Abstract:
A system and method for processing plural wafers in a plasma processing system using a single upper electrode. By placing plural wafer holders into a single plasma processing chamber, the footprint of a resulting plasma chamber may be made smaller than the total footprint of an equivalent number of individual chambers. Moreover, pumping may be increased by placing plural pumps below the wafer holders, and preferably in positions not obstructed by the wafer holders.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    The present application claims priority to U.S. provisional application serial No. 60/315,340, filed on Aug. 29, 2001, the entire contents of which are herein incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention is directed to a design and implementation of a wafer processing machine and to a method of using the same.  
           [0004]    2. Discussion of the Background  
           [0005]    Manufacturers of semiconductor integrated circuits (ICs) are faced with intense competitive pressure to improve their products and as a result, pressure to improve the processes used to fabricate those products. This pressure in turn is driving the manufacturers of the equipment used by IC manufacturers to improve the value of their equipment, and in particular to reduce the operating cost to users of their equipment.  
           [0006]    One such cost is the cost of the clean room. The larger the equipment, the larger the clean room and its associated costs. Thus, manufacturers strive to reduce the size of their manufactured equipment such that the total overhead cost of producing circuits in the clean room is also reduced.  
         SUMMARY OF THE INVENTION  
         [0007]    It is an object of the present invention to provide a plasma processing system utilizing a single upper electrode covering plural wafers on corresponding wafer holders.  
           [0008]    It is another object of the present invention to provide a multi-wafer plasma processing chamber in which the gate valves controlling access to the pumping system are offset with respect to the wafer holders. In one such embodiment, a two-wafer system includes two wafer holders positioned, with respect to a unit circle, at zero and 180 degrees while the gate valves are positioned below the wafer holders at 90 and 270 degrees. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The invention is better understood by reading the following Detailed Description of the Preferred Embodiments with reference to the accompanying drawing figures, in which like reference numerals refer to like elements throughout, and in which:  
         [0010]    [0010]FIG. 1 is a plan view of one embodiment of a plasma processing system according to the present invention;  
         [0011]    [0011]FIG. 2 is a side view of the embodiment of the plasma processing system according to FIG. 1;  
         [0012]    [0012]FIGS. 3A and 3B are top views of two upper electrode designs covering two wafer holders; and  
         [0013]    [0013]FIGS. 4A and 4B are top views of two additional upper electrode designs covering two wafer holders. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.  
         [0015]    [0015]FIG. 1 is a plan view of one embodiment of a plasma processing system according to the present invention. In that embodiment, a plasma processing system  100  generally includes (1) a plasma processing chamber  105 , (2) a robot  130  for moving wafers into and out of the chamber  105 , and (3) the electronics  150  for controlling the processing of wafers within the chamber  105 . The chamber  105  generally includes (A) series of gate valves  110 A and  110 B positioned and connecting to a bottom of the system  100  and (B) wafer holders  120 A and  120 B (also known as “chucks”). (Although the phrase “wafer holder” is used throughout for illustrative purposes, the holder may actually hold any type of work piece to be processed, e.g., an LCD panel.) The robot arm  135  of the robot  130  removes wafers from a cassette ( 140 A or  140 B) and places them, one at a time, on an available one of the wafer holders (either  120 A or  120 B). The wafers are then simultaneously processed within the chamber  105  and returned, one at a time, to a corresponding cassette ( 140 A or  140 B) using the robot arm  135 .  
         [0016]    In order to maintain the proper processing environment (including pressures), the chamber  105  is sealed off from the robot  130  and its associated chamber (commonly referred to as the substrate transfer chamber) by way of a slot valve  160 A. This enables the robot  130  and its associated chamber to be “pumped down” to the pressure of the processing chamber before attempting to place wafers into or remove wafers from the process chamber  105 . Similarly, the robot  130  can be brought back to atmospheric pressure before attempting to place wafers into or remove wafers from a cassette ( 140 A or  140 B) via slot valve  160 B. Such pumping actions can be performed by vacuum components  175  housed within the system  100 . The various methods of equalizing pressure between chambers to accommodate substrate transfer are well known to those of skill in the art.  
         [0017]    As shown in FIG. 2, the gate valves  110 A and  110 B provide access to corresponding vacuum pumps ( 170 A and  170 B) to draw gas out of the chamber  105  during processing. Vacuum pumps  170 A,  170 B are preferably turbo-molecular vacuum pumps (TMP) capable of a pumping speed up to 5000 liters per second or greater. In conventional plasma processing devices utilized for dry plasma etch, a 1000 to 3000 liter per second TMP is employed. TMPs are useful for low pressure processing, typically less than 50 mTorr. At higher pressures, the TMP pumping speed falls off dramatically. For high pressure processing (e.g., processing greater than 100 mTorr), a mechanical booster pump and dry roughing pump is recommended. An exemplary TMP is a 3300 liter/second vacuum pump offered by Mitsubishi (Model #FT3300W). By providing two pumps in the positions shown, increased gas flow is achieved while providing a smaller footprint compared to two separate plasma processing chambers. As would be understood by one of ordinary skill in the art, the exact size and position of the gate valves can be different than shown in FIGS. 1 and 2. Generally, at least a portion of the space left empty by the placement of the wafer holders  120  should be utilized as the gate valves. (Although only one gate valve may be used in some embodiments, the chamber  105  preferably maintains a generally uniform flow over the wafers being processed to ensure uniform processing.) Moreover, although the process chamber  105  is larger than either of the two chambers that it replaces, the pumping conductance is better in light of the less obstructed flow path as compared to a side mounted pump and, therefore, better flow conductance between the processing region and pump inlet.  
         [0018]    As shown in FIG. 2, a single upper electrode assembly  190  can be utilized (as compared with two separate assemblies when utilizing independent chambers). The electrode assembly  190  includes an upper electrode  195  that covers both wafer holders  120 A and  120 B. The upper electrode  190  can either be circular, as shown in FIG. 3A, or of a shape that reduces the size and/or cost of the upper electrode  190  while still covering both wafer holders  120 A and  120 B. One such embodiment is an oval, although a more “figure-8” like structure is also possible. In an alternate embodiment, a plurality of electrodes  195  ( 195 A and  195 B; see FIG. 4A) are employed, one for each wafer holder ( 120 A,  120 B), and directly opposing each wafer holder ( 120 A,  120 B). The corresponding diameter of each electrode  195  can be similar to that of the wafer holder ( 120 A,  120 B) or larger. Further, in an alternate embodiment, radio frequency (RF) power is applied to electrode  195  via RF generator and impedance match network to form a plasma to assist material processing of the substrates on wafer holders  120 A and  120 B. RF power can be applied in a frequency range from 10 MHz to 200 MHz at power levels ranging from 1 to 5 kW. The impedance match network serves to maximize the transfer of power to the plasma. The above design and implementation is well known to those skilled in the art.  
         [0019]    In an alternate embodiment, the electrode  195  is grounded. In an alternate embodiment, the electrode  195  is grounded and an inductive coil  295  (see FIG. 4B) surrounds the chamber  105 , to which RF power is coupled in order to form a plasma via inductive coupling.  
         [0020]    In an alternate embodiment, both an inductive coil  295  (see FIG. 4B) and the electrode  195  are driven with RF power.  
         [0021]    In an alternate embodiment, the electrode  195  further serves as a gas injection electrode through which process gas is injected into the processing region adjacent each substrate. One such gas injection design is commonly referred to as a showerhead gas injection system comprising a plurality of gas injection orifices coupled to a gas delivery system, there between a common plenum (or plurality of gas plenums) and a series of baffle plates is inserted to distribute the gas flow.  
         [0022]    The substrate(s) can be transferred into and out of chamber  105  through slot valve  160 A (as described above) via robotic substrate transfer system  130  where it is received by substrate lift pins (not shown) housed within substrate holder ( 120 A,  120 B) and mechanically translated by devices housed therein. Once a substrate is received from robot  130  (substrate transfer system), it is lowered to an upper surface of a substrate holder ( 120 A,  120 B) and affixed to substrate holder ( 120 A,  120 B) via an electrostatic clamp (not shown). Moreover, gas can be delivered to the back-side of the substrate to improve the gas-gap thermal conductance between a given substrate and substrate holder ( 120 A,  120 B). Moreover, RF power can be applied to each substrate holder  120 A,  120 B via a RF generator and impedance match network. As before, such design and implementation is well known to those skilled in the art.  
         [0023]    Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described.