Patent Publication Number: US-7582167-B2

Title: Apparatus for reducing entrapment of foreign matter along a moveable shaft of a substrate support

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. patent application Ser. No. 10/775,769 filed Feb. 5, 2004 now U.S. Pat. No. 7,279,049, which is incorporated by reference in its entirety. 

   BACKGROUND OF THE DISCLOSURE 
   1. Field of Invention 
   The invention relates generally to the processing of semiconductor wafers, and relates more particularly to an apparatus for reducing entrapment of foreign matter along a moveable shaft of a substrate support. 
   2. Background of the Invention 
   Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit density that demand increasingly precise fabrication techniques and processes. One fabrication process frequently used is chemical vapor deposition (CVD). Chemical vapor deposition is generally employed to deposit a thin film on a substrate or a semiconductor wafer. 
   Chemical vapor deposition is generally accomplished by introducing a precursor gas into a vacuum chamber. The precursor gas is typically directed through a showerhead situated near the top of the chamber. The precursor gas reacts to form a layer of material on the surface of the substrate that is positioned on a heated substrate support (e.g., a heater) typically fabricated from aluminum. In some systems, the substrate support is mounted upon a moveable (e.g., moveable longitudinally, or rotatable) shaft that is disposed within a sleeve. Purge gas is routed through holes in the support to the edge of the substrate to prevent deposition at the substrate&#39;s edge that may cause the substrate to adhere to the support. Deposition by-products produced during the reaction are pumped from the chamber through an exhaust system. 
   In operation, particles or loose foreign matter may be generated by the system, or inadvertently introduced thereto, and these particles can travel within the confines of the chamber. In particular, particles may travel near the shaft utilized to control the elevation of a substrate support within the processing chamber. The particles may stick to the moving shaft and accumulate in the annulus, or gap, between the shaft and the sleeve that guides the shaft through the bottom of the chamber. The accumulation of particles between the shaft and sleeve can damage both components, leading to premature wear and/or failure of the system. 
   Reducing the annulus between the sleeve and the shaft is one method for minimizing the area in which particles may travel and/or become trapped. Although reducing the gap is a generally effective method for reducing particle accumulation and damage, a small gap still exists that is typically large enough to trap smaller particles. Alternatively, some designs have employed o-rings (sometimes in conjunction with a lubricant) positioned to seal the gap. However, standard o-rings are subjected to abrasion by particulates disposed on the shaft, and thus may not effectively seal the gap after a period of use. Furthermore, standard o-rings tend to generate particles when subjected to processing chamber conditions, exacerbating the particle entrapment problem rather than solving it. 
   Therefore, there is a need for an apparatus for reducing the entrapment of particles and foreign matter along a moveable shaft of a substrate support. 
   SUMMARY OF INVENTION 
   In one embodiment, a guard ring for reducing particle entrapment along a moveable shaft of a substrate support is provided. In one embodiment, a substantially annular guard ring is positioned within a step formed in a sleeve that circumscribes the shaft. The guard ring is positioned to substantially seal a gap separating the shaft from the sleeve, advantageously reducing component wear due to particulate entrapment. 
   In another embodiment, a guard ring comprises a base portion having an inner perimeter and an outer perimeter, a first flange coupled to the inner perimeter, a second flange coupled to the outer perimeter, and a continuous channel separating the first flange from the second flange. The first flange is adapted to bias the ring against the shaft, thereby accommodating displacement and/or misalignment of the shaft relative to the processing chamber. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     So that the manner in which the above recited features of the present invention may be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. 
       FIG. 1  depicts a schematic, sectional view of one embodiment of a processing chamber in which one embodiment of a guard ring according to the present invention is deployed; 
       FIG. 2  is a cross-sectional view of one embodiment of a guard ring for use with the present invention; 
       FIG. 3  is a cross-sectional view of another embodiment of a guard ring for use with the present invention; 
       FIG. 4  is a top view of one embodiment of a guard ring according to the present invention; 
       FIG. 5A  is a top view of another embodiment of a guard ring according to the present invention, before installation; 
       FIG. 5B  is a top view of the guard ring illustrated in  FIG. 5A , after installation; 
       FIG. 6A  is a cross-sectional view of another embodiment of a guard ring for use with the present invention, wherein the shaft is centered within the guard ring; 
       FIG. 6B  is a cross-sectional view of the guard ring illustrated in  FIG. 6A , wherein the guard ring functions as a spring against a displaced shaft; 
       FIG. 7  is a detailed cross-sectional view of the guard ring illustrated in  FIGS. 6A and 6B ; 
       FIG. 8  is a top view of one embodiment of the guard ring illustrated in  FIG. 7 , wherein the guard ring is a unitary component; 
       FIG. 9  is a top view of another embodiment of the guard ring illustrated in  FIG. 7 , wherein the guard ring comprises two pieces; and 
       FIG. 10  is a top view of another embodiment of the guard ring illustrated in  FIG. 7 , wherein the guard ring is a unitary piece used in conjunction with an insert. 
   

   To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
   It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
   DETAILED DESCRIPTION OF INVENTION 
   The invention is a guard ring for preventing particle entrapment along a moveable shaft of a substrate support. The invention is illustratively described below as deployed in a chemical vapor deposition system, such as a barrier chemical vapor deposition (BCVD) system, available from Applied Materials, Inc. of Santa Clara, Calif. However, it should be understood that the invention has utility in other system configurations such as physical vapor deposition systems, ion implant systems, etch systems, chemical vapor deposition systems and any other wafer processing system in which the reduction of particle damage to a moving shaft is necessary or desirable. 
     FIG. 1  is a cross-sectional view of one embodiment of a chemical vapor deposition system  100  that is advantageously adapted to benefit from the present invention. The system  100  generally includes a chamber body  102  coupled to a gas source  104 . The chamber body  102  has walls  106 , a bottom  108  and a lid  110  that define a process volume  112 . The walls  106  and bottom  108  are typically fabricated from a unitary block of aluminum. The chamber body  102  contains a pumping ring  114  that couples the process volume  112  to an exhaust port  116 . The exhaust port  116  is coupled to various pumping components such as roughing, throttle valves and turbomolecular pumps (not shown) that exhaust and control the pressure within the process volume  112 . 
   The lid  110  is supported by the walls  106  and can be removed to service the chamber body  102 . The lid  110  is generally comprised of aluminum and may additionally contain heat transfer fluid channels for regulating the temperature of the lid  110  by flowing a heat transfer fluid therethrough. 
   A showerhead  118  is coupled to an interior side  120  of the lid  110 . The showerhead  118  is typically fabricated from aluminum. The showerhead  118  generally includes a perimeter mounting ring  122  that surrounds a “dish-shaped” center section  124 . The mounting ring  122  includes a plurality of mounting holes  126  that pass therethrough, each accepting a mounting screw  128  that threads into a mating hole  130  in the lid  110 . The center section  124  includes a perforated area  132  that facilitates passage of gases therethrough. 
   A mixing block  134  is disposed in the lid  110 . The mixing block  134  is coupled to the gas source  104 , such that process and other gases may be introduced to the process volume  112  by passing through the mixing block  134  and showerhead  118 . Typically, cleaning gases from a cleaning source (not shown) are also introduced through the mixing block  134  to the process volume  112 . A perforated blocker plate  136  is disposed between the showerhead  118  and mixing block  134  to enhance the uniform distribution of gases passing through the showerhead  118  and into the chamber body  102 . The blocker plate  136  is typically fabricated from aluminum. 
   A substrate support assembly  138  is disposed beneath the showerhead  118 , typically centrally disposed within the chamber body  102 . The support assembly  138  supports a substrate  140  during processing and includes an elevator shaft  142  coupled thereto. The support assembly  138  generally is fabricated from aluminum, ceramic or a combination of aluminum and ceramic. The support assembly  138  typically includes a vacuum port (not shown) and at least one embedded heating element (not shown). The vacuum port is used to apply a vacuum between the substrate  140  and support assembly  138 , for securing the substrate to the substrate support assembly  138  during processing. The heating element, such as an electrode disposed in the support assembly  138 , is coupled to a power source (not shown) for heating the support assembly  138  and substrate  140  positioned thereon to a predetermined temperature. In one embodiment, the heating element maintains the substrate  140  at a uniform temperature of about 150 to 400 degrees. Alternatively, heating lamps or other heat sources may be utilized to heat the substrate  140 . 
   The shaft  142  is coupled between the support assembly  138  and an actuator  144 . The shaft  142  provides a conduit for electrical leads, vacuum and gas supply lines between the support assembly  138  and other components of the system  100 . The actuator  144  moves the support assembly  138  between an elevated position as shown for processing and a lowered position for facilitating substrate transfer. In addition, the actuator  144  may include a mechanism for rotating the shaft  142 . A bellows  146  disposed between the support assembly  138  or shaft  142  and the chamber bottom  108  provides a vacuum seal between the process volume  112  and the atmosphere outside the chamber body  102  while facilitating movement of the support assembly  138 . 
   In one embodiment, the shaft  142  is disposed substantially centrally through an aperture  152  formed in the chamber bottom  108 . In another illustrated, the aperture  152  is formed in sleeve disposed in the chamber bottom  108 . Alternatively, a sleeve may be formed integrally in the bottom  108  of the chamber body  102 . The sleeve  150  is generally a bushing positioned in the chamber bottom  108  to prevent gauling or other wear issues as the shaft  142  moves through the aperture  152  formed in the bottom  108 . 
   The support assembly  138  generally is grounded such that RF power supplied by a power source (not shown) to the showerhead  118  (or other electrode positioned within or near the lid assembly of the chamber) may excite the gases disposed in the process volume  112  between the support assembly  138  and the showerhead  118 . The RF power, generally having a frequency of between a few Hz to 13 MHz or higher is provided in a wattage suitable for the substrate surface area. In one embodiment, the power source comprises a dual frequency source that provides a low frequency power at less than about 2 MHz (preferably about 200 to 500 kHz) and a high frequency power at greater than 13 MHz (preferably about 13.56 kHz). The frequencies may be fixed or variable. Illustratively, for a 550 mm×650 mm substrate, the low frequency power is about 0.3 to about 2 kW while the high frequency power is about 1 to 5 kW. Generally, the power requirements decrease or increase with a corresponding decrease or increase in substrate size. 
   As illustrated in  FIG. 1 , the bottom  108  of the chamber body  102  includes a guard ring  162  for reducing the entrapment of foreign matter between the shaft  142  and the aperture  152  of the sleeve  150 . The guard ring  162  is an annular ring formed from a material that is chemically inert material to process chemistries and other conditions, such as polytetrafluoroethylene or polyetheretherketone. The guard ring  162  is positioned within a step  164  in the aperture  152  of the sleeve  150 . In one embodiment, the guard ring  162  projects above the bottom  108  of the chamber body  102 . 
   In operation, the semiconductor substrate  140  is secured to the support assembly  138  by providing a vacuum therebetween. The temperature of the substrate  140  is elevated to a pre-determined process temperature by regulating thermal transfer to the support assembly by the heating element. During the deposition process, the substrate is heated to a steady temperature, typically between 300° C. and 550° C. 
   Gaseous components, which in one embodiment may include silane and tungsten hexafluoride, are supplied from a gas panel to the process chamber through the mixing block  134  and showerhead  118  to form a gaseous mixture. The gaseous mixture reacts to form a layer of tungsten on the substrate  140 . To prevent deposition at the substrate&#39;s edge and possible adherence of the substrate  140  to the support assembly  138 , purge gases flow from a conduit in the support assembly  138  around the perimeter of the substrate  140 . 
     FIG. 2  is a cross-sectional view of the guard ring  162  illustrated in  FIG. 1 . As discussed with reference to  FIG. 1 , the guard  162  is disposed within the sleeve  150 . In one embodiment, the guard ring  162  is fixed to the sleeve  150  by adhesive. In another embodiment, the guard ring  162  is molded to the sleeve  150 . The sleeve  150  circumscribes an outer surface  202  of the shaft  142  and is separated from the shaft  142  by a first gap g 1 . A first end  204  of the aperture  152  formed in the sleeve  150  facing the interior of the chamber  102  includes the step  164  for receiving the guard ring  162 . In one embodiment illustrated in  FIG. 3 , the step  364  further comprises a radially inward extending lip  352  positioned proximate to the first end  304  of the sleeve  350  for retaining the guard ring  362  within the aperture  152 . 
   Returning to  FIG. 2 , the guard ring  162  includes an outer circumference  210  (i.e., the surface of the guard ring  162  that contacts the sleeve  150 ) and an inner perimeter  220 . In one embodiment, the outer circumference  210  is formed substantially vertically to fit the shape of the step  164 . In the embodiment illustrated in  FIG. 3 , the outer circumference  310  flares (radially) outward to facilitate engagement of the guard ring  362  with the lip  350  of the step  364 . 
   Returning to  FIG. 2 , in one embodiment, the inner perimeter  220  is formed substantially as a wedge, so that the innermost point of the guard ring  162  forms a substantially V-shaped sealing lip  240  that extends upwardly and inwardly toward the center of the guard ring  162  and the shaft  142 . The sealing lip  240  may contact the shaft  142  at a chiseled contact point. In one embodiment, the inner perimeter  220  of the guard ring  162  extends slightly above the step  164  on the sleeve  150 , so that a surface of the guard ring  162  slopes slightly upward from the sleeve  150  to the shaft  142 . The upward slope enables the guard ring  162  to capture and/or wipe particles from the shaft  142  as the shaft  142  moves along its longitudinal axis within the sleeve  150 , thereby substantially preventing the particles from entering the gap g 1 . 
   In one embodiment, the shaft  142  is positioned substantially concentrically within the sleeve  150 , and the lip  240  is substantially continuous around the circumference of the shaft  142 . However, if the shaft  142  shifts so that the shaft  142  becomes positioned eccentrically within the sleeve  150 , the distance from the shaft  142  to the sleeve  150  will vary around the diameter of the shaft  152 . Thus in one embodiment, the guard ring  162  is formed of a resilient material, and the sealing lip  240  has a diameter that is smaller than the diameter of the shaft  142  so that contact is maintained around the shaft&#39;s diameter even when there is eccentricity between the shaft  142  and sleeve  150 . 
   The guard ring  162  is positioned to substantially prevent the entrapment of particles and loose foreign matter between the shaft  142  and the sleeve  150 . Referring back to  FIG. 1 , a particle p that is generated within or introduced into the chamber body  102  may be free to move about the chamber and potentially become trapped between the shaft  142  and the sleeve  150 , creating a hazard to the components of the chamber body  102 . The guard ring  162  prevents the particle p, and similar particles, from entering and passing through the gap (e.g., g 1  in  FIG. 2 ) between the shaft  142  and the sleeve  150 , thereby substantially reducing particle damage to the shaft  142  and associated mechanisms. 
   In an embodiment illustrated in a top view of a guard ring  400  in  FIG. 4 , the guard ring  400  is formed as a continuous, closed ring. The geometry of the guard ring  400  may be formed similarly to the guard rings  162  and  604  discussed with relation to the preceding Figures. In another embodiment, illustrated in top view in  FIG. 5A , a guard ring  500  is formed as a split ring, wherein first and second ends  502 ,  504  of the ring  500  are separated by a small gap  506 . The size of the gap  506  will vary depending on the size of the guard ring  500 .  FIG. 5A  illustrates the guard ring  500  before installation. The sleeve compresses the guard ring  500  upon installation of the guard ring  500 , closing the gap  506  as shown in  FIG. 5B . 
     FIG. 8  illustrates a top view of one embodiment of a guard ring  800  for use with a shaft having a flat surface on a portion of its circumference (not shown). In one embodiment, a guard ring  800  comprises a substantially continuous, closed ring. The guard ring  800  has an outer circumference  802  and an inner perimeter  804 . The outer circumference  802  is formed substantially as a continuous ring; however, the inner perimeter  804  comprises a round portion  805  and a flat portion  806  that is outset perpendicular to the centerline of the guard ring  800 . The flat portion  806  is positioned to contact a flat surface  880  of a shaft  882 . The flat surface  880  of the shaft  882  prevents the guard ring  800  from rotating relative to the shaft  882 . 
   In another embodiment illustrated in  FIG. 9 , a guard ring  900  comprises a first component  902  and a second component  904  that sealingly engage each other to form a substantially annular ring  900 . In one embodiment, the first component  902  is substantially C-shaped and comprises an outer circumference  906  and an inner perimeter  908 . The first component  902  further comprises two ends  910   a  and  910   b  adapted to retain the second component  904  therebetween. The second component  904  comprises a substantially wedge-shaped piece having an arcuate outer surface  912  and a flat inner surface  914  that is sized to be substantially equal to a chord defined by the open ends  910   a  and  910   b  of the first component  902 . The arcuate outer surface  912  is formed to substantially the same radius as the outer circumference  906  of the first component  902  when the second component  904  and the first component  902  are fit together; the flat inner surface  914  is positioned to contact the flat surface of the shaft (not shown) and is adapted to be positioned substantially parallel to a diameter d of the ring  900 . 
   In another embodiment illustrated in  FIG. 10 , a guard ring  1000  comprises a ring  1002  and an insert  1004 . In one embodiment, the ring  1002  is a substantially continuous, closed component, such as the guard ring  400  illustrated in  FIG. 4 , and has an outer circumference  1006  and an inner perimeter  1008 . The insert  1004  comprises an arced surface  1010  and a flat surface  1012 . The arced surface  1010  is formed to substantially conform to a portion of the inner perimeter  1008  of the ring  1002 ; the flat surface  1012  is positioned to face radially inward to contact the flat surface of a shaft (such as shown in  FIG. 8 ), and is sized to be substantially equal to a chord defined by the flat surface of the shaft. 
     FIGS. 6A and 6B  illustrate cross-sectional views of another embodiment of a guard ring  604  according to the present invention. The guard ring  604 , like the assemblies illustrated in  FIGS. 2 and 3 , comprises a resilient, annular ring  604  adapted to be positioned within a sleeve  602 . The sleeve  602  is formed in a bottom of a chamber (not shown) and positioned to circumscribe the outer surface  606  of a shaft  608 . A first end  610  of the sleeve  602  comprises a step  612  formed in an inner perimeter  620  for receiving the guard ring  604 . In one embodiment, the step  612  further comprises a lip  614  that extends radially inward for holding the guard ring  604  within the step  612 . A portion  616  of the unstepped region of the sleeve  602  is separated from the shaft  608  by a first gap g 3 . In the embodiment illustrated in  FIG. 6A , the shaft  608  is substantially centered within the guard ring assembly  600  so that the first gap g 3  is substantially constant around the circumference of the shaft  608 . By contrast,  FIG. 6B  depicts the shaft  608  offset from the centerline of the sleeve  602  (and centerline of the chamber body, not shown). 
     FIG. 7  illustrates a detailed cross-sectional view of the guard ring  604 . The guard ring  604  comprises first and second flanges  702 ,  704  and a base portion  706 . The first and second flanges  702 ,  704  each have first ends  701   a ,  701   b  and second ends  703   a ,  703   b , respectively. The first ends  701   a ,  701   b  are coupled to opposite ends of the base portion  706 , which is substantially flat. The first and second flanges  704 ,  706  are separated by a channel  708 . A substantially fixed width w 1  separates the first ends  701   a ,  701   b  of the flanges  702 ,  704  (i.e., the portion of the channel proximate the base portion  706 ). The width of the channel  708  gradually increases in a direction away from the base portion  706 , achieving the greatest width w 2  at a point that separates the second ends  703   a ,  703   b  of the flanges  702 ,  704 . 
   Referring simultaneously to  FIGS. 6B and 7 , in one embodiment, the first flange  702  forms substantially a right angle with the base portion  706  of the guard ring  604 , so that the first flange  702  and the base portion  706  lie substantially flat against first and second surfaces  622 ,  624  of the step  612 . In another embodiment, a portion  714  of the first flange  702  that contacts the step  612  slopes slightly (radially) inward to facilitate installation of the guard ring  604  on the step  612 . In one embodiment, the outer surface of the first flange  702  includes a small recess  716  located proximate to the second end  703   a  for engaging the retaining lip  614  on the step  612  of the sleeve  602 . The second flange  704  has a tapered shape that extends radially inward (i.e., away from the first flange  702 ). The second end  703   b  of the second flange  704  comprises a chiseled contact point  720  adapted for contacting the shaft  608 . In one embodiment, an outer edge  722  of the contact point  720  is tapered so that the remainder of the second flange&#39;s second end  703   b  substantially avoids contact with the shaft  608 . 
   The guard ring  604  illustrated in  FIGS. 6A-7  is designed to maintain contact with the shaft  608 , while accommodating movement of the shaft  608  in a direction normal to the shaft&#39;s longitudinal axis and/or misalignment of the shaft  608  with respect to the sleeve  602 . The first flange  702  remains substantially fixed in place against the step  612  of the sleeve  602 ; however, the curved shape of the second flange  704  allows the second flange  704  to function essentially as a spring, thereby allowing the guard ring  604  to maintain continuous contact with the perimeter of the shaft  608 , even when the shaft  608  and guard ring  604  are not concentrically aligned. Thus, as illustrated in  FIG. 6B , as the shaft  608  shifts position, force exerted by the shaft  608  on the second end  703   b  of the second flange  704  may cause the second flange  704  to bend radially outward (i.e., toward the first flange  702 ). The channel  708  between the flanges  702  and  704  is sufficiently wide at its narrowest point w 1  to substantially prevent the second flange  704  from physically contacting the first flange  702  when the second flange  704  is bent due to contact with the shaft  608 . 
   Thus, the present invention represents a significant advancement in the fabrication and processing of integrated circuits. A guard ring and assembly are provided that substantially prevent the entrapment of particles and foreign matter between a sleeve and a substrate support having a moveable shaft. Therefore, the occurrence of premature wear and/or failure of a processing system due to particle entrapment is substantially reduced. 
   Although the teachings of the present invention that have been shown and described in detail in a plasma enhanced chemical vapor deposition chamber, those skilled in the art can readily devise other varied embodiments in other processing chambers that incorporate the use of lift pins to separate a substrate from a support surface that still incorporate the teachings and do not depart from the scope and spirit of the invention.