Patent Publication Number: US-2005133166-A1

Title: Tuned potential pedestal for mask etch processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      The present application claims priority to previously filed provisional patent application Ser. No. 60/531,062, filed Dec. 19, 2003, entitled “Tuned Potential Pedestal for Mask Etch Processing Apparatus.” The provisional application is incorporated herein by referenced in its entirety. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention generally relates to the fabrication of integrated circuits. More specifically, the invention relates to an apparatus for manufacturing a photomask, or “reticle,” useful in manufacturing semiconductors.  
      2. Description of the Related Art  
      Integrated circuits (IC) are manufactured by forming discrete semiconductor devices on a surface of a semiconductor substrate. An example of such a substrate is a silicon (Si) or silicon dioxide (SiO 2 ) wafer. To interconnect the devices on the substrate, a multi-level network of interconnect structures is formed. Material is deposited on the substrate in layers and selectively removed in a series of controlled steps.  
      Increasing circuit densities have placed additional demands on processes used to fabricate semiconductor devices. For example, as circuit densities increase, the widths of vias, contacts and other features, as well as the dielectric materials between them, decrease to sub-micron dimensions. However, the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i.e., their height divided by width, increases. Reliable formation of high aspect ratio features is important to the success of sub-micron technology and to the continued effort to increase circuit density and the quality of individual substrates and die.  
      Reliable formation of high aspect ratio features with desired critical dimensions requires precise patterning and subsequent etching of the substrate. A technique commonly used to form precise patterns on substrates is photolithography. The technique generally involves the direction of light energy through a lens, or “reticle” and onto the substrate. In conventional photolithographic processes, a photoresist material is first applied on a substrate layer to be etched. In the context of optical resists, the resist material is sensitive to light energy, such as ultraviolet or laser sources. The resist material defines a polymer that is tuned to respond to the specific wavelength of light used, and to different exposing sources.  
      After the resist is deposited onto the substrate, the light source is actuated to emit ultraviolet (UV) light or low X-ray light, for example, directed at the resist-covered substrate. The selected light source chemically alters the composition of the photoresist material. However, the photoresist layer is only selectively exposed. In this respect, a photomask, or “reticle,” is positioned between the light source and the substrate being processed. The photomask is patterned to contain the desired configuration of features for the substrate. The patterned photomask causes the light energy to strike the resist material in accordance with the pattern.  
      Photolithographic reticles are fabricated from an optically transparent material, such as quartz (i.e., silicon dioxide, SiO 2 ). The reticle includes a pattern of opaque material that inhibits the light from exposing portions of the substrate in accordance with the desired pattern. A thin opaque layer of metal, typically chromium, is disposed on the surface of the reticle. This light-shielding layer is patterned to correspond to the features to be transferred to the substrate, such as transistors or polygates. The metallic material is patterned using conventional laser or electron beam patterning equipment to define the critical dimensions to be transferred to the metal layer. The metal layer is then etched to remove the metal material not protected by the patterned resist, thereby exposing the underlying quartz material and forming a patterned photomask layer. Photomask layers thus allow light to pass therethrough in a precise pattern onto the substrate surface.  
      In photolithography, the exposed material may either be a positive resist or a negative resist. In a positive resist, the exposed resist material on the substrate is removed, while in a negative resist, the unexposed portions are removed. Removal is typically by a chemical process to expose an underlying substrate material. The exposed underlying substrate material may then be etched to form patterned features in the substrate surface while the retained resist material remains as a protective coating for the unexposed underlying substrate material. In this manner, contacts, vias, or interconnects may be formed by exposing the resist to a pattern of light through a photolithographic reticle having a photomask layer disposed thereon.  
      In an iterative convergence, the method for fabricating a patterned reticle itself involves a deposition and subsequent etching process. In this respect, a metal layer is first deposited on a top surface of a glass reticle. Thereafter, selected portions of the metal layer are removed through etching. Various types of etching processes are used for etching the metal layer from a reticle. One such etching method is known as plasma etching. In order to perform plasma etching, a glass reticle is first placed within a process chamber. More specifically, the glass reticle is placed on a pedestal. In a plasma etching process, the pedestal serves as a cathode. To this end, the metallic pedestal is given RF power. Power applied to the pedestal creates a substrate bias in the form of a negative voltage on the upper surface of the reticle. This negative voltage is used to attract ions from a plasma formed above the reticle in the chamber. The plasma is formed by the application of power to one or more inductive coils at the top of the chamber. The inductive coils generate and sustain the plasma above the pedestal and reticle. Thus, a voltage drop is induced across the pedestal that draws ions to the upper surface of the reticle, thereby etching a metallic layer.  
      Because the reticle is formed from a material having a low dielectric constant, e.g., glass or quartz, the amount of RF power that is coupled through the reticle is low. This inhibits the gas plasma in reacting with the reticle surface. This limitation is compounded by a gap typically existing between the reticle and the supporting pedestal therebelow. In addition, when the surface area of the pedestal is large compared to the reticle area, the RF power may preferentially couple to other regions of the pedestal, producing a loss of RF power. Further, it has been observed that the use of a pedestal cover, e.g., cover ring and capture ring, fabricated from a dielectric material is inadequate to lessen the power coupled through the region of the pedestal that is not immediately below the reticle.  
      Therefore, there is a need for a plasma etching apparatus that aids in the chemical reaction between a gas plasma and a reticle. In addition, there is a need for a pedestal fabricated from a material that does not contribute to the power loss across the reticle during a plasma etching procedure.  
     SUMMARY OF THE INVENTION  
      The present invention generally provides an improved pedestal for supporting a substrate and related substrate support hardware. The pedestal has greatest application during a plasma etching process, such as for a quartz photomask, or “reticle.” 
      The pedestal defines a body, and a base along on an upper surface of the body. The body receives an RF power during substrate processing. The substrate support base has an outer edge, and an intermediate substrate support ridge for receiving and supporting the substrate. At least a portion of the substrate support base outside of the intermediate substrate support ridge is fabricated from a dielectric material, or material having a lower dielectric constant than the remaining support base. An example is quartz. Quartz has a lower dielectric constant than the materials typically used for fabricating the pedestal body or cover, e.g., alumina. The placement of quartz allows greater RF power to be coupled through the reticle, thereby enhancing the plasma etching process. It also provides greater control over the relative amount of RF power coupled through the reticle.  
      In one aspect, a layer of dielectric material is placed along the top of the support base of the pedestal body. In another embodiment, the entire cross-sectional thickness of the support base that encompasses the supporting ridge is fabricated from a dielectric material. In one embodiment, a separate substrate support assembly is disposed on the base to facilitate the transfer of the substrate onto and off of the pedestal, with the substrate support assembly being fabricated from a dielectric material.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are, therefore, not to be considered limiting of its scope.  
       FIG. 1  is a cross-sectional view of a plasma etching chamber as might contain the pedestal of the present invention. The chamber shown in  FIG. 1  is exemplary.  
       FIG. 2  presents an exploded perspective view of the substrate support member of  FIG. 1 .  
       FIG. 3  shows a perspective cutaway view of one embodiment of a pedestal of the present invention.  
       FIG. 4  provides a cross-sectional schematic view of a pedestal of the present invention. A portion fabricated from a dielectric material is shown.  
       FIG. 5  presents a cross-sectional schematic view of a pedestal of the present invention, in an alternate embodiment. A portion fabricated from a dielectric material is again shown. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Aspects of the invention will be described below in reference to an inductively coupled plasma etch chamber. Suitable inductively coupled plasma etch chambers include the Decoupled Plasma Source (DPS™) chamber available from Applied Materials, Inc., of Santa Clara, Calif., or the ETEC Tetra™ photomask etch chamber available from ETEC of Hayward, Calif. A two-coil chamber, such as the Tetra II™ decoupled plasma source chamber available from Applied Materials, Inc. may also be employed. Other process chambers may be used including, for example, capacitively coupled parallel plate chambers and magnetically enhanced ion etch chambers, as well as inductively coupled plasma etch chambers of different designs. Although the processes are advantageously performed with the DPS™ processing chamber, the description in conjunction with the DPS™ processing chamber is illustrative and should not be construed or interpreted to limit the scope of aspects of the invention.  
      In order to perform plasma etching, a substrate, e.g., a glass reticle, is placed within a processing chamber. An example of such a chamber is schematically shown in  FIG. 1 . The process chamber  100  of  FIG. 1  has a substrate support member  200  disposed therein, and a substrate handler blade  300  positioned adjacent thereto. Substrates  222  are shown positioned on both the substrate support member  200  and the handler blade  300 .  
      The processing chamber  100  is configured to receive a substrate  222 , such as a glass reticle to be processed through plasma etching. The substrate  222  enters and exits the chamber  100  through a gate  161 . The gate  161  serves as a port, and also isolates the chamber  100  environment during reticle processing. The substrate  222  is transported via a substrate cassette, using the substrate handling blade  300 . The substrate handling blade  300  transfers the substrate  222  between a separate transfer chamber (not shown) and various processing chambers. In this respect, it is understood that the reticle fabrication process involves multiple steps, and that different steps are typically conducted in different chambers that mechanically cooperate with the substrate handling blade  300 . An example of such a processing system is a Centura™ processing system available from Applied Materials, Inc. of Santa Clara, Calif.  
      The process chamber  100  generally includes a cylindrical side wall  162 . The side wall  162  helps define the chamber body, and also supports the gate  161 . The chamber  100  is also defined by a chamber bottom  167 , and an energy transparent ceiling or lid  163 . An inductive coil  176  is disposed around at least a portion of the lid  163 . The chamber body  162  and chamber bottom  167  of the chamber  100  can be made from a metal, such as anodized aluminum. The lid  163  is fabricated from an energy transparent material such as a ceramic or other dielectric material.  
      As mentioned above, the chamber  100  holds a substrate support member  200 . The support member  200  supports the substrate  222  during processing. A plasma zone  164  is defined by the process chamber  100  above an upper surface of the substrate support member  200 . During processing, process gases are introduced into the plasma etch chamber  100  through a gas distributor  172 . The gas distributor  172  is peripherally disposed about the substrate support member  200 . The gas distributor  172  is shown illustratively, and may be disposed in other configurations, such as disposed at the top of lid  163 . Process gases and etchant byproducts may be exhausted from the process chamber  100  through an exhaust system (not shown). An optional cooling line  184  is provided in the pedestal  200 . for controlling the pressure in the plasma etch chamber  100 . An endpoint measurement device may optionally be included to determine the endpoint of a process performed in the chamber  100 .  
      With respect to the substrate support member  200  itself, the support member  200  defines a pedestal for the substrate  222  during processing. The support member  200  first comprises a body  206 . The body  206  has an upper surface that defines a substrate support base  210  (seen in  FIG. 2 ). In one arrangement, the substrate support base  210  is a separate piece mounted on an upper surface of the body  206 . An optional substrate supporting assembly  215  is preferably provided over the base  210  to aid in transporting the substrate  222  into and out of the chamber  100 . The substrate supporting assembly  215  is shown in detail in  FIG. 2 . Only the capture ring  216  of the supporting assembly  215  is seen in  FIG. 1 .  
      Referring back to  FIG. 1 , the body  206  of the substrate support member  200  is mounted on a bulk head assembly, or shaft,  102 . In the embodiment shown, the body  206  is stationary in the chamber  100 ; however, in an alternative embodiment, the body  206  (or a portion of the body  206 ) may be moveable within the chamber  100 . In one arrangement, the body  206  of the substrate support member  200  is mounted on a stainless steel base  104 . The base  104  is typically disposed on the bottom of the processing chamber (not shown in  FIG. 2 ), with the bulk head assembly  102  mounted through the bottom of the processing chamber  100  and coupled to the body  206 . The substrate support member  200  is adapted to maintain vacuum isolation between the interior of the chamber  100  and the outside environment. Power, electrical controls, and backpressure gases may be provided to the substrate support member  200  via the shaft  102 .  
       FIG. 2  presents an exploded perspective view of one embodiment of a substrate support member  200 . From  FIG. 2 , the body  206  and support base  210  are more clearly seen. It can also be seen that a cathode  112  is disposed in the support base  210 . The cathode  112  may optionally vertically extend above the surface of the body  206 . The cathode  112  is electrically coupled to an electrode power supply  178  to generate a capacitive electric field in the plasma etch chamber  100 . Typically an RF voltage is applied to the cathode  112  while the chamber body  162  is electrically grounded. Power applied to the pedestal  200  creates a substrate bias in the form of a negative voltage on the upper surface of the substrate  222 . This negative voltage is used to attract ions from the plasma formed in the chamber  100  to the upper surface of the substrate  222 . The capacitive electric field forms a bias which accelerates inductively formed plasma species toward the substrate  222  to provide a more vertically oriented anisotropic etching of the substrate  222 .  
      Channels  211  (three are shown) are also disposed through the body  206 , and house internally movable lift pins  214  therein. As will be discussed further below, the lift pins  214  engage the lower surface of a capture ring  220  to move the capture ring  220  vertically within the chamber  100  relative to the cover ring  216 . The body  206  may comprise a temperature controlled base adapted to regulate the temperature of the substrate support assembly  215 , and thus, a substrate  222  disposed thereon. The body  206  can be made of a material inert to the process formed in the processing chamber including, for example, aluminum oxide, or aluminum, and substrate support assembly  215  components can be made of aluminum or aluminum oxide. The body  206  may include fluid channels, heating elements, e.g., resistive heating elements or other temperature control members.  
      In the support member arrangement of  FIG. 2 , the substrate support member  200  includes a separate substrate supporting assembly  215 . The substrate supporting assembly  215  generally includes a cover ring  216  and a capture ring  220 .  
      Referring first to the cover ring  216 , the cover ring  216  is preferably a circular ring having an upper surface  219  and support shoulders  218 . The substrate supports  218  define shoulders for receiving a substrate (not shown). In one arrangement, the substrate supports  218  define opposing raised surfaces  221 ,  223  that each includes an inner sloped surface for receiving a substrate. A central opening  225  is formed in the upper surface  219  of the cover ring  216 . The two raised surfaces  221 ,  223  are generally disposed on opposing sides of the central opening  225 . The first raised surface  221  defines an essentially linear raised surface extending along the length of one side of the central opening  225 . The second raised surface  223  defines an arcuate raised surface  221  having an outer diameter  224  and an inner diameter  226 . The outer diameter  224  generally matches the radius of the cover ring  216 , while the inner diameter  226  conforms to the geometry of the central bore  225  along one or more sides of the bore  225 . The upper surface  219  and the raised surfaces  221 ,  223  may be monolithic or may be made of separate components connected together.  
      The capture ring  220  defines an arcuate base plate having an inner diameter  207  and an outer diameter  202 . A central bore  206  is formed within the inner diameter  207  of the capture ring  220 . The diameters  207 ,  202  of the capture ring  220  are not continuous, but retain an opening that serves as part of the bore  206 . As with the cover ring  216 , the capture ring  220  includes substrate supports  204 ,  205 . The substrate supports  204 ,  205  generally follow the inner diameter  207  of the capture ring  220 . In the arrangement of  FIG. 2 , the supports  204 ,  205  define shoulders disposed along the inner perimeter  207 . The substrate supports  204 ,  205  and the base plate  202  form a substrate receiving area. The shoulders  204 ,  205  and the base plate  202  are adapted to mate with the substrate supports  218  on the cover ring  216 . When the capture ring  220  is rested upon the cover ring  216 , the substrate supports  205  for the capture ring  220  are co-planar with the substrate supports  218  for the cover ring. The capture ring  220  is dimensioned to rest on the cover ring  216  without covering the two raised surfaces  221 ,  222  on the cover ring  216 . Together, the substrate supports  205 ,  218  may then seamlessly receive a substrate (not shown).  
      The capture ring  220  moves vertically above the cover ring  216 . In operation, the lift pins  214  move the capture ring  220  vertically above the cover ring  216  during substrate transfer, and then lower the capture ring  220  onto the cover ring  216  for substrate processing. The use of lift pins in the semiconductor fabrication business is known, and those of ordinary skill in the art will understand from this disclosure how the lift pins may be fabricated.  
      Channels  217  are formed through the cover ring  216  to enable the lift pins  214  disposed through the body  206  to move therethrough and lift the capture ring  220  vertically. The vertical movement imparted by the lift pins  214  is used to lift the capture ring  220  to effectuate substrate transfer between the substrate handler blade  300  and the capture ring  220 . The lift pins  214  move the capture ring  220  vertically above the cover ring  216  during substrate transfer, and then lower the capture ring  220  onto the cover ring  216  for substrate processing.  
      To begin processing, the reticle  222  (or other substrate) is positioned on the surface of the pedestal  200 . Etch gases are then introduced into the chamber  100 . To this end, a process gas source supplies gas, such as an oxygen based gas, through a gas input line  172 . In the arrangement of  FIG. 1 , the input line  172  feeds gas into the side of the lid  163 . However, gas may also be introduced through nozzles (not shown) in the top of the lid  163 . Chamber pressure is controlled by a closed-loop pressure control system (not shown).  
      As gas is injected into the chamber  100 , a gas plasma is created. Plasma is formed by the application of power to one or more inductive coils  176  at the top of the lid  163 . In the chamber  100  of  FIG. 1 , two RF coils  176  are used, with one being an outer coil and one being an inner coil. A power supply  177  and matching network is used to apply power to the inductive coils  176 . The inductive coils  176  generate and sustain the plasma above the pedestal  200  and substrate  222 . In one arrangement, approximately 125 Watts is applied to the coils  176  at a frequency of about 13.56 MHz, to produce and maintain an oxygen-comprising plasma over the surface of the reticle  222 . In one arrangement for a dual coil system, approximately 400 Watts is applied to the coils  176  at a frequency of about 13.56 MHz, to produce and maintain a chlo7rine-and-oxygen-comprising plasma over the surface of the reticle  222 . For a single coil system, the coils may provide a DC bias of about 340 to 410 Volts on the reticle surface.  
       FIG. 3  shows a perspective cutaway view of one embodiment of a pedestal  300  of the present invention. The pedestal  300  is configured to receive and support a substrate in a plasma etching chamber. Preferably, the substrate is a photolithographic reticle, and the chamber is a plasma etching chamber, such as the chamber shown in  FIG. 1 , and discussed above.  
      The pedestal first comprises a body  306 . In the arrangement of  FIG. 3 , the body  306  is a generally cylindrical object, though other shapes may be employed. The body  306  includes an upper surface  310  that serves as a substrate support base. In the arrangement shown in  FIG. 3 , the support base  310  has a radial outer diameter  324 . The base  310  also has an intermediate shoulder  326  that forms a four-sided support ridge  325 . The support ridge  325  serves to support the reticle above the pedestal  300  during processing. The support ridge  325  is preferably fabricated from a metallic material. The term “support ridge” means any raised surface feature of any height or shape along the support base  310  that contacts and supports a substrate  222  during processing.  
      The support base  310  is typically configured to receive a cover (not shown) to further support a reticle during processing. The cover may be configured to operate as the substrate support assembly  215  described above.  
      In the novel pedestal  300  of the present invention, at least a portion of the body  306  is fabricated from a dielectric material. In the cutaway view of  FIG. 3 , the dielectric material portion of the body  306  is shown at  318 . Dielectric material  318  is selectively used in the upper surface  310  so as to define a dielectric ring generally about the perimeter of the body  306 . The dielectric material  318  is placed outside of the contact point, e.g., support ridge  326 , for the reticle  222  on the pedestal  300 . The dielectric material portion  318  of the body  306  may comprise two or more separate components (not shown) joined together to form the dielectric portion  318  of the body  306 . The two or more dielectric members may be fabricated from materials having different dielectric properties. The benefit of using material of different dielectric properties is to control the relative amount of RF power coupled through the reticle, as the thickness and dielectric property of the reticle substrate, e.g., quartz, is fixed.  
      The dielectric material portion  318  of the body  306  may be of different thicknesses. This is demonstrated in the schematic embodiments shown in  FIGS. 4 and 5 .  FIG. 4  provides a cross-sectional view of a pedestal  300 ′ of the present invention. The pedestal  300 ′ is shown schematically. Likewise,  FIG. 5  presents a cross-sectional view of a pedestal  300 ′ of the present invention, in an alternate embodiment. The pedestal  300 ″ is again shown schematically. In each view, a reticle  222  is shown being supported on the respective pedestal  300 ′,  300 ″. Further, in each view a cover  315  is provided. The cover  315  may be configured in accordance with the cover  215  shown in the exploded view of  FIG. 2 . The cover  315  is preferably fabricated from a dielectric material. The use of different dielectric material thickness is to adjust or control the relative RF power coupled to the reticle. One benefit of using a dielectric material is it enables the use of two control knobs, that is knobs for dielectric constant and thickness. This, in turn, enables the operator to change the relative amounts of RF that goes into the reticle versus the RF power that goes to the pedestal area surrounding the reticle. The dielectric thickness and type may be such that the relative amount is the same for uniform power distribution, or different if needed for compensating for the etch process.  
      Dielectric material is shown at  318  in both  FIG. 4  and in  FIG. 5 . In  FIG. 4 , the dielectric material  318  resides along the top of the upper support base  306 . In  FIG. 5 , the dielectric material  318  defines substantially the entire thickness of the upper support base  306 . In either instance, the dielectric material  318  is preferably placed outside of the contact point for the reticle  222  on the pedestal  300 .  
      As can be seen, the pedestals  300 ,  300 ′,  300 ″ place dielectric material along a periphery of the upper substrate support body  306 . The dielectric material  318  may be polymeric or ceramic. An example of a polymeric material is Ardel™ polyarylate material manufactured by Amoco polymers. Another example is Vespel™ polyimide from DuPont. Still another example is a plastic material sold under the trade name Ultem™. Yet another example is a synthetic rubber material. An example of a suitable ceramic material is aluminum oxide. Another example of an acceptable dielectric material is quartz. The selected use of dielectric material  318  has the effect of changing the amount of RF power coupling into the reticle during a plasma etching procedure. In this respect, during a plasma etching procedure, the body  306  receives power, such as an RF power. By using dielectric material on the periphery of the body, the potential drop across the pedestal is changed to have a value less than the region where the reticle rests, i.e., inside of the substrate support ridge  326 . The portion of the pedestal  300  within the substrate support ridge  326  remains metallic in order to efficiently conduct waste heat away from the reticle  222 .  
      While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.