Abstract:
A new and improved fully-sealing throttle valve which is capable of selectively varying or stopping the flow of gas from one gas flow channel to an adjacent gas flow channel. The throttle valve includes a valve body in which is slidably disposed a tapered valve plug having a tapered plug sealing surface. A motor operably engages the valve plug for progressively moving the valve plug toward a correspondingly-tapered, complementary valve plug seat in the valve body in order to impede flow of gas between the plug sealing surface and the valve plug seat, through the valve body. The motor is capable of moving the plug sealing surface of the valve plug in firm engagement with the valve plug seat of the valve body to selectively prevent further flow of gas through the valve body.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to throttle valves for regulating the flow of a fluid through conduit or channel. More particularly, the present invention relates to a combined isolation valve and fully-sealing throttle valve which is particularly suitable for controlling the flow of gases in a plasma etching system used in the fabrication of integrated circuits.  
         BACKGROUND OF THE INVENTION  
         [0002]    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. Etching processes may then 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.  
           [0003]    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.  
           [0004]    As discussed above, plasma includes high-energy ions, free radicals and electrons which react chemically with the surface material of the semiconductor wafer to form reaction produces that leave the wafer surface, thereby etching a geometrical pattern or a via in a wafer layer. Plasma intensity depends on the type of etchant gas or gases used, as well as the etchant gas pressure and temperature and the radio frequency generated at an electrode in the process chamber by an RF generator. If any of these factors changes during the process, the plasma intensity may increase or decrease with respect to the plasma intensity level required for optimum etching in a particular application. Decreased plasma intensity results in decreased, and thus incomplete, etching. Increased plasma intensity, on the other hand, can cause overetching and plasma-induced damage of the wafers. Plasma-induced damage includes trapped interface charges, material defects migration into bulk materials, and contamination caused by the deposition of etch products on material surfaces. Etch damage induced by reactive plasma can alter the qualities of sensitive IC components such as Schottky diodes, the rectifying capability of which can be reduced considerably. Heavy-polymer deposition during oxide contact hole etching may cause high-contact resistance.  
           [0005]    Throttle valves are known in the art for controlling the rate of flow of a gas through a channel. In a plasma etcher used in the etching of material layers on semiconductor wafers, a throttle valve is a component part of a pressure servo system which leads from the chamber and conducts gases from the chamber to control the intra-chamber gas pressures. Throttle valves typically include a generally cylindrical valve body for allowing gas or other fluid to flow therethrough. A movable valve disk disposed inside the valve body is provided on a rotatable shaft that is engaged by a step motor. By rotating the valve disk from a position parallel to the flow direction to a position perpendicular to the flow direction of the gas, the step motor decreases the rate of flow of the gas through the valve body. While it is positioned perpendicular to the gas flow direction the valve disk impedes, rather than prevents, flow of the gas through the valve body. It is desirable in many applications during semiconductor fabrication to prevent, rather than merely regulate, flow of a gas from one channel to another. Isolation valves are commonly used in the industry for this purpose.  
           [0006]    Referring to FIG. 1, a pressure servo system  10  of a dry etching chamber  12  used in the semiconductor industry is shown. The pressure servo system  10  includes a pumping line  14  which leads from the chamber  12 . A throttle valve  16  and an isolation valve  22  are provided in series in the pumping line  14 . A pressure controller  32  is operably connected to the control elements of the throttle valve  16  and the isolation valve  22 , respectively. A manometer  34  is connected to the chamber  12  for measuring gas pressures therein.  
           [0007]    As shown in FIG. 2, the throttle valve  16  typically includes a valve body  17  having a valve interior  18 . A valve disk  19  is mounted inside the valve interior  18  on a motor shaft  20  that is engaged by a stepper motor (not shown). Gas  33  is introduced into the side of the chamber  12  through gas entry ports (not shown), and the gas  33  is drawn from the chamber  12  through the pumping line  14  by operation of a pump (not shown). By operation of the pressure controller  32 , the motor shaft  20  is actuated to rotate the valve disk  19  to various orientations with respect to the direction of flow of gas  33  flowing through the valve body  17  in order to control the rate of flow of the gas  33  through the pumping line  14 , and thus, the interior gas pressures of the chamber  12 .  
           [0008]    As shown in FIG. 3, the isolation valve  22  typically includes a valve body  23  having a valve interior  24  which communicates with a gas entry arm  25  and a gas exit arm  26  disposed in perpendicular relationship to each other. A shaft  28  in the valve interior  24  is mounted on a shaft mount block  27 . An O-ring  31  is normally biased by a spring  29  in an open position to facilitate free flow of gas from the gas entry arm  25  to the gas exit arm  26 . A diaphragm  30  in the valve interior  24  may enclose the spring  29 . The pressure controller  32  facilitates slidable extension of the shaft  28  through the shaft mount block  27  and engagement of the O-ring  31  against the valve body  23  to close the isolation valve  22  by facilitating the flow of clean dry air (CDA) through a port  36  in the valve body  23 .  
           [0009]    In the pressure servo state, the isolation valve  22  is in the fully-open position. By varying the positions of the valve disk  19  in the throttle valve  16  through the step motor (not shown), the pressure controller  32  regulates the conductance of the pumping line  14  and thereby adjusts the interior pressure of the process chamber  12  to establish and maintain the chamber pressure at the desired set point value. Simultaneously, the chamber pressure, monitored by the manometer  34 , is continually compared with the set point pressure. The controller  32  responds to any differences by continually repositioning the valve disk  19  with respect to the direction of gas flow  33  through the throttle valve  16 . In the idle state, the isolation valve  22  is fully closed and the throttle valve  16  is fully opened.  
           [0010]    A common problem that is inherent in the conventional throttle valve  16  used in pressure servo systems  10  of plasma etchers is that polymer residues from the plasma gases flowing through the throttle valve are deposited on the valve disk  19  over time. This tends to damage the valve disk  19 , interfere with the stability of gas flow through the valve body and compromise pressure stability in the etching chamber. A new and improved valve is needed which combines the gradual gas flow reduction functions of a throttle valve with the complete gas flow prevention function of an isolation valve, in a single device.  
           [0011]    An object of the present invention is to provide a new and improved throttle valve which is suitable for a processing chamber for the fabrication of integrated circuits.  
           [0012]    Another object of the present invention is to provide a fully-sealing throttle valve which combines the functions of a throttle valve and an isolation valve in one device.  
           [0013]    Still another object of the present invention is to provide a throttle valve which is capable of precisely controlling interior gas pressures inside a processing chamber.  
           [0014]    Yet another object of the present invention is to provide a throttle valve which is capable of both teminating flow of gas through a pumping line and impeding flow of gas through the pumping line to various degrees.  
           [0015]    A still further object of the present invention is to provide a new and improved, fully-sealing throttle valve which is capable of reducing the polymer deposition-induced pressure servo failure rate which is characteristic of conventional throttle valves.  
           [0016]    Yet another object of the present invention is to provide a new and improved throttle valve which is capable of a variety of applications including but not limited to controlling the pressure of gases inside a semiconductor processing chamber such as an etcher.  
           [0017]    A still further object of the present invention is to provide a new and improved throttle valve which has a variety of industrial applications.  
         SUMMARY OF THE INVENTION  
         [0018]    In accordance with these and other objects and advantages, the present invention is generally directed to a new and improved fully-sealing throttle valve which is capable of selectively varying or stopping the flow of gas from one gas flow channel to an adjacent gas flow channel. The throttle valve includes a valve body in which is slidably disposed a tapered valve plug having a tapered plug sealing surface. A motor operably engages the valve plug for progressively moving the valve plug toward a correspondingly-tapered, complementary valve plug seat in the valve body in order to impede flow of gas between the plug sealing surface and the valve plug seat, through the valve body. The motor is capable of moving the plug sealing surface of the valve plug in firm engagement with the valve plug seat of the valve body to selectively prevent further flow of gas through the valve body. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0020]    [0020]FIG. 1 is a schematic view of a typical conventional pressure servo system for a dry etcher used in the semiconductor fabrication industry;  
         [0021]    [0021]FIG. 2 is a schematic view of a conventional throttle valve used in the pressure servo system of FIG. 1;  
         [0022]    [0022]FIG. 3 is a schematic view of a conventional isolation valve used in the pressure servo system of FIG. 1;  
         [0023]    [0023]FIG. 4 is a schematic view of a pressure servo system for a dry etcher in implementation of the present invention;  
         [0024]    [0024]FIG. 5 is a cross-sectional, partially schematic view of a fully-sealing throttle valve of the present invention, with the throttle valve shown in the open configuration;  
         [0025]    [0025]FIG. 5A is an enlarged cross-sectional view illustrating partial constriction of a gas flow pathway through the throttle valve; and  
         [0026]    [0026]FIG. 6 is a cross-sectional, partially schematic view of the fully-sealing throttle valve of the present invention, with the throttle valve shown in the closed configuration. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    The present invention has particularly beneficial utility in controlling gas pressures in a plasma etch chamber used in the fabrication of integrated circuits on semiconductor wafer substrates. However, the invention is not so limited in application and while references may be made to such plasma etch chamber, the invention is more generally applicable to controlling interior chamber pressures in a variety of industrial and mechanical applications. Furthermore, while the invention will hereinafter be described as regulating or preventing the flow of a process gas or gases from a process chamber to a pump, it is understood that the invention may be adapted for regulating or preventing the flow of a liquid between first and second conduits, containers or chambers.  
         [0028]    Referring initially to FIG. 4, a pressure servo system which incorporates a fully-sealing throttle valve  46  of the present invention is generally indicated by reference numeral  40 . The pressure servo system  40  includes a pumping line  44  which leads from a process chamber  42 . The process chamber  42  may be a dry etch chamber manufactured by the Lam Research Corp. of Fremont, Calif., for example, although the invention is equally applicable to other types of process chambers known by those skilled in the art. Accordingly, the process chamber  42  may be used to etch material layers from a semiconductor wafer substrate (not shown) placed in the process chamber  42  in the fabrication of integrated circuits on the substrate, as is known by those skilled in the art. A manometer  64  is connected to the process chamber  42  for measuring gas pressures therein. Process gases  43  are introduced into the process chamber  42  through one or multiple gas entry ports (not shown) typically provided in the side of the process chamber  42 . As hereinafter further described, the throttle valve  46  of the present invention is provided in the pumping line  44  and is adapted for controlling the rate of flow of process gases from the process chamber  42  to a pump (not shown), thereby controlling the interior gas pressures of the process chamber  42 . The throttle valve  46  is also capable of completely terminating or preventing flow of the process gases from the process chamber  42  to the pump, as needed. Accordingly, the fully-sealing throttle valve  46  is capable of assuming the function of both the conventional throttle valve and the conventional isolation valve, which are separate components of the conventional pressure servo system. A pressure controller  66  is operably connected to the actuating components of the throttle valve  46  and receives continuous input from the manometer  64  to control the interior gas pressures of the process chamber  42  through the throttle valve  46 , as hereinafter described.  
         [0029]    Referring to FIGS. 5 and 6, the fully-sealing throttle valve  46  of the present invention includes an elongated valve body  47  which may have a cylindrical or any alternative cross-sectional shape that is consistent with the use requirements of the throttle valve  46 , to be hereinafter described. A gas entry arm  58  extends from the valve body  47 , adjacent to one end thereof, and a gas exit arm  60  extends from the valve body  47 , at the end thereof and typically in substantially perpendicular relationship to the gas entry arm  58 . Alternatively, the gas entry arm  58  and the gas exit arm  60  may extend from opposite sides of the throttle valve  46 , in linear or 180-degree relationship to each other. Both the gas entry arm  58  and the gas exit arm  60  communicate with a valve interior  48  defined by the valve body  47 . A sloped, annular valve plug seat  62  is defined by the interior surface of the valve body  47 , between the gas entry arm  58  and the gas exit arm  60 . In operation of the throttle valve  46  as hereinafter described, the gas entry arm  58  is disposed in fluid communication with the pumping line  44  of the pressure servo system  40 , whereas the gas exit arm  60  is disposed in fluid communication with an outlet line  45  that communicates with the inlet port (not shown) of the pump (not shown).  
         [0030]    As further shown in FIGS. 5 and 6, a motor housing  50  which contains a typically electric motor  49  is provided on the valve body  47 , typically at the end opposite the gas exit arm  60 . An elongated valve stem  51  is operably engaged by the motor  49  for bidirectional linear movement of the valve stem  51  in the valve interior  48 . The pressure controller  66  is operably connected to the motor  49  in such a manner as to actuate the motor  49  to move the valve stem  51  in a selected linear direction, as indicated by the double-headed arrow and according to the knowledge of those skilled in the art. A resilient valve plug  52 , which includes an annular tapered plug sealing surface  53  and a circular, flat front surface  54 , is provided on the extending end of the valve stem  51 , inside the valve interior  48 . The valve plug  52  may be a corrosion-resistant plastic or rubber such as neoprene, for example, and the slope angle of the plug sealing surface  53  matches and is complementary to the slope angle of the valve plug seat  62 . An annular mount collar  56  may be provided on the motor housing  50 , in the valve interior  48 , in which case a flexible sheath  55  spans the valve plug  52  and the mount collar  56  and encloses the valve stem  51 .  
         [0031]    Referring next to FIGS. 4-6, in application the fully-sealing throttle valve  46  is capable of operation in each of three modes: the “pressure servo” mode, the “pump down” mode and the “idle” mode. In the “pump down” mode, the throttle valve  46  is in the fully-open position of FIG. 5, wherein the plug sealing surface  53  of the valve plug  52  is disposed in maximally-spaced relationship to the valve plug seat  62  of the valve body  47 . In the “idle” mode, the throttle valve  46  is in the fully-closed position of FIG. 6, wherein the plug sealing surface  53  firmly engages the valve plug seat  62  and prevents the flow of process gases  43  from the process chamber  42 , through the valve interior  48  and to the pump. In the “pressure servo” mode, to be hereinafter described in detail, the throttle valve  46  is between the fully-open position of FIG. 5 and the fully-closed position of FIG. 6 in order to achieve and maintain a selected set point pressure in the process chamber  42  during an etching or other process therein.  
         [0032]    In operation of the throttle valve  46  in the “pressure servo” mode, the purpose of which is to achieve and maintain gas pressures in the process chamber  42  for the proper execution of an etching or other process therein, the pressure controller  66  is initially programmed to achieve and maintain a selected set point pressure for the interior of the process chamber  42 , depending on the particular etching or other process to be carried out in the process chamber  42 . As process gases  43  flow into the process chamber  42  through the gas entry ports (not shown) therein, the process gases  43  exit the process chamber  42  through the pumping line  44 . The throttle valve  46  is initially in the open configuration shown in FIG. 5, wherein the plug sealing surface  53  of the valve plug  52  disengages and is spaced-apart from the valve plug seat  62  of the valve body  47 . Accordingly, as shown in FIG. 5, the process gases  43  flow substantially unimpeded from the pumping line  44 , through the gas entry arm  58  and the valve interior  48  of the valve body  47 , respectively, to exit the valve interior  48  through the gas exit arm  60 , and finally, enter the pump. Because the process gases  43  flow substantially freely through the throttle valve  46  to the pump, the initial pressures inside the process chamber  42  may be lower than the programmed set point pressure for the process, in which case the area available for gas flow between the plug sealing surface  53  and the valve plug seat  62  may require narrowing in order to impart additional resistance to the flowing process gases  43  and thereby increase the gas pressure inside the process chamber  42 . The manometer  64  continually monitors the gas pressure inside the process chamber  42  and relays this information to the pressure controller  66 . In the event that the actual gas pressure as indicated by the manometer  64  is lower than the set point pressure programmed into the pressure controller  66 , the pressure controller  66  actuates the motor  49  of the throttle valve  46  to move the valve stem  51  to the right in FIGS. 5 and 6, in order to cause the plug sealing surface  53  on the valve plug  52  to approach the valve plug seat  62  of the valve body  47 , and thereby narrow the area available for gas flow between the gas entry arm  58  and the gas exit arm  60  in the valve interior  48 , as shown in FIG. 5A. This partially restricts the area available for flow of the process gases  43  through the valve interior  48 , thereby increasing gas pressures inside the process chamber  42  in such a manner that the actual gas pressure read by the manometer  64  rises toward and eventually reaches the set point pressure programmed into the pressure controller  66 . In the event that the actual gas pressure as read by the manometer  64  rises above the programmed set point pressure, the pressure controller  66  actuates the motor  49  to move the valve stem  51  to the left in FIG. 5, to widen or enlarge the area available for flow of the process gases  43  through the valve interior  48 . This action reduces impedance imparted to flow of the process gases  43  to the pump, thereby correspondingly reducing gas pressures inside the process chamber  42  toward the set point pressure. By continually adjusting the distance between the plug sealing surface  53  and the valve plug seat  62  through actuation of the motor  49  in the foregoing manner, the pressure controller  66  maintains the gas pressures inside the process chamber  42  at the programmed set point pressure. In the event that it becomes necessary during or after the process to completely terminate or prevent flow of the process gases  43  from the pumping line  44 , through the throttle valve  46  and to the pump, as in the pump idle state, the process controller  66  actuates the motor  49  to move the valve stem  51  to the right in FIG. 6 until the plug sealing surface  53  firmly engages the valve plug seat  62 , thereby preventing flow of the process gases  43  through the valve interior  48 , as shown in FIG. 6.  
         [0033]    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.