Medium pressure plasma system for removal of surface layers without substrate loss

Abstract

A system and method for removing photoresist or other organic compounds from semiconductor wafers is provided. Non-fluorinated reactant gases (O 2 , H 2 , H 2 O, N 2 etc.) are activated in a quartz tube by a medium pressure surface wave discharge. As the plasma jet impinges on a substrate, volatile reaction products (H 2 O, CO 2 , or low molecular weight hydrocarbons) selectively remove the photoresist from the surface. The medium pressure also enables high gas temperatures that provide an effective source of heat in the reactive zone on the wafer that enhances etch rates and provides a practical means of removing ion implanted photoresist.

1 . An apparatus for selectively removing surface layers from a workpiece in a manufacturing process, comprising: 
 a process chamber for defining an atmospheric to subatmospheric environment and receiving the workpiece therein;    a plasma applicator for generating a plasma, including 
 a pressurized supply of reactant process gas;  
 a plasma discharge tube in fluid communication with said pressurized supply of reactant process gas;  
 an electromagnetic power source for directing electromagnetic power to said plasma discharge tube to generate a plasma therein; and  
 a nozzle opening situated at an end of said plasma discharge tube for jetting the plasma gas into said process chamber in a direction toward the workpiece; and  
   a cooling system including a conduit substantially surrounding said plasma discharge tube for circulating a gaseous coolant therethrough, thereby forming a cooling channel around said plasma discharge tube.    
     
     
         2 . The apparatus of  claim 1 , further including a waveguide for transmitting the electromagnetic power to said plasma discharge tube.  
     
     
         3 . The apparatus of  claim 2 , further including a microwave trap for containing the electromagnetic power within said plasma applicator.  
     
     
         4 . The apparatus of  claim 1 , wherein the reactant process gas comprises O 2 , H 2 , H 2 O, N 2  or a combination thereof.  
     
     
         5 . The apparatus of  claim 1 , wherein the reactant process gas consists of O 2 , H 2 , H 2 O, N 2  or a combination thereof and wherein said reactant process gas does not comprise fluorine.  
     
     
         6 . The apparatus of  claim 1 , wherein said plasma discharge tube is made of quartz or other electromagnetically insensitive ceramic materials  
     
     
         7 . The apparatus of  claim 1 , whereby said cooling system has a thermodynamic performance that provides for operation of said electromagnetic power source at a power dissipation of at least 2.5 kW, or at a power density of at least 1.5 kW/cm 3 .  
     
     
         8 . The apparatus of  claim 1 , wherein said electromagnetic power source operates at frequencies between about 100 kHz and 2.45 GHz.  
     
     
         9 . The apparatus as recited in  claim 1 , further comprising: 
 a mechanical positioning system including a chuck for receiving and maintaining the workpiece thereon to scan the workpiece relative to said nozzle such that a surface layer of said workpiece is exposed to said plasma.    
     
     
         10 . The apparatus of  claim 9 , wherein said mechanical positioning system comprises a plurality of mechatronic translation stages for scanning said surface of the workpiece, operable such that said chuck may be accelerated greater than about 2.5 times the acceleration of gravity and positioned at a linear velocity greater than about 100 cm/s.  
     
     
         11 . The apparatus of  claim 1 , wherein the distance between said nozzle and the workpiece is greater than about 2 mm and less than about 20 mm.  
     
     
         12 . The apparatus of  claim 9 , wherein said plurality of mechatronic translation stages are arranged for positioning according to Cartesian or polar coordinates.  
     
     
         13 . The apparatus as recited in  claim 9 , wherein said chuck further includes a layer of thermal material on a surface thereof having thermally insulating or thermally conducting characteristics for modifying a thermal contact conductance between said chuck and the workpiece.  
     
     
         14 . The apparatus as recited in  claim 9 , further comprising: 
 means for removing and introducing a workpiece onto said chuck with a pressure pressure within said process chamber in a raised state to ambient pressure while said plasma applicator is maintained operational, thereby eliminating a need for extinguishing and reigniting the plasma for each workpiece to be processed in said process chamber.    
     
     
         15 . The apparatus as recited in  claim 9 , further comprising: 
 means for clamping a workpiece onto said chuck by a force supplied by process atmosphere or a vacuum, or by an electrostatic force.    
     
     
         16 . A method for selectively removing surface layers from a wafer in a semiconductor manufacturing process, comprising the following steps: 
 introducing the wafer into a process chamber defining an atmospheric to subatmospheric processing environment;    exposing a reactant gas flowing through a discharge tube to a surface wave discharge provided by an electromagnetic power source to generate an activated reactant gas flowing through said discharge tube; and    jetting the activated reactant gas onto into said chamber and onto a surface of the wafer, whereby a surface layer thereof is selectively removed without substantial loss of substrate material.    
     
     
         17 . The method of  claim 16 , further including the step of cooling said plasma discharge tube by forming a cooling channel thereabout, and circulating a gaseous coolant through said cooling channel.  
     
     
         18 . The method of  claim 16 , wherein said reactant process gas comprises O 2 , H 2 , H 2 O, N 2  or a combination thereof.  
     
     
         19 . The method of  claim 16 , wherein the surface layer comprises an unimplanted photoresist or other organic or inorganic material.  
     
     
         20 . The method of  claim 16 , wherein the surface layer comprises an ion implanted photoresist material or other organic or inorganic material.  
     
     
         21 . The method as recited in  claim 16 , further comprising the step of: 
 scanning the wafer via relative motion of the wafer with respect to the jetted reactant gas at a first speed whereby an implanted photoresist crust is rendered permeable to gases.    
     
     
         22 . The method as recited in  claim 21 , further comprising the step of: 
 scanning the wafer via relative motion of the wafer with respect to the jetted reactant gas at a second speed, whereby photoresist and/or crust is removed from the wafer.    
     
     
         23 . The method as recited in  claim 16 , further comprising the step of: 
 exposing the reactant gas to the surface wave discharge at a first power level whereby an implanted photoresist crust is rendered permeable to gases.    
     
     
         24 . The method as recited in  claim 23 , further comprising the step of: 
 exposing the reactant gas to the surface wave discharge at a second power level, whereby photoresist and/or crust is removed from the wafer.    
     
     
         25 . The method as recited in  claim 16 , further comprising the step of: 
 scanning the wafer via relative motion of the wafer with respect to the jetted reactant gas at a first temperature, whereby an implanted photoresist crust is rendered permeable to gases.    
     
     
         26 . The method as recited in  claim 25 , further comprising the step of: 
 scanning the wafer via relative motion of the wafer with respect to the jetted reactant gas at a second temperature, whereby photoresist and/or crust is removed from the wafer.    
     
     
         27 . The method as recited in  claim 16 , wherein said activating step further comprises: 
 exciting an electromagnetic power source for generating a surface wave on said plasma discharge tube;    transmitting electromagnetic power to said plasma discharge tube through a waveguide engaged to said plasma discharge tube; and    containing electromagnetic radiation using a trap within said plasma applicator.    
     
     
         28 . The method of  claim 16 , wherein said electromagnetic power source operates at frequencies between about 100 kHz and 2.45 GHz.  
     
     
         29 . The method as recited in  claim 16 , further comprising the steps of: 
 placing a wafer on a chuck; and    scanning the chuck relative to the jetted reactant gas via a mechanical positioning system mounted to said chuck, whereby the chuck having the wafer placed theron is positioned such that a surface layer thereof is exposed to the jetted reactant gas.    
     
     
         30 . The method of  claim 29 , wherein said mechanical positioning system is operated such that said chuck may be accelerated greater than about 2.5 times the acceleration of gravity and positioned at a linear velocity greater than about 100 cm/s.  
     
     
         31 . The method as recited in  claim 29 , further comprising the step of: 
 varying the temperature of the wafer via a layer of thermally insulative or conductive material situated between the wafer and a wafer holder mounted on said chuck, whereby a thermal contact conductance between said wafer holder and the wafer is modified.    
     
     
         32 . The method as recited in  claim 29 , further comprising: 
 removing and introducing a wafer onto said chuck when a pressure within said process chamber is at ambient pressure, thereby eliminating a need for igniting the activated reactant gas for each wafer processed in said process chamber.    
     
     
         33 . The method as recited in  claim 31 , further comprising: 
 clamping semiconducting wafers onto said chuck by a force supplied by process atmosphere or a vacuum, or by an electrostatic force.