Abstract:
A disclosed device for use with an electrostatic chuck configured to hold a substrate in a plasma environment comprises an edge ring configured to be placed either in contact with portions of only a ceramic top piece, a base plate, or coupled to the base plate through a plurality of pins and pin slots. The edge ring is further configured to be concentric with the ceramic top piece. In one embodiment, the edge ring includes an inner edge having an edge step arranged to provide mechanical coupling between the edge ring and the outer periphery of the ceramic top piece. The edge ring further includes an outer edge and a flat portion located between the inner edge and the outer edge. The flat portion is arranged to be both horizontal when the edge ring is placed around the outer periphery of the ceramic top piece and parallel to the substrate.

Description:
CLAIM OF PRIORITY 
     The present application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application Ser. No. 61/090,182, filed Aug. 19, 2008, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to the field of process equipment used in the semiconductor, data storage, flat panel display, as well as allied or other industries. More particularly, the present invention relates to a system for enhancing performance of electrostatic chucks used in plasma-based process tools. 
     BACKGROUND 
     Semiconductor device geometries (i.e., integrated circuit design rules) have decreased dramatically in size since integrated circuit (IC) devices were first introduced several decades ago. ICs have generally followed “Moore&#39;s Law,” which means that the number of devices fabricated on a single integrated circuit chip doubles every two years. Today&#39;s IC fabrication facilities are routinely producing 65 nm (0.065 μm) feature size devices, and future fabs will soon be producing devices having even smaller feature sizes. 
     As IC design rules shrink, an increasing trend in semiconductor manufacturing is utilizing single-wafer processing for a variety of fabrication steps, including plasma etching and deposition chambers. Single-wafer reactors must be designed to unobtrusively secure the wafer (or other substrate-type) during processing, while controlling both temperature and temperature uniformity across the wafer. 
     Mechanical wafer clamps which engage a portion of front surfaces of the wafer where processing is to be performed potentially create process uniformity problems by interfering with gas flow, altering plasma distribution, and acting as a heat sink. If improperly designed, mechanical wafer clamps may also produce particulates with resulting contamination of the wafer as well as other problems. 
     An electrostatic chuck (ESC) uses an electrostatic potential to hold a wafer in place during processing, thus avoiding the problems of mechanical clamping by having contact with only the back side of the wafer. Electrostatic chucks operate by inducing opposing charges on the substrate and the chuck thereby resulting in an electrostatic attraction between the chuck and the substrate. A degree of attraction is dependent on an amount of charge induced as well as a rate at which the charge dissipates due to conductive effects. Voltage biasing is employed to induce and control the electrostatic force and may be applied for only a portion of a processing cycle, for example, just after a substrate is transferred to the chuck. Alternatively, voltage biasing may be applied continuously throughout a processing cycle. For instance, using the conduction properties of plasma can provide a means of electrical connection to one terminal of a ESC and wafer system. 
     Various types of electrostatic chucks may include consumable (i.e., sacrificial) edge rings positioned below and around the substrate for purposes of confining plasma to the area immediately proximate to and above the substrate. The edge rings may also protect the ESC from erosion by the plasma. 
     With reference to  FIG. 1 , a portion of an exemplary prior art ESC structure  100  includes an anodized aluminum base  101 , a heater bond layer  103 , a heater  105 , a heater plate  107 , and a ceramic bond layer  109 . The ESC structure  100  is capped with a ceramic top piece  111 . The heater bond layer  103 , heater  105 , heater plate  107 , and ceramic bond layer  109  are protected from direct contact with a surrounding plasma environment and caustic chemicals by an edge bonding seal  113 . The edge bonding seal  113  thus protects the heater  105 , the heater plate  107 , and the heater  103  and ceramic  109  bonding layers from plasma erosion. 
     The heater bond layer  103  is typically comprised of a silicone layer impregnated with silica (e.g., amorphous SiO x ). The heater  105  is frequently comprised of metallic resistance elements encapsulated in a polyimide while the heater plate  107  is typically fabricated from aluminum. A ceramic-filled (e.g., alumina (Al 2 O 3 )) silicone material is commonly employed for the ceramic bond layer  109 . The ceramic top piece  111  is commonly fabricated from alumina and is configured to allow a substrate  115 , such as a silicon wafer, to be securely held in place over the ceramic top piece  111 . 
     An edge ring  117  is typically circular in overall shape and is secured to a periphery of an inner portion of the exemplary prior art ESC structure  100 . The edge ring  117  is placed concentrically about the inner portion of the ESC structure  100  and features a vertical, single-surface inner diameter. The single-surface inner diameter constrains the edge ring  117  against the aluminum base  101 , the edge bonding seal  113 , and the ceramic top piece  111  thus nominally centering the edge ring  117 . 
     Moreover, the edge ring  117  depends upon both critical tolerances and concentricity of at least the aluminum base  101  and the ceramic top piece  111 . Any variation in either the tolerance of either piece or the concentricity may lead to breakage of the edge ring  117  upon either installation or use. Thus, the edge ring  117  must accommodate an overall worst-case tolerance between at least the aluminum base  101  and the ceramic top piece  111 . Conversely, if the tolerances of the two pieces are not at a worst case condition, then the edge ring  117  is oversized and unable to adequately enhance process conditions with regard to the substrate. Therefore, the edge ring must be designed to accommodate worst case tolerances while still not being oversized in order to minimize yield impacts, decrease total tool operating costs, and improve overall performance of plasma-based processes. 
     Therefore, what is needed is an edge ring that may be easily applied to an ESC. The edge ring should be readily centered around the ESC and not require overly tight design tolerances while still maintaining well-centered concentricity about the ESC over a wide range of temperatures. 
     SUMMARY 
     In an exemplary embodiment, a device for use with an electrostatic chuck configured to hold a substrate in a plasma environment is disclosed. The device comprises an edge ring being configured to be placed around an outer periphery of a ceramic top piece of the electrostatic chuck and coupled to at least portions of only the ceramic top piece. The edge ring is further configured to be concentric with the ceramic top piece. The edge ring comprises an inner edge having an edge step arranged to provide mechanical coupling between the edge ring and the outer periphery of the ceramic top piece, an outer edge, and a flat portion located between the inner edge and the outer edge. The flat portion is arranged to be both horizontally oriented when the edge ring is placed around the outer periphery of the ceramic top piece and parallel to the substrate when in operation within the plasma environment. 
     In another exemplary embodiment, a device for use with an electrostatic chuck configured to hold a substrate in a plasma environment is disclosed. The device comprises an edge ring being configured to be placed around an outer periphery of a base plate of the electrostatic chuck and coupled to at least portions of only the base plate. The edge ring is further configured to be concentric with the base plate. The edge ring comprises an inner edge having an edge step arranged to provide mechanical coupling between the edge ring and the outer periphery of the base plate, an outer edge, and a flat portion located between the inner edge and the outer edge. The flat portion is arranged to be both horizontally oriented when the edge ring is placed around the outer periphery of the base plate and parallel to the substrate when in operation within the plasma environment. 
     In another exemplary embodiment, a device for use with an electrostatic chuck configured to hold a substrate in a plasma environment is disclosed. The device comprises an edge ring configured to be coupled to a base plate of the electrostatic chuck through a plurality of pins. A plurality of pin slots is arranged near a periphery of the edge ring and configured to be placed over the plurality of pins and center the edge ring concentrically with the electrostatic chuck. The plurality of pin slots is further configured to allow variations in thermal expansion between the edge ring and the base plate while still maintaining the concentric centering of the edge ring. 
     In another exemplary embodiment, a device for use with an electrostatic chuck configured to hold a substrate in a plasma environment is disclosed. The device comprises an edge ring configured to be coupled to a base plate of the electrostatic chuck through a plurality of pins. A plurality of pin slots is arranged near a periphery of the base plate and configured to be placed over the plurality of pins and center the edge ring concentrically with the electrostatic chuck. The plurality of pin slots is further configured to allow variations in thermal expansion between the edge ring and the base plate while still maintaining the concentric centering of the edge ring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various ones of the appended drawings merely illustrate exemplary embodiments of the present invention and must not be considered as limiting its scope. 
         FIG. 1  is a cross-sectional view of a portion of a prior art electrostatic chuck. 
         FIG. 2A  includes both an exemplary top view and an accompanying isometric view of a shoulder-centered edge ring of the present invention. 
         FIG. 2B  is a cross-sectional view of the shoulder-centered edge ring of  FIG. 2A . 
         FIG. 2C  is a magnified portion of the edge ring of  FIG. 2B  showing a specific exemplary shoulder design. 
         FIG. 2D  is a magnified portion of the edge ring of  FIG. 2B  showing another specific exemplary shoulder design. 
         FIG. 3A  is a bottom view of an exemplary pin-centered edge ring of the present invention. 
         FIG. 3B  is a cross-sectional view of the pin-centered edge ring of  FIG. 3A . 
         FIG. 3C  is a magnified portion of the edge ring of  FIG. 3B  showing a specific exemplary pin centering design. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments discussed below describe an improved edge ring designed to enhance process performance. Process performance is enhanced by ensuring the edge ring is placed concentrically (i.e., centered) about an aluminum base piece or ceramic top piece of an ESC, thus resulting in the edge ring being arranged precisely and accurately about a substrate. 
     With reference to  FIG. 2A , a plan view  200  of an exemplary embodiment of a shoulder-centered edge ring  201  includes a stepped inner diameter shape  205  and a substantially flat top surface  203 . In use, the shoulder-centered edge ring  201  surrounds an ESC structure (not shown but readily understandable to one skilled in the art) with the flat top surface  203  being substantially horizontal and parallel to a substrate placed on the ESC. An isometric view  230  provides an additional reference view of the shoulder-centered edge ring  201 . 
     The stepped inner diameter shape  205  improves centering about the ESC structure since the shoulder-centered edge ring  201  contacts only the ceramic top piece of the ESC. The shoulder-centered edge ring  201  may be friction fit about the ceramic top piece or, alternatively, held in place with adhesives or mechanical fasteners known independently in the art. In a specific exemplary embodiment, the stepped inner diameter shape  205  is approximately 1.9 mm (approximately 0.075 inches) high and 0.4 mm wide (approximately 0.016 inches) wide. More specific details are provided below. Overall, the stepped inner diameter shape  205  of the shoulder-centered edge ring  201  provides approximately a 50% improvement in edge ring centering resulting ultimately in improved process performance. 
     Referring now to  FIG. 2B , a cross-sectional view  250  of the shoulder-centered edge ring  201  is shown at section A-A. The shoulder-centered edge ring  201  may be formed from a variety of materials such as aluminum oxide (Al 2 O 3 , “alumina”) or other type of ceramic. Silicon, silicon carbide, silicon dioxide (e.g., crystalline or amorphous (SiO x )), and transitional metals such as solid yttrium are also suitable materials from which to fabricate the shoulder-centered edge ring  201 . Additionally, various other types of metallic, insulating, and semiconducting materials may also be readily employed. Thermal expansion compatibility between the shoulder-centered edge ring  201  and the ceramic over, for example, a 100° C. temperature range may need to be considered if the shoulder-centered edge ring  201  is designed to provide a friction fit with the ceramic of the ESC. In a typical application, the shoulder-centered edge ring  201  may be machined to have a proper press-fit at ambient temperature (e.g., 20° C.). 
     In a specific exemplary embodiment, the shoulder-centered edge ring  201  is fabricated from aluminum oxide (Al 2 O 3 ) and coated with an yttrium oxide finish 75 micrometers (μm) to 125 μm (approximately 0.003 to 0.005 inches) in thickness. The yttrium oxide finish may be applied by, for example, thermo-spraying or applied from a physical vapor deposition (PVD) system. In this embodiment, the yttrium oxide finish may taper in certain areas as required or entire portions of the shoulder-centered edge ring  201  may be left uncoated. 
     With continued reference to  FIG. 2B , specific exemplary dimensions are given in Table I, below, to accommodate a 300 mm diameter substrate. 
     
       
         
               
               
               
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                   
                   
                 Tolerance 
                 Size 
                 Tolerance 
               
               
                   
                 Dimension 
                 Size (mm) 
                 (mm) 
                 (inches) 
                 (inches) 
               
               
                   
                   
               
             
             
               
                   
                 D 1   
                 351.03 
                 0.05 
                 13.820 
                 0.002 
               
               
                   
                 D 2   
                 301.37 
                 0.05 
                 11.865 
                 0.002 
               
               
                   
                 D 3   
                 297.97 
                 0.05 
                 11.731 
                 0.002 
               
               
                   
                 D 4   
                 320.39 
                 0.08 
                 12.610 
                 0.003 
               
               
                   
                   
               
             
          
         
       
     
     The exemplary dimensions are provided merely to aid a skilled artisan in fully understanding fabrication details of the shoulder-centered edge ring  201 . The dimensions given may be suitably scaled for other common substrate sizes (e.g., 200 mm or 450 mm diameter wafers or rectangular sections of flat panel displays). 
     Referring now to  FIG. 2C , an enlarged section  270  of section A-A of  FIG. 2B  provides details of a specific exemplary embodiment of a first edge step  271 . The first edge step  271  is designed to mechanically contact at least portions of only the ceramic top piece  111  ( FIG. 1 ) of a typical ESC. The first edge step  271  thus provides a gap of approximately 0.4 mm (about 0.016 inches) between the shoulder-centered edge ring  201  and the aluminum base plate  101  of the ESC while being precisely and accurately centered about the ceramic top piece  111 . 
     With reference to  FIG. 2D , another enlarged section  290  provides details of another specific exemplary embodiment of a second edge step  291 . Dimensions of the second edge step  291  are similar to the first edge step  271  described immediately above and function in a similar fashion. A skilled artisan may readily envision a variety of other shapes an edge step could take based on the information provided herein. 
     In  FIG. 3A , a bottom view  300  of a pin-centered edge ring  301  includes a plurality of pin slots  303  arranged to fit over or around a plurality of pins  305 . In this exemplary embodiment, the plurality of pin slots are spaced at approximately 120° intervals for a total of three slots. In other exemplary embodiments (not shown), a smaller or larger number of the plurality of pin slots  303  may be incorporated into the pin-centered edge ring  301 . 
     Each of the plurality of pins is mounted into the aluminum base plate portion (not shown, but readily envisioned from  FIG. 1 ) of the ESC. The plurality of pins  305  is sized to provide a press-fit of the pin-centered edge ring  301  thereby centering the edge ring around a periphery of the main portion of the ESC. The elongated nature of the plurality of pin slots  303  however allows for variations in thermal expansion of the pin-centered edge ring  301  and the aluminum base plate. 
     In another embodiment (not shown but readily understood to one of skill in the art), each of the plurality of pins  305  may be affixed to the pin-centered edge ring  301  and a plurality of pin slots may be machined into the aluminum base plate. In still another embodiment, the plurality of pins  305  may be machined directly as a portion of either the pin-centered edge ring  301  or the aluminum base plate. 
     If the plurality of pins  305  are “loose” (i.e., not machined as a portion of either the pin-centered edge ring  301  or the aluminum base plate), the plurality of pins  305  may be fabricated from a variety of materials. The materials include stainless steel (e.g., 316L), high-temperature plastics, aluminum oxide or other ceramics, solid yttrium, or a number of other materials known in the art that are capable of both being machined and withstanding relatively high temperatures (up to, for example, 400° C. or more). 
     Referring now to  FIG. 3B , a cross-sectional view  350  of the pin-centered edge ring  301  is shown at section B-B. The cross-sectional view  350  indicates a location of one of the plurality of pin slots  303 . 
     The pin-centered edge ring  301  may be formed from a variety of materials such as aluminum oxide (Al 2 O 3 , “alumina”) or other type of ceramic. Silicon, silicon carbide, silicon dioxide (e.g., crystalline or amorphous (SiO x )), and transitional metals such as solid yttrium are also suitable materials from which to fabricate the pin-centered edge ring  301 . Additionally, various other types of metallic, insulating, and semiconducting materials may also be readily employed. Thermal expansion compatibility between the pin-centered edge ring  301  and the aluminum base plate over, for example, a 100° C. temperature range will generally be automatically compensated for by the elongated nature of the plurality of pin slots  303  while still maintaining concentric centering with the ESC. In a typical application, the pin-centered edge ring  301  may be machined to have a proper press-fit at ambient temperature (e.g., 20° C.). 
     In a specific exemplary embodiment, the pin-centered edge ring  301  is fabricated from aluminum oxide (Al 2 O 3 ) and coated with an yttrium oxide finish 75 micrometers (μm) to 125 μm (approximately 0.003 to 0.005 inches) in thickness. The yttrium oxide finish may be applied by, for example, thermo-spraying or applied from a physical vapor deposition (PVD) system. In this embodiment, the yttrium oxide finish may taper in certain areas as required or entire portions of the pin-centered edge ring  301  may be left uncoated. 
     With continued reference to  FIG. 3B , specific exemplary dimensions are given in Table I, above, to accommodate a 300 mm diameter substrate. The exemplary dimensions are provided merely to aid a skilled artisan in fully understanding fabrication details of the pin-centered edge ring  301 . The dimensions given may be suitably scaled for other common substrate sizes (e.g., 200 mm or 450 mm diameter wafers). 
     Referring now to  FIG. 3C , an enlarged section  370  of section B-B of  FIG. 3B  provides details of a specific exemplary embodiment of one of the plurality of pin slots  303 . The pin-centered edge ring  301  is designed to mechanically contact only the aluminum base plate  101  ( FIG. 1 ) of a typical ESC and the plurality of pins  305 . The plurality of pin slots  303  and the plurality of pins  305  may be machined to provide a gap of approximately 0.4 mm (about 0.016 inches) between the pin-centered edge ring  301  and the ceramic top piece  111 . Additionally, although the plurality of pin slots is shown as a blind hole construction, a skilled artisan will readily recognize that a through-hole configuration may be used as well. 
     The present invention is described above with reference to specific embodiments thereof. It will, however, be evident to a skilled artisan that various modifications and changes can be made thereto without departing from the broader spirit and scope of the present invention as set forth in the appended claims. 
     For example, particular embodiments describe various material types and placements. A skilled artisan will recognize that these materials and placements may be varied and those shown herein are for exemplary purposes only in order to illustrate various aspects of the described edge ring. For example, upon reading the information disclosed herein, a skilled artisan will quickly recognize that the shoulder-centered embodiment of the edge ring could be placed about the ESC base plate as well without touching the ceramic top piece. Additionally, a skilled artisan will further recognize that the techniques and methods described herein may be applied to any similar sort of structure operating in a harsh plasma and chemical environment in which precise and accurate concentricity and placement need to be maintained. The application to an electrostatic chuck of the semiconductor industry is purely used as an exemplar to aid one of skill in the art in describing various embodiments of the present invention. 
     Moreover, the term semiconductor should be construed throughout the description to include data storage, flat panel display, as well as allied or other industries. These and various other embodiments are all within a scope of the present invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.