Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2000-08-11
2002-10-15
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C156S345420
Reexamination Certificate
active
06463874
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to apparatus for the simultaneous physical vapor deposition (“PVD”) and chemical vapor deposition (“CVD”) of thin film material onto a substrate, and more particularly, to a novel apparatus for the simultaneous sputtering and microwave chemical vapor deposition of thin film material onto a substrate, most preferably an elongated web of substrate material.
BACKGROUND OF THE INVENTION
A variety of products may be fabricated by thin film processes. Examples of the products that may be fabricated by the deposition of thin film materials include interferometer stacks for optical control and solar control. An example of a solar control product is disclosed in U.S. Pat. No. 5,494,743 to Woodard, et al entitled “ANTIREFLECTION COATINGS”, the disclosure of which is incorporated herein by reference. More specifically, Woodard, et al disclose a polymeric substrate having antireflective coatings disposed thereon. The anti-reflective coatings consist of one or more inorganic metal compounds with indices of refraction higher than that of the polymeric substrate.
Thin film materials that are used for optical control an generally comprised of a series of layers of metals and dielectrics of varying dielectric constants and indices of refraction. These thin film materials may be used, for example, to reduce glare or reflection. Thin film materials may also be used as solar control films for low emission of infrared radiation in order to reduce the loss of heat.
In the manufacture of thin film materials for optical control, many interferometer stacks will have a top layer of silicon dioxide. An antireflective layer for a single layer of material having an index of refraction greater than 1.00 will have an index of refraction equal to the square root of the index of refraction of the single layer material. The thickness of the material calculated at the center wavelength of the frequency band at issue, more precisely, the optical thickness is ¼ of the wavelength at the center frequency. For example, the human eye generally sees light having a wavelength between 4000 Å and 7000 Å Therefore, the thickness of the optical coating for anti-reflection at 5500 Å is about 1375 Å Optical properties including the index of refraction and transparency as well as with the mechanical properties of silicon dioxide make it the material of choice for anti-reflective coatings.
A number of processes are currently utilized to deposit thin film materials, some of which are described in
Thin Film Processes
. John L. Vossen and Warner Kern, eds., Academic Press, Inc., New York, N.Y., 1978. The fundamentals of chemical vapor deposition are disclosed in Chapter III-2 of Thin Film Processes by Warner Kern and Vladimir S. Ban. Chemical vapor deposition, CVD, as a method of forming and depositing material causes the constituents of a gas or vapor phase of a material to form a product which is deposited on some surface. Therefore, the chemical reaction may be either endothermic or exothermic.
The reactants of a CVD process are the logical result of the stack design and are determined by the precursor materials. For example, if silicon dioxide (SiO
2
) is desired to be deposited, silane (SiH
4
) may be oxidized by oxygen (O
2
) to yield silicon dioxide as the desired product and a by-product of hydrogen (H
2
). Alternatively, silane may be decomposed to deposit an amorphous silicon alloy material on a substrate. For example, products may be formed by energizing the reactants to a reaction temperature. The reaction temperature may be achieved by any suitable method known in the art including R.F. glow discharge and electrical resistive heating. A CVD reaction may occur in a wide range of pressures from above an atmosphere to a less than a millitorr.
Low pressure CVD processes offer substantial advantages over CVD processes operating at about atmospheric pressure. The diffusity of a gas and the mean free path of gas molecules is inversely related to pressure. As the pressure is lowered from about atmospheric pressure to 1 torr, the effect is an increase of approximately 2 orders of magnitude in the diffusion constant. Commonly assigned, U.S. Pat. Nos. 4,517,223 and 4,504,518 to Ovshinsky, et al both entitled “METHOD OF MAKING AMORPHOUS SEMICONDUCTOR ALLOYS AND DEVICES USING MICROWAVE ENERGY”, the disclosures of which are incorporated herein by reference, described processes for the deposition of thin films onto a small area substrate in a low pressure, microwave glow discharge plasma. As specifically noted in these patents, operation in low pressure regimes not only eliminates powder and polymeric formations in the plasma, but also provide the most economic mode of plasma deposition.
A low pressure microwave initiated plasma process for depositing a photoconductive semiconductor thin film on a large area cylindrical substrate using a pair of radiative waveguide applicators in a high power process is disclosed in commonly assigned, U.S. Pat. No. 4,729,341 to Fournier, et al for “METHOD AND APPARATUS FOR MAKING ELECTROPHOTOGRAPHIC DEVICES”, the disclosure of which is incorporated herein by reference. However, the principles of large area deposition described in the '341 patent are limited to cylindrically shaped substrates and the teachings provided therein are not directly transferable to an elongated web of substrate material.
The use of a microwave radiating applicator has been extended to chemical vapor deposition onto an elongated web of substrate material in commonly assigned U.S. Pat. No. 4,893,584 to Doehler, et al for “LARGE AREA MICROWAVE PLASMA APPARATUS”, the disclosure of which is incorporated herein by reference. By optimizing the isolating window to withstand compressive forces, the thickness of the window may be minimized to provide for rapid thermal cooling, whereby the '584 patent achieves a high power density without cracking the window. Furthermore, by maintaining the apparatus of the '584 patent at subatmospheric pressures, it is possible to operate the apparatus at a pressure approximating that required for operation near the minimum of a modified Paschen curve. As disclosed in commonly assigned U.S. Pat. No. 4,504,518, a Paschen curve is the voltage needed to sustain a plasma at each pressure. A modified Paschen curve is related to the power required to sustain a plasma at each pressure. The normal operating range is dictated by the minimum of the curve. Additionally, the low pressures allow for a longer mean free path of travel for the plasma species, thereby contributing to overall plasma uniformity.
In a CVD process, a sufficient proportion of feedstock gases are provided to achieve a correct stoichiometric deposition of materials. An excellent method for chemical vapor deposition is disclosed in commonly assigned U.S. Pat. No. 5,411,591 to Izu, Dotter, Ovshinsky, and Hasegawa entitled “APPARATUS FOR THE SIMULTANEOUS MICROWAVE DEPOSITION OF THIN FILMS IN MULTIPLE DISCRETE ZONES”, the disclosure of which is incorporated by reference herein, Izu, et al disclose an apparatus for the microwave plasma enhanced chemical vapor deposition of thin film material onto a web of substrate material utilizing a linear microwave applicator. By maintaining the plasma region at subatmospheric pressures, a longer mean free path of travel for the plasma species is available, which contributes to the overall plasma uniformity.
In order to maintain a uniform plasma over a much wider substrate, about 1 meter or wider, spacing between the windows must be decreased. As the spacing between the windows of the linear applicator decrease, the potential for shorting increases. It is not possible to maintain a plasma if the linear applicator is prone to shorting. One advantage of a CVD process is the film deposition rate. The product formation rate in a CVD apparatus is related to the flow rate of the feedstock gases. As the rate of product formation increases, the deposition rate also increases. So long as enough energy is provided
Doehler Joachim
Dotter, II Buddie R.
Ellison Timothy
Izu Masatsugo
Ovshinsky Herbert C.
Energy Conversion Devices Inc.
Hassanzadeh P.
Mills Gregory
Watson Dean B.
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