Abstract:
An inverted pressure vessel system for conducting automated industrial processes requiring elevated pressure and temperatures has a vertically movable pedestal for opening and closing the underside loading port, with pedestal drive system and locking mechanism located below the pedestal top and isolated from the chamber opening. The chamber is connectible to a pressure control and process fluid supply system, and has heat exchangers connected to an external source for temperature control. Process fluids are distributed across a central process cavity through divergent inflow and convergent outflow process fluid channels.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of and claims priority to pending U.S. application Ser. No. 09/632,770 filed Aug. 4, 2000, still pending, and prior U.S. provisional patent applications No. 60/147,251 filed Aug. 5, 1999, and No. 60/155,454 filed Sep. 20, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     This invention relates to pressure vessels used in process operations requiring extreme cleanliness and operated at elevated pressures and temperatures, and in particular to pressure vessel design and shielded closure mechanisms that facilitate easier and cleaner loading and closing of pressure vessels used in automated wafer treatment processes in a production environment. 
     2. Background Art 
     There is a general requirement in the semiconductor industry, and in other industries as well such as the medical industry, for conducting processes that require enclosures or pressure vessels that can be loaded with wafers or other objects to be processed, permit the admittance and removal of process fluids or materials necessary to the process after the enclosure is sealed, and be elevated and ranged in pressure and temperature. Some processes are much more critical as to contamination, and require quick and close control of temperature, pressure, and the volume and timing of the introduction of process fluids to the pressure vessel. Add to that the demand for conducting these processes in a production mode, and the growing sophistication of the processes themselves, and it is amply clear that improvements in pressure vessels are needed. 
     This disclosure relates in particular to pressure vessels used in operations requiring extreme cleanliness and operated at elevated or high pressures up to 10,000 psi (pounds per square inch) or more, and further, to pressure vessel design and isolated lid locking mechanisms that facilitate easier and cleaner loading and locking of pressure vessels used in automated wafer treatment processes in a production environment. 
     An example of a process to which these criteria apply, there is the manufacture of MEMS (Micro Electro Mechanical Systems) devices where the process agent is carbon dioxide, used in both liquid and supercritical form. Other actual and prospective process agents operated in supercritical phase conditions which require much higher temperature and pressure than does carbon dioxide. Other semiconductor related applications with strict cleanliness requirements, such as photoresist stripping, wafer cleaning, particulate removal, dry resist developing, and material deposition, all suffer from the same pressure vessel deficiencies, which include particle generation upon closing that causes contamination, closure mechanisms that are not suited for quick and automated closing, problems with automatically loading and unloading the vessel, and problems with the integration of the apparatus in a production line. 
     In many laboratory and production setups currently in use, the pressure vessel is loaded by vertical placement through an open top port of the same or larger diameter of the wafers being processed, and is unloaded by reverse action. The vessel is typically closed by manually bolting or mechanically clamping the process vessel flanges and its cover flanges together around the perimeter to form a pressure seal. This apparatus and methodology is both slow and prone to introducing particulate contamination due to the mechanical interface and constant wearing of mating surfaces. The particulate is generated immediately within the loading and processing environment, and inevitably contaminates the materials being processed to some degree. 
     These contaminants are of particular concern in the semiconductor industry, as even trace amounts are sufficient to plague product quality and production efficiencies. When these perimeter flange latching mechanisms are semi-automated for faster closure or production purposes, the contamination problem is simply placed in a free-running mode that gets progressively worse if unattended. 
     There are many examples in prior art. One such example is an autoclave with a quick opening door assembly. It typically consists of a chamber flange, a rotating locking ring and the door flange. The door and vessel are clamped and unclamped by the rotation of the locking ring only. As the ring rotates, surfaces of the mating wedges force the chamber flange tight against the gasket providing a leak proof static seal. Due to the contact of the wedges sliding across each other, particles are generated and debris put into motion that eventually contaminate the process beyond acceptable tolerances. 
     A further problem with traditional pressure vessels in a production environment is the difficulty in adapting them to the standard wafer handling robots of the semiconductor industry. Complex carriage systems are often necessary for automation of the loading and extracting of materials being processed, involving complex transitions between horizontal and vertical transport of the wafers between processing stations. Newer industry standards anticipate and provide for cluster tool arrangements, where rotary transport systems move wafers between connected wafer processing machines. It is this need and this environment to which the following disclosure is addressed. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an inverted pressure vessel system with shielded closure mechanisms for conducting automated industrial processes under elevated pressure and temperatures. To that end, there is disclosed a pressure chamber with an underside loading port, a vertically movable pedestal arranged directly below the pressure chamber for opening and closing the loading port, the top of the pedestal functioning as the floor of the pressure chamber when the pedestal is raised to a closed position and as a loading platform when the pedestal is lowered to an open position. 
     There is included a motor and vertical drive system for moving the pedestal between open and closed positions, and a pedestal locking system consisting of another motor and lateral drive system for wedge locking the pedestal in a sealing relationship with the pressure chamber so as to define a process volume within which to conduct the processes. 
     It being another goal to avoid contamination of the processing environment by loosened particles and debris put in motion by the closing and locking systems, there is provided a shield between the loading and unloading area encompassing the pedestal top and pressure chamber, and the pedestal lateral support structure, and vertical drive and closed position locking mechanisms. 
     It being a further goal to provide for handling processes requiring control of pressure and temperature within the chamber, there is provided an inlet manifold and an outlet manifold communicating with the process volume within the chamber, the manifolds being connectable to a process fluid control source for delivering process fluids under controlled pressure to the process volume and removing byproducts therefrom. There is also provided a heat exchanging platen in the roof of the process volume which is connectible by fluid lines to an external fluid temperature control system, a heat exchanging platen incorporated onto the pedestal and likewise connectible by fluid lines to the external fluid temperature control system, and a thermocouple sensor configured for sensing temperature in the process volume and connectible for communicating with the external fluid temperature control system. 
     It is yet another goal of the invention to provide for optimal flow and distribution of the process fluids through the central processing cavity of the pressure chamber. To this end, there are provided divergent inflow channels connecting the inlet manifold to the central processing cavity, and convergent outflow channels connecting the cavity to the outlet manifold. 
     In further support of the goal of reducing contamination of the process, there is a horizontal shelf structure vertically positioned below the top of the pedestal and with a center hole through which the pedestal operates, with lateral support for the pedestal being attached thereto. There is a vertically collapsible bellows, the upper end thereof being attached by an upper bellows flange around the top of the pedestal and the lower end thereof being attached by a lower bellows flange to the perimeter of the hole in the shelf so as to encircle the pedestal and isolate the lateral support structure and drive and lock mechanisms from the loading and processing environment above. 
     Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein we have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by us on carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation cross section illustrating the principle components of the preferred embodiment with the pedestal and lock blocks in closed and locked positions, respectively. 
     FIG. 2 is a side elevation cross section of the preferred embodiment, with the pedestal and lock blocks in open and retracted positions, respectively. 
     FIG. 3 is a front elevation of the preferred embodiment, partially cut away to illustrate the pedestal in the open position. 
     FIG. 4 is a plan view of the preferred embodiment, illustrating the tie plate bolt heads, and the lock block drive screw motor and gearboxes on the backside of the machine. 
     FIG. 5 is a close up side elevation cross section view showing the upper compartment of the preferred embodiment, illustrating the process chamber with process fluid and heating fluid supply lines, with the pedestal and bellows in the mid range position between open and closed. 
     FIG. 6 is a plan view cross section through the process chamber of the preferred embodiment, illustrating the vanes and flow channels affecting the fluid flow through the process volume. 
     FIG. 7 is a plan view cross section view through the tie plates and pedestal column of the preferred embodiment, illustrating the pedestal guide bars and guide bar holders on each side of the column. 
     FIG. 8 is a plan view cross section through the tie plates and lock blocks of the preferred embodiment, illustrating the lock block drive system, LVDT sensor and pneumatic position sensor/interlock. 
     FIG. 9 is a side elevation close up cross section view of the lock blocks and base of the pedestal of the preferred embodiment. 
     FIG. 10 is a multi view illustration of the side elevation and plan view aspects of the pedestal locking wedge components of the preferred embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     To those skilled in the art, the invention admits of many variations. What follows is a description of the preferred embodiment, and should not be construed as limiting the scope of the claims that follow. 
     The preferred embodiment described herein is a component of a cluster tool arrangement for the production processing of semiconductor wafers or pressure and temperature sensitive treatment of other small articles. It is an inverted pressure vessel with an isolated door closure mechanism, and a specially configured process volume for handling a through flow of processing fluids in a closely controlled temperature and pressure cycling environment. It conforms the cluster tool geometry SEMI/MESC (Semiconductor/Modular Equipment Standards Committee) standards. It contemplates a maximum operating pressure in the order of 4500 psi, (pounds per square inch), and in an embodiment with a cavity design size of 200 millimeters diameter and a total process volume of about three quarters of a liter, the structure is required to resist up to about 400,000 pounds of force from within the process volume. The temperature range of the preferred embodiment is −20 to +150 degrees centigrade. Higher pressures and temperatures may be desired for some processes, and are simply a function of design. No warranty is expressed or implied in this disclosure as to the actual degree of safety, security or support of any particular specimen of the invention in whole or in part, due to differences in actual production designs, materials and use of the invention. 
     The pressure vessel of the invention is assumed to be connected to a suitable dynamic process supply and control system that supplies process fluid under controlled pressure as required by the process, exerts temperature control via heat exchangers in the processing volume, excepts outflow byproducts of the process for recycling or other suitable disposition, and provides the necessary computer control and operator interface to be integrated into the production process. The pressure vessel and associated systems are configured with industry standard interlocks and safety features appropriate to the process conditions. 
     The preferred embodiment is configured for a cluster tool arrangement as part of an automated production system for processing semiconductor wafers, as it described below. It is adaptable to other systems for other elevated pressure/temperature processing in an automated system, incorporated into or combined with a horizontal, pass-through conveyor system, a wafer handling robot system, or any other handling system for delivering and loading articles to be processed under pressure, onto the open top of the pedestal. The vertically operated pedestal can carry a wafer cassette, a single wafer, or other object being processed into the pressure vessel for processing, and out again for pickup and further transport. The lift and lock mechanism for operating the pedestal is fully shielded so as to isolate any particulate matter generated and any debris put into motion by the lift and lock mechanism, from the loading and processing environment. 
     Referring to the figures, an inverted process chamber  10  with an underside loading port, is bolted to front tie plates  3  and rear tie plates  4 , which in turn are bolted to lower support plate  2 . This assemblage is supported by frame  1 . Within this assemblage is arranged a vertically movable pedestal  50 , a columnar structure the upper end of which terminates in a large, circular, flat top or loading platform, the same surface of which functions as the floor to inverted pressure chamber  10  when used to close the underside loading port. Pedestal  50  is vertically moveable between an upper closed, and a lower open position relative to process chamber  10 . Movement is effected by means of a pedestal drive motor and gearbox  52  mounted in frame  1 , which turns a vertically oriented pedestal drive screw  54  in a lift nut  59  in the base of pedestal  50 . 
     Process chamber  10  is machined and configured to provide a final wafer cavity  8  there within, generally sized to accommodate a single wafer diameter and thickness. 
     Referring in particular to FIG. 6, flow channels  6 , divided by flow vanes  7  promote uniform distribution of process fluids into and out of wafer cavity  8 , between inlet and outlet manifolds  14  and  18 . The combination of inlet and outlet flow channels  6  and wafer cavity  8  make up the internal process volume of the pressure chamber. 
     Referring in particular to FIG. 7, pedestal  50  is configured with two opposing flats on its vertical wall, within each of which is machined a vertical channel or groove  55 . Lateral support and alignment is provided pedestal  50  throughout its vertical range of motion by opposing bronze pedestal guide bars  56  which closely conform to the cross section of grooves  55 , and which are attached to respective adjustable guide bar holders  58  that are in turn mounted on shelf  5 . The guide bars are lubricated for a sliding interface. 
     Shelf  5  divides the region between process chamber  10  and lower support plate  2  into upper and lower compartments, the upper compartment being the region where the loading and unloading of the process chamber occurs, and for which it is important to maintain the highest practical degree of cleanliness to avoid contamination of the process during loading and unloading of the chamber. To that end, bellows  60  is attached by bellows flanges  62  and  64  to shelf  5  and pedestal  50  so as to isolate pedestal and lock block drive systems from the upper compartment. 
     Referring back to FIGS. 1,  2  and  5 , a process fluid inlet line  12  is connected via inlet manifold  14  to the front of chamber  10  so as to provide an inflow path for process fluid into the process volume and wafer cavity  8 . A process fluid outlet line  16  is connected via outlet manifold  18  to the back side of process chamber  10  so as to provide an outflow path from the process volume and wafer cavity  8  for byproducts of the process. The fluid inlet and outlet lines are connected to a suitable process fluid supply source for the controlled supply of process fluids under very high pressures. Fluid lines  12  and  16  of the illustrated embodiment are one quarter inch inside diameter, but either or both lines may be larger or smaller, depending on the particular process requirements and the effects of line volume and control valve location with respect to the process volume within the pressure chamber. Either or both manifolds  14  and  18  may be modified to incorporate control valves, with their actuators connected to the process control system. 
     The preferred embodiment employs a motor and lateral drive mechanism for inserting a wedge structure in one form or another beneath the pedestal when it is in the closed position. Referring in particular to FIGS. 8-10, a pair of lock blocks  90  are interlocked by lock block screws  92  for closure from opposing sides of the base of pedestal  50 . Lock block screws  92  are supported in screw blocks attached to lower support plate  2  at a height that permits lock blocks  90  to bear and slide on hardened support plates  2 A, let into lower support plate  2 . Lock blocks  90  are configured with hardened bottom plates  91 , which bear on and slide over hardened support plates  2 A when lock blocks  90  are operated for movement. As noted above, lock blocks  90  are interlocked by screws  92 , and are jointly movable between a retracted position clear of the pedestal&#39;s vertical motion, to a locking position beneath the base of pedestal  50  when the pedestal is raised up into a closed position against pressure chamber  10 . 
     Steel hardened locking wedge components  101  and  102 , having a two degree angle of ramp or wedge angle, are mounted on the top of the lock block  90  and the base of pedestal  50  respectively, so as to provide a sliding interface with a very high vertical component of force in response to the horizontal closing force applied to lock blocks  90  by the lock block screw motor  98  at low speed/high torque and gear boxes  96 . The sliding interface between wedge components  101  and  102  has about a three inch horizontal stroke, provided by the range of motion of locking blocks  90  between open and locked positions. A suitable lubricant can be applied to all sliding interfaces. 
     The resulting vertical range for the two degree slope wedge angle of wedge components  101  and  102  is in the order of ⅛ inch, so pedestal  50  must be lifted on screw  54  by motor and gearbox  52  to within ⅛ inch of full closure with chamber  10  before locking blocks  90  are actuated. A smaller slope angle can be used to obtain a greater locking force, the vertical component of motion of the locking mechanism being correspondingly smaller. 
     Upper and lower proximity sensors  57  and  58 , attached to a vertical rod mounted on shelf  5  adjacent pedestal  50  so as to sense the edge of the pedestal, control the range of pedestal  50  as driven by motor and gearbox  52 . Upon sensing pedestal  50  to be at the upper limit, motor and gearbox  52  are stopped and locking blocks  90  can be actuated for sealing pedestal  50  to process chamber  10 . Lift nut  59  is configured with some vertical play within the base of pedestal  50 , to avoid placing the pedestal drive screw in tension when locking blocks  90  are engaged. 
     Referring to FIG. 8, the control mechanism for lock blocks  90  includes an LVDT (linear variable displacement transducer) sensor  91 , which is configured to monitor the position of a lock block  90  within its normal range of motion. Lock block drive motor  98  is a two speed, brushless D.C. motor. Lock blocks  90  are driven at high speed/low torque to a predetermined position just short of where wedge components  101  and  102  come into engagement, as sensed by LVDT sensor  91 . Motor  98  is then switched to low speed/high torque and driven to the pre-determined final lock position, again as sensed by LVDT sensor  91 . Pneumatic interlock valve  93  is engaged when locking blocks  90  are fully closed into the locking position, permitting the process to be initiated within the closed and locked pressure chamber. 
     Referring to FIG. 5, a floating seal  51  embedded in the top of pedestal  50  provides a very high pressure sealing capability for the process volume when the pedestal is raised to the closed position and lock blocks  90  are placed in the locking position. Floating seals are known in the art for having compliant sealing characteristics suitable to the perimeter sealing problem of high pressure processing chambers. 
     In order to provide quick temperature control of the process volume when the pedestal is closed and locked, there is a heating platen  20  installed in the roof of wafer cavity  8 , and a similar heating platen  80  incorporated into pedestal  50 . Wafer crib  9  on platen  80  provides for receiving wafers delivered by an automated process, lifting and holding the wafer between the two platens when the chamber is closed for processing, and presenting the processed wafer for automated pickup when the process cycle is complete and the pedestal is lowered. The necessary thermal energy transfer to and from platens  20  and  80  for the temperature control and cycling according to the desired process is accomplished by the circulation of heating/cooling fluid through respective line sets  22  and  82 , which are connected to a suitable temperature control system. Process chamber thermocouple  30  is mounted on outlet manifold  18 , configured to sense temperature within the process volume of chamber  10 , and connects to the process control system. 
     As will be readily apparent to those skilled in the art, there are many useful embodiments within the scope of the invention. For example, the pedestal may be locked in the closed position by a rotate-to-actuate locking lug ring mounted on the lower support plate, that partially rotates so as to slidingly engage its internally extending wedge lugs with a uniformly spaced set of locking wedge lugs extending outward from around the column of the pedestal, instead of the linear slide block mechanism of the preferred embodiment. The ring and pedestal wedge lugs have a ramped or slightly sloping interface analogous to the lock block wedge components of the preferred embodiment. The rotate to lock mechanism is shielded from the loading and unloading compartment in the same manner as the preferred embodiment, by the shelf and bellows arrangement. 
     As another example, the pedestal may be of other and various cross sections, including square, channel, or I beam. The pedestal may be hollow or have a rigid skirt over a core element, where the skirt may be configured with a flexible rolling wall diaphragm-like structure with a flange that seals to the shelf to perform the isolating function of the bellows of the preferred embodiment. Another embodiment may have a vertically operable piston diaphragm, more accurately described here as a pedestal skirt diaphragm, sealing the top of the pedestal to the shelf so as to shield or isolate the lateral supports and the drive mechanisms in the same fashion. The shelf embodiment extends to a partial or full enclosure around the mouth or underside port of the pressure chamber, with a door or opening for allowing a transport mechanism to insert and remove articles or wafers being processed from on top of the open pedestal between processing cycles, with a center hole in the bottom of the enclosure through which the pedestal operates, and a pedestal skirt diaphragm sealed to the edge of the center hole to fully contain the loading and unloading environment within the enclosure. 
     The lateral support structure for the pedestal can be of various configurations so long as it provides continuous lateral support to the vertically movable pedestal structure. Guide bars, channels, and linear bearings are all within the scope of the invention, so long as they are excluded by the shield from exposure to the loading environment of the open pressure chamber along with the vertical driving and lock mechanisms. 
     As yet another example, the tie plate framework of the preferred embodiment can be configured for bi-directional or pass through access to the loading platform and wafer crib when the pedestal is down and the pressure vessel open, so as to accommodate a horizontal wafer pass-through conveyor system or robotic placement and removal of wafers from opposite sides. Also, particularly suitable for higher pressure systems, the tie plate and bolt system can be replaced with a large closed yoke structure, within which are arranged the inverted pressure chamber and the pedestal and motion systems, so that the yoke provides the structural tie that sustains the closing pressure between the pedestal and the pressure chamber. 
     As still yet another example, in order to maintain the closing force between the pedestal and the pressure vessel within an acceptable range during extended production cycles, with the aid of the pressure vessel computer control system, data such as pedestal back pressure, lock block motor torque, and lock block closing pressure can be continuously monitored with suitable sensors for trend information which can then be used for making on-the-fly adjustments to start, stop and gear shift positions for lock block motion and pedestal height. As an additional example, the lift mechanism for the pedestal may be hydraulic, threaded screw, or any other manner of jacking or extension mechanisms sufficiently robust to elevate the pedestal weight to the pre-locking closing height, and designed to tolerate the additional small vertical motion of the locking action. 
     The objects and advantages of the invention may be further realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.