Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2003-07-10
2004-06-29
Ghyka, Alexander (Department: 2812)
Coating apparatus
Gas or vapor deposition
With treating means
C118S7230ER, C118S733000
Reexamination Certificate
active
06755151
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a new thin film deposition method and a new deposition apparatus that employs a heated coiled filament and multiple gas inlets. At least one inlet directs at least one type of suitable reactant gas, or gases, into a gas confinement cup contained with a chamber such that the gases pass through the heated coiled filament. The method of the present invention is used to deposit advanced thin films at both a high quality and at high deposition rate. Hot-filament process is used to deposit semiconductor materials with improved materials properties onto desired substrates.
BACKGROUND OF THE INVENTION
Thin film semi-conductors are useful in a variety of electronic devices such as solar panels, liquid crystal displays and other related technologies. One method for making these thin semi-conductors, such as amorphous silicon or microcrystalline silicon, is to deposit a thin film onto a suitable substrate using a chemical vapor deposition (CVD) process. The most commonly used CVD method to deposit amorphous or microcrystalline silicon is plasma enhanced chemical vapor deposition (PECVD). However, such a PECVD method leads to low rate of film deposition.
An alternative chemical vapor deposition process that leads to a higher deposition rate is a hot-wire chemical vapor deposition (HW CVD) process which uses a thin foil or small metal diameter wire filament as the hot-element of the process. The element, which can comprise tungsten, tantalum or molybdenum, for example, is heated to a high temperature and a gas is caused to flow over or into contact with the hot filament. The hot filament breaks down the gas into its constituents. These constituents then are deposited on an adjacent substrate.
However, there are many drawbacks associated with these conventional hot-wire chemical vapor deposition processes. Several groups have studied the use of hot-wire CVD process to deposit advanced thin films such as amorphous silicon based films. Mahan et al. (U.S. Pat. Nos. 5,397,737, 5,776,819), Iwancizko et al. (U.S. Pat. No. 6,251,183), Madan et al. (U.S. Pat. No. 6,214,706), and Molenbroek at al. (U.S. Pat. No. 6,124,186) deposited films using a hot-wire process that employs a wire spanning within the chamber to dissociate gases introduced into the chamber. However, the rate of deposition for this method is typically less than 50 A/sec. In addition, due to the lack of high controllability of the concentration of radicals, these methods have failed to produce amorphous silicon based solar cells with efficiency comparable to state-of-the-art solar cells produced using PECVD method.
Ichikawa M., Takeshita, J., Yamada, A., and Kongal, M., Jpn J. Appl. Phys. 38, L24 (1999) used a coiled hot-filament near the gas inlet to deposit polycrystalline silicon and microcrystalline silicon materials. Although such a filament design could, in theory, lead to a higher deposition rate, it has failed to be used to produce photovoltaic devices with reasonable efficiency. This is again due to the lack of sufficient control of the concentrations of reactive species in the reactor. For example, during the deposition of amorphous silicon, there are significant amounts of the Si, SiH, and SiH
2
species in the mixture, while the species responsible for high-quality film is believed to be the SiH3 species.
Yu, S., Gulari, E., and Kanicki, J., Appl. Phys. Lett, 68, 2681 (1996) used a filament spanning inside the chamber plus a gas dispersal ring closer to the substrate to deposit large-grain size polycrystalline silicon for application in flat panel displays. However, high quality film suitabl for flat panel display device application or photovoltaic application could not be demonstrated using this method. As indicated above, all of these methods do not allow practioners to achieve high controllability of the concentration of radicals, and, therefore are difficult to use to produce high quality thin film materials such as amorphous silicon based materials for high-efficiency photovoltaic applications. Further, the rates of deposition that are achieved using HW CVD with span filaments inside the chamber are not sufficiently acceptable, and therefore, add to the cost of manufacturing useful products.
Therefore, there is needed in the art of hot-wire chemical vapor deposition processes a method and an apparatus which provide improved deposition results and at an increased deposition rate.
There is a further need to provide a method and an apparatus to increase the efficiency of deposition of a desired element onto a substrate.
There is a further need for an apparatus which avoids contamination during the deposition process.
Further, there is a need for a commercially practical hot-wire chemical vapor deposition process which is reliable in a manufacturing setting.
It is also desirable to have an improved method to produce amorphous silicon and microcrystalline silicon products having improved properties.
DESCRIPTION OF THE INVENTION
This invention relates generally to apparatus and method for hot-filament chemical vapor deposition of thin film material onto a substrate, and more particularly, to a novel apparatus and method for depositing advanced thin films and coatings for use in a broad range of applications including photovoltaic devices, thin film transistors, as color plasma display panels and hard coatings for tools.
Until the present invention, no one had thought to combine the advantages of using hot-wire coil filament and using multiple gas inlets to produce high quality semi conductors. The hot-wire coil filament is employed to achieve a most-efficient excitation and/or disassociation of the gas. The gas is directed into the reactor near the coiled filament, thus, achieving a high deposition rate. According to the present invention, at least one suitable reactant gas is directed into the reactor through inlets near the substrates (and not near the filament). This gas can be remotely (i.e., not directly) excited by the gas species which are introduced from inlets near the filament. Such a combination allows for maximum control of reactive species inside the deposition chamber. This method is useful to deposit various films with desirable optoelectronic and mechanical properties that are ideal for use in a broad range of devices.
According to certain methods of the present invention, a-Si thin films are deposited at a rate at least about 400 to at least about 800 A/sec, which is a factor of 100 to 200 times faster than currently used processes.
The hot-wire deposition system of the present invention includes an apparatus for and a method for a hot filament chemical vapor deposition process. The apparatus includes at least one coiled hot filament in a chemical vapor deposition (CVD) chamber. Such a system is useful for the fabrication of high efficiency amorphous silicon based solar cells at a high rate. The hot-wire CVD process is especially useful for the deposition of 1) high quality a-Si (amorphous silicon), and a-SiGe (amorphous silicon germanium) materials at high deposition rates, 2) high quality poly-Si (polycrystalline silicon) and &mgr;c-Si (microcrystalline silicon) films for the narrow bandgap absorber layer, and 3) high-quality diamond-like carbon coatings.
In one aspect, the present invention relates to a method for the deposition of a thin film material on a substrate which includes:
providing a deposition chamber and a substrate in the deposition chamber,
applying a vacuum for evacuating the deposition chamber to a sub-atmospheric pressure,
heating a dense hot filament to about 1500 C. or higher,
introducing at least one first reactant gas into at least one first gas inlet, the first gas inlet being adjacent the dense filament, and
introducing at least one second gas into at least one second gas inlet, the at least one second gas inlet being in a spaced apart relationship to the dense filament, and, in certain embodiments, adjacent the substrate.
In another aspect, the method can include at least one further step of heating the substrate to a temp
Deng Xunming
Povolny Henry S.
Emch, Schaffer, Schaub & Porcello & Co., L.P.A.
Ghyka Alexander
The University of Toledo
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