Plasma immersion ion implantation apparatus including a capacitively coupled plasma source having low dissociation and low minimum plasma voltage

Abstract

A plasma immersion ion implantation reactor for implanting a species into a workpiece includes an enclosure which has a side wall and a ceiling defining a chamber, and a workpiece support pedestal within the chamber for supporting a workpiece having a surface layer into which the species are to be ion implanted, the workpiece support pedestal facing an interior surface of the ceiling so as to define therebetween a process region extending generally across the diameter of the wafer support pedestal. The reactor further includes an RF plasma source power generator connected across the ceiling or the sidewall and the workpiece support pedestal for capacitively coupling RF source power into the chamber. A gas distribution apparatus is provided for furnishing process gas into the chamber and a supply of process gas is provided for furnishing to the gas distribution devices a process gas containing the species. An RF bias generator is connected to the workpiece support pedestal and has an RF bias frequency for establishing an RF bias.

1 . A plasma immersion ion implantation reactor for implanting a species into a workpiece, comprising: 
 an enclosure comprising a side wall and a ceiling defining a chamber, and a workpiece support pedestal within the chamber comprising: 
 (a) a conductive wafer support plate,  
 (b) a grounded conductive base plate forming at least a void between said support and base plates,  
 (c) a side wall around said support and base plates forming at least a void between said side wall and said support and base plates,  
 (d) a dielectric filler material having a break-down voltage in excess of 5000 volts filling said voids;  
   an RF plasma source power generator connected across said ceiling or said sidewall and said workpiece support pedestal;    gas distribution apparatus for furnishing process gas into said chamber;    a supply of process gas for furnishing to said gas distribution apparatus a process gas containing said species; and    an RF bias generator coupled to said workpiece support pedestal and having an RF bias frequency.    
   
   
       2 . The reactor of  claim 1  wherein said dielectric filler material has a sufficiently high dielectric constant to prevent arcing across said voids.  
   
   
       3 . The reactor of  claim 1  wherein said dielectric filler material has a dielectric constant that is sufficiently high to limit the breakdown voltage across said voids to greater than on the order of 10,000 volts.  
   
   
       4 . The reactor of  claim 1  wherein said workpiece support pedestal further comprises: 
 a conductive insert coupled to said bias power generator and a conductive female receptacle for tightly receiving said conductive insert, said conductive female receptable being connected to said conductive wafer support plate, said conductive insert and said conductive female receptable extending through said conductive base plate to said conductive wafer support plate, and insulating layer insulating said conductive insert from said conductive base plate.    
   
   
       5 . The reactor of  claim 4  wherein said workpiece support pedestal further comprises at least one lift pin assembly extending through said conductive base plate and said conductive wafer support plate and a axial void between said lift pin assembly and said lift pin assembly, and a high dielectric filler material having a high breakdown voltage within the void between said lift pin assembly and said conductive wafer support plate.  
   
   
       6 . The reactor of  claim 5  wherein said workpiece support pedestal further comprises a fastening bolt extending at least partially through said conductive wafer support plate and to said conductive base plate, and a high dielectric filler material having a high breakdown voltage surrounding a portion of said bolt within said conductive wafer support plate.  
   
   
       7 . The reactor of  claim 1  wherein said gas distribution apparatus comprises: 
 concentric inner and outer gas injection radial zones in said ceiling, said inner zone comprising at least one gas injection orifice, said outer zone comprising plural gas injection orifices.    
   
   
       8 . The reactor of  claim 7  wherein said process gas supply comprises plural separate gas supplies of respective different process gases, said gas distribution apparatus further comprising: 
 a gas distribution controller comprising at least a first valve coupling at least one of said separate gas supplies to said at least one orifice of said inner gas injection zone and a second set of valves coupling at least some of said separate gas supplies to said plural orifices of said outer gas injection zone.    
   
   
       9 . The reactor of  claim 1  wherein the workpiece support pedestal comprises an electrostatic chuck, said electrostatic chuck comprising thermal control apparatus for workpiece temperature control.  
   
   
       10 . The reactor of  claim 1  further comprising a controller for controlling said bias generator to produce a desired bias voltage at said workpiece support pedestal for a predetermined single burst duration.  
   
   
       11 . The reactor of  claim 10  wherein said controller comprises: 
 a timer for switching the output of said bias power generator on and off in accordance with said predetermined duration;    a peak voltage detector coupled to said workpiece support pedestal;    a threshold comparator connected to said timer for comparing the output of said peak voltage detector with a predetermined threshold voltage;    a subtractor having a pair of inputs connected to the output of said peak voltage detector and to a predetermined target voltage, respectively, and a feedback conditioner for processing the output of said subtractor;    a first switch for coupling an output of said feedback conditioner to a power level control input of said bias power generator.    
   
   
       12 . The reactor of  claim 11  wherein said controller further comprises a control element for controlling said bias power generator (a) empirically in absence of a plasma in said chamber and (b) in a feedback control loop in the presence of plasma in said chamber.  
   
   
       13 . The reactor of  claim 12  wherein said control element comprises: 
 a voltage-to-power look-up table having an input connected to said predetermined target voltage and an output;    a second switch coupled between the output of said voltage-to-power look-up table and said power level control input of said bias power generator; and    a plasma detector in said chamber connected to control said first and second switches in complementary fashion in response to detection of plasma in said chamber.    
   
   
       14 . The reactor of  claim 13  wherein said plasma detector is further connected to enable said timer.  
   
   
       15 . The reactor of  claim 14  wherein said feedback conditioner is an integral proportional controller.  
   
   
       16 . The reactor of  claim 11  wherein said predetermined threshold voltage and said predetermined target voltage are identical.  
   
   
       17 . The reactor of  claim 11  further comprising a process controller for furnishing said predeterminded target voltage and said predetermined threshold voltage.  
   
   
       18 . The reactor of  claim 1  further comprising a vacuum pump and a vacuum control valve coupling said vacuum pump to said chamber, said vacuum control valve comprising: 
 a valve housing having a valve opening defined by an opening side wall having a surface parallel to an axis of said valve opening;    a rotatable flap subject to process control and having an area conformal with said valve opening and side wall and rotatably mounted within said valve opening to define a gap therebetween; and    a plurality of small indentational voids in said side wall that are covered by said rotatable flap whenever said flap is in a co-planar relationship with said housing and are gradually exposed as said flap rotates away from said rotational position and before a bottom corner edge of said flap passes a top surface of said valve housing.    
   
   
       19 . The apparatus of  claim 1  wherein said RF source power generator and said RF bias generator comprise first and second pulsed RF supplies, respectively, wherein said first and second pulsed RF supplies are in one of: 
 a push-pull relationship;    an in-synchronism relationship;    a symmetric relationship;    a non-symmetric relationship.    
   
   
       20 . The reactor of  claim 7  wherein: 
 said inner gas injection zone consists of said one gas injection orifice;    the plural orifices of said outer gas injection zone are arranged in a generally annular array that is generally concentric with said single gas injection orifice of said inner gas injection zone;    said one gas supply contains oxygen; and    said first valve of said gas distribution controller is coupled directly between said gas supply containing oxygen to said one gas injection orifice of said inner gas injection zone.