Apparatus for growing thin films

Details Apparatus for growing thin films Apparatus for growing thin films

1996-09-25

1999-01-05

Bueker, Richard

Coating apparatus

Gas or vapor deposition

Multizone chamber

118725, 118726, C23C 1600

Patent

active

058556800

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Background of the Invention
The present invention relates to an apparatus according to the preamble of claim 1 for growing thin films on a substrate, in which apparatus the substrate is subjected to alternately repeated surface reactions of vapor-phase reactants for the purpose of forming a solid-state thin film on the substrate through said surface reactions.
The apparatus comprises a reaction chamber pack into which the substrate can be placed, 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 chamber pack, reactant inflow channels suited for connecting the reactant sources to the reaction chamber pack, and outflow channels connected to the reaction chamber pack suited for removing the gaseous reaction products of the growth process and the excess reactants.
2. Related Art
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 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 method, or in short, ALE. In the MBE and CVD methods, the growth-rate-affecting process variables also include 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 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 mutual reaction arises. Then, the risk of microparticle formation already within the inflow channels ol 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 not 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 variables to control the deposition rate. The only prerequisite in the ALE process is that the starting material is available in sufficient concentration for 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. Nos. 4,058,430 and 4,389,973, in which also some apparatus embodiments suited to implement this method are disclosed. Equipment constructions for growing thin films are also to be found in the following publications: Thin Solid Films, 225 (1993), pp. 96-98, 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 continuously sweep over the substrates thus 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 starting material and the gaseous reaction products from above the substrate. The successive pulses of starting materials and diffusion barriers of inert gas separating the former accomplish the growth of the thin film at a rate controlled by the surface chemistry properties of the different

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