Capacitivley coupled plasma reactor having a cooled/heated wafer support with uniform temperature distribution

Abstract

A plasma reactor for processing a workpiece includes a reactor chamber, an electrostatic chuck within the chamber for supporting a workpiece, an RF plasma bias power generator coupled to apply RF power to the electrostatic chuck and a refrigeration loop having an evaporator inside the electrostatic chuck with a refrigerant inlet and a refrigerant outlet. Preferably, the evaporator includes a meandering passageway distributed in a plane beneath a top surface of the electrostatic chuck. Preferably, refrigerant within the evaporator is apportioned between a vapor phase and a liquid phase. As a result, heat transfer between the electrostatic chuck and the refrigerant within the evaporator is a constant-temperature process. This feature improves uniformity of temperature distribution across a diameter of the electrostatic chuck.

1 . A plasma reactor for processing a workpiece, comprising:
 a reactor chamber;   an electrostatic chuck within said chamber for supporting a workpiece;   an RF plasma bias power generator coupled to apply RF power to said electrostatic chuck;   a refrigeration loop comprising:
 an evaporator inside said electrostatic chuck and having a refrigerant inlet and a refrigerant outlet; 
 a compressor coupled at least indirectly to said outlet of said evaporator; 
 a condenser coupled to an outlet of said compressor; and 
 an expansion valve coupled between an output of said condenser and said inlet of said evaporator. 
   
     
     
         2 . The reactor of  claim 1  wherein said evaporator comprises a meandering passageway distributed in a plane beneath a top surface of said electrostatic chuck. 
     
     
         3 . The reactor of  claim 1  further comprising an accumulator coupled between said outlet of said evaporator and an input of said compressor, for converting liquid form of said refrigerant received from said evaporator outlet into vapor. 
     
     
         4 . The reactor of  claim 1  wherein said refrigeration loop contains a refrigerant susceptible of being forced to circulate through said refrigeration loop by said compressor. 
     
     
         5 . The reactor of  claim 4  wherein refrigerant within said evaporator is apportioned between a vapor phase and a liquid phase. 
     
     
         6 . The reactor of  claim 5  wherein heat transfer between said electrostatic chuck and said refrigerant within said evaporator is a constant-temperature process, whereby to optimize uniformity of temperature distribution across a diameter of said electrostatic chuck. 
     
     
         7 . The reactor of  claim 5  wherein the liquid-to-vapor ratio of refrigerant flowing through said evaporator is greater at said refrigerant outlet than at said refrigerant inlet of said evaporator, whereby heat transfer from said electrostatic chuck to said refrigeration loop occurs principally through contribution to the latent heat of vaporization of said refrigerant. 
     
     
         8 . The reactor of  claim 7  wherein a difference between said liquid to vapor ratios at said refrigerant inlet and outlet of said evaporator is a function of a contribution to the latent heat of vaporization of said refrigerant by heat from said electrostatic chuck. 
     
     
         9 . The reactor of  claim 1  further comprising an overhead electrode, a plasma source power RF generator, an impedance matching tuning stub having a stub resonant frequency and coupled between said plasma source power RF generator and said overhead electrode, said overhead electrode forming a resonance with plasma in said chamber at a plasma-electrode resonant frequency, said plasma-electrode resonant frequency, said stub resonant frequency and the frequency of said plasma source power RF generator being VHF frequencies that are nearly equal with a small offset between them. 
     
     
         10 . The reactor of  claim 1  wherein said electrostatic chuck comprises:
 an insulating puck layer having a top surface for receiving a wafer; 
 a conductive base layer supporting said insulating puck layer; 
 an ESC electrode buried in said insulating puck layer; 
 a bias power feed conductor extending axially through said base and puck layers of said electrostatic, chuck and having a top end connected to a feed point of said ESC electrode and a bottom end coupled to said RF plasma bias power generator; and 
 a plurality of dielectric cylindrical sleeves surrounding respective portions of said bias power feed conductor and having respective lengths and dielectric constants that optimize uniformity of electric field distribution across said top surface of said insulating puck layer. 
 
     
     
         11 . The reactor of  claim 1  further comprising a dielectric ring lying on or in a plane of said top surface of said puck layer and surrounding a circumference corresponding to a workpiece diameter of said electrostatic chuck, said dielectric ring having a dielectric constant enabling said ring to compensate for RF edge effects over said electrostatic chuck during plasma processing of a workpiece. 
     
     
         12 . The reactor of  claim 1  further comprising:
 a temperature probe in said electrostatic chuck; 
 a feedback loop control processor governing said expansion valve coupled to receive (a) an output of said temperature probe and (b) a desired temperature. 
 
     
     
         13 . The reactor of  claim 12  wherein said feedback loop control processor is programmed to change an opening size of said expansion valve so as to minimize a difference between the output of said temperature probe and said desired temperature. 
     
     
         14 . The reactor of  claim 12  wherein said electrostatic chuck comprises an upper insulating puck layer having a top surface for supporting a workpiece and a lower conductive base layer containing said evaporator, and an axially extending cylindrical probe hole through said base layer and through a into said puck layer, and wherein said temperature probe comprises:
 an upper probe comprising:
 an elongate opaque insulative cylindrical upper probe housing extending axially into said probe hole beginning at a bottom end of the upper probe housing and terminating at a top end of the upper probe housing, said top end being located at a top end of said probe hole beneath said top layer, said bottom end being located at a bottom opening of said probe hole; 
 an optically responsive temperature transducer within said upper probe housing at said top end; and 
 an optical fiber having a top end coupled to said optically responsive temperature transducer and extending axially through said upper probe housing. 
 
 
     
     
         15 . The reactor of  claim 14  wherein said temperature probe further comprises a lower probe comprising:
 an elongate cylindrical lower probe housing extending axially from a top end facing and contacting said bottom end of said upper probe housing; and 
 an optical fiber having a top end coupled to a bottom end of said optical fiber of said upper probe and extending axially through said lower probe housing. 
 
     
     
         16 . The apparatus of  claim 14  wherein said upper probe housing has a diameter less than a Debeye length of a plasma in said reactor. 
     
     
         17 . The apparatus of  claim 15  wherein said temperature probe further comprises:
 an upper coil spring biasing said upper probe housing toward said top end of said probe hole; and 
 a lower coil spring biasing said lower probe housing toward the bottom end of said upper probe housing, said upper coil spring having greater stiffness than said lower coil spring. 
 
     
     
         18 . The reactor of  claim 1  wherein said electrostatic chuck is divided into at least inner and outer temperature zones, said inner temperature zone extending from an axial center of said electrostatic chuck to a first radius intermediate said center and a peripheral edge of said electrostatic chuck, and said outer temperature zone being an annular region extending radially outwardly from said first radius, and wherein said evaporator comprises an inner zone evaporator confined within said inner temperature zone of said electrostatic chuck, and said refrigeration loop constitutes an inner zone refrigeration loop, said reactor further comprising:
 an outer zone evaporator inside said electrostatic chuck and confined within said outer temperature zone of said electrostatic chuck; and 
 an outer zone refrigeration loop coupled to said outer zone evaporator. 
 
     
     
         19 . The reactor of  claim 18  further comprising:
 respective inner and outer temperature probes in said inner and outer temperature zones of said electrostatic chuck; and 
 respective inner zone and outer zone feedback loop control processors governing, respectively, the expansion valves of said inner and outer refrigeration loops and coupled to receive (a) an output of the respective one of said inner and outer temperature probes and (b) a respective desired temperature. 
 
     
     
         20 . The reactor of  claim 19  wherein each of said inner and outer feedback loop control processors is programmed to change an opening size of the corresponding expansion valve so as to minimize a difference between the output of the respective temperature probe and the respective desired temperature.