Process for wafer backside polymer removal and wafer front side scavenger plasma

Abstract

A process is provided for removing polymer from a backside of a workpiece. The process includes supporting the workpiece on the backside in a vacuum chamber while leaving a peripheral annular portion of the backside exposed. The process further includes confining gas flow at the edge of the workpiece within a gap at the edge of the workpiece on the order of about 1% of the diameter of the chamber, the gap defining a boundary between an upper process zone containing the front side and a lower process zone containing the backside. A first plasma is generated in a lower external chamber from a polymer etch precursor gas, and an etchant by-product is introduced from the first plasma into the lower process zone. A second plasma is generated in an upper external plasma chamber from a precursor gas of a scavenger of the etchant by-product, and scavenger species are introduced from the second plasma into the upper process zone.

1 . A process for removing polymer from a backside of a workpiece, comprising:
 supporting said workpiece on the backside in a vacuum chamber while leaving a peripheral annular portion of the backside exposed;   confining gas flow at the edge of said workpiece within a gap at the edge of said workpiece on the order of about 1% of the diameter of the chamber, said gap defining a boundary between an upper process zone containing said front side and a lower process zone containing said backside;   generating a first plasma in a lower external chamber from a polymer etch precursor gas, and introducing an etchant by-product from said first plasma into said lower process zone; and   generating a second plasma in an upper external plasma chamber from a precursor gas of a scavenger of the etchant by-product, and introducing scavenger species from said second plasma into said upper process zone.   
   
   
       2 . The process of  claim 1  further comprising:
 confining said upper process zone between the front side and a ceiling of the reactor to an upper process zone height on the order of about 1% of the diameter of the chamber.   
   
   
       3 . The process of  claim 1  further comprising:
 evacuating said upper process zone through a slit opening surrounding said upper process zone.   
   
   
       4 . The process of  claim 3  further comprising:
 evacuating said lower process zone through a slit opening surrounding said lower process zone near the edge of said workpiece.   
   
   
       5 . The process of  claim 2  wherein said gap and said upper process zone height are both about 2 mm. 
   
   
       6 . The process of  claim 1  wherein said polymer etch precursor gas comprises oxygen gas. 
   
   
       7 . The process of  claim 6  wherein said scavenger precursor gas comprises hydrogen or nitrogen gas. 
   
   
       8 . The process of  claim 6  further comprising promoting dissociation of oxygen in said first plasma by furnishing nitrogen gas to said lower external plasma source. 
   
   
       9 . The process of  claim 7  further comprising:
 removing photoresist from the workpiece front side by supplementing the hydrogen gas supplied to the upper external plasma source with an oxygen-containing gas.   
   
   
       10 . The process of  claim 9  wherein said oxygen-containing gas comprises one of H2O, N2O, CO. 
   
   
       11 . The process of  claim 1  wherein the upper process zone height is sufficiently small to limit residency time of gases in said upper process zone to less than 1% to 5% of the residency time of gases in said lower process zone. 
   
   
       12 . The process of  claim 1  wherein the step of confining is a carried out by one of: (a) defining said gap between the workpiece edge and the sidewall of the chamber, (b) defining said gap between the workpiece edge and a ring surrounding the workpiece. 
   
   
       13 . The process of  claim 1  further comprising:
 confining the flow of the etchant by-product from said first plasma through axial conduits underlying the backside of the workpiece.   
   
   
       14 . A process for removing polymer from a backside of a workpiece, comprising:
 supporting said workpiece on the backside in a vacuum chamber while leaving a peripheral annular portion of the backside exposed, said workpiece corresponding to a boundary between an upper process zone and a lower process zone of said chamber;   confining the front side of said workpiece by a ceiling of said chamber to as to establish a height of the upper process zone that is less than 1% of the diameter of said workpiece;   generating a first plasma in an external chamber from a polymer etch precursor gas, and introducing an etchant by-product from said first plasma into said lower process zone; and   generating a second plasma in an upper external plasma chamber from a precursor gas of a scavenger of the etchant by-product and introducing scavenger by-product from said second plasma into said upper process zone.   
   
   
       15 . The process of  claim 14  further comprising:
 evacuating said upper process zone through a first slit opening surrounding said upper process zone.   
   
   
       16 . The process of  claim 15  further comprising:
 evacuating said lower process zone through a second slit opening surrounding said lower process zone near the edge of said workpiece.   
   
   
       17 . The process of  claim 13  wherein said polymer etch precursor gas comprises oxygen gas. 
   
   
       18 . The process of  claim 13  wherein said scavenger precursor gas comprises hydrogen or nitrogen gas. 
   
   
       19 . The process of  claim 18  further comprising:
 removing photoresist from the workpiece front side by supplementing hydrogen gas furnished to the upper external plasma source with an oxygen-containing gas.   
   
   
       20 . A process for removing polymer from a backside of a workpiece, comprising:
 supporting said workpiece on the backside in a vacuum chamber while leaving a peripheral annular portion of the backside exposed, said workpiece corresponding to a boundary between an upper process zone and a lower process zone of said chamber;   confining the front side of said workpiece by a ceiling of said chamber to as to establish a height of an upper process zone that is sufficiently small to limit residency time of gas in said upper process zone to less than 1% to 5% of the residency time of gases in said lower process zone;   generating a first plasma in a first external chamber from a polymer etch precursor gas, and introducing an etchant by-product from said first plasma into said lower process zone; and   generating a second plasma in a second external plasma chamber from a precursor gas of a scavenger of said etchant by-products and introducing a scavenger by-product from said second plasma into said upper process zone.