Coating processes – Coating by vapor – gas – or smoke – Mixture of vapors or gases utilized
Reexamination Certificate
2003-02-13
2004-12-28
Lund, Jeffrie R. (Department: 1763)
Coating processes
Coating by vapor, gas, or smoke
Mixture of vapors or gases utilized
C427S294000, C427S248100
Reexamination Certificate
active
06835416
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for growing thin films on a surface of a substrate. More particularly, the present invention relates to an apparatus for producing thin films on a surface of a substrate by subjecting the substrate to alternately repeated surface reactions of vapor-phase reactants.
DISCUSSION OF RELATED ART AND SUMMARY OF THE INVENTION
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 organometallic CVD and plasma-enhanced CVD) or a deposition method of alternately repeated surface reactions called the Atomic Layer Epitaxy (ALE) or Atomic Layer Deposition (ALD).
In MBE and CVD methods, the thin film growth rate is determined by the concentrations of the provided starting material in addition to other process variables.
To achieve a uniform thickness of the layers deposited by these methods, the concentrations and reactivities of starting materials must be carefully kept constant on different surface areas of the substrate. If the different 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, a risk of microparticle formation already within the infeed channels of the gaseous reactants is imminent. Such microparticles generally have a deteriorating effect on the quality of the deposited thin film. Therefore, the possibility of premature reactions in MBE and CVD reactors, for instance, 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 discharge or other similar activating means.
In the MBE and CVD processes, the growth of thin films is primarily adjusted by controlling the infeed rates of starting materials impinging on the substrate. In contrast, the growth rate in the ALE process is controlled by the substrate surface qualities, rather than the starting material concentrations or flow variables. The only prerequisite in the ALE process is that the starting material is available in sufficient concentration to saturate the surface of the substrate. The ALE method is described, for example, in FI patent publications 52,359 and 57,975 and in U.S. patent publications 4,058,430 and 4,389,973. Equipment constructions suited to implement this method are disclosed in patent publications U.S. Pat. No. 5,855,680 and FI 100,409. Apparatuses for growing thin films are also described in the following publications: Material Science Report 4(7) (1989), p. 261, and Tyhjiötekniikka (Finnish publication for vacuum techniques), ISBN 951-794-422-5, pp. 253-261. These references are incorporated herein by reference.
In the ALE growth method described in FI Pat. No. 57,975, the reactant atoms or molecules are arranged to sweep over the substrates, thus impinging on their surface until a fully saturated molecular layer is formed thereon. Next, the excess reactant and the gaseous reaction products are removed from the substrates with the help of inert gas pulses passed over the substrates or, alternatively, by pumping the reaction space to a vacuum before the next gaseous pulse of a different reactant is admitted. The succession of the different gaseous reactant pulses and the diffusion barriers formed by the separating inert gas pulses or cycles of vacuum pumping result in a thin film growth controlled by the individual surface-chemical reactions of all these components. If necessary, the effect of the vacuum pumping cycle may be augmented by the inert gas flow. For the function of the process, it is typically irrelevant whether the gaseous reactants or the substrates are kept in motion; it only matters to keep the different reactants of the successive reactions separate from each other and to have them sweep successively over the substrate.
Most vacuum evaporators operate on the so-called “single-shot” principle. Hereby, a vaporized atom or molecule can impinge on the substrate only once. If no reaction with the substrate surface occurs, the atom/molecule is rebound or revaporized so as to hit the apparatus walls or the vacuum pump, undergoing condensation therein. In hot-walled reactors, an atom or molecule that collides with the process chamber wall or the substrate can undergo revaporization and, hence, repeated impingements on the substrate. When applied to ALE process chambers, this “multi-shot” principle can offer a number of benefits including improved efficiency of material consumption.
ALE reactions operating on the “multi-shot” principle generally are designed for the use of a cassette unit in which a plurality of substrates can be taken simultaneously into the process chamber or, alternatively, the substrates can be placed unmountedly into the process space formed by a pressure vessel, whereby the process space also serves as the reaction chamber wherein the vapor-phase reactants are reacted with the substrate surface in order to grow thin film structures. If a cassette unit designed for holding several substrates is employed, the reaction chamber is formed in the interior of the cassette unit. Use of a cassette unit shortens the growth time per substrate in respect to single-substrate cycling, whereby a higher production throughput is attained. Furthermore, a cassette unit arranged to be movable into and out from the process chamber can be dismantled and cleaned without interrupting the production flow because one cassette unit can be used in the process chamber while another one is being cleaned.
Batch processing is preferred in conventional ALE thin film processes because of the relatively slow production pace of the ALE method relative to other thin film growth techniques. The overall growth time per substrate of a thin film structure can be reduced in a batch process to a more competitive level. For the same reason, larger substrate sizes are also preferred.
In one embodiment of the ALE technique, the framework of the cassette unit is formed by a holder box made from titanium, for instance, having a structure with open top and bottom ends, whereby the holder box can support a plurality of substrates inserted therein into a longitudinally parallel position. The substrates have their ends or perimeters mounted in frames that are further placed into grooves formed at opposite ends of the substrate holder box. Each substrate frame has two substrates mounted therein with the back sides of the substrates facing each other. Herein, the back side of a substrate refers to that face of the substrate on which no thin film is to be grown. The access of reactants into any space that remains between the back sides of the substrates is prevented by covering the longitudinal top and bottom edges of the substrates with protecting continuous seal sections. The reactants and the inert gas are passed into the holder box via the infeed holes of the parallel infeed channels of a sprayhead manifold located above the holder box. Of course, the sprayhead construction may be varied as required. The excess reactants and reaction gases are removed from the holder box via discharge channels of a suction box connected to, at the bottom part of the holder box. In this manner, the gases are forced to flow through the spaces remaining between the faces of the substrates on which a thin film is to be grown.
Feeding the gaseous reactants into the holder box from one end only may cause stronger film growth on substrate surface areas located closer to the infeed of reactants. In order to compensate for this effect, the gases can be fed onto the substrates alternately from opposite directions. In such an arrangement, the exhaust suction through the outfeed channel are typically arranged to also take place alternately at opposite ends. Due to the alternating infeed cycles, infeed/discharge nozzles must be located at both th
ASM International N.V.
Knobbe Martens & Olson Bear LLP.
Lund Jeffrie R.
LandOfFree
Apparatus for growing thin films does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for growing thin films, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for growing thin films will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3304835