Method and equipment for growing thin films

Details Method and equipment for growing thin films Method and equipment for growing thin films

1996-10-02

1998-01-27

Breneman, R. Bruce

Coating apparatus

Condition responsive control

Valve actuator

118725, 118715, C23C 1600

Patent

active

057118116

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
In the present method, a substrate located in a reaction space is subjected to alternately repeated surface reactions of at least two different reactants employed in the thin-film growth process. In the method, the reactants are admitted in vapor-phase repetitively and alternately each reactant from its own source into the reaction space, where the reactants are allowed to react with the substrate surface for the purpose of forming a solid-state thin film on the substrate. Reaction products not adhering to the substrate as well as possible excess reactants are removed in gas phase from the reaction space.
2. Related Art
Conventionally, thin-films are grown using vacuum evaporation deposition, the Molecular Beam Epitaxy (MBE) and other similar vacuum deposition methods, different variants of the Chemical Vapor Deposition (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 precursor inflows. To achieve a uniform thickness of the layers deposited by the first category of conventional methods, the concentrations and reactivities of precursors must hence be carefully kept constant all over the substrate area. If the different precursors 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 generally have a deteriorating effect on the quality of the thin film. Therefore, the possibility of premature reactions in MBE and CVD reactors is avoided by heating the precursors 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 precursors impinging tin the substrate. By contrast, the ALE process is based on allowing the substrate surface qualities rather than the precursor concentrations or flow variables to control the deposition rate. The only prerequisite in the ALE process is that the precursor is available in sufficient concentration for thin-film formation on all sides of the substrate.
The ALE method is described in the FI patent publications 52,359 and 57,975 and in the U.S. Pat. No. 4,058,430 and 4,389,973, in which also some equipment embodiments suited for implementing this method are disclosed. Equipment constructions for growing thin films are also to be found in the following publications: Material Science Reports 4(7) (1989), p. 261, and Tyhjiotekniikka (Finnish publication for vacuum techniques), ISBN 951-794-422-5, pp. 253-261.
In the ALE growth method, atoms or molecules are arranged to sweep over the substrates thus continuously impinging on their surface so that a fully saturated molecular layer is formed thereon. According to the conventional techniques known from the FI patent publication No. 57,975, the saturation step is followed by an inert gas pulse forming a diffusion barrier which sweeps away the excess precursor and the gaseous reaction products from above the substrate. The successive pulses of different precursors and of diffusion barriers of an inert gas separating the former accomplish the growth of the thin film at a rate controlled by the surface kinetics of the different materials. Such a reactor is called a "traveling-wave" reactor. For the function of the process it is irrelevant whether the gases or the substrates are moved, but rather, it is imperative that the different precursors of the successive reaction steps are separated from each other and arrang

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