Abstract:
The valve blades of the present invention facilitate delayed onset and gradual or fine variations in the flow of gas through the throttle valve to achieve a process interval of interior chamber gas pressures over a broader valve blade step range, achieve aggressive PI over a broad range for enhanced tool throughput, enhance stability of interior chamber gas pressures during substrate processing, and increase tool uptime and production efficiency. In one embodiment, each of the two valve blades in the throttle valve includes at least one, and typically, multiple notches or gaps for a delayed onset, and finely-graded increase, in flow of gas through the valve throughout the step range of the valve blades. In another embodiment, the semicircular valve blades have a cam-shaped configuration and are capable of varying the radius of the circle defined by the two blades.

Description:
FIELD OF THE INVENTION 
     The present invention relates to valves for regulating chamber pressures of process chambers used in the fabrication of semiconductor integrated circuits. More particularly, the present invention relates to multi-unit pressure control valves for the rapid and accurate attainment of interior chamber gas pressures of process chambers such as etch chambers and CVD chambers. 
     BACKGROUND OF THE INVENTION 
     Integrated circuits are formed on a semiconductor substrate, which is typically composed of silicon. Such formation of integrated circuits involves sequentially forming or depositing multiple electrically conductive and insulative layers in or on the substrate. Chemical vapor deposition (CVD) processes are widely used to form layers of materials on a semiconductor wafer. CVD processes include thermal deposition processes, in which a gas is reacted with the heated surface of a semiconductor wafer substrate, as well as plasma-enhanced CVD processes, in which a gas is subjected to electromagnetic energy in order to transform the gas into a more reactive plasma. Forming a plasma can lower the temperature required to deposit a layer on the wafer substrate, to increase the rate of layer deposition, or both. 
     After the material layers are formed on the wafer substrate, etching processes may be used to form geometric patterns in the layers or vias for electrical contact between the layers. Etching processes include “wet” etching, in which one or more chemical reagents are brought into direct contact with the substrate, and “dry” etching, such as plasma etching. Various types of plasma etching processes are known in the art, including plasma etching, reactive ion (RI) etching and reactive ion beam etching. In each of these plasma processes, a gas is first introduced into a reaction chamber and then plasma is generated from the gas. This is accomplished by dissociation of the gas into ions, free radicals and electrons by using an RF (radio frequency) generator, which includes one or more electrodes. The electrodes are accelerated in an electric field generated by the electrodes, and the energized electrons strike gas molecules to form additional ions, free radicals and electrons, which strike additional gas molecules, and the plasma eventually becomes self-sustaining. The ions, free radicals and electrons in the plasma react chemically with the layer material on the semiconductor wafer to form residual products which leave the wafer surface and thus, etch the material from the wafer. 
     Referring to the schematic of FIG. 1, an etch reactor  30 , such as an eMax etch reactor available from Applied Materials, Inc. of Santa Clara, Calif., includes a grounded reaction chamber  32 , typically fitted with liners (not shown) to protect the interior wall surfaces thereof. A wafer  34  is inserted into the chamber  32  typically through a slit valve opening  36  and is placed on a cathode pedestal  38  having an electrostatic chuck  40  that clamps the wafer  34  in place. A cooling fluid circulates through cooling channels (not shown) in the pedestal  38  to control the temperature of the pedestal  38 , and thus, the temperature of the wafer  34 . A thermal transfer gas such as helium may be supplied to grooves (not shown) provided in the upper, wafer-supporting surface of the pedestal  38 . The thermal transfer gas enhances the efficiency of thermal coupling between the pedestal  38  and the wafer  34 . 
     An RF power supply  42  is connected to the cathode pedestal  38  and generates the etchant plasma while controlling the DC self-bias. Magnetic coils  44  encircle the chamber  32  and generate a slowly-rotating, horizontal, essentially DC magnetic field to increase the intensity of the plasma. A vacuum pump  46  pumps the gaseous contents of the chamber  32  through an adjustable throttle valve  48 . Shields  50 ,  52  may serve to both protect the chamber  32  and pedestal  38  from the etchant plasma and define a pumping channel  54  connected to the throttle valve  48 . 
     Processing gases are supplied from gas sources  58 ,  60 ,  62  through respective mass flow controllers  64 ,  66 ,  68  to a quartz gas distribution plate  70  positioned in the top of the chamber  32  overlying and separated from the wafer  34  across a processing region  72 . The gas distribution plate  70  includes a manifold  74  that receives the processing gas and communicates with the processing region  72  through a showerhead having a large number of distributed apertures  76  which facilitate a substantially uniform flow of processing gas into the processing region  72 . 
     By regulating the flow of gases from the interior of the vacuum chamber  32  to the vacuum pump  46 , the throttle valve  48  of the etch reactor  30  is typically used to control the interior pressures of the chamber  32 . As shown in FIGS. 2 and 3, the throttle valve  48  typically contains a valve frame  78  having a circular valve opening  79 . A pair of adjacent valve blades  80  is pivotally mounted in the valve opening  79 , and each of the valve blades  80  is operably engaged by a stepper motor (not shown). As shown in FIG. 2, in the closed position the valve blades  80  are disposed in coplanar relationship to each other and interlock to close the valve opening  79 . As shown in FIG. 3, upon flow of gases  81  from the vacuum chamber  32  to the vacuum pump  46 , the valve blades  80  are pivoted from the coplanar configuration to angled positions in stepwise fashion, thereby opening the valve opening  79  to varying degrees and regulating the rate of flow of the gas from the vacuum chamber  32  to the vacuum pump  46 , and thus, the interior pressure of the chamber  32 . The valve blades  80  can typically be incrementally opened throughout a range of finely-graded “steps” from 0 (in which the valve blades  80  are disposed in substantially coplanar relationship, or 0 degrees, with respect to the planar surface  82  of the valve frame  78 ), through 800 (in which the valve blades  80  are disposed at a substantially 90-degree angle with respect to the planar surface  82 ). The “0” step corresponds to the configuration of the valve blades  80  at which the valve opening  79  presents no area for gas flow, whereas the “800” step corresponds to the configuration of the valve blades  80  at which the valve opening  79  presents the largest area for gas flow through the throttle valve  48 . 
     Referring next to the graph of FIG. 4, wherein the area of the valve opening  79  available for flow of gas through the throttle valve  48  is plotted on the Y axis as a function of the various step positions of the valve blades  80 , which are plotted along the x axis. It can be seen from the graph that a typical etch process is carried out in the chamber  32  when the valve blades  80  are between steps  10  and  45 . In this relatively narrow process region interval, which begins when the valve blades  80  are close to the 0-step position, PI is aggressive and pressures in the chamber  32  are optimal for the etch process; on either side of the process region interval, pressures in the chamber  32  fluctuate rapidly and are unstable. Accordingly, a throttle valve is needed which is characterized by a wider process region interval that begins at a higher valve blade step to enhance pressure stability and maintain aggressive PI over a broader valve blade step range to increase throughput of wafers through the chamber and prolong hardware lifetime. 
     An object of the present invention is to provide new and improved blades for a throttle valve used in conjunction with a process chamber for substrate processing. 
     Another object of the present invention is to provide new and improved throttle valve blades which facilitate a broader process interval for the processing of substrates. 
     Still another object of the present invention is to provide new and improved throttle valve blades which enhance stability in chamber pressures during the processing of substrates. 
     Yet another object of the present invention is to provide new and improved throttle valve blades which maintain aggressive PI throughout a broader operational range of a process chamber for substrates. 
     A still further object of the present invention is to provide new and improved throttle valve blades for a throttle valve on a process chamber, which throttle valve blades increase tool throughput. 
     Yet another object of the present invention is to provide new and improved throttle valve blades which include notches provided therein to facilitate delayed onset and gradual variations in the rate of gas flow through a throttle valve throughout the step range of the valve blades. 
     Still another object of the present invention is to provide new and improved throttle valve blades the radius of which may be varied to facilitate delayed onset and gradual variations in the rate of gas flow through a throttle valve. 
     SUMMARY OF THE INVENTION 
     In accordance with these and other objects and advantages, the present invention is generally directed to new and improved valve blades for a throttle valve which is typically used to control gas pressures in a process chamber for substrates. The valve blades of the present invention facilitate delayed onset and gradual or fine variations in the flow of gas through the throttle valve to achieve a process interval of interior chamber gas pressures over a broader valve blade step range, achieve aggressive PI over a broad range for enhanced tool throughput, enhance stability of interior chamber gas pressures during substrate processing, and increase tool uptime and production efficiency. In one embodiment, each of the two valve blades in the throttle valve includes at least one, and typically, multiple notches or gaps for a delayed onset, and finely-graded increase, in flow of gas through the valve throughout the step range of the valve blades. The notches or gaps may have a rectangular cross-section or a triangular cross-section. 
     In another embodiment, the semicircular valve blades have a cam-shaped configuration and are capable of varying the radius of the circle defined by the two blades as the blades are stepped between the closed and fully-opened positions. Due to the unique configuration of the valve blades, flow of gas through the throttle valve is characterized by delayed onset of gas flow through the valve upon initial stepped opening of the valve blades, as well as gradual or finely-graded increases in flow of the gas through the throttle valve throughout the process interval to enhance pressure stabilization, tool uptime and production capability. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic view of a typical conventional plasma etching system, suitable for implementation of the present invention; 
     FIG. 2 is a perspective view of a pair of valve blades of a conventional throttle valve for a plasma etching system, with the valve blades in the closed position; 
     FIG. 3 is a perspective view of a pair of valve blades of a conventional throttle valve for a plasma etching system, with the valve blades in the open position; 
     FIG. 4 is a graph wherein the area of the valve opening available for flow of gas through the conventional throttle valve is plotted on the Y axis, as a function of the various step positions of the valve blades in the throttle valve, plotted along the X axis; 
     FIG. 5 is a perspective view of a pair of valve blades in a first embodiment of the present invention; 
     FIG. 6 is a rear view of one of the valve blades of the pair of valve blades shown in FIG. 5; 
     FIG. 7A is a schematic view illustrating a zero-step or closed position of the valve blades of FIG. 6; 
     FIG. 7B is a schematic view illustrating a 100-step open position of the valve blades of FIG. 6, in implementation of the present invention; 
     FIG. 7C is a schematic view illustrating a 300-step open position of the valve blades of FIG. 6, in implementation of the present invention; 
     FIG. 8 is a top view of the valve blades of FIG. 5; 
     FIG. 9 is a graph wherein the area of the valve opening available for flow of gas through the valve blades of FIG. 5 is plotted along the Y axis, as a function of the various step positions of the valve blades, plotted along the X axis; 
     FIG. 10 is a top view of a pair of valve blades in a second embodiment of the present invention; 
     FIG. 11 is a rear view of one of the pair of valve blades in the second embodiment of the invention illustrated in FIG. 10; 
     FIG. 12 is a rear perspective view of the valve blade illustrated in FIG. 11; 
     FIG. 13 is a top view of a third embodiment of the valve blades of the present invention; 
     FIG. 14A is a cross-sectional view, taken along section lines  14 — 14  in FIG. 13, with the valve blades shown in the closed or 0-step position; 
     FIG. 14B is a cross-sectional view, taken along section lines  14 — 14  in FIG. 13, with the valve blades shown in an open position; 
     FIG. 15 is a rear perspective view of a valve blade element of the third embodiment of the present invention illustrated in FIG. 13; and 
     FIG. 16 is a cross-sectional view, taken along section line  16 — 16  in FIG.  15 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is generally directed to valve blades for a throttle valve which is typically used to control gas pressures in a process chamber for substrates. The invention has particularly beneficial utility in the stabilization of operational chamber pressures for an etch chamber used in the etching of material layers on a semiconductor wafer substrate during the fabrication of integrated circuits on the substrate. However, the invention is not so limited in application, and while references may be made to such etch chamber, the present invention is more generally applicable to stabilizing chamber pressures in a variety of industrial and mechanical applications. 
     Referring to FIGS. 5-8, a first embodiment of a throttle valve  15  of the present invention is shown in FIG.  8  and is typically installed in a gas outlet conduit or opening (not shown) of an etch chamber (not shown) such as an eMAX etch chamber available from Applied Materials, Inc., of Santa Clara, Calif. A vacuum pump (not shown) is provided in fluid communication with the throttle valve  15  for drawing etchant gases and by-products from the chamber, through the throttle valve  15 . The throttle valve  15  includes a generally planar valve frame  9  that is mounted in a valve housing  14 , having an inlet end  14   a  confluently connected to the etch chamber (not shown) and an outlet end  14   b  confluently connected to the vacuum pump (not shown). A circular valve opening  10  extends through the valve frame  9 , and an elongated blade mount member  12  bisects the valve opening  10 , dividing the valve opening  10  into two semicircular openings of substantially equal area. A valve blade  1  is mounted in each of the two semicircular portions of the valve opening  10 , on respective sides of the blade mount member  12 . As shown in FIG. 6, each valve blade  1  includes a blade body  2  having a substantially flat or planar outlet surface  2   a.  A mount flange  8  extends along the straight front edge of the blade body  2  and is pivotally attached to the blade mount member  12 , according to the knowledge of those skilled in the art. As shown in FIG. 8, a stepper motor  16  operably engages each blade body  2  through a motor shaft  17 , according to the knowledge of those skilled in the art, for stepwise pivoting of the valve blades  1  in the valve opening  10 . A curved sealing surface  7  on each valve body  2  slidably and sealingly engages the valve frame  9  at the edge of the valve opening  10  as the valve body  2  is pivoted in the valve opening  10 , as hereinafter further described. A rear flange  3  extends along the arcuate rear edge of the valve body  2  and removably engages the bottom surface of the valve frame  9  when the valve body  2  is disposed in the closed position in the valve opening  10 , as shown in FIG.  7 A and hereinafter described. 
     A pair of spaced-apart gas flow gaps  6  is provided in the valve body  2 , defining a pair of lateral protrusions  4  and a middle protrusion  5  that are separated from each other by the gas flow gaps  6 . Each of the lateral protrusions  4  includes a generally sloped inlet surface  4   a,  and the middle protrusion  5   a  likewise includes a generally sloped inlet surface  5   a.  As shown in FIG. 6, each of the gas flow gaps  6  may have a generally rectangular cross-sectional configuration. The convex seal surface  7  extends between the rear flange  3  and the gap bottom  6   a  of each gas flow gap  6 . The seal surface  7  further defines the rear surface of the middle protrusion  5  and each lateral protrusion  4 . 
     Referring next to FIGS. 7A-7C, the stepper motor  16  is capable of rotating or pivoting each valve blade  1  throughout a range of steps typically from 0 to 800. At step  0  of the stepper motor  16 , the outlet surface  2   a  of the blade body  2  is disposed in coplanar relationship with the outlet surface  2   a  of the valve frame  9  and the rear flange  3  engages the outlet surface  2   a,  as shown in FIG.  7 A. At step  0 , the valve opening  10 , being completely closed by the valve blades  1 , presents no area for flow of gas  11  through the throttle valve  15 . At step  800  of the stepper motor  16 , the outlet surface  2   a  of the blade body  2  is disposed at a substantially 90-degree angle with respect to the valve frame  9 , and the valve opening  10  thus presents the maximum area available for flow of the gas  11  through the throttle valve  15 . As the stepper motor  16  pivots the respective valve blades  1  in stepwise fashion from step  0 , the mount flange  8  of each blade body  2  pivots on the blade mount member  12  as the convex seal surface  7  slidably and sealably engages the valve frame  9  at the concave edge of the valve opening  10 , until the gap bottom  6   a  of each gas flow gap  6  is eventually displaced beyond the bottom surface of the valve frame  9 , as shown in FIG.  7 B. In a preferred embodiment, at step  100  of the stepper motor  16  the valve frame  9  is disposed about midway between the gap bottom  6   a  and the inlet surface  5   a  of the middle protrusion  5 , as further shown in FIG.  7 B. This facilitates flow of the gas  11  past the valve plate  9  through the gas flow gaps  6 . Continued stepwise pivoting of the valve blades  1  from step  100  to step  300  results in complete clearing of the gas flow gaps  6  beyond the valve frame  9  in incremental fashion for eventual unrestricted flow of the gas  11  through the respective gas flow gaps  6 , as shown in FIG.  7 C. This unrestricted flow of the gas  11  through the gas flow gaps  6  occurs at step  300  of the stepper motor  16 , wherein the inlet surface Sa of the middle protrusion  5  is located at the level of the bottom surface of the valve frame  9 . 
     Referring next to the graph of FIG. 9, wherein the area of the valve opening  10  available for flow of the gas  11  through the throttle valve  15  is plotted along the Y axis, as a function of the various step positions of the valve blades  1 , plotted along the X axis. It can be seen from the graph that the process region interval, corresponding to the stepped positions of the valve blades  1  in which the interior chamber pressures are optimum for carrying out an etching process, occurs between step  100  and step  300  of the stepper motor  16 . This process region interval is broader than that which can be achieved using conventionally-shaped valve blades, and moreover, presents both a delayed onset of gas flow and gradual increase in available gas flow area through the throttle valve over the range of the process region interval. These characteristics promote aggressive PI and stability in the interior chamber pressures, resulting in enhanced tool throughput and efficiency. 
     Referring next to FIGS. 10-12, in another embodiment of the throttle valve  15 , the blade body  19  of each valve blade  1   a  includes gas flow gaps  18  each having a generally triangular-shaped cross-section. Like the valve blades  1  of FIGS. 5-8, the gas flow gaps  18  separate a middle protrusion  5  from a pair of lateral protrusions  4 . The triangular shape of the gas flow gaps  18  provide a smaller area for gas flow at step  100  as compared to the rectangular cross-sectional gas flow gaps  6  of the valve blades  1 , and thus, provide a more gradual change in the rate of gas flow through the throttle valve  15 , enhancing chamber pressure stabilization. 
     Referring next to FIGS. 13-16, in another embodiment of the invention, the valve blades  89  are mounted in a circular valve opening  88  of a valve frame  87 . The valve frame  87  is mounted in a valve housing  86  of a throttle valve  85 . Each of a pair of parallel plate mount shafts  98 , engaged by a motor shaft  21  of a stepper motor  20  and spanning the valve opening  88 , is capable of stepwise rotation by operation of the stepper motor  20 , as hereinafter described. A circular frame flange  87   a  extends from the valve frame  87  and circumscribes the valve opening  88 . 
     As shown in FIG. 15, each of the valve blades  89  includes a semicircular, cam-shaped blade body  90  that has a curved rear flange  91  which extends along the convex bottom rear edge, and a straight plate flange  92  which extends along the straight front edge, of the blade body  90 . The blade body  90  further includes a convex sealing surface  99  which extends above the rear flange  91 , a sloped, flat inlet surface  99   a  which extends between the plate flange  92  and the upper edge of the sealing surface  99 , and a flat or planar outlet surface  102 . Fastener openings  93  provided at spaced intervals in the plate flange  92  receive respective fasteners  94  that fasten the plate flange  92  of each blade body  90  to the corresponding plate mount shaft  98  in the valve opening  88 , as shown in FIG.  14 A. The convex sealing surface  99  of each blade body  90  slidably and sealingly engages the frame flange  87   a,  as further shown in FIG.  14 A. As shown in FIG. 16, the lower dimension “R0”, which represents the depth of the outlet surface  102 , is greater than the upper dimension “R1”, which represents the depth of the inlet surface  99   a.    
     As shown in FIGS. 14A and 14B, a generally rectangular top plate  95  is mounted to one of the plate mount shafts  98 , typically using the multiple fasteners  94 . A generally curved top plate flange  95   a  extends downwardly along the front edge of the top plate  95 , and a plate extension  96  extends forwardly from the top plate  95 , above the top plate flange  95   a.  A generally rectangular bottom plate  97  is mounted to the other of the plate mount shafts  98 , and a generally curved bottom plate flange  97   a  extends downwardly along the front edge of the bottom plate  97 . As shown in FIG. 14A, when the valve blades  89  are disposed in the closed position, the rear flanges  91  of the respective blade bodies  90  engage the frame flange  87   a  of the valve frame  87 . The top plate  95  and the bottom plate  97  are in coplanar relationship to each other, with the plate extension  96  engaging the upper surface of the bottom plate  97 . 
     In operation, the throttle valve  85  is used to control the flow of gases  100  from an etch chamber (not shown), through the throttle valve  85  and to a vacuum pump (not shown). Accordingly, as the plate mount shafts  98  are rotated by the stepper motor  20  in stepwise fashion to position the respective valve blades  89  from the closed position of FIG. 14A to the fully-opened position of FIG. 14B, the convex sealing surface  99  of each blade body  90  slidably traverses the concave frame flange  87   a.  This movement gradually reduces the radius of the circle represented by the two semicircular valve blades  89 , thereby gradually increasing the area of the valve opening  88  which is available for flow of the gases  100  through the throttle valve  85 . As further shown in FIG. 14B, the gradually-decreasing radius of the valve blades  89  together defines an annular flow gap  101  which does not exist in the closed position of FIG. 14A but gradually increases in width for the flow of the gases  100  at an increasing rate between the blade body  90  and the frame flange  87   a,  through the gap  101  as the valve blades  89  are rotated by the respective plate mount shafts.  98 . Simultaneously, the top plate  95  and the bottom plate  97  angle upwardly as the plate extension  96  disengages the bottom plate  97  and the top plate extension  95   a  rotates against the bottom plate flange  97   a.  In a preferred embodiment, the radius of the circle represented by the valve blades  89  is reduced by about 2.5 mm as the valve blades  89  are rotated from the closed position, wherein the outlet surface io 2  is disposed at a 0 degree angle with respect to the outlet surface of the valve frame  87 , to an open position wherein the outlet surface  102  is disposed at a 37 degree angle with respect to the outlet surface of the valve frame  87 . 
     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.