Abstract:
Generally, an electrostatic chuck having a dielectric coating is provided. In one embodiment, an electrostatic chuck includes a support surface, a mounting surface disposed opposite the support surface and at least one side separating the support surface and the mounting surface which defines a support body. One or more conductive members are disposed within the support body to generate an electrostatic attraction between the body and a substrate disposed thereon. A dielectric coating is disposed on the mounting surface of the support body to minimize undesired current leakage therethrough. Optionally, the dielectric coating may be additionally disposed on one or more of the sides and/or the support surface.

Description:
BACKGROUND OF THE DISCLOSURE  
         [0001]    1. Field of the Invention  
           [0002]    Embodiments of the invention generally relate to an electrostatic chuck for supporting a substrate within a substrate processing system.  
           [0003]    2. Description of the Background Art  
           [0004]    Substrate supports are widely used to support substrates within semiconductor wafer processing systems. A particular type of substrate support used in semiconductor wafer processing systems, such as a reactive ion etch (RIE) chamber or other processing systems, is an electrostatic chuck. Electrostatic chucks are used to retain substrates, such as semiconductor wafers or other workpieces, in a stationary position during processing. Typically, electrostatic chucks contain one or more electrodes embedded within a dielectric material such as ceramic. As power is applied to the electrode, an attractive force is generated between the electrostatic chuck and the substrate disposed thereon.  
           [0005]    The attractive force is commonly generated through either a coulombic or a Johnsen-Rahbeck effect. Generally, electrostatic chucks utilizing coulombic attraction have electrodes disposed in bodies having high resistivities. The insulating properties of the body maintain a capacitive circuit (i.e., charge separation) between the electrodes and the substrate when an electrical potential is applied therebetween. Electrostatic chucks utilizing Johnsen-Rahbeck attraction have electrodes disposed in bodies having lower resistivities which allow charge migration through the body when power is applied to the electrodes. Charges (i.e., electrons) within the body migrate to portions of the surface of the electrostatic chuck making contact with the substrate when voltage is applied to the electrodes. Some minimal current passes between the chuck surface and the substrate at the contact point but generally not enough to result in device damage. Thus, as the charges accumulate at both sides of the contact points, a highly localized and powerful electric field is established between the substrate and electrostatic chuck. Since the attractive force is proportional to the distance between the opposite charges, the substrate is secured to the chuck with less power than necessary in chucks comprising high resistivity material (i.e., chucks having solely Coulombic attraction) as charge accumulates on the chuck&#39;s support surface close to the substrate. Examples of electrostatic chucks comprised of low resistivity material are described in U.S. Pat. No. 5,117,121 issued May 26, 1992 to Watanabe et al. and U.S. Pat. No. 5,463,526 issued Oct. 31, 1995 to Mundt, both of which are hereby incorporated by reference in their entireties.  
           [0006]    As electrostatic chucks generally rely on the electric potential developed between the embedded electrodes and the substrate for the generation of attractive force, prevention of unintended and parasitic current leakage through the chuck body is paramount. For example, in a Johnsen-Rahbeck electrostatic chuck, plasma may contact the surface of the electrostatic chuck. As the plasma provides a current path between the electrostatic chuck and the chamber sidewalls that are normally grounded, the movement of charge through the body is diverted from the support surface to ground, substantially reducing the charge accumulation on the support surface resulting in diminished or lost attractive force. As the attractive force is decreased or lost, the substrate may move or become dislodged. A dislodged substrate is likely to become damaged or improperly processed. Current leakage from this or other reasons through the sides or bottom of the electrostatic chuck has a similar effect.  
           [0007]    Therefore, a need exists for an improved electrostatic chuck.  
         SUMMARY OF THE INVENTION  
         [0008]    Generally, an electrostatic chuck having a dielectric coating is provided. In one embodiment, an electrostatic chuck includes a support surface, a mounting surface disposed opposite the support surface and at least one side separating the support surface and the mounting surface which define a support body. One or more conductive members are disposed within the support body. A dielectric coating is disposed on the mounting surface of the support body to minimize undesired current leakage therethrough. Optionally, the dielectric coating may be additionally disposed on one or more of the sides and/or support surface.  
           [0009]    In another embodiment, an electrostatic chuck includes a ceramic support body having one or more conductive members disposed therein. The ceramic support body has a support surface adapted to support a substrate and an opposing mounting surface. A ceramic porous member is disposed within the body and is fluidly coupled to the support surface. A coating is disposed on the mounting surface of the support body.  
           [0010]    In another aspect of the invention, a process chamber for processing a substrate is provided. In one embodiment, a process chamber for processing a substrate includes an evacuable chamber defining an interior volume and having a gas supply fluidly coupled thereto. A temperature control plate is disposed in the interior volume and supports an electrostatic chuck. The electrostatic chuck includes a support body having one or more conductive members disposed therein. The support body has an upper portion that includes a support surface. A lower portion of the support body has a mounting surface having a dielectric coating disposed thereon and is disposed on the temperature control plate. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    So that the manner in which the above-recited features of the present invention are attained can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in 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, for the invention may admit to other equally effective embodiments.  
         [0012]    [0012]FIG. 1 is a cross sectional schematic of a process chamber having one embodiment of a substrate support disposed therein;  
         [0013]    [0013]FIG. 2 is a sectional view of the substrate support of FIG. 1; and  
         [0014]    [0014]FIG. 3 depicts another embodiment of a substrate support;  
     
    
       [0015]    To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures.  
       DETAILED DESCRIPTION  
       [0016]    Generally, a process chamber having an electrostatic chuck disposed therein is provided. The electrostatic chuck generally includes a dielectric coating that minimizes current leakage from the electrostatic chuck, advantageously enhancing the attractive or chucking force. Although one embodiment of an electrostatic chuck is described illustratively in a Silicon Decoupled Plasma Source (DPS) CENTURA® etch system available from Applied Materials, Inc. of Santa Clara, Calif., the invention has utility in other process chambers including physical vapor deposition chambers, chemical vapor deposition chambers, other etch chambers and other applications where electrostatic chucking of a substrate is desired.  
         [0017]    [0017]FIG. 1 depicts a schematic diagram of a DPS etch process chamber  100  that comprises at least one inductive coil antenna segment  112  positioned exterior to a dielectric, dome-shaped ceiling  120  (referred to hereinafter as the dome  120 ). An example of a process chamber that may be adapted to benefit from the invention is described in U.S. Pat. No. 5,583,737 issued Dec. 10, 1996 to Collins et al., which is hereby incorporated by reference in its entirety.  
         [0018]    The antenna segment  112  is coupled to a radio-frequency (RF) source  118  that is generally capable of producing an RF signal. The RF source  118  is coupled to the antenna  112  through a matching network  119 . Process chamber  100  also includes a substrate support pedestal  116  that is coupled to a second RF source  122  that is generally capable of producing an RF signal. The source  122  is coupled to the pedestal  116  through a matching network  124 . The chamber  100  also contains a conductive chamber wall  130  that is connected to an electrical ground  134 . A controller  140  comprising a central processing unit (CPU)  144 , a memory  142 , and support circuits  146  for the CPU  144  is coupled to the various components of the process chamber  100  to facilitate control of the etch process.  
         [0019]    In operation, the semiconductor substrate  114  is placed on the substrate support pedestal  116  and gaseous components are supplied from a gas panel  138  to the process chamber  100  through entry ports  126  to form a gaseous mixture  150 . The gaseous mixture  150  is ignited into a plasma in the process chamber  100  by applying RF power from the RF sources  118  and  122  respectively to the antenna  112  and the pedestal  116 . The pressure within the interior of the etch chamber  100  is controlled using a throttle valve  127  situated between the chamber  100  and a vacuum pump  136 . The temperature at the surface of the chamber walls  130  is controlled using liquid-containing conduits (not shown) that are located in the walls  130  of the chamber  100 . Chemically reactive ions are released from the plasma and strike the substrate; thereby removing exposed material from the substrate&#39;s surface.  
         [0020]    The pedestal  116  generally comprises an electrostatic chuck  102  disposed on a temperature control plate  104 . The temperature of the substrate  114  is controlled by stabilizing the temperature of the electrostatic chuck  102  and flowing helium or other gas from a gas source  148  to a plenum defined between the substrate  114  and a support surface  106  of the electrostatic chuck  102 . The helium gas is used to facilitate heat transfer between the substrate  114  and the pedestal  116 . During the etch process, the substrate  114  is gradually heated by the plasma to a steady state temperature. Using thermal control of both the dome  120  and the pedestal  116 , the substrate  114  is maintained at a predetermined temperature during processing.  
         [0021]    [0021]FIG. 2 depicts a vertical cross-sectional view of a first embodiment of the pedestal  116 . The pedestal  116  is generally comprised of the temperature control plate  104  and the electrostatic chuck  102 . The pedestal  116  is generally supported above the bottom of the chamber  100  by a shaft  202  coupled to the temperature control plate  104 . The shaft  202  is typically welded, brazed or otherwise sealed to the temperature control plate  104  to isolate various conduits and electrical leads disposed therein from the process environment within the chamber  100 .  
         [0022]    The temperature control plate  104  is generally comprised of a metallic material such as stainless steel or aluminum. The temperature control plate  104  typically includes one or more passages  212  disposed therein that circulate a heat transfer fluid to maintain thermal control of the pedestal  116 . Alternatively, the temperature control plate  104  may include an external coil, fluid jacket or thermoelectric device to provide temperature control.  
         [0023]    The temperature control plate  104  may be screwed, clamped, adhered or otherwise fastened to the electrostatic chuck  102 . In one embodiment, a heat transfer enhancing layer  204  is adhered between the temperature control plate  104  and the electrostatic chuck  102  thereby securing the plate  104  to the chuck  102 . The heat transfer enhancing layer  204  is comprised of a number of thermally conductive materials and composites, including but not limited to conductive pastes, brazing alloys and adhesive coated, corrugated aluminum films.  
         [0024]    The electrostatic chuck  102  is generally circular in form but may alternatively comprise other geometries to accommodate non-circular substrates, for example, square or rectangular flat panels. The electrostatic chuck  102  generally includes one or more electrodes  208  embedded within a support body  206 . The electrodes  208  are typically comprised of an electrically conductive material such as copper, graphite and the like. Typical electrode structures include, but are not limited to, a pair of coplanar D-shaped electrodes, coplanar interdigital electrodes, a plurality of coaxial annular electrodes, a singular, circular electrode or other structure. The electrodes  208  are coupled to the RF source  118  by a feed through (not shown) disposed in the pedestal  116 . One feed through that may be adapted to benefit from the invention is described in U.S. Pat. No. 5,730,803 issued Mar. 24, 1998, which is hereby incorporated by reference in its entirety.  
         [0025]    The body  206  may comprise aluminum, ceramic, dielectric or a combination of one or more of the aforementioned materials. In one embodiment, the chuck body  206  is fabricated from a low resistivity ceramic material (i.e., a material having a resistivity between about 1xE 9  to about 1×E 11  ohm-cm). Examples of low resistivity materials include doped ceramics such as alumina doped with titanium oxide or chromium oxide, doped aluminum oxide, doped boron-nitride and the like. Other materials of comparable resistivity, for example, aluminum nitride, may also be used. Such ceramic materials having relatively low resistivity generally promote a Johnsen-Rahbek attractive force between the substrate and electrostatic chuck  102  when power is applied to the electrodes  208 . Alternatively, chuck body  206  comprising ceramic materials having resistivities equal to or greater than 1E×11 ohms-cm may also be used.  
         [0026]    The electrostatic chuck  102  generally includes a dielectric coating  224  on at least one of the sides  220  or the bottom  222  of the chuck body  206 . Generally, the dielectric coating  224  has a substantially higher resistivity (or lower dielectric constant) than the material comprising the chuck body  206 . In one embodiment, the coating  224  is an electrically insulating material having a dielectric constant in the range of about 2.5 to about 7. Examples of such insulating materials include, but are not limited to, silicon nitride, silicon dioxide, aluminum dioxide, tantalum pentoxide, silicon carbide, polyimide and the like. The high surface or contact resistivity between the body  206  and the coating  224  substantial prevents electrons from passing therebetween. Moreover, the low dielectric constant of the coating  224  electrically insulates the chuck body  206  from the surrounding structure and environment (e.g., the temperature control plate  104 , process gases, plasma and other conductive pathways) thus minimizing parasitic electrical losses that may reduce the electrical potential between the electrostatic chuck  102  and the substrate thereby resulting in reduction in the attractive forces.  
         [0027]    In the preferred embodiment, the coating  224  is disposed on at least the bottom  222  of the chuck body  206 . In another embodiment, the coating  224  is disposed on the side  220  of the chuck body  206 . In yet another embodiment, the coating  224  is disposed on the support surface  106  of the chuck body  206 . Alternatively, the coating  224  may be disposed on any combination of surfaces comprising the chuck body  206 .  
         [0028]    The coating  224  may be applied to the chuck body  206  using a variety of methods including adhesive film, spraying, encapsulation and other methods that coat one or more of the outer surfaces of the body  206 . In one embodiment, the coating  224  is integrally fabricated to the body  206  by chemical vapor deposition, plasma spraying or by sputtering. Alternatively, when the coating  224  comprises a ceramic material, the coating  224  may be sintered or hot-pressed to the body  206  creating a single, monolithic ceramic member.  
         [0029]    In one embodiment, the support surface  106  of the chuck body  206  may include a plurality of mesas  216  formed on the support surface  106 . The mesas  216  are formed from one or more layers of an electrically insulating material having a dielectric constant in the range of about 2.5 to about 7. Examples of such insulating materials include, but are not limited to, silicon nitride, silicon dioxide, aluminum dioxide, tantalum pentoxide, silicon carbide, polyimide and the like. Alternatively, the mesas  216  may be formed from the same material as the chuck body and then coated with a high resistivity dielectric film.  
         [0030]    In an embodiment of the chuck  102  utilizing the Johnson-Rahbeck effect, the ceramic chuck body  206  is partially conductive due to the relatively low resistivity of the ceramic thus allowing charges to migrate from the electrode  208  to the surface  106  of the chuck body  206 . Similarly, charges migrate through the substrate  114  and accumulate on the substrate  114 . The insulating material comprising or coating the mesas  216  prevents current flow therethrough. Since each of the mesas  216  has a significantly higher resistivity (i.e. lower dielectric constant) than the chuck body  206 , the migrating charges accumulate proximate each of the mesas  216  on the surface  106  of the chuck  102 . Although charges also migrate to the portions of the surface  106  between mesas  216 , the dielectric constant of the mesa  216  is substantially greater than the dielectric constant of the backside gas within the plenum  210  between the backside of the substrate  114  and the chuck body surface which results in the electric field being substantially greater at each mesa than at locations outside of a mesa. Consequently, the clamping force is greatest at each mesa  216  and the invention enables the clamping force to be strictly controlled by placement of the mesas to achieve a uniform charge distribution across the backside of the substrate. One electrostatic chuck having mesas disposed on a support surface that may be adapted to benefit from the invention is described in U.S. Pat. No. 5,903,428 issued May 11, 1999 to Grimard et al., which is hereby incorporated by reference in its entirety.  
         [0031]    To promote a uniform temperature across a substrate that is retained by the electrostatic chuck, a backside gas (e.g., helium or argon) is introduced to a plenum  210  defined between a support surface  106  of the electrostatic chuck  102  and the substrate  114  to provide a heat transfer medium therebetween. The backside gas is generally applied to the plenum through one or more outlets  214  formed through the chuck body  206 .  
         [0032]    [0032]FIG. 3 depicts a partial sectional view of another embodiment of a pedestal  300 . The pedestal  300  includes an electrostatic chuck  324  disposed on a temperature control plate  302 . The pedestal  300  is generally configured similar to the pedestal  116  of FIGS. 1 and 2 except that the pedestal  300  includes a plurality of backside gas outlets  310  disposed proximate a perimeter  326  of a support surface  312  of the electrostatic chuck  324 .  
         [0033]    Generally, the electrostatic chuck  324  includes a body  328  having a bottom  316 , sides  314  and the support surface  312 . The body  328  may be comprised of materials similar to the body  206  described above. In one embodiment, the body  328  includes an upper portion  322  disposed on a lower portion  320 . The lower portion  320  is coupled to a temperature control plate  302  and is generally comprised of a ceramic having a resistivity higher than a resistivity of the upper portion  322 . One or more of the electrodes  304  are disposed between the upper and lower portions  322 ,  320  of the body  328 . Alternatively, the electrodes  304  may be disposed on or in either the upper or lower portions  322 ,  320 .  
         [0034]    In the embodiment shown in FIG. 3, the upper portion  322  is disposed over the lower portion  320 , thus encapsulating the electrodes  304 . The upper portion  322  of the chuck body  328  is generally comprised of a low resistivity ceramic. As power is supplied to the electrodes  304 , the low resistivity material comprising the upper portion  322  of the body  328  allows charge migration therethrough, thus establishing a Johnson-Rahbeck attraction force with a substrate disposed on the support surface  312 . The higher resistivity material of the lower portion  320  substantially insulates the sides  314  and bottom  316  of the chuck body  328 , thus minimizing the current leakage through those areas. To further protect the chuck  324  against parasitic current leakage, a coating  306  may be disposed on the bottom  316 , sides  314  and support surface  312  or any combination thereof.  
         [0035]    Backside gas is generally provided through the plurality of outlets  310  disposed on the support surface  312 . The outlets  310  are generally coupled to a passage  308  disposed through the chuck body  328 . A porous plug  318  is generally disposed between the outlets  310  and the passage  308 . The porous plug  318  is generally comprised of a ceramic material such as aluminum oxide. The porous plug  318  is generally disposed in the upper portion  322  of the chuck body  328  while in the green state. The plug  318 , the electrodes  304  and the upper and lower portions  322  of the body  328  are typically hot-pressed or sintered into a single monolithic ceramic member. Generally, the porous plug  318  prevents arcing and plasma ignition of the backside gas during processing and plasma cleaning by blocking a direct current path through the backside gas between the substrate and portions of the chuck in the passage  308  proximate the electrodes  304  while minimizing the surface area available for charge accumulation adjacent the backside gas flow path.  
         [0036]    Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.