Wafer flattening process and system

Abstract

A wafer flattening process and system enables a reduction of the surface roughness of a wafer resulting from local etching. A silicon wafer W is brought into close proximity to a nozzle portion 20 to feed SF 6 gas to an alumina discharge tube 2, a plasma generator 1 is used to cause plasma discharge and spray a first activated species gas from the nozzle portion 20 to the silicon wafer W side, an X-Y drive mechanism 4 is used to make the nozzle portion 20 scan to perform a local etching step. Then the silicon wafer W is moved away from the nozzle portion 20 and O 2 gas and CF 4 gas are fed to the alumina discharge tube. At this time, the O 2 gas is set to be greater in amount than the CF 4 gas. When this mixed gas is made to discharge to generate plasma, a second activated species gas diffuses from the nozzle portion 20 to the entire surface of the silicon wafer W. Since there is a larger amount of O radicals than F radicals, the reaction product resulting from the O radicals deposit in fine depressions causing roughness and the front surface of the silicon wafer W is smoothed.

What is claimed is:  
     
         1 . A wafer flattening system comprising: 
 a local etching device provided with a first gas feed unit for supplying to a first discharge tube having an opening of a nozzle portion facing the front surface of the wafer a fluorine compound gas or a first mixed gas containing a fluorine compound, a first plasma generation unit for causing the fluorine compound gas or first mixed gas containing a fluorine compound in the first discharge tube to discharge to generate a plasma and generate a first activated species gas, and first drive unit for causing the nozzle portion to move relatively along the front surface of the wafer; and    a smoothing device provided with a second discharge tube having a nozzle portion for spraying a second activated species gas over the entire surface of the wafer, a second gas feed unit for feeding a second mixed gas containing carbon tetrafluoride and oxygen to the second discharge tube, and a second plasma generation unit for causing the second mixed gas in the second discharge tube to discharge to generate a plasma and generate the second activated species gas.    
     
     
         2 . A wafer flattening system as set forth in    claim 1   , wherein the fluorine compound in the first gas feed unit is one of carbon tetrafluoride, sulfur hexafluoride, and nitrogen trifluoride.  
     
     
         3 . A wafer flattening system as set forth in    claim 1   , wherein the ratio of oxygen to carbon tetrafluoride in the second gas feed unit is set to 200 to 400 percent.  
     
     
         4 . A wafer flattening system as set forth in    claim 3   , wherein the opening of the nozzle portion of the second discharge tube is made to face the front surface of the wafer and the distance between the opening and front surface of the wafer is set to a distance where the second activated species gas diffuses over the entire front surface of the wafer.  
     
     
         5 . A wafer flattening system as set forth in    claim 4   , wherein the smoothing device is provided with a second drive unit for making the nozzle portion of the second discharge tube relatively along with front surface of the wafer.