Patent Publication Number: US-2020286717-A1

Title: Electrostatic chuck for high bias radio frequency (rf) power application in a plasma processing chamber

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. provisional patent application Ser. No. 62/815,919, filed Mar. 8, 2019, which is herein incorporated by reference in its entirety. 
    
    
     FIELD 
     Embodiments of the present disclosure generally relate to substrate processing systems, and more specifically, to electrostatic chucks for use in substrate processing systems. 
     BACKGROUND 
     Radio frequency (RF) power is often used in etching processes, for example, requiring very high aspect ratio holes to make contacts or deep trenches for laying infrastructure for electrical pathways. RF power can be used for plasma generation and/or for creating bias voltage on a substrate being processed to attract ions from bulk plasma. An electrostatic chuck is used to electrostatically hold a substrate to control substrate temperature during processing. The electrostatic chuck typically includes an electrode embedded in a dielectric plate and a cooling plate disposed below the dielectric plate. An RF power source for creating bias is applied to the cooling plate. A backside gas may be introduced between the substrate and a top surface of the electrostatic chuck via gas channels in the electrostatic chuck as a heat transfer medium. However, the inventors have observed that RF power applied to the cooling plate to induce a bias voltage on the substrate creates a DC potential difference between the substrate and the cooling plate which can undesirably lead to arcing in the gas channels. 
     Accordingly, the inventors have provided an improved electrostatic chuck. 
     SUMMARY 
     Embodiments of an electrostatic chuck are provided herein. In some embodiments, an electrostatic chuck for use in a substrate processing chamber includes a plate having a first side and a second side opposite the first side; a first electrode embedded in the plate proximate the first side; a second electrode embedded in the plate proximate the second side; a plurality of conductive elements coupling the first electrode to the second electrode; a first gas channel disposed within the plate and between the first electrode and the second electrode; a gas inlet extending from the second side of the plate to the first gas channel; and a plurality of gas outlets extending from the first side of the plate to the first gas channel. 
     In some embodiments, an electrostatic chuck for use in a substrate processing chamber includes a plate having a first side and a second side opposite the first side; a first electrode embedded in the plate proximate the first side; a second electrode embedded in the plate proximate the second side; a third electrode embedded in a peripheral region of the plate, between the first electrode and the second electrode; and a plurality of first posts extending from the first electrode to the second electrode to electrically couple the first electrode and the second electrode; and a plurality of second posts extending from at least one of the first electrode or the second electrode to the third electrode to electrically couple the third electrode to the at least one of the first electrode or the second electrode. 
     In some embodiments, a process chamber includes a chamber body having a substrate support disposed within an inner volume of the chamber body, wherein the substrate support includes an electrostatic chuck comprising a cooling plate; a dielectric plate disposed above the cooling plate and having a first electrode, a second electrode, and a plurality of posts electrically coupling the first electrode to the second electrode; one or more first gas channels extending from a bottom surface of the electrostatic chuck into the dielectric plate; a plurality of second gas channels that extend from the one or more first gas channel horizontally across the electrostatic chuck between the first electrode and the second electrode; and a plurality of third gas channels extending from the plurality of second gas channels to a top surface of the electrostatic chuck. 
     Other and further embodiments of the present disclosure are described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present disclosure, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the disclosure depicted in the appended drawings. However, the appended drawings illustrate only typical embodiments of the disclosure and are therefore not to be considered limiting of scope, for the disclosure may admit to other equally effective embodiments. 
         FIG. 1  depicts a schematic side view of a process chamber having an electrostatic chuck in accordance with at least some embodiments of the present disclosure. 
         FIG. 2  depicts a schematic partial side view of an electrostatic chuck in accordance with at least some embodiments of the present disclosure. 
         FIG. 3  depicts a schematic side view of an electrostatic chuck in accordance with at least some embodiments of the present disclosure. 
         FIG. 4  depicts a cross-sectional top view of an electrostatic chuck in accordance with at least some embodiments of the present disclosure. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. Elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     DETAILED DESCRIPTION 
     Embodiments of electrostatic chucks for use in a substrate processing chamber are provided herein. The electrostatic chuck includes a dielectric plate having a support surface to support a substrate. The dielectric plate is disposed on a cooling plate. In some embodiments, one or more gas channels extend from a bottom surface of the electrostatic (e.g., bottom surface of the cooling plate) to a top surface of the electrostatic chuck (e.g., top surface of the dielectric plate). The one or more gas channels are configured to provide backside gas, such as nitrogen (N) or helium (He), to the top surface of the electrostatic chuck to act as a heat transfer medium. 
     In some embodiments, a RF power source is coupled to the cooling plate and configured to provide negative bias to a substrate being processed. As RF power is applied to the cooling plate, a peak-to-peak voltage (Vpp) on the cooling plate and Vpp on the substrate is different depending on the impedance of the dielectric plate. The difference in respective peak-to-peak voltages creates an electric field between the cooling plate and the substrate, which can undesirably cause backside gas to be ionized and consequently lead to arcing. In some embodiments, multiple electrodes are disposed in the dielectric plate to advantageously reduce the difference between the Vpp on the cooling plate and the Vpp on the substrate. 
       FIG. 1  is a schematic cross-sectional view of process chamber (e.g., a plasma processing chamber) in accordance with some embodiments of the present disclosure. In some embodiments, the plasma processing chamber is an etch processing chamber. However, other types of processing chambers configured for different processes can also use or be modified for use with embodiments of the electrostatic chuck described herein. 
     The chamber  100  is a vacuum chamber which is suitably adapted to maintain sub-atmospheric pressures within a chamber interior volume  120  during substrate processing. The chamber  100  includes a chamber body  106  covered by a lid  104  which encloses a processing volume  119  located in the upper half of chamber interior volume  120 . The chamber  100  may also include one or more shields  105  circumscribing various chamber components to prevent unwanted reaction between such components and ionized process material. The chamber body  106  and lid  104  may be made of metal, such as aluminum. The chamber body  106  may be grounded via a coupling to ground  115 . 
     A substrate support  124  is disposed within the chamber interior volume  120  to support and retain a substrate  122 , such as a semiconductor wafer, for example, or other such substrate as may be electrostatically retained. The substrate support  124  may generally comprise an electrostatic chuck  150  (described in more detail below with respect to  FIGS. 2-4 ) and a hollow support shaft  112  for supporting the electrostatic chuck  150 . The electrostatic chuck  150  comprises a dielectric plate  152  having one or more electrodes  154  disposed therein and a cooling plate  136 . The hollow support shaft  112  provides a conduit to provide, for example, backside gases, process gases, fluids, coolants, power, or the like, to the electrostatic chuck  150 . 
     In some embodiments, the hollow support shaft  112  is coupled to a lift mechanism  113 , such as an actuator or motor, which provides vertical movement of the electrostatic chuck  150  between an upper, processing position (as shown in  FIG. 1 ) and a lower, transfer position (not shown). A bellows assembly  110  is disposed about the hollow support shaft  112  and is coupled between the electrostatic chuck  150  and a bottom surface  126  of chamber  100  to provide a flexible seal that allows vertical motion of the electrostatic chuck  150  while preventing loss of vacuum from within the chamber  100 . The bellows assembly  110  also includes a lower bellows flange  164  in contact with an o-ring  165  or other suitable sealing element which contacts the bottom surface  126  to help prevent loss of chamber vacuum. 
     The hollow support shaft  112  provides a conduit for coupling a backside gas supply  141 , a chucking power supply  140 , and RF sources (e.g., RF plasma power supply  170  and RF bias power supply  117 ) to the electrostatic chuck  150 . In some embodiments, RF energy supplied by the RF plasma power supply  170  may have a frequency of about 40 MHz or greater. The backside gas supply  141  is disposed outside of the chamber body  106  and supplies heat transfer gas to the electrostatic chuck  150 . In some embodiments, RF plasma power supply  170  and RF bias power supply  117  are coupled to the electrostatic chuck  150  via respective RF match networks (only RF match network  116  shown). In some embodiments, the substrate support  124  may alternatively include AC, DC, or RF bias power. 
     A substrate lift  130  can include lift pins  109  mounted on a platform  108  connected to a shaft  111  which is coupled to a second lift mechanism  132  for raising and lowering the substrate lift  130  so that the substrate  122  may be placed on or removed from the electrostatic chuck  150 . The electrostatic chuck  150  may include thru-holes to receive the lift pins  109 . A bellows assembly  131  is coupled between the substrate lift  130  and bottom surface  126  to provide a flexible seal which maintains the chamber vacuum during vertical motion of the substrate lift  130 . 
     The electrostatic chuck  150  includes gas distribution channels  138  extending from a lower surface of the electrostatic chuck  150  to various openings in an upper surface of the electrostatic chuck  150 . The gas distribution channels  138  are in fluid communication with the backside gas supply  141  via gas conduit  142  to control the temperature and/or temperature profile of the electrostatic chuck  150  during use. 
     The chamber  100  is coupled to and in fluid communication with a vacuum system  114  which includes a throttle valve (not shown) and vacuum pump (not shown) which are used to exhaust the chamber  100 . The pressure inside the chamber  100  may be regulated by adjusting the throttle valve and/or vacuum pump. The chamber  100  is also coupled to and in fluid communication with a process gas supply  118  which may supply one or more process gases to the chamber  100  for processing a substrate disposed therein. 
     In operation, for example, a plasma  102  may be created in the chamber interior volume  120  to perform one or more processes. The plasma  102  may be created by coupling power from a plasma power source (e.g., RF plasma power supply  170 ) to a process gas via one or more electrodes near or within the chamber interior volume  120  to ignite the process gas and creating the plasma  102 . A bias power may also be provided from a bias power supply (e.g., RF bias power supply  117 ) to the one or more electrodes  154  within the electrostatic chuck  150  to attract ions from the plasma towards the substrate  122 . 
       FIG. 2  depicts a schematic partial side view of an electrostatic chuck  200  for use in the chamber  100  in accordance with at least some embodiments of the present disclosure. The electrostatic chuck  200  may be used as the electrostatic chuck  150  described above with respect to  FIG. 1 . The electrostatic chuck  200  includes a dielectric plate  210  and a cooling plate  220 . In some embodiments, the dielectric plate  210  is attached to the cooling plate  220  using a bond layer. In some embodiments, the dielectric plate  210  has a first side  202  and a second side  204  opposite the first side  202 . In some embodiments, the first side  202  corresponds with a support surface  232  of the electrostatic chuck  200 . In some embodiments, the substrate  122  is disposed on the support surface  232 . In some embodiments, the cooling plate  220  is made of an electrically conductive material, for example, aluminum (Al). In some embodiments, the cooling plate  220  includes passageways (not shown) to accommodate a flow of coolant. 
     A first electrode  208  is embedded in the dielectric plate  210  proximate the first side  202 . A second electrode  218  is embedded in the dielectric plate  210  proximate the second side  204 . In some embodiments, the first electrode  208  and the second electrode  218  are substantially parallel. The first electrode  208  and the second electrode  218  may be disk shaped or any other shape corresponding with a shape of the dielectric plate  210 . A plurality of conductive elements  212  electrically couple the first electrode  208  to the second electrode  218 . In some embodiments, the plurality of conductive elements  212  are a plurality of posts. In some embodiments, a first distance  228  between the first electrode  208  and the first side  202  is about 0.8 mm to about 1.2 mm. In some embodiments, a second distance  230  between the second electrode  218  and the second side  204  is about 0.8 mm to about 1.2 mm. In some embodiments, the first distance  228  is substantially equal to the second distance  230 . The first electrode  208 , the second electrode  218 , and the plurality of conductive elements  212  may be formed of suitable process-compatible materials, such as molybdenum (Mo), titanium (Ti), or the like. 
     Placing the first electrode  208  close to the first side  202  of the dielectric plate and the second electrode  218  close to the second side  204  with the plurality of conductive elements  212  coupling the first electrode  208  to the second electrode  218  advantageously reduces the potential difference between the support surface  232  and the cooling plate  220  created as RF power goes through the dielectric plate  210 . The reduced potential difference advantageously consequently reduces arcing potential in the gas distribution channels  138 . 
     In some embodiments, the gas distribution channels  138  include one or more inlets disposed on a bottom surface of the electrostatic chuck (e.g., bottom surface of the cooling plate). In some embodiments, the gas distribution channels  138  include one or more outlets disposed on the support surface  232 , or top surface, of the electrostatic chuck  200 . In some embodiments, the gas distribution channels  138  extend from one or more inlets disposed on a bottom surface  214  of the electrostatic chuck  200  to one or more outlets disposed on the top surface of the electrostatic chuck  200 . The gas distribution channels  138  are configured to provide backside gas, such as nitrogen (N) or helium (He), to the top surface of the electrostatic chuck. 
     An area between the first electrode  208  and the second electrode  218  has no electric field. In some embodiments, the gas distribution channels  138  are substantially disposed between the first electrode  208  and the second electrode  218  to advantageously reduce or prevent arcing potential therein. In some embodiments, the gas distribution channels  138  includes a first gas channel  222  disposed within the dielectric plate  210  and between the first electrode  208  and the second electrode  218 . The location of the first gas channel  222  between the first electrode  208  and the second electrode  218  advantageously prevents arcing in the first gas channel  222 . The first gas channel  222  is coupled to a gas inlet  224  disposed on the second side  204  of the dielectric plate  210 . The first gas channel  222  is coupled to a plurality of gas outlets  226  disposed on the first side  202  of the dielectric plate  210 . In some embodiments, a cross-sectional width of the first gas channel  222  is about 0.8 mm to about 1.2 mm. In some embodiments, a cross-sectional height of the first gas channel  222  is about 0.8 mm to about 1.2 mm. 
     In some embodiments, a porous plug  206  is disposed in the gas distribution channels  138  at an interface between the dielectric plate  210  and the cooling plate  220 . In some embodiments, the porous plug  206  is made of alumina. The porous plug  206  is configured to reduce or prevent arcing potential of backside gas at the interface between the dielectric plate  210  and the cooling plate  220 . 
       FIG. 3  depicts a schematic side view of an electrostatic chuck in accordance with at least some embodiments of the present disclosure. A central connector  306  is coupled to the chucking power supply  140  and extends from the bottom surface  214  of the electrostatic chuck  200  into the dielectric plate  210 . In some embodiments, the central connector  306  is directly coupled to the first electrode  208  to couple the chucking power supply  140  to the first electrode  208  to provide chucking power to the first electrode  208 . In some embodiments, the central connector  306  is directly coupled to the second electrode  218 . In some embodiments, an insulator  304  is disposed about the central connector  306  in the cooling plate  220  to electrically isolate the central connector  306  from the cooling plate  220 . 
     In some embodiments, an edge ring  302  is disposed about the dielectric plate  210  to guide a substrate disposed on the dielectric plate  210 . In some embodiments, the edge ring  302  is rests in a notch at an upper peripheral edge of the dielectric plate  210 . In some embodiments, the edge ring  302  rests on a quartz ring (not shown) disposed about the cooling plate  220 . In some embodiments, the edge ring  302  is disposed about the dielectric plate  210  and the substrate  122 . In some embodiments, the edge ring  302  is made of silicon (Si), silicon carbide (SiC), or graphite to reduce contamination on the substrate  122  during processing. 
     In operation, RF power applied on the cooling plate  220  creates a sheath in between the substrate  122  and the plasma  102 . As a result, ions from the plasma  102  are attracted to the substrate  122  that is biased, and the ions accelerate through the sheath perpendicular to equipotential lines within the sheath. When the edge ring  302  is disposed about the dielectric plate  210 , the voltage potential on the edge ring is different compared to a voltage potential on the substrate  122 . The difference in voltage potential causes the sheath to have a thicker shape above the edge ring  302  than above the substrate  122 . As such, the equipotential lines within the sheath do not have a flat profile near an edge of the substrate  122 , causing ions accelerate at an angle around the edge ring  302  and leading to an etching profile tilting issue around the edge ring  302 . 
     In some embodiments, a third electrode  310  is embedded in a peripheral region of the dielectric plate  210  and directly coupled to at least one of the first electrode  208  and the second electrode  218  via a plurality of conductive elements  308 . In some embodiments, the plurality of conductive elements  308  are a plurality of second posts. The third electrode  310  is disposed vertically between the first electrode  208  and the second electrode  218 . In some embodiments, a third distance  312  between the third electrode  310  and a bottom surface of the notch in the upper peripheral edge of the dielectric plate  210  is about 0.8 mm to about 1.2 mm. In some embodiments, the third distance  312  is substantially equal to the first distance  228  and the second distance  230 . The third electrode  310  advantageously creates a flatter sheath profile around the edge ring  302  to reduce or prevent the etching profile tilting issue. 
       FIG. 4  depicts a cross-sectional top view of the electrostatic chuck at a location between the first electrode  208  and the second electrode  218 , in accordance with at least some embodiments of the present disclosure. As discussed above, the first gas channel  222  is coupled to a gas inlet  224  disposed on the second side  204  of the dielectric plate  210 . The first gas channel  222  includes a first end  418  coupled to the gas inlet  224 . In some embodiments, the first gas channel  222  comprises a network of gas channels that extend horizontally across the dielectric plate  210  from the first end  418  to a plurality of second ends  426  to define a first plenum  404 . The plurality of second ends  426  are coupled to corresponding ones of the plurality of gas outlets  226 . In some embodiments, the network of gas channels are configured to split evenly to provide substantially equal flow length and conductance along each pathway of the first gas channel  222  from the first end  418  to each respective second end  426 . Substantially equal conductance means within about ten percent. 
     In some embodiments, a second gas inlet  402  is disposed on the second side  204  of the dielectric plate  410  and coupled to the second gas channel  330 . A plurality of gas outlets are disposed on the first side  202  of the plate and coupled to the second gas channel  330 . The second gas channel  330  includes a first end  420  coupled to the second gas inlet  402 . In some embodiments, the second gas channel  330  comprises a network of gas channels that extend horizontally across the dielectric plate  210  from the first end  420  to a plurality of second ends  414  to define a second plenum  406 . The plurality of second ends  414  are coupled to corresponding ones of the plurality of gas outlets on the first side  202  coupled to the second gas channel  330 . In some embodiments, the network of gas channels are configured to split evenly to provide substantially equal flow length and conductance along each pathway of the second gas channel  330  from the first end  420  to each respective second end  414 . Substantially equal conductance means within about ten percent. 
     In some embodiments, the first plenum  404  is fluidly independent from the second plenum  406  within the dielectric plate  210  to advantageously provide greater uniformity or control over the temperature profile of the electrostatic chuck  200 . In some embodiments, the plurality of gas outlets  226  coupled to the first gas channel  222  are disposed in a peripheral region of the dielectric plate  210 , while the plurality of gas outlets coupled to the second gas channel  330  are disposed in a central region of the dielectric plate  210 . In some embodiments, the plurality of gas outlets  226  coupled to the first gas channel  222  are disposed in the central region of the dielectric plate  210 , while the plurality of gas outlets coupled to the second gas channel  330  are disposed in the peripheral region of the dielectric plate  210 . 
     In some embodiments, the dielectric plate  210  consists of two plates that are machined to form the first gas channel  222  and the second gas channel  330 . In some embodiments, the two plates are sintered. In some embodiments, the two plates are diffusion bonded together once machined. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof.