Patent Application
20100252602
This invention relates generally to valve structures used to isolate a region in a processing system. More specifically, the invention relates to a pinch valve which is operable to engage a web of substrate material in a vacuum deposition system and establish a high quality vacuum seal thereagainst.
The high volume production of large area semiconductor devices, such as photovoltaic devices, is often carried out in a continuous deposition process. In processes of this type, one or more webs of substrate material are continuously advanced from a payoff station through a series of deposition chambers wherein various layers of semiconductor material are deposited thereonto, and the substrates are then wound into rolls in a take-up chamber. The deposition process often includes high vacuum conditions. Periodically, it is necessary to halt the deposition process so as to remove the coated web or webs of substrate material from the take-up station and replace them with fresh web material in the payout station, while isolation of certain process areas is maintained. In the prior art, it is standard practice to vent the entire deposition system to atmospheric pressure when changing webs of substrate material. In most instances, deposition of the semiconductor materials takes place at elevated temperatures and it is also necessary to cool the entire apparatus to ambient temperatures prior to venting it and replacing the substrate web.
The steps of cooling, venting and subsequently pumping the system back down to low pressure conditions and reheating the deposition chambers is very time consuming. In addition, exposure to ambient atmospheric conditions can introduce moisture or other contaminants into the deposition system. Therefore, the prior art has attempted to find systems which would allow for replacement of substrate webs without requiring venting of the deposition chambers of the apparatus. Toward that end, the prior art has implemented pinch valve systems in which the substrate payout station and take-up station are provided with a valving assembly which closes against a portion of a halted substrate web retained therein. In this manner, the deposition chambers of the apparatus may be maintained under vacuum conditions with a portion of the length of the substrate therein. A new web of substrate material is joined to the halted substrate web by welding it or otherwise affixing it to a portion of the substrate web projecting from apparatus of the system. Following pump down of the substrate station, the pinch valve is opened and the deposition process resumed. Pinch valves used in a system of this type must be capable of maintaining a very good seal at a pressure differential of 1 atmosphere. Also, given the fact that mechanical tolerances and spatial clearances within continuous process deposition apparatus of this type are generally quite small and very precise, any such pinch valve must not significantly deform the substrate material so as to minimize jamming, misalignment or other undesirable effects when the apparatus is restarted.
The prior art has recognized the need for pinch valves of the type described and has implemented a number of embodiments. For example, U.S. Pat. No. 5,157,851 discloses a pinch valve comprised of two movable members which engage a base. U.S. Pat. No. 6,338,872 discloses a pinch valve in which a blade-like gate member pushes a substrate against a resilient, planar, support surface. A similar pinch valve incorporating a rubber plate is described in general terms in U.S. Pat. No. 5,824,566.
As will be explained in detail hereinbelow, the present invention provides a pinch valve which is simple in construction, reliable, and which is capable of engaging a substrate so as to provide a very high isolation seal without significantly deforming or damaging the substrate. These and other advantages of the invention will be apparent from the drawings, discussion and description which follow.
The present invention is directed to a pinch valve which includes a valve body having a slot defined therein. The slot is configured to allow a web of substrate material to pass through the pinch valve. The valve body has a sealing surface which includes a first curved portion having a first radius of curvature. The pinch valve includes a dynamic seal element having a sealing surface which includes a second curved portion having a second radius of curvature which is larger than the first radius of curvature. The pinch valve further includes an actuator for selectively biasing the dynamic seal element into and out of engagement with the valve body so that when the dynamic seal element is biased into engagement with the valve body the web of substrate material is engaged between the the sealing surfaces of the dynamic seal element and the valve body.
In particular embodiments of the invention, at least one of the valve body and the dynamic seal element has a resilient sealing member disposed upon at least a portion of its respective sealing surface. The resilient sealing member may be comprised of a silicone polymer, and in particular instances both the valve body and the dynamic seal element include a resilient sealing member disposed thereupon. In particular instances, the sealing surface of the valve body includes at least one planar segment extending from its first curved portion. In further instances, the sealing surface of the dynamic seal element includes at least one planar segment extending from its second curved portion. In some embodiments, the dynamic seal element includes a resilient sealing member having two different thicknesses.
The actuator, in some instances, may include an eccentric cam which operates to move a push rod which push rod biases the dynamic seal element into and out of engagement with the valve body. The biasing force exerted by the actuator may be in the range of 40-80 psi. In specific embodiments, the pinch valve is characterized in that at a pressure differential of 1 atmosphere maintained thereacross. In another instance, the pinch valve manifests a leak rate which is in the range of 5×10−5 to 5×10−9 torr liter/minute. In certain instances, the leak rate is no more than 5×10−7 torr liter/minute.
Also disclosed is a system for depositing a semiconductor material onto a web of substrate material in a continuous roll-to-roll process, which system includes at least one of the pinch valves. In specific embodiments, the deposition system is a multiple web system for simultaneously depositing a material onto a plurality of webs moving therethrough. Specifically disclosed is a multi-web pinch valve which may be used in such deposition or other processing systems.
The present invention will be described with reference to pinch valves incorporated into systems for continuously depositing semiconductor material onto a moving web of substrate material. However, it is to be understood that the principles of the present invention may be extended to variously configured pinch valves used in other applications where it is desirable to isolate/maintain an area of a processing system using the pinch valve during a stop cycle or while another operation is performed at another portion of the processing system. For example, it may be desirable to maintain a condition (e.g. temperature, pressure, composition, etc.) within an area adjoining the pinch valve. In one application, it may be desirable to maintain the adjoining area free from atmosphere elements or contaminate. In another application, it may be desirable to contain a composition within a chamber and not release portions thereof outside the chamber, for example, not releasing a hazardous gas from within the chamber of the processing system. Further and as previously discussed herein, isolating and maintaining a desirable condition of a processing area without damage to the substrate, for example during a stop cycle of the processing system, can save time and resources otherwise applied to return the isolated area back to the desirable condition to resume operation of the processing system.
Referring now to
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Further shown in
As shown, the sealing surface 28 of the dynamic seal element also includes planar portions which project from the curved portion and these portions cooperate with the corresponding planar positions on the valve body 14. It is also to be noted that the dynamic seal element 26 includes two curved segments 32 and 34 which are optional; however, from which an additional planar portion depends away from each of the curved segments to provide for some mechanical clearance between the dynamic seal element 26 and the valve body 14. The additional planar portions provide more attachment surface area (here, improved adhesion) for a sealing element, such as a gasket, to be secured to the sealing surface 28 of the dynamic seal element 26 so the gasket material is less likely to become detached from the seal surface at the area of engagement between the dynamic seal element and the valve body. In other implementations of the invention, other modifications may be made as apparent to those of skill in the art.
Referring now to
The sealing surface 28 of the dynamic seal element 26 also includes a resilient member 29 disposed thereupon. In this embodiment, this resilient member 29 is also a body of silicone rubber, which may be of the type described above, having a thickness of 0.6 inches. As will be further noted, a portion of the sealing surface 28 of the dynamic seal element 26 includes a shim member 29a thereupon. This shim member 29a is also resilient and may comprise a 0.3 inch thick portion of the aforedescribed silicone rubber. The inclusion of the shim has been found to further enhance the degree of vacuum seal achieved by this valve. As noted above, other natural and synthetic elastomers may be used for the resilient member 29. In an alternative embodiment, the shim can be an integral portion of a composite resilient member. The shim member 29a is disposed so as to be in that portion of the sealing surface 28 of the dynamic seal element 26 which will contact a predetermined area of the substrate web disposed in the pinch valve at engagement. The presence of the shims changes the effective thickness and/or resiliency of those portions of the sealing surface 28 with which it is associated so as to provide for sealing conditions which will vary across the width of a web associated therewith. For example, the shim can be configured and the dynamic seal element actuated to provide a greater sealing pressure against a surface of the web near and/or at an edge of the web, compared to a sealing pressure against other portions of the substrate web across its width. It is to be understood that the pinch valve can have a plurality of shims and shim configurations to provide a variety of pressures for sealing and isolation about the substrate web. As will be discussed hereinbelow, the pinch valve can be further configured to have multiple degrees of compliance for controlling one or more sealing areas about the substrate web within the pinch valve.
As previously mentioned, the sealing surface 22 of the valve body 14 includes planar portions projecting from the curved portion 24. As is specifically illustrated in
As will further be seen in
It is a significant feature of the pinch valve of the present invention that it can be closed onto a web of substrate material without causing any major damage to the web, such as a wrinkle, burr, indentation, crease, crack, etc. In that regard, the geometry of the sealing surfaces of the valve body and dynamic seal element are selected so as to avoid imposing excessive forces on the web. In the embodiment shown in
Referring now to
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In the operation of the pinch valve 10, the dynamic seal element 26 is biased into and out of engagement with the valve body 14, and in this specific embodiment, such biasing is accomplished by an actuator. Referring now to
The
It has been found that the pinch valve described in the foregoing provides a very high degree of isolation of a region for a deposition apparatus. In a typical application, the pinch valve provides desirable sealing pressures against portions of the substrate web, for instance in the ranges of 20-120 psi, 40-80 psi, and in specific instances approximately 60 psi. In an experimental series, valve assemblies configured in accord with the foregoing were closed against a substrate web of 5 mil thick stainless steel and when subjected to a pressure differential of 1 atmosphere were found to have a leak rate in the range of 5×10−5 to 5×10−9 torr liter/minute, and in particular instances a leak rate of no more than 5×10−7 torr liter/minute.
The pinch valve of the present invention may be configured in a variety of embodiments and incorporated into various deposition systems for the deposition of materials over a web of substrate material. In particular instances an embodiment of the pinch valve may be advantageously employed in multi-web systems of the type wherein a plurality of substrate webs are simultaneously advanced through one or more coating stations and thence to a take-up chamber. Some such systems are shown in U.S. Pat. No. 4,423,701 and U.S. Patent Application Publication 2004/0040506. The disclosures of both of these documents are incorporated herein by reference.
In a multiple web deposition system, each web may have a discrete pinch valve disposed between a payout chamber and a deposition station and another discrete pinch valve disposed between a deposition station and a take-up chamber. Alternatively, a multiple web pinch valve may be configured and disposed so as to seal a plurality of webs therebetween. All of such pinch valves may be configured to operate in accord with the present invention.
Referring now to
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Further visible in the
It is to be understood that yet other embodiments of multi-web pinch valve may be configured in accord with the principles of the present invention in view of the teaching presented herein.
The foregoing has described some specific embodiments of the present invention with regard to their incorporation into a system for the continuous deposition of thin film bodies of semiconductor material. It is to be understood that the present invention may be implemented in various other configurations and may be adapted for other uses. All of such modifications, variations and applications will be apparent to those of skill in the art in view of the teaching presented herein. It is to be understood that the figures of this disclosure are not drawn to scale, rather the figures are drawn to illustrate most clearly the principles of this disclosure discussed herein. The foregoing drawings, discussion and description are illustrative of specific embodiments of the invention, but are not meant to be limitations upon the practice thereof. It is the following claims, including all equivalents, which define the scope of the invention.
