Patent Publication Number: US-2022223345-A1

Title: Gas capacitor for semiconductor tool

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a national stage filing of PCT/US20/32396, filed on May 11, 2020, which has the same title and the same inventors, and which is incorporated herein by reference in its entirety; which claims priority to U.S. provisional patent application No. 62/846,360, which was filed on May 10, 2019, which has the same title and inventors, and which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention pertains generally to tools used for semiconductor fabrication, and more particularly, to a gas capacitor for such tools. 
     BACKGROUND OF THE INVENTION 
     In a typical semiconductor manufacturing process, a single wafer is exposed to a number of sequential processing steps including, but not limited to, chemical vapor deposition (CVD), physical vapor deposition (PVD), etching, planarization, and ion implantation. These processing steps are typically performed by robots, due in part to the ability of robots to perform repetitive tasks quickly and accurately and to work in environments that are dangerous to humans. 
     Many modern semiconductor processing systems are centered around robotic cluster tools that integrate a number of process chambers. This arrangement allows multiple sequential processing steps to be performed on the wafer within a highly controlled processing environment, and thus minimizes exposure of the wafer to external contaminants. The combination of chambers in a cluster tool, as well as the operating conditions and parameters under which those chambers are utilized, may be selected to fabricate specific structures using a specific process recipe and process flow. Some commonly used process chambers include degas chambers, substrate pre-conditioning chambers, cool down chambers, transfer chambers, chemical vapor deposition chambers, physical vapor deposition chambers and etch chambers. 
       FIG. 1  is a schematic diagram of the integrated cluster tool  10  of U.S. Pat. No. 6,222,337 (Kroeker et al.). Wafers are introduced into, and withdrawn from, the cluster tool  10  through a cassette loadlock  12 . A robot  14  having an end effector  17  is located within the cluster tool  10  to transfer wafers from one processing chamber  20  to another. These processing chambers may include a cassette load lock  12 , a degas wafer orientation chamber  20 , a pre-clean chamber  24 , a PVD TiN chamber  22  and a cool-down chamber  26 . The end effector  17  is illustrated in the retracted position in which it can rotate freely within the chamber  18 . 
     A second robot  28  is located in transfer chamber  30  and is adapted to transfer wafers between various chambers, such as a cool-down chamber  26 , a pre-clean chamber  24 , a CVD Al chamber (not shown) and a PVD AlCu processing chamber (not shown). The specific configuration of chambers illustrated in  FIG. 1  is designed to provide an integrated processing system capable of both CVD and PVD processes in a single cluster tool. A microprocessor controller  29  is provided to control the fabricating process sequence, conditions within the cluster tool, and the operation of the robots  14 ,  28 . 
       FIG. 2  is a schematic view of the magnetically coupled robot of  FIG. 1  shown in both the retracted and extended positions. The robot  14  (see  FIG. 1 ) includes a first strut  81  which is rigidly attached to a first magnet clamp  80 , and a second strut  82  which is rigidly attached to a second magnet clamp  80 ′. A third strut  83  is attached by a pivot  84  to strut  81  and by a pivot  85  to end effector  86 . A fourth strut  87  is attached by a pivot  88  to strut  82  and by a pivot  89  to end effector  86 . The structure of struts  81 - 83 ,  87  and pivots  84 ,  85 ,  88 , and  89  form a “frog leg” type connection of end effector  86  to magnet clamps  80 , 80 ′. 
     When magnet clamps  80 ,  80 ′ rotate in the same direction with the same angular velocity, then the robot also rotates about axis x in this same direction with the same velocity. When magnet clamps  80 ,  80 ′ rotate in opposite directions with the same absolute angular velocity, then there is no rotation of assembly  14 , but instead there is linear radial movement of end effector  86  to a position illustrated by dashed elements  81 ′- 89 ′. 
     Referring still to  FIG. 2 , a wafer  35  is shown being loaded on end effector  86  to illustrate that the end effector can be extended through a wafer transfer slot  90  in a wall  91  of a chamber  32  to transfer such a wafer into or out of the chamber  32 . The wafer transfer slot  90  commonly takes the form of a pneumatically actuated rectangular transfer valve or slit valve, an example of which is shown in  FIG. 3 . 
     Still referring to  FIG. 2 , the mode in which both magnet clamps  80 ,  80 ′ rotate in the same direction at the same speed can be used to rotate the robot from a position suitable for wafer exchange with one of the adjacent chambers  12 ,  20 ,  22 ,  24 ,  26  (see  FIG. 1 ), to a position suitable for wafer exchange with another of these chambers. The mode in which both magnet clamps  80 ,  80 ′ rotate with the same speed in opposite directions is then used to extend the end effector into one of these chambers and then extract it from that chamber. Some other combination of clamp rotation may be used to extend or retract the end effector as the robot is being rotated about axis x. 
     There is considerable pressure in the semiconductor industry to increase throughput at semiconductor fabs. Consequently, cluster tools of the type depicted in  FIGS. 1-2  have been required to operate at increasingly higher speeds to keep up with increasing throughput requirements. 
     During their operation, cluster tools are frequently required to pneumatically isolate a particular processing chamber from the rest of the tool. This is typically accomplished through the use of pneumatically actuated slit valves. An example of one embodiment of a slit valve  101  is depicted in  FIG. 3  (the slit valve  101  is seated in the wafer transfer slot  90  of  FIG. 2 ). The particular slit valve  101  depicted in  FIG. 3  is a V74 Series slit valve which is commercially available from the Kurt J. Lesker Company (Jefferson Hills, Pa.). This slit valve  101  comprises a frame  103  having a window  105  disposed therein, and is further equipped with a pneumatic inlet  107  that is fluidically coupled to a gas supply line (not shown). Other commonly utilized slit valves include those which are available from SMC Corporation (Tokyo, Japan) such as, for example, the pneumatic slit valve sold under the product designation SMC US13394. 
     Slit valves are commonly used as partition valves between the load lock chamber and the transfer chamber, or between the transfer chamber and the process chamber, in semiconductor manufacturing equipment. The gas supply line provides a working gas (typically clean dry air (CDA)) that serves to open and close the slit valves. 
     SUMMARY OF THE INVENTION 
     In one aspect, a combination of a gas capacitor and a semiconductor tool is provided. The semiconductor tool comprises (a) a gas supply line which supplies gas from a remote gas source and which is equipped with a first one-way valve, (b) a central chamber, and (c) a plurality of process chambers, wherein each of said plurality of process chamber is equipped with a pneumatically actuated valve which is in fluidic communication with the gas supply line and which transforms the process chamber from a first state in which the process chamber is in fluidic communication with said central chamber, to a second state in which the process chamber is fluidically isolated from said central chamber. The gas capacitor comprises a pressurized gas reservoir which is disposed downstream from said one-way valve, and which is in fluidic communication with said plurality of process chambers. 
     In another aspect, a system is provided which comprises (a) a gas supply; (b) a fluidic circuit which includes first and second sub-circuits, wherein said first sub-circuit includes a first one-way valve, and wherein said second sub-circuit includes a second one-way valve and a gas capacitor disposed downstream of said second one-way valve; and (c) a pneumatically operated semiconductor tool in fluidic communication with said gas supply by way of said fluidic circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features. 
         FIG. 1  is an illustration of a prior art cluster tool equipped with a robotic wafer handling system. 
         FIG. 2  is an illustration of the arm assembly of the robot depicted in  FIG. 1 , and illustrates the retracted and extended positions of the arm assembly. 
         FIG. 3  is a front view of a prior art slit valve. 
         FIG. 4  is a side view of the slit valve of  FIG. 3 . 
         FIG. 5  is an illustration of a semiconductor fab layout featuring a remote gas supply and a plurality of cluster tools. 
         FIG. 6  is a schematic illustration of a system which includes a gas supply and a semiconductor tool and which is equipped with a gas capacitor in accordance with the teachings herein. 
         FIG. 7  is a detailed illustration of the gas capacitor of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The trend toward operating cluster tools at higher speeds has resulted in more slit valve actuations occurring simultaneously. Cluster tools are typically equipped with a long length of piping that supplies the working gas for the pneumatic system. Since this piping has a finite flow capacity, the simultaneous operation of an increasing number of slit valves (as necessary to accommodate higher throughput speeds) places increasing demands on the pneumatic system. This frequently results in dramatic fluctuations in pneumatic pressure at the cluster tool, which can lead to tool alarms, chamber leaks and slow actuations of the slit valves. In order to reduce such pressure fluctuations and to accommodate the necessary flow requirements, the clean dry air (CDA) pressure at the tool is frequently increased beyond the suggested limitations of the slit valves. 
     It has been found that, as a result of their frequent exposure to CDA pressures that exceed their design capabilities, the slit valves in a cluster tool suffer frequently exhibit premature wear. This is often manifested as a breakdown of the O-ring material in the valve, which may lead to particle generation. 
     On the other hand, if CDA pressures in the tool drop below the required level, the slit valves may not fully actuate, which may leave them in an unknown open/closed state. If these faults occur during wafer transfer, the robot and wafer may be left in an unknown position. Similarly, if the CDA supply is depleted, tool technicians may have no options for wafer recovery, and may be forced to wait for the CDA supply to recover. Either of these scenarios may lead to wafer scrap that may have been averted if the tool technicians had been able to quickly remove the wafers from the tool. 
     It has now been found that some or all of the foregoing issues may be addressed with the systems and methodologies disclosed herein. In a preferred embodiment of such a system, a gas capacitor, preferably in the form of a pressurized vessel, is added locally to the cluster tool at a location near (and upstream from) the slit valves. The gas capacitor, which is in fluidic communication with the slit valves, provides an additional local reservoir of working gas (preferably CDA) local to the tool. The availability of this additional reservoir local to the tool increases the effective volume of CDA available to the tool, while also decreasing the effective length of pipe supplying the CDA. This arrangement significantly reduces or eliminates the pressure fluctuations which otherwise arise from the simultaneous operation of an increasing number of slit valves. Consequently, the operating pressure may be set at lower values (e.g., those recommended by the tool manufacturer), even if the remote supply of CDA is servicing multiple tools and/or a large number of slit valves simultaneously. 
     Moreover, the gas capacitor may be configured to allow the tool to cease operation if the facility CDA pressure drops sufficiently (as is currently the case), but to maintain a reservoir of CDA of sufficient volume and pressure to allow for manual operation of the slit valves in the tool. This provides a means by which in-process wafers may be recovered, thus avoiding some of the cost and waste attendant to CDA disruptions. 
     In some embodiments, the auxiliary gas supply may be configured to be removable from (or fluidically or pneumatically isolated from) the tool. This may be accomplished, for example, through the provision of a bypass line. This feature allows the auxiliary gas supply to be removed for maintenance or replacement without disrupting the operation of the associated tool, and without introducing moisture or other contaminants into the gas circuit. 
       FIG. 5  depicts a particular, non-limiting embodiment of a semiconductor fab layout. As seen therein, the layout  201  comprises a plurality of cluster tools  203  that are in fluidic communication with a remote gas supply  205  via a gas supply line  207 . Each of the cluster tools  203  is equipped with a one-way check valve  209  which isolates the tool from the gas supply line  207  in the event of a sufficiently large pressure drop. The check valve  209  preferably serves as a pneumatic lock-up valve which functions to shut off the signal pressure line of pneumatic actuators when the pressure in the gas supply line falls below a predetermined threshold value. This typically causes the pneumatically activated actuators in the tool (including those in the slit valves) to remain in their last position. 
     The check valve  209  is characterized by a cracking pressure P crack . At pressures above the cracking pressure, the valve assumes an open state in which fluidic flow between the remote gas supply and the tool occurs. Similarly, at pressures below the cracking pressure, the valve assumes a closed state in which no fluidic flow between the gas reservoir and the gas supply line occurs. The gas supply line will typically experience operating pressure fluctuations while the semiconductor tool is in operation. These operating pressure fluctuations are characterized by a maximum pressure P max  and a minimum pressure P min . Preferably, the check valve is designed such that 0&lt;P crack &lt;P min . Typically, P min &gt;30 psi, and preferably, P min ≥60 psi. Typically, P max &lt;100 psi, and preferably, P max ≤90 psi. Moreover, typically, 10 psi&lt;P crack &lt;60 psi, and preferably, 20 psi&lt;P crack &lt;50 psi. 
     Each cluster tool  203  is also equipped with a gas capacitor  211  of the type disclosed herein, which is preferably located downstream of the check valve  209 . As described below, the gas capacitor  211  serves as a local supply of gas, in contrast to the remote gas supply  205  from the facility. It will be appreciated that, while the check valve  209  is depicted as a separate component from the gas capacitor  211  in  FIG. 5 , in some embodiments, the check valve will actually be a component of the gas capacitor. 
       FIGS. 6-7  depict a first particular, non-limiting embodiment of a system  301  incorporating a gas capacitor  307  in accordance with the teachings herein. As seen therein, the system  301  comprises a pneumatically powered semiconductor tool  303  which is in fluidic communication with a facility gas supply  305  via a fluidic circuit  306  that includes first  308  and second  310  sub-circuits. The first  308  and second  310  sub-circuits are in fluidic communication with each other via first  309  and second  311  T-joints. The first sub-circuit  308  includes check valve  313 , and the second sub-circuit includes gas capacitor  303 . Check valve  313  maintains a one-way flow in the first sub-circuit  308  in the direction going from the first T-joint  309  to the second T-joint  311 . The semiconductor tool  303  is equipped with a plurality of slit valves  323  that are in fluidic communication with fluidic circuit  306  via a manifold  321 . 
     The gas capacitor  303  is depicted in greater detail in  FIG. 7 . As seen therein, the gas capacitor  307  comprises a gas reservoir  314  equipped with a pressure gauge  343 . The gas reservoir  314  is preferably a gas cylinder, and more preferably, an aluminum gas cylinder. The use of aluminum in the construction of the gas reservoir  314  is preferred here because aluminum poses a lower contamination threat than other metals commonly used in the construction of gas cylinders. The pressure gauge  343  is preferably fitted with a filtered exhaust. The pressure gauge  343  is useful during initial installation and charging of the gas reservoir  314  to ensure that the initial pressure remains steady (i.e., there are no leaks present in the gas capacitor  307 ). 
     The gas capacitor  307  further comprises first  335  and second  337  manually operated isolation valves. The first isolation valve  335  is associated with fittings  331  and  339 , and the second isolation valve  337  is associated with fitting  333 . The first  335  and second  337  isolation valves are preferably disposed immediately upstream and immediately downstream, respectively, from the gas reservoir  314 , and thus provide a means to readily remove the gas reservoir  314  from the pneumatic circuit  306  as, for example, for repair or maintenance. The gas capacitor  307  is further equipped with a check valve  341 , which maintains a one-way flow in the direction going from the first isolation valve  335  to the second isolation valve  337 . 
     In some embodiments, the gas capacitor  307  may include additional components. Thus, for example, in some embodiments, the gas capacitor  307  or the fluidic circuit  306  may include a gas dryer, which is preferably a modular adsorption dryer. The gas dryer serves to remove water vapor from the gas supply, thus preventing condensation, corrosion and the growth of microorganisms. In some embodiments, the gas dryer may be equipped with a suitable desiccant. One or more filters may also be provided in the gas capacitor  307  or the fluidic circuit  306  to remove impurities therefrom such as, for example, liquid water, water aerosols, oil, particulates, or microorganisms. 
     In normal use of the system  301 , as pressure fluctuations are propagated through fluidic circuit  306 , the check valve  313  remains open so long as the pressure in fluidic sub-circuit  308  upstream of the check valve  313  does not fall below P min . These pressure fluctuations are compensated for by the gas capacitor  307  as a result of the additional, localized reservoir of pressurized gas it provides via gas reservoir  314 . 
     However, if the pressure in fluidic sub-circuit  308  upstream of the check valve  313  line falls below P crack , the check valve  313  is activated (that is, moves from an open position in which fluidic flow through the check valve  313  is permitted, to a closed position in which fluidic flow through the check valve  313  is not permitted), and the gas supply to the tool  303  is cut off. Since the check valve  313  is a one-way valve, the portion of the first sub-circuit  318  upstream of the check valve  313  remains fluidically isolated from the tool  303 , and hence, working gas pressure is maintained in the portion of the first sub-circuit  308  downstream of the check valve  313 . Similarly, the one-way flow provided by check valve  341  (see  FIG. 7 ) ensures that the portion of the second sub-circuit  310  upstream of the check valve  341  remains fluidically isolated from the tool  303 , and hence, working gas pressure is maintained in the portion of the second sub-circuit  310  downstream of the check valve  313 . Since check valves  313  and  341  provide a one-way flow of fluid, and since the gas reservoir  314  of the gas capacitor  307  is downstream from the check valve  341 , the additional, localized reservoir of pressurized gas provided by gas reservoir  314  may be utilized to manually operate slit valves  323  or other pneumatically operated components of the tool  303 . This allows for wafer recovery and temporary operation of the slit valves, even if the facility gas supply  305  remains offline. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.