Capacitively coupled plasma reactor with magnetic plasma control

Abstract

A plasma reactor includes a vacuum enclosure including a side wall and a ceiling defining a vacuum chamber, and a workpiece support within the chamber and facing the ceiling for supporting a planar workpiece, the workpiece support and the ceiling together defining a processing region between the workpiece support and the ceiling. Process gas inlets furnish a process gas into the chamber. A plasma source power electrode is connected to an RF power generator for capacitively coupling plasma source power into the chamber for maintaining a plasma within the chamber. The reactor further includes at least a first overhead solenoidal electromagnet adjacent the ceiling, the overhead solenoidal electromagnet, the ceiling, the side wall and the workpiece support being located along a common axis of symmetry. A current source is connected to the first solenoidal electromagnet and furnishes a first electric current in the first solenoidal electromagnet whereby to generate within the chamber a magnetic field which is a function of the first electric current, the first electric current having a value such that the magnetic field increases uniformity of plasma ion density radial distribution about the axis of symmetry near a surface of the workpiece support.

1 . In a plasma reactor chamber for processing a semiconductor workpiece, a method of controlling plasma ion distribution within the chamber relative to a desired distribution, comprising:
 providing an RF power applicator for said chamber;   providing plural separate concentric coils of different diameters overlying said chamber concentric with a cylindrical axis of symmetry of said chamber and lying in respective exclusive planes parallel with a workpiece support plane of said chamber;   applying RF plasma source power to said RF power applicator to generate a plasma within said chamber, said plasma having an ambient radial distribution in absence of said magnetic field;   changing distribution of said plasma in said chamber from said ambient distribution to a distribution that approximates said desired plasma distribution, by (1) determining a difference between said ambient distribution and said desired distribution, (2) computing a set of D.C. electric currents that, when applied to respective ones of said coils, corrects said difference, and (3) applying respective ones of said set of D.C. currents to respective ones of said coils.   
     
     
         2 . The method of  claim 1  wherein the step of changing said plasma distribution comprises:
 determining a difference between said ambient distribution and said desired distribution; 
 determining an electric current flow in said coil apparatus that corresponds to said difference. 
 
     
     
         3 . The method of  claim 2  wherein the step of determining an electric current flow that corresponds to said difference comprises:
 determining a magnetic pressure on said plasma that would produce said difference; and 
 determining an electric current flow in said coil apparatus that would produce said magnetic pressure. 
 
     
     
         4 . The method of  claim 2  wherein said ambient distribution of said plasma ions and said desired distribution of plasma ions are radial distributions relative to said cylindrical axis, and wherein said step of determining an electric current flow corresponding to said difference comprises:
 computing, from said difference between said distributions, a function of a radial component of a corresponding magnetic field; 
 determining a current flow in said coil apparatus that would cause said coil apparatus to produce a magnetic field that approximates said corresponding magnetic field. 
 
     
     
         5 . The method of  claim 3  wherein said function of a radial component of a corresponding magnetic field comprises a radial component of a gradient of a square of said corresponding magnetic field. 
     
     
         6 . The method of  claim 4  wherein the step of determining a current flow that would produce a magnetic field that approximates said corresponding magnetic field comprises:
 computing a set of magnetic fields from a set of current flows in said coil apparatus; 
 determining which one of said set of magnetic fields most closely approximates said corresponding magnetic field; 
 selecting the current flow associated with said one magnetic field as the current flow to be applied to said coil apparatus. 
 
     
     
         7 . The method of  claim 1  wherein:
 the step of providing plural separate concentric coils comprises providing plural separately powered overhead concentric coils having different diameters. 
 
     
     
         8 . The method of  claim 7  arranging said coils in increasing order of diameter with descending distance from said chamber. 
     
     
         9 . The method of  claim 8  wherein said set of currents comprises D.C. currents of different magnitudes and polarities in respective ones of said coils. 
     
     
         10 . The method of  claim 1  wherein said desired distribution is a uniform radial distribution. 
     
     
         11 . The method of  claim 7  wherein different ones of said coils produce respective magnetic fields, whereby a composite of said respective magnetic fields corresponds to said difference. 
     
     
         12 . The method of  claim 1  wherein said desired distribution is a radial distribution of plasma ion density near said plane of said workpiece. 
     
     
         13 . The method of  claim 1  wherein said desired distribution is a radial distribution of plasma ion density near a plane of said ceiling electrode. 
     
     
         14 . The method of  claim 1  wherein said desired distribution is a uniform radial distribution of plasma ion density. 
     
     
         15 . The method of  claim 1  wherein said desired distribution is a non-uniform radial distribution of plasma ion density. 
     
     
         16 . In a plasma reactor chamber for processing a workpiece, a method of controlling plasma ion distribution within the chamber relative to a desired distribution, comprising:
 providing an RF power applicator for said chamber;   providing plural separately powered overhead concentric coils having different diameters and centered at different heights overlying said chamber and facing a plane of said workpiece, wherein respective ones of said coils produce, respective magnetic fields as a function of current flow in said respective coils, resulting in a composite magnetic field in said chamber, said composite magnetic field being a combination of said respective magnetic fields;   applying RF plasma source power to said RF power applicator to generate a plasma within said chamber, said plasma having an ambient radial distribution in absence of said composite magnetic field;   changing distribution of said plasma in said chamber from said ambient distribution to a distribution that approximates said desired distribution, by (1) determining a difference between said ambient distribution and said desired distribution, (2) computing a set of D.C. electric currents that, when applied to respective ones of said coils, corrects said difference, and (3) applying respective ones of said set of D.C. currents to respective ones of said coils.   
     
     
         17 . The method of  claim 16  wherein the step of computing a set of electric currents that corrects said difference comprises:
 determining a magnetic pressure on said plasma that would produce said difference; and 
 determining a set of currents in said plural coils that would produce said magnetic pressure. 
 
     
     
         18 . The method of  claim 17  wherein said ambient distribution of said plasma ions and said desired distribution of plasma ions are radial distributions relative to a cylindrical axis of said chamber, and wherein said step of computing a set of currents that produce said difference comprises:
 computing, from said difference between said distributions, a function of a radial component of a corresponding magnetic field; 
 determining a set of currents in said plural coils that would cause said coils to produce respective magnetic fields whose composite magnetic field approximates said corresponding magnetic field. 
 
     
     
         19 . The method of  claim 18  wherein said function of a radial component of a corresponding magnetic field comprises a radial component of a gradient of a square of said corresponding magnetic field. 
     
     
         20 . The method of  claim 1  wherein said computing comprises:
 (a) determining a mathematical relationship between a magnetic pressure and a radial component of a magnetic field function dependent upon D.C. coil current for each one of said coils; and 
 (b) in a computer, searching for a set of respective coil currents in respective ones of said coils that produce, in accordance with said relationship, a composite magnetic pressure from all of said coils corresponding to said difference. 
 
     
     
         21 . The method of  claim 16  wherein said computing comprises:
 (a) determining a mathematical relationship between a magnetic pressure and a radial component of a magnetic field function dependent upon D.C. coil current for each one of said coils; and 
 (b) in a computer, searching for a set of respective coil currents in respective ones of said coils that produce, in accordance with said relationship, a composite magnetic pressure from all of said coils corresponding to said difference.