Abstract:
An upper electrode assembly (UEL) is supported in an insulator in an opening in the top of an etch chamber in which large diameter substrates are processed with a flange of the UEL overlying the chamber wall around the opening with the insulator in between so that the insulator experiences primarily compressive and minimal shear loads. The electrode nonetheless fills the otherwise vacuum space between the UEL and the chamber wall above a shield ring that covers the insulator and portions of the adjacent UEL face and chamber wall.

Description:
[0001]     The present invention relates to vacuum processing equipment, particularly to the construction and maintenance of vacuum processing chambers used for semiconductor wafer manufacturing.  
       DESCRIPTION OF RELATED ART  
       [0002]     Manufacturers of semiconductor integrated circuits are faced with competitive pressures to improve their products and the productivity of their manufacturing operations. This has caused a trend toward larger substrates, which allow for more devices to be produced at once. The use of larger substrates requires larger processing systems. Larger processing systems with larger vacuum processing chambers must withstand loads from atmospheric pressure as well as loads from heavier components.  
         [0003]     Capacitively coupled plasma (CCP) processing systems, for example, include sources that are usually downwardly facing or include upper electrodes (UELs) that rest on the tops of the chambers. A source or electrode of this type is isolated from the chamber and rests upon an annular insulator, which must typically support the weight and vacuum loads.  
         [0004]     The prior art etch systems, for example, utilize annular insulators surrounding and supporting an upper electrode. These insulators are clamped and sealed to the upper electrode assembly by inner diameter features and are clamped to the process chamber by outer diameter features. All mass and vacuum loads are supported by the insulator on the inner and outer features.  
         [0005]     As process chambers of etch systems become larger, the upper electrode insulators correspondingly becomes larger. As the diameter of the insulator increases, a larger cross-section is necessary to support mass and vacuum loads. Current art using very large diameter insulators can support the loads necessary, but are fragile and have very expensive parts to manufacture and maintain.  
         [0006]     Deposition systems with their less aggressive chemistries can avoid structural problems by minimizing insulator size and relying on spaces in the vacuum of the chamber to isolate the electrode or source assembly. For example, dark space vacuum regions surrounding sputtering targets partially accomplish this. Etch systems, on the other hand, use solid insulator elements to more fully surround and occupy substantially all of the vacuum space around the upper electrode to isolate the electrode. In addition, etch systems typically add process compatible shields or surface coatings or both to protect the insulator and other chamber components in the chamber from the etch process. The extensive presence of fragile dielectric and semi- or non-conductive materials has resulted in a heavy reliance on insulators and other such members for structural purposes in etch chambers.  
         [0007]     For example, much of the support of such an isolated upper assembly in a common etch chamber is found to be borne by sheer loading within the typical insulator. Because the insulators are usually made of brittle dielectric materials, a large insulator cross-section is required to support the sheer loading. Large cross-section insulators have a relatively high cost. Because these insulators accumulate electrically conductive deposits that make their replacement necessary, their cost is a recurring one.  
         [0008]     As the diameters of semiconductor wafers are typically 200 millimeters, 300 millimeters or larger, UELs are typically even larger. When such elements are downwardly facing, their weight that is borne by the support structure is significant, particularly with dynamic loads that result in even minor impacts when chambers are opened or closed for servicing. More significant static loads also result during chamber operation when the chamber is pumped down to a vacuum and the full force of atmospheric pressure bears on the larger area of the UEL or source, often amounting to a ton or more.  
         [0009]     Accordingly, there is a need for reducing the cost of insulators in vacuum processing systems and improving the load bearing properties of processing chamber components in large diameter wafer processing systems particularly those that employ downwardly facing UELs for etching.  
       SUMMARY OF THE INVENTION  
       [0010]     One object of the present invention is to provide a method of supporting UELs in large diameter semiconductor wafer etching systems. A further objective is to provide a UEL insulator and etching system that overcomes problems of the prior art.  
         [0011]     A particular objective of the present invention is to eliminate sheer loading within a UEL insulator. A further objective is to reduce the recurring cost of insulator replacement.  
         [0012]     Another objective of the present invention is provide an insulator and processing apparatus for processing semiconductor wafers of 200 millimeter, 300 millimeter and larger diameters, particularly in systems having downwardly facing UELs.  
         [0013]     According to one embodiment of the invention, a processing apparatus is provided that comprises a vacuum chamber having an opening in its top, a UEL with an electrode face larger than 200 millimeters in diameter, or larger than 300 millimeters in diameter, and with a support rim larger in diameter than the opening. An insulator supports the UEL in the opening and lies between, and in vertical alignment with, the rim of the UEL and chamber wall around the opening.  
         [0014]     In certain embodiments of the invention, an annular shield ring covers the insulator and adjacent portions of the UEL and chamber wall inside of the chamber, while the insulator occupies substantially all of the potential vacuum space between the UEL and the chamber wall and above the shield.  
         [0015]     An insulator according to principles of the present invention is an annular ring formed at least in part of electrically insulating material. The inner portion of the ring is larger than the UEL which, in turn, is larger than 300 millimeters or larger than the diameter of a wafer being processed, that is, larger than at least 200 millimeters, and upwardly facing. An upwardly facing electrode supporting surface is configured to support the UEL. A downwardly facing supporting surface on an outer portion of the insulator is configured to rest on the chamber wall around the opening and to support the insulator with the UEL supported on the insulator such that at least a portion of the rim of the UEL aligns vertically with the wall around the opening and the insulator.  
         [0016]     In accordance with other principles of the invention, the insulator is configured to extend sufficiently below the top of the chamber to support a shield ring thereon in the processing chamber and to substantially displace all vacuum space between the UEL and the top of the chamber above an underlying shield ring.  
         [0017]     According to some embodiments of the invention, the insulator is formed of the electrically insulating material throughout, while in other embodiments the insulator is formed of a metal core material having a coating of the electrically insulating material. The coating may be an anodic layer. For example, the coating may contain at least one column III element, or may contain at least one element selected from the group consisting of Yttrium, Scandium, Lanthanum, Cerium, Dysprosium, and Europium. For example, the insulator may contain at least one element selected from the group consisting of Y 2 SO 3 , Sc 2 O 3 , Sc 2 F 3 YF 3 , La 2 O 3 , Y 2 SO 3 CeO 2 , Eu 2 O 3  and DyO 3 .  
         [0018]     According to certain aspects of the invention, the insulator may be formed of a material selected from the group consisting of alumina, quartz, ceramic material, silicon, silicon nitride, sapphire, polymide and silicon carbide.  
         [0019]     Further according to principles of the present invention, a method is provided for supporting a downwardly facing RF electrode in an opening in the top of a vacuum processing chamber that is configured to process a wafer of at least 200 millimeters in diameter, for example, 300 millimeters or larger in diameter. The method includes providing an insulator having outer and inner integral portions. The outer portion has an outside diameter larger than the diameter of the opening and a downwardly facing support surface. The inner portion extends below the downwardly facing support surface of the outer portion and has an outside diameter smaller than the diameter of the opening, an inside diameter larger than that of the wafer to be processed, and an upwardly facing support surface. The method further comprises providing an upper electrode assembly having a flange at the top thereof that has an outside diameter that is larger than the diameter of the opening, and a lower electrode face formed of a material compatible with the process to be performed on the wafer in the chamber and having an outside diameter larger than the diameter of the wafer to be processed. Additionally, the method comprises providing an electrically non-conductive shield ring having an outside diameter that is greater than the outside diameter of the inner portion of the insulator and an inside diameter that is less than the outside diameter of the lower electrode face of the upper electrode assembly. The insulator supporting the upper electrode assembly is placed in the opening and the shield ring is secured adjacent the lower electrode face such that the downwardly facing support surface of the insulator rests on the top of the chamber around the opening with the flange at the top of the upper electrode assembly resting on the upwardly facing support surface of the inner portion of the insulator with the insulator between the flange and the chamber wall. The insulator substantially fills the volume between the outside diameter of the lower electrode face and the inside diameter of the opening and between the downwardly facing support surface of the insulator and the shield ring. With this configuration, RF power is then coupled between the electrode and the chamber.  
         [0020]     Advantages of the invention are that smaller cross-sections can be used because axial shear loads are reduced, being rather supported by metallic chamber structures of the system, while the insulator still occupies the space around and isolates the upper electrode. The apparatus is of a type having a plasma chamber for processing semiconductor substrates. It is provided with an insulator supporting the upper electrode assembly from electrical grounding structures in a capacitively coupled plasma source. The plasma processing system is constructed in such a way that the mechanical load applied to the insulator is supported by the grounded structures of the system.  
         [0021]     With the present invention, mechanical and vacuum loads traversing through the UEL insulator are supported by metallic chamber structures. This invention exploits the fact that brittle dielectric materials do support compression loads very well by ensuring that mass and vacuum loads traversing through the UEL insulator are compression loads that are supported by the chamber structure. The present invention, while allowing for large diameters necessary in large plasma processing systems, does not require insulators having large cross-sectional areas. Thus the parts are lighter and cheaper to manufacture and maintain but perform the same function as current art. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     In the accompanying drawings:  
         [0023]      FIG. 1  is an elevational view, partially cut away, of a vacuum processing chamber of the prior art.  
         [0024]      FIG. 1A  is an enlarged cross-sectional view of the encircled portion A of  FIG. 1 .  
         [0025]      FIG. 2  is a cross-sectional view, similar to  FIG. 1A , illustrating a portion of a vacuum processing chamber according to one embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0026]     In the following description, to facilitate a thorough understanding of the invention and for purposes of explanation and not limitation, specific details are set forth, such as a particular geometry of the high pressure processing system and various descriptions of the internal members. However, it should be understood that the invention may be practiced with other embodiments that depart from these specific details.  
         [0027]     Nonetheless, it should be appreciated that, contained within the description are features which, notwithstanding the inventive nature of the general concepts being explained, are also of an inventive nature.  
         [0028]      FIG. 1  illustrates an etch system  10  of a type found in the prior art. The system  10  might typically include a vacuum processing chamber  12  surrounded by a chamber wall  11 , usually made of a structural metal such as aluminum or stainless steel. A substrate support  14  is usually contained within the chamber  12  and may have an upwardly facing wafer supporting surface  15 . The inside of the chamber wall  11  is often lined with a chamber liner  13 , formed of one or more parts, that prevent deposits directly onto, or erosion of, the chamber wall  11  as a result of deposition and etching processes performed on wafers supported on the surface  15  within the chamber  12 . In an etch system  10 , where process gases can be aggressive, the chamber liner  13  is often made of a durable, process-compatible material such as quartz.  
         [0029]     The system  10  also includes a source assembly  20  situated on top of the chamber  12 . The source assembly  20  delivers material and energy into the chamber for performing vacuum processes on wafers in the chamber  12 . In a deposition system, the source assembly can be a source of coating material as well as the energy needed for the deposition process, such as DC power to a sputtering target. In an etch system such as the illustrated system  10 , the source assembly  20  typically usually includes a processing gas or chemistry source, including, for example, reactive and inert gases, along with an RF energy source to generate a plasma in the gases within the chamber  12 . The source assembly  20  has a lower flange  21  by which it is supported on, and sealed against, the upper end  16  of the chamber wall  11 .  
         [0030]     In the apparatus  10 , the gases can be introduced through a gas inlet or showerhead  22  from an inlet chamber  23  in an upper electrode (UEL) assembly  25 . The UEL can serve as an electrode to produce a plasma in gas within the chamber  12  by coupling RF electric energy into the chamber  12 . One or more of the showerhead  22  or other parts of the UEL assembly  25  may be made of metal, for example aluminum, or other electrically conductive material to which an RF energy is applied. The showerhead  22  is often formed of a metal core  26  and is provided with a face plate  24  made of a process-compatible material, for example silicon, that protects the metal of the showerhead  22 . The face plate  24  protects the body of the showerhead  22  from the plasma and prevents contamination of the plasma with aluminum vaporized from the showerhead by the plasma. The application of RF energy to the UEL calls for the electrical insulation of the UEL  25  relative to the chamber wall  11 . The insulation is achieved by supporting the UEL assembly  25  in the source  20  on an annular insulator  30  and spacing the UEL sufficiently inward from the chamber wall  11  or metal chamber top  21  to reduce unwanted coupling from the electrode to ground.  
         [0031]     As can be seen in  FIG. 1A , the insulator  30  of prior art etch systems of this type has an annular shoulder  31  formed on its inner diameter to which is clamped the UEL assembly  25 . This shoulder  31  supports the weight of the UEL assembly  25 . Similarly, a lip  32  on the outer diameter of the insulator  30  is clamped to the support flange  21  of the source  20 . This configuration results in a downward load on the insulator  30 , as indicated by the arrow  33 , which is resisted by upward force from the flange  16 , as indicated by the arrow  34 . This produces a sheer stress in the insulator  30 , indicated by the arrows  35 .  
         [0032]     The total force borne by the insulator  30  is greater than the weight of the UEL assembly  25  due to the pressure differential that develops across the UEL assembly  25  during operation of the system  10 . This force is the result of atmospheric pressure on the top of the UEL assembly  25  and the vacuum within the chamber  12 . The chamber vacuum pressure can be orders of magnitude less than one percent of atmospheric pressure, or approximately zero for purposes of structural analysis of the loads being discussed. The UEL assembly  25  has a diameter larger than that of a wafer being processed, which, with current technology, may be 300 millimeters (12 inches) in diameter. As the showerhead is at least as large as or larger than the diameter of the wafer, the area of the source inside of the annular insulator is even larger. Thus, the atmospheric force downward on the UEL assembly  25  may be 2,000 to 3,000 pounds. This force, which is transmitted through the insulator  30  as a sheer force, places substantial structural requirements on the design of the insulator  30 , resulting in an insulator  30  of substantial cross-section, as typical insulator materials are brittle and do not readily hold up to sheer stresses that are large.  
         [0033]     According to principles of the present invention, a processing system  40  is provided having the large diameters necessary for the plasma processing of large diameter semiconductor wafers, but does not require insulators having large cross-sectional areas. Features of the system  40  are illustrated in  FIG. 2 . The system  40  is an etch system having a downwardly facing upper electrode (UEL) assembly  42 , The UEL assembly  42  has an upper flange  45  by which the UEL  42  is supported on the metal top wall  46  of the processing chamber  12 . The top wall  46  is sealed to the upper edge of chamber wall  11 . The UEL assembly  42  rests on an annular insulator  50  which, in turn, rests on the rim of an opening  43  in the top wall  46  of the chamber  12 .  
         [0034]     The insulator  50  has an inner portion  56  and an outer portion  57 . The inner portion  56  has an inner shoulder  51  having an upwardly facing support surface  58  on which is clamped and rests the UEL assembly  42 . This inner portion  56  has a lower part  53  that extends downwardly below the top wall  46 . This lower part  53  has an inner diameter slightly greater than the outer diameter of the showerhead  22 . The outer portion  57  of the insulator  50  has an outer lip  52  that defines the outer diameter of the insulator  50  and by which the insulator  50  is clamped to the source flange that forms the top wall  46  of the chamber  12 . This outer lip  52  has a downwardly facing support surface  54  by which the insulator rests upon the top wall  46  of the chamber.  
         [0035]     Either the UEL assembly  42  or the top wall  46  may be geometrically the same as the UEL assembly  25  or the flange  16 , respectively, of the prior art system  10  of  FIGS. 1 and 1 A. But to replace the insulator  30  of the prior art system  10  with the insulator  50  of the present invention, either the outer portion  57  of the UEL assembly  45  or the top wall  46  will be geometrically different than the UEL assembly  25  or the flange  16 , respectively, of the system  10 . Alternatively, the basic flange or electrode unit may be similar to flange  16  or electrode  20 , respectively, but modified by an adapter that makes it different, so that the outer diameter  47  of the upper flange  45  of the UEL assembly  42 , which supports the UEL assembly  42  on the lid  46 , is larger than the inside diameter  48  of the of the opening  43  in the top wall  42 .  
         [0036]     Accordingly, with the insulator  50  in an appropriately configured chamber, the load that is made up of the weight of the UEL assembly  42  and the atmospheric pressure on the UEL assembly  42  passes downwardly through the insulator  50  from the UEL assembly  42  to the top wall or flange  46 , subjecting the insulator  50  to predominantly compressive stress, with minimal shear stress, as indicated by the arrow  55 .  
         [0037]     The mating features on the chamber  12 , namely the top wall flange  46 , and the upper flange  45  of the electrode assembly  42 , can be made to match as set forth above or be retrofitted to match. Retrofit to existing plasma processing systems such as system  10  of  FIGS. 1 and 1 A might be accomplished using some number of annular adapter rings, for example. In most cases, system redesign in this particular area can also be carried out to utilize the features of the present invention.  
         [0038]     Referring again to  FIG. 2 , the lower part  53  of the inner portion  56  of the insulator  50  has an outer diameter  61  slightly less than the inside diameter of the opening  43 , an inside diameter  62  that is slightly larger than the outside diameter of the showerhead  22  portion of the UEL, and a substantial thickness between these two diameters that fills the space between the showerhead  22  and the chamber wall top  46 . This lower part  53  also extends downward from the support surface  54  of the outer portion  53  to below the chamber wall top  46  and further to slightly below the lower face of the face plate  24  of the showerhead  22  of the UEL assembly  42 .  
         [0039]     A shield ring  65  made of a process compatible material, often quartz, protects the insulator  50  from the plasma and process gases and protects mounting screws  66  that hold the face plate  24  to the core  26  of the showerhead  22 . The shield ring  65  has an inner lip  67  having an inside diameter smaller than the outside diameter of the UEL showerhead  22  and a recess in the top thereof that is larger than the outside diameter of the insulator  50  for fitting the shield ring  65  over the insulator  50 . A groove  68  is formed in the outside diameter of the lower part  54  of the insulator  50  to receive the tips of a plurality of setscrews  69  spaced around the outside of the recess in the shield ring  65 . The tips of the setscrews  69  project inwardly into the groove  68  of the insulator  50  to allow the shield ring  65  to hang on the insulator  50 . The groove  68  may be formed as a plurality of L-shaped grooves around the outside diameter  61  of the insulator  50  to allow the shield ring  65  to be inserted onto the insulator  50  from below and twist-locked in place. When so locked in place, the shield ring  65  leaves a small clearance  71  between it and the top wall  46  of the chamber and a small clearance  72  between it and the face plate  24  of the showerhead  22 .  
         [0040]     The insulator  50  and the related parts are less expensive, lighter, and have smaller parts with systems  40 , according to the invention compared to those of systems  10  of the prior art. Since UEL insulators can be a consumable part, any weight or cost reduction is realized many times and would be beneficial. To most easily utilize the present invention, new hardware can be produced.  
         [0041]     The improved insulator  50  may be made from a metallic material, if the material is coated to sufficient thickness to insure insulating properties. The coating may be an anodic layer. The coating may be a plasma resistant coating made from a III-column element such as, for example, Yttrium, Scandium and Lanthanum, or a combination thereof, and a Lanthanon element such as, for example, Cerium, Dysprosium, and Europium or a combination thereof. A plasma resistant coating may be made, for example, from one or a combination of Y 2 SO 3 , Sc 2 O 3 , Sc 2 F 3 YF 3 , La 2 O 3 , Y 2 SO 3 CeO 2 , Eu 2 O 3  or DyO 3 .  
         [0042]     The UEL insulator  50  may be made from one or a combination of dielectric materials, or made from a partially dielectric and metallic structure. The dielectric or metallic parts may, but need not necessarily, be partially or fully coated. The dielectric material may be made from alumina, quartz, ceramic material, silicon, silicon nitride, sapphire, polymide and silicon carbide, or a combination thereof, or other such material.  
         [0043]     Although only certain exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.