Patent Publication Number: US-2007113785-A1

Title: Radio frequency grounding apparatus

Description:
RELATED U.S. APPLICATIONS  
      Not applicable.  
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
      Not applicable.  
     REFERENCE TO MICROFICHE APPENDIX  
      Not applicable.  
     FIELD OF THE INVENTION  
      The present invention relates to a radio frequency (RF) grounding apparatus, and more particularly to an RF grounding apparatus using a clamp and a flexible conductive sheet to form a grounding path, which is especially suitable for a plasma reaction chamber.  
     BACKGROUND OF THE INVENTION  
      The deposition of dielectric material is one of the important steps in the semiconductor manufacturing process. Dielectric material is used as an intermetal dielectric (IMD) to isolate the adjacent metal lines electrically, as a passivation layer to protect the circuits on a chip from moisture and metal ions, and as a dielectric anti-reflection coating (DARC) in the lithography process.  FIG. 1  illustrates a commonly used dielectric deposition system  1 , which comprises a reaction chamber  11 , an RF generator  18 , an RF matching box  19  and an RF matching circuit  19 ′. The reaction chamber  11 , which contains a heater  17  and an anode plate  14 , is used to conduct the dielectric deposition process. The heater  17  is used to sustain and heat a wafer  16 , which maintains a specific process temperature to conduct a process. The anode plate  14 , an RF mesh  10  in the heater  17  and an RF grounding rod  13  form a conductive path to generate plasma  15 . The RF generator  18 , the RF matching box  19  and the RF matching circuit  19 ′ form an RF system to deliver the energy stably to the reaction chamber  11  to sustain the plasma  15  to conduct the dielectric deposition. The portion contacting the wafer  16  of the heater  17  is a ceramic surface (not shown). The RF mesh  10  is disposed under the ceramic surface and connected to the top of the RF grounding rod  13  whose bottom end is grounded. A resistive heater (not shown) inside the heater  17  is used to increase the temperature of the wafer  16  to the process temperature (in general, above 200°, which depends on different processes), to facilitate a dielectric film deposited on the surface of the wafer  16 .  
       FIG. 2  illustrates a cross-section of the bottom of the heater  17  of  FIG. 1 , which shows the way to ground the RF grounding rod  13  in the prior art. Some prominent reeds  130 , conductive electrically, are used to connect the bottom of the heater  17  and the bottom end of the RF grounding rod  13  by point contact. However, under a high-temperature environment for a long time, the prominent reeds  130  will decay and the spring force thereof applied to the bottom end of the RF grounding rod  13  will decrease. Therefore, the contact resistance between the bottom end of the RF grounding rod  13  and the prominent reeds  130  increases. Once the contact resistance increases, the RF energy passing through is apt to cause arcing, which results in high reflected power, unstable process conditions and oxidation of the bottom end of the RF grounding rod  13 . The contact resistance deteriorated by the oxidation will increase the possibility of arcing. Accordingly, such a vicious cycle will seriously affect the yield rate of wafers and cause shutdown of the dielectric deposition system  1 .  
      In the dielectric deposition process, the process temperature, in general, is above 200°, which expands the RF grounding rod  13  thermally and upward to press against the RF mesh  10  and then to break the ceramic surface above the RF mesh  10 . Therefore, arcing is generated during the plasma-enhanced dielectric deposition process, which causes micro particles and results in micro-contamination and thus decreases the yield rate of wafers.  
      In addition, when the ceramic surface is broken, the whole heater  17  needs replacement, which shortens the lifetime of the heater  17  and decreases the up-time of the equipment (i.e., the dielectric deposition system). Consequently, the cost is increased. Therefore, it is necessary to improve the method of grounding the heater  17 .  
     BRIEF SUMMARY OF THE INVENTION  
      The objective of the present invention is to provide an RF grounding apparatus, and more particularly to an RF grounding apparatus using a clamp and a flexible conductive sheet to form a grounding path. The RF grounding apparatus utilizes the surface contact provided by the clamp and the flexible connection provided by the flexible conductive sheet to prevent arcing generated at a bottom part of a plasma reaction chamber (e.g., the heater of a plasma-enhanced chemical vapor deposition chamber). Additionally, the RF grounding apparatus of the present invention can avoid breakage of the ceramic surface that sustains a wafer, which would be caused by thermal expansion of the RF grounding rod. Thus, the lifetime of the bottom part of the plasma reaction chamber is extended.  
      In order to achieve the objective, the present invention discloses an RF grounding apparatus, which is applied to an RF grounding rod of a plasma reaction chamber. The RF grounding rod is installed in a bottom part of a plasma reaction chamber. The top of the RF grounding rod is fixed to an RF mesh and the RF grounding rod extends downward. The RF grounding apparatus comprises a clamp and a flexible conductive sheet. The clamp clamps the bottom of the RF grounding rod firmly and electrically. The flexible conductive sheet connects the clamp and a grounding base of the plasma reaction chamber to form a grounding path. When the RF grounding rod expands thermally and downward, the RF grounding rod moves in relation to the grounding base, i.e., a relative displacement is generated between the RF grounding rod and the grounding base, through the flexible connection provided by the flexible conductive sheet. Thus, the ceramic surface of the bottom part is prevented from breakage, which would be caused by thermal expansion of the RF grounding rod.  
      The RF grounding apparatus of the present invention can solve the issue of the decay of clamp force in prior arts, improve the grounding, extend the lifetime of the bottom part of the plasma reaction chamber, and further reduce the production cost. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      The invention will be described according to the appended drawings.  
       FIG. 1  is a schematic view illustrating a known dielectric deposition system.  
       FIG. 2  is a cross-sectional view illustrating a cross-section of the bottom of the heater shown in  FIG. 1 .  
       FIG. 3  is a perspective view illustrating an embodiment of the applications of the RF grounding apparatus of the present invention.  
       FIG. 4  is an exploded perspective view illustrating the RF grounding apparatus. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 3  shows one embodiment of the applications of the RF grounding apparatus of the present invention, which is upside-down for easy understanding. The RF grounding apparatus  50  is applied to an RF grounding rod  13  of a plasma reaction chamber.  FIG. 4  shows an exploded view of the RF grounding apparatus  50 . The RF grounding apparatus  50  comprises a clamp  52  and a flexible conductive sheet  53 . The clamp  52  comprises two side portions  523  and an arced portion  524 , which form a hollow portion to accommodate the bottom of the RF grounding rod  13 . The flexible conductive sheet  53  is a U-like structure, which comprises two side plates  528  and a middle plate  527  connecting the two side plates  528 . The thickness of the flexible conductive sheet, which is a metal sheet in the current embodiment, is from 0.1 mm to 5 mm. Each of the two side portions has a plurality of threaded holes  525  (two threaded holes in each side portion  523  in the current embodiment, and another two threaded holes are not shown due to the angle of view). Each threaded hole  525  corresponds to a through-hole  526  in the side plate  528 . Thus, two fasteners  51  (two bolts in the current embodiment, refer to  FIG. 3 ) can be used to fix one side plate  528  of the flexible conductive sheet  53  to the two side portions  523  of the clamp  52 . Similarly, another side plate  528  can use another two bolts  51  through the through-holes  526  to fix itself to the grounding base  54  of the heater  17 . The grounding base  54  is connected to a grounded terminal to form a grounding path (refer to  FIG. 1 ). The space of the hollow portion  524  is compressed due to the two bolts  51  to clamp the bottom of the RF grounding rod  13  by surface contact.  
      The grounding path formed by the clamp  52  and the flexible conductive sheet  53  utilizes surface contact instead of point contact in the prior art. Therefore, a stable electrical connection between the grounding base  54  and the RF grounding rod  13  is maintained under high temperature and arcing is effectively eliminated. In addition, the flexible conductive sheet  53  cannot be too thick and should exhibit flexibility to allow the RF grounding rod  13  to move downward in relation to the grounding base  54  when the RF grounding rod  13  expands thermally due to high temperature. Accordingly, the RF grounding apparatus  50  can prevent the ceramic surface of the heater  17  from breakage, which would be caused by thermal expansion of the RF grounding rod  13 .  
      In addition, a layer of conductive corrosion-resistant material (e.g., gold) can be coated on the surfaces of the RF grounding rod  13 , the bolts  51 , the clamp  52  and the flexible conductive sheet  53  to enhance the electrical conductivity, the property of anti-corrosion and lifetime thereof.  
      In the present invention, the connection between the flexible conductive sheet and the grounding base, and the connection between the clamp and the RF grounding rod, are not limited to the bolts and the threaded holes described in the embodiment. Other connection methods, which keep effective electrical connections, can be used, for example, bolts and a nut, and direct welding. Also, the RF grounding apparatus of the present invention can be applied in any reaction chamber of the semiconductor manufacturing process that is involved with plasma reaction, for example, a plasma-enhanced chemical vapor deposition chamber, a physical vapor deposition chamber, a plasma-enhanced etching chamber, and so on, to improve the grounding of the plasma reaction chamber.  
      The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by persons skilled in the art without departing from the scope of the following claims.