Patent Publication Number: US-2007113786-A1

Title: Radio frequency grounding rod

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 is related to a radio frequency (RF) grounding rod, more specifically, to an RF grounding rod employed in a plasma process chamber.  
     BACKGROUND OF THE INVENTION  
      Plasma is commonly used for wafer manufacturing in the semiconductor industry, e.g., chemical vapor deposition (CVD), physical vapor deposition (PVD) or etching, all using plasma. Plasma contains ionized gases and high-energy electrons generated by ionization of molecules, so that ion bombardment or adsorption occurs on a surface of a wafer to perform etching or deposition. Although plasma could speed up process reaction and lower required process temperature, electrical charges may accumulate and even induce arcing from time to time.  
      Therefore, the components of the semiconductor process chamber, especially a platform for carrying a wafer, are usually equipped with grounding devices. A dielectric chemical vapor deposition (CVD) chamber is exemplified as follows for explanation.  
      Dielectric deposition is crucial in the semiconductor process and can form an inter-metal dielectric layer (IMD), a passivation process to prevent the device circuit from being influenced by external moisture and metal ions, or a dielectric anti-reflective coating (DARC) to avoid light reflection in lithography.  FIG. 1  illustrates a dielectric deposition system  1  including a process chamber  11 , a radio frequency (RF) generator  18 , an RF match box  19  and an RF match circuit  19 ′. The process chamber  111  is configured to perform dielectric deposition, and includes a heater  17  and an anode plate  14 . The heater  17  is employed to carry and heat a wafer  16  to be of a process temperature. An RF mesh  10  and an RF grounding rod  13  in the heater  17 , and the anode plate  14  are connected as an electrical conduction path so as to generate plasma  15 . The RF generator  18 , the RF match box  19  and the RF match circuit  19 ′ form an RF system so as to stably deliver the RF power for generating plasma to the process chamber  11  for dielectric deposition. The surface carrying (in contact with) the wafer  16  of the heater  17  is a ceramic surface (not shown), and the RF mesh  10  is disposed below the ceramic surface and connected to the top of the RF grounding rod  13 , whereas the bottom of the RF grounding rod  13  is grounded. A heater resistor (not shown) is provided in the heater  17  to heat the wafer  16  to be of a process temperature (dependent on various processes, usually higher than 200°) for the dielectric deposition on the surface of the wafer  16 .  
       FIG. 2  is a cross-sectional view of the bottom of the heater  17  to show the application of the RF grounding rod  13 . An end of the heater  17  secures an end of the RF grounding rod  13  by projected springs  130  in a point-contact manner so as to establish electrical connection therebetween. However, the projected springs  130  are usually exposed in an environment of a high temperature over a long period. As a result, the elastic forces of the projected springs  130  pressing on the end of the RF grounding rod  13  will become weak and may cause fatigue, inducing the contact resistance between them to increase. As a result of higher contact resistance, arcing may occur as an RF power goes therethrough. Not only does the reflected power of the input power become higher, causing unstable manufacturing processing, but also the end of the RF grounding rod  13  is oxidized. Accordingly, the higher resistance due to arcing increases the probability of repeated arcing, and such a vicious cycle seriously affects the yield of the wafers and the equipment has to be shut down for repair.  
      Moreover, the RF grounding rod  13 , or even the entire heater  17 , has to be replaced if the RF grounding rod  13  is damaged, so that the lifetime of the heater  17  is shortened and the up-time of the equipment is decreased. Therefore, the cost for wafer manufacturing will be increased.  
     BRIEF SUMMARY OF THE INVENTION  
      The objective of the present invention is to provide an RF grounding rod, more specifically, an RF grounding rod applied in a plasma chamber, which can increase conductive efficiency so as to reduce the probability of arcing. If the RF grounding rod is damaged, it can be reused after being refurbished. Therefore, the manufacturing cost can be tremendously reduced and the up-time of the equipment can be increased.  
      To achieve the above objective, an RF grounding rod employed in a plasma chamber of semiconductor equipment is disclosed in accordance with the present invention. The RF grounding rod comprises a contact head and a main rod. The contact head is electrically connected to an RF mesh of the plasma chamber. The main rod is coated with a conductive layer of gold, silver, nickel, aluminum or copper. One end is connected to the contact head, and the other end is electrically connected to a grounding base of the plasma chamber to form an electrical conductive path.  
      In accordance with an embodiment of the present invention, the main rod is constituted of an upper rod, a lower rod and connection means connecting the upper and lower rods. The connection means may be formed by soldering gold, silver, nickel, aluminum, copper or the alloy thereof, or in the form of an engagement of a screw portion and a nut portion.  
      In view of the design in accordance with the present invention, the damaged portion of the main rod, e.g., the lower rod, can be replaced, and then the entire RF grounding rod is coated with a conductive layer to increase the electrical grounding effect. Therefore, neither the entire RF grounding rod nor the entire heater needs to be replaced, so that the manufacturing cost is reduced and the up-time of the process equipment is increased. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       FIG. 1  is a schematic view illustrating a known dielectric deposition system.  
       FIG. 2  is a cross-sectional view of the bottom of the heater shown in  FIG. 1 .  
       FIG. 3  is a schematic view illustrating an application of the RF grounding rod in accordance with the present invention.  
       FIG. 4 ( a ) is a perspective view illustrating a first embodiment of the RF grounding rod in accordance with the present invention.  
       FIG. 4 ( b ) is the cross-sectional view along line  1 - 1  in  FIG. 4 ( a ).  
       FIG. 5  is another perspective view illustrating a second embodiment of the RF grounding rod in accordance with the present invention.  
       FIG. 6  is a perspective view illustrating a third embodiment of the RF grounding rod in accordance with the present invention.  
      FIGS.  7 ( a ) and  7 ( b ) are perspective and schematic views illustrating a fourth embodiment of the RF grounding rod in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The RF grounding rod of the present invention is described with reference to the appended drawings as follows, so as to clearly show the features of the present invention.  
       FIG. 3  illustrates an application of an RF grounding rod in accordance with the present invention. The structure shown in  FIG. 3  is upside down compared to actual practice for the ease of explanation. An RF grounding rod  13 ′ is applied in a heater  17  of a plasma chamber, e.g., a chamber for plasma-enhanced chemical vapor deposition (PECVD) in this embodiment. Two heater rods  12  and the RF grounding rod  13 ′ project out of the bottom of the heater  17 .  
       FIG. 4 ( a ) illustrates a structure of the RF grounding rod  13 ′, and  FIG. 4 ( b ) is a cross-sectional view along line  1 - 1  in  FIG. 4 ( a ). The RF grounding rod  13 ′ comprises a main rod  132  and a contact head  131  connected to the top of the main rod  132 . The contact head  131  is employed to be electrically connected to the RF mesh  10 , and is in need of high electrical conductivity and high temperature endurance to ground the charges generated by plasma. The contact head  131  can be made of nickel alloy or aluminum alloy. The lower portion of the main rod  132  is secured by the projected springs  130  so as to further guide the charges to a grounding base (not shown) for electrical grounding. The main rod  132  is made of nickel alloy, copper alloy or aluminum alloy, and is coated with a conductive layer  140  made of gold, silver, nickel, aluminum or copper. The thickness of the conductive layer  140  is less than 3 mm. As a result, the conductivity between the main rod  132  and the projected springs  130  is increased, so that the probability of arcing due to inferior contact therebetween can be decreased significantly.  
      As shown in  FIG. 5 , the RF grounding rod  13 ′ may comprise an upper rod  133  and a lower rod  134  with different diameters, and the diameter of the lower rod  134  is less than that of the upper rod  133  by 0.1-4 mm, so that the lower rod  134  can easily protrude from the heater  17 .  
      As shown in  FIG. 6 , if arcing occurs on the known RF grounding rod  13 , the damaged portion by arcing, i.e., the corresponding portion to the lower rod  134  in this embodiment, can be cut off, and then a conductive metal rod is soldered to the bottom of the upper rod  133  as a new lower rod  134 , and consequently connection means  135  is formed therebetween. The conductive metal rod can be made of gold, silver, copper or the alloy thereof, and the connection means  135  between the upper rod  133  and the lower rod  134  can be formed by soldering gold, silver, copper, nickel, aluminum or the alloy thereof. Sequentially, the entire rod including the upper rod  133 , the connection means and the lower rod  134  is coated with metal, e.g., gold, silver or copper, so as to form an RF grounding rod  13 ′ of an embodiment of the present invention.  
       FIG. 7 ( a ) illustrates an RF grounding rod in accordance with another embodiment of the present invention, and  FIG. 7 ( b ) is a cross-sectional view along line  2 - 2  in  FIG. 7 ( a ). In addition to the use of soldering, the connection means  135  can be an engagement of a screw portion and a nut portion  139  to connect the upper rod  133  and the lower rod  134 . For example, the lower end of the upper rod  133  is provided with a screw portion and the upper end of the lower rod  134  is provided with a corresponding nut portion for engagement. Furthermore, a soldering block  138  can be formed along the circumference of the contact interface by soldering gold, silver, copper, nickel, aluminum or the alloy thereof so as to increase the conductivity. In this embodiment, the lower rod  134  is designed to be a structure including a wider upper portion for accommodating the screw portion and the nut portion  139  and a narrower lower portion of the same diameter for being secured by the projected springs  130 .  
      As mentioned above, the portion of the known RF grounding rod  13  protruding from the bottom of the heater  17  is in contact with the projected springs  130 , and arcing occurs thereon from time to time due to the fatigue of the projected springs  130 . Therefore, the RF grounding rod  13  often needs to be replaced. Through the design of the connection means  135 , if the lower portion of the RF grounding rod  13  is damaged by arcing, the RF grounding rod  13 , or even the entire heater  17 , does not need to be replaced. Instead, the damaged portion can be directly replaced with a new one and coated with a conductive layer  140 . As a result, the cost can be reduced tremendously and the up-time of the process equipment can be increased.  
      The application of the present invention is not limited to the PECVD process chamber exemplified above, and can be used for other semiconductor process equipment, e.g., CVD, PVD or etching chambers.  
      The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by those skilled in the art without departing from the scope of the following claims.