALE) method is subjected to alternately repeated surface reactions of at least two different reactants. According to the present method, the reactants are admitted repetitively and alternately each reactant at a time from its own source in the form of vapor-phase pulses into the reaction space. Here, the vapor-phase reactants are allowed to react with the substrate surface for the purpose of forming a solid-state thin film on the substrate.
While the method is most appropriately suited for producing so-called compound thin films using as the reactants such starting materials that contain component elements of the desired compound thin-film, it may also be applied to growing elemental thin films. Of compound films typically used in the art, reference can be made to ZnS films employed in electroluminescent displays, whereby such films are grown on a glass substrate using zinc sulfide and hydrogen sulfide as the reactants in the growth process. Of elemental thin films, reference can be made to silicon thin films.
The invention also concerns an apparatus comprising a reaction chamber with gas flow channels suited for an inflow of vapor phase reactant pulses and an outflow of reaction products, wherein at least a portion of the gas flow channels have a narrow, oblong cross section for minimizing the volume of the reaction space suited for producing thin films.
The apparatus comprises a reaction space into which the substrate can be placed, and at least two reactant sources from which the reactants used in the thin-film growth process can be fed in the form of vapor-phase pulses into the reaction space. The sources are connected to the reaction space via reactant inflow channels, and outflow channels are connected to the reaction space for removing
2. Related Art
The gaseous reaction products of the thin-film growth process as well as the excess reactants in vapor phase.
Conventionally, thin-films are grown using vacuum evaporation deposition, the Molecular Beam Epitaxy (MBE) and other vacuum deposition methods, different variants of the Chemical Vapor Dcposition (CVD) method, including low-pressure and metal-organic CVD and plasma-enhanced CVD, or alternatively, the above-described deposition method of alternately repeated surface reactions called the Atomic Layer Epitaxy (ALE) method. In the MBE and CVD methods, besides other process variables, the thin-film growth rate is also affected by the concentrations of the starting material inflows. To achieve a uniform thickness of the layers deposited by the first category of conventional methods, the concentrations and reactivities of starting materials must hence be carefully kept constant all over the substrate area. If the starting materials are allowed to mix with each other prior to reaching the substrate surface as is the case in the CVD method, for instance, a chance of their premature mutual reaction arises. Then, the risk of microparticle formation already within the inflow channels of the gaseous reactants is imminent. Such microparticles have a deteriorating effect on the quality of the thin film growth. Therefore, the possibility of premature reactions in MBE and CVD reactors is avoided by heating the starting materials no earlier than at the substrate surfaces. In addition to heating, the desired reaction can be initiated using, e.g., a plasma or other similar activating means.
In the MBE and CVD processes, the growth of thin films is primarily adjusted by controlling the inflow rates of starting materials impinging on the substrate. By contrast, the ALE process is based on allowing the substrate surface qualities rather than the starting material concentrations or flow
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Lindfors Sven
Suntola Tuomo
Beck Shrive
Chen Bret
Neste Oy
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