Patent Publication Number: US-2003227737-A1

Title: Method and apparatus for fabricating a protective layer on a chuck

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     [0001] This application claims benefit of U.S. provisional patent application serial No. 60/385,692, filed Jun. 4, 2002, which is incorporated herein by reference. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] Embodiments of the present invention generally relate to processing semiconductor substrates, and more particularly, to electrostatic chucks configured to retain the substrates during processing.  
       [0004] 2. Description of the Related Art  
       [0005] Semiconductor device geometries have dramatically decreased in size since such devices were first introduced several decades ago. Since then, integrated circuits have generally followed the two-year/half-size rule (often called “Moore&#39;s Law”), which means that the number of devices that will fit on a chip doubles every two years. Today&#39;s wafer fabrication plants are routinely producing devices having 0.13 μm and even 0.1 μm feature sizes, and tomorrow&#39;s plants soon will be producing devices having even smaller feature sizes. In the quest to achieve ever-smaller devices, certain issues have become of great concern to the industry.  
       [0006] One such issue relates to contamination that may occur in a semiconductor substrate processing chamber, such as a plasma etching chamber. During processing, reactive gases inside the processing chamber may corrode the electrostatic chuck that retains the substrate, which may cause the electrostatic chuck to disintegrate and cause certain particles making up the electrostatic chuck to be released into the processing chamber, thereby contaminating the chamber.  
       [0007] Therefore, a need exists for an improved apparatus for retaining a substrate in a processing chamber that would be resistant to corrosion caused by reactive gases inside the chamber.  
       SUMMARY  
       [0008] Embodiments of the present invention are generally directed to an apparatus for supporting a substrate in a processing chamber. In one embodiment, the apparatus includes a chuck made of a dielectric material sintered with binders and a protective layer disposed on the chuck. The protective layer is made from a dielectric material.  
       [0009] Embodiments of the present invention are also directed to a method for fabricating a chuck. In one embodiment, the method includes providing the chuck having an upper surface and a side peripheral surface, introducing dielectric powder particles into a combustible gas mixture, combusting the dielectric powder particles and the gas mixture together, and propelling the combusted powder particles onto the chuck to form a protective layer over at least one of the upper surface and the side peripheral surface of the chuck. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010] 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 embodiments, some of 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.  
     [0011]FIG. 1 illustrates an example of a plasma etch reactor that includes various embodiments of the invention.  
     [0012]FIG. 2 illustrates a schematic cross sectional view of an electrostatic chuck in accordance with one embodiment of the invention.  
     [0013]FIG. 3 illustrates a plasma gun in accordance with one embodiment of the invention.  
     [0014]FIG. 4 illustrates a detonation gun in accordance with one embodiment of the invention.  
     [0015] FIGS.  5 A-C illustrate schematic cross sectional views of one or more masks in accordance with one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION  
     [0016]FIG. 1 illustrates an example of a plasma etch reactor  100  that includes various embodiments of the invention. The plasma etch reactor  100  includes a grounded vacuum chamber  32 , which may include liners to protect the walls. A substrate  34  is inserted into the chamber  32  through a slit valve opening  36  and is placed on a cathode pedestal  105  with an electrostatic chuck  40  selectively clamping the substrate. Various embodiments of the electrostatic chuck  40  will be described in the following paragraphs with reference to FIGS.  2 - 5 .  
     [0017] Fluid cooling channels may be positioned through the pedestal  105  to maintain the pedestal at reduced temperatures. A thermal transfer gas, such as helium, is supplied to grooves in the upper surface of the pedestal  105 . The thermal transfer gas increases the efficiency of thermal coupling between the pedestal  105  and the substrate  34 , which is held against the pedestal  105  by the electrostatic chuck  40  or an alternatively used peripheral substrate clamp.  
     [0018] An RF power supply  200 , operating at 13.56 MHz, is connected to the cathode pedestal  105  and provides power for generating the plasma while also controlling the DC self-bias. Magnetic coils  44  powered by current supplies surround the chamber  32  and generate a slowly rotating (on the order of seconds and typically less than 10 ms), horizontal, essentially DC magnetic field in order to increase the density of the plasma. A vacuum pump system  46  pumps the chamber  32  through an adjustable throttle valve  48  and a plenum  56 . Shields  50 ,  52  not only protect the chamber  32  and pedestal  105  but also define a baffle  54  and a pumping channel  54  connected to the throttle valve  48 .  
     [0019] Processing gases are supplied from gas sources  60 ,  61 ,  62  through respective mass flow controllers  64 ,  66 ,  68  to a gas distribution plate  125  positioned in the roof of the chamber  32  overlying the substrate  34  and across from a processing region  72 . The distribution plate  125  includes a manifold  74  configured to receive the processing gases and communicate with the processing region  72  through a showerhead having a large number of distributed apertures  76 , thereby injecting a more uniform flow of processing gases into the processing region  72 . An unillustrated VHF power supply, operating at about 162 MHz, may be electrically connected to the gas distribution plate  125  to provide power to the gas distribution plate  125  for generating the plasma.  
     [0020] Other details of the etch reactor  100  are further described in commonly assigned U.S. Pat. No. 6,451,703, entitled “Magnetically Enhanced Plasma Etch Process Using A Heavy Fluorocarbon Etching Gas”, issued to Liu et al. and U.S. Pat. No. 6,403,491, entitled “Etch Method Using A Dielectric Etch Chamber With Expanded Process Window”, issued to Liu et al., which are both incorporated by reference herein to the extent not inconsistent with the invention. Although various embodiments of the invention will be described with reference to the above-described reactor, the embodiments of the invention may also be used in other reactors, such as one described in commonly assigned U.S. Ser. No. 10/028,922 filed Dec. 19, 2001, entitled “Plasma Reactor With Overhead RF Electrode Tuned To The Plasma With Arcing Suppression”, by Hoffman et al., which is also incorporated by reference herein to the extent not inconsistent with the invention.  
     [0021] Various embodiments of the electrostatic chuck  40  will now be described with reference to FIGS.  2 - 5 . FIG. 2 illustrates a schematic cross sectional view of an electrostatic chuck  240  in accordance with one embodiment of the invention. The electrostatic chuck  240  may also be referred to as an insulation layer or a puck. The chuck  240  is disposed on a cathode pedestal  205 . The chuck  240  may include an electrically conductive electrode, e.g., mesh layer  260 . The chuck  240  further includes a protective layer  250  disposed thereon. More specifically, the protective layer  250  is disposed on an upper surface  240   a  and a side peripheral surface  240   b  of the electrostatic chuck  240 . A substrate (not shown) is generally disposed on top of the protective layer  250 . The cathode pedestal  205  may be made from a metallic material, such as aluminum and the like. The chuck  240  may be made from a dielectric material, such as aluminum oxide sintered with silica binders, such as silicon oxide. The protective layer  250  may be made from a dielectric material, such as alumina (aluminum oxide), aluminum nitride and the like.  
     [0022] The electrically conductive electrode  260  may actually be in the form of a dual-electrode, such as a first electrically conductive mesh layer and a second electrically conductive mesh layer. The first electrically conductive mesh layer may be configured to supply an RF bias voltage to control ion bombardment energy at the surface of the substrate  34 , while the second electrically conductive mesh layer may be coupled to a DC voltage source.  
     [0023] Details of the protective layer  250  will now be described in the following paragraphs. As mentioned above, the protective layer  250  may be made from a dielectric material, which has the characteristic of being resistant to corrosion from gases introduced into the chamber. Such gases may include silicon-containing gases, oxygen-containing gases, fluorine-containing gases, nitrogen-containing gases, and the like. The protective layer  250  may have a thickness from about 0.001″ to about 0.020″. Since the protective layer  250  is disposed on the upper surface  240   a  and the side peripheral surface  240   b  of the electrostatic chuck  240 , the protective layer  250  is configured to protect the electrostatic chuck  240  from being corroded by the reactive gases introduced into the chamber. In one embodiment, the protective layer  250  is made from alumina, while the chuck  240  is made from alumina particles sintered with silica binders and the reactive gases are silicon-containing gases.  
     [0024] The protective layer  250  may be formed on the chuck  240  using a variety of methods, such as plasma glow discharge spraying, flame spraying, electric wire melting, electric-arc melting and detonation gun techniques and the like. FIG. 3 illustrates an exemplary plasma gun  340  that may be used to form the protective layer  250  on the chuck  240 . The plasma gun  340  includes a cone-shaped cathode  342  inside a cylindrical anode  344  that forms a nozzle. Other details of the plasma gun  340  may be described in commonly assigned U.S. Pat. No. 6,414,834 entitled “Dielectric Covered Electrostatic Chuck”, issued to Weldon et al., which is incorporated by reference herein to the extent not inconsistent with the invention.  
     [0025]FIG. 4 schematically illustrates a representative detonation gun  400  that may be used to form the protective layer  250  on the chuck  240 . The detonation gun  400  has a main body  402  defining an inner combustion chamber  403  and a gun barrel  404  defining an inner passage  406  in communication with combustion chamber  403 . The gun barrel  404  includes a nozzle  408  for discharging powder particles  410  onto a workpiece  412 , such as the upper surface  240   a  and the side peripheral surface  240   b  of the chuck  240 . The detonation gun  400  further includes a powder inlet port  414  and two fuel gas inlet ports  416 ,  418  for injecting a fuel gas mixture of at least one combustible gas. A spark plug  420  extends into the chamber  403  for igniting the fuel gas mixture.  
     [0026] The fuel gas mixture, such as oxygen-acetylene, is ignited to produce a detonation wave which travels along the barrel  404  of the detonation gun  400 , where the fuel gas mixture heats the coating material and propels the coating material from the detonation gun  400  and onto the generally planar surface of the workpiece  412 . The coating material may be in the form of powder particles  410 . In one embodiment, the coating material is made from a dielectric material, such as alumina. Other dielectric materials, such as aluminum nitride, are also contemplated by embodiments of the present invention.  
     [0027] The detonation gun  400  generally utilizes at least two combustible gases selected from the group of saturated and unsaturated hydrocarbons. The group may include acetylene, propylene, methane, ethylene, methyl acetylene, propane, ethane, butadienes, butylenes, butanes, cyclopropane, propadiene, cyclobutane and ethylene oxide. The fuel mixture comprises oxygen and acetylene. A variety of detonation guns having the structure described above or an equivalent structure can be adapted for use in the inventive process. For example, detonation guns that are suitable for the present invention are known under the trade names of D-gun™ and Super D-gun™ manufactured by Praxair S. T., Inc. of Indianapolis, Ind.  
     [0028] In use, a mixture of oxygen and acetylene is fed through ports  416 ,  418  into the combustion chamber  403  and a charge of powder particles  410  is fed through port  414  via a carrier gas, such as nitrogen or air, into the chamber  402 . The powder particles  410  may be made from a dielectric material, such as alumina. The fuel gas is ignited with the spark plug  420  and the resulting detonation wave accelerates the powder particles  410  through the passage  406  of the barrel  404  and heats the powder particles  410  to a temperature above its melting point. The detonation wave typically attains a velocity of about 2800 to 3300 m/s and the particle velocity is typically about 700 to 1000 m/s. The nozzle  408  of the gun barrel  404  is positioned between about 50 to 200 mm from the target surface of the workpiece  412  so that the powder particles  410  spray onto the workpiece  412  to form the protective layer  250  on the surface of the workpiece  412 , such as the upper surface  240   a  or the side peripheral surface  240   b  of the chuck  240 .  
     [0029] In one embodiment of the present invention, the detonation gun process is carried out in pressure and temperature conditions that maintain substantially all of the powder particles  410 , e.g., the dielectric material, in the gamma phase. In another embodiment, at least 80% of the powder particles  410  remains in the gamma phase. The gamma phase of powder particles  410  is a distorted or non-ordered crystalline phase of powder particles  410 . Allowing the powder particles  410  to transform back to the alpha phase may cause a change in volume, which leads to cracks in the coating. Thus, maintaining the gamma phase throughout the detonation gun process minimizes cracking in the final protective layer. In addition, providing a protective layer with a substantially uniform single phase (i.e., 99% gamma phase) offers a number of advantages. For example, a single-phase protective layer is easier to inspect because it has a generally uniform appearance. A single-phase protective layer also distributes charge more uniformly, which facilitates uniform positioning of the wafer over the electrostatic chuck during processing. Other details of the detonation gun  400  may be described in commonly assigned U.S. Pat. No. 6,175,485 entitled “Electrostatic Chuck And Method For Fabricating The Same”, issued to Krishnaraj et al., which is incorporated by reference herein to the extent not inconsistent with the invention.  
     [0030] As mentioned above, the rapidly expanding mixture of ignited gases in the detonation gun  400  imparts a high kinetic energy detonation wave to propel the protective layer  250  onto the workpiece  412 , such as the chuck  240 , upon impact. However, when the detonation gun  400  is applied to a corner region of the workpiece  412 , the kinetic energy of the detonation wave may be reduced due to the geometrical effect at the corner of the workpiece  412 . As a result, a portion of the powdered particles  410  fails to reach a melting point and remains in its solid state, thereby causing pitting to occur near the corner region of the workpiece  412  upon impact.  
     [0031] Accordingly, one or more masks (described below with reference to FIGS.  5 A- 5 C) may be disposed on the workpiece  412  to eliminate the reduction of kinetic energy occurring at the corner region of the workpiece  412 . The masks provide a uniform surface upon which the protective layer is applied, thereby allowing the detonation wave to maintain a high kinetic energy upon impact with the corner region of the workpiece  412 . In this manner, the masks may be used to minimize the occurrence of pitting that typically occurs near the corner region of the workpiece  412 . The masks may be made from any material that would be conducive to protecting the workpiece  412  from the coating material being disposed thereon by the gun  400 .  
     [0032]FIG. 5A illustrates a schematic cross sectional view of a mask  510  disposed adjacent the side peripheral surface  240   b  of the electrostatic chuck  240  in accordance with one embodiment of the invention. In one embodiment, mask  510  may be annularly disposed around the chuck  240  and is configured to substantially cover the side peripheral surface  240   b.  Placing mask  510  adjacent the side peripheral surface  240   b  provides a uniform surface on the upper surface  240   a  upon which the protective layer  250  is to be applied. That is, mask  510  positioned adjacent the side peripheral surface  240   b  allows the coating material to be impelled at the upper surface  240   a  of the chuck at a high velocity. In this manner, the protective layer  250  may be formed uniformly on the upper surface  240   a  of the electrostatic chuck  240  without the occurrence of pitting on the upper surface  240   a.    
     [0033]FIG. 5B illustrates a schematic cross sectional view of a mask  520  disposed adjacent the upper surface  240   a  of the electrostatic chuck  240  in accordance with one embodiment of the invention. In one embodiment, mask  520  may have shaped like a disk and is configured to substantially cover the entire upper surface  240   a.  Placing mask  520  adjacent the upper surface  240   a  provides a uniform surface on the side peripheral surface  240   b  upon which the protective layer  250  is to be applied. That is, mask  520  positioned adjacent the upper surface  240   a  allows the coating material to be impelled at the side peripheral surface  240   b  of the chuck at a high velocity. In this manner, the protective layer  250  may be formed uniformly on the side peripheral surface  240   b  of the electrostatic chuck  240  without the occurrence of pitting on the side peripheral surface  240   b.    
     [0034]FIG. 5C illustrates a schematic cross sectional view of a mask  530  disposed adjacent the upper surface  240   a  and the side peripheral surface  240   b  of the electrostatic chuck  240  in accordance with one embodiment of the invention. In one embodiment, mask  530  may include a top portion  530 A and a bottom portion  530 B. The top portion  530 A may be in the shape of a cone, while the bottom portion  530 B may be in the shape of a ring, similar to mask  510 . Placing mask  530  adjacent the upper surface  240   a  and the side peripheral surface  240   b  provides a uniform surface on the corner regions upon which the protective layer  250  is to be applied. That is, mask  530  positioned adjacent the upper surface  240   a  and the side peripheral surface  240   b  allows the coating material to be impelled at the corner regions of the chuck at a high velocity. In this manner, the protective layer  250  may be formed uniformly on the corner regions of the electrostatic chuck  240  without the occurrence of pitting on either the upper surface  240   a  or the side peripheral surface  240   b.    
     [0035] 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.