Plasma processing method and apparatus with control of plasma excitation power

Abstract

The amount of RF power supplied to a plasma in a vacuum plasma processing chamber is gradually changed on a preprogrammed basis in response to signals stored in a computer memory. The computer memory stores signals so that other processing chamber parameters (pressure, gas species and gas flow rates) remain constant while the gradual change occurs. The stored signals enable rounded corners, instead of sharp edges, to be etched, e.g., at an intersection of a trench wall and base.

We claim:  
     
         1 . A method of processing a workpiece in a vacuum plasma processor chamber wherein a gas species is converted into an AC plasma, the vacuum chamber being subject to operating at different pressures while the workpiece is being processed, the gas species being subject to flowing into the chamber at different flow rates while the workpiece is being processed, comprising, gradually changing on a pre-programmed basis, the amount of AC power supplied to the plasma during processing of the workpiece.  
     
     
         2 . The method of  claim 1  wherein the gradual power change occurs while no change is made in (a) the species, (b) the pressure or (c) the flow rate.  
     
     
         3 . The method of  claim 1  wherein the AC power is supplied by an electrode coupling an AC electric field to plasma in the chamber.  
     
     
         4 . The method of  claim 3  wherein the electrode is responsive to an AC power source that supplies RF bias voltage to the electrode, the electrode being on a holder for the workpiece.  
     
     
         5 . The method of  claim 3  wherein the electrode is responsive to an AC power source that supplies RF plasma excitation voltage to the electrode, the electrode responding to the RF voltage to supply RF electric field to the plasma to excite the gas to the plasma.  
     
     
         6 . The method of  claim 3  wherein the AC power is supplied by a coil coupling an RF plasma excitation electromagnetic field to the chamber.  
     
     
         7 . The method of  claim 1  wherein a gradual transition in the shape of material in the workpiece being processed occurs in response to the gradual power change.  
     
     
         8 . The method of  claim 7  wherein the species is ionized into a plasma that etches the material, the gradual power change and the species being such that the material is shaped to have a rounded corner in response to changes in the ionized plasma etchant resulting from the gradual power change.  
     
     
         9 . The method of  claim 8  wherein the etching, which occurs in response to changes in the ionized plasma etchant resulting from the gradual power change, forms a trench wall including the rounded corner.  
     
     
         10 . The method of  claim 9  wherein the rounded corner is at an intersection of a wall and a base of a trench.  
     
     
         11 . The method of  claim 7  wherein the rounded corner is at an intersection of a wall and a surface intersecting the wall, the surface extending generally at right angles to the wall.  
     
     
         12 . The method of  claim 1  wherein the gradual change includes steps having power changes no greater than about several watts, the power remaining at a constant wattage for no more than about 1 second.  
     
     
         13 . The method of  claim 12  wherein the power steps are a few milliwatts and remain at a constant power for about 1 millisecond.  
     
     
         14 . A vacuum plasma processor for processing a workpiece in a vacuum plasma processor chamber wherein a gas species is converted into an AC plasma comprising a reactive element for supplying an electric field to plasma in the chamber, and an electric source for supplying gradually changing amounts of power on a preprogrammed basis to the reactive element.  
     
     
         15 . The processor of  claim 14  further including a controller for causing the source to supply the gradually changing amounts of power on the preprogrammed basis to the reactive element while a single workpiece is being processed.  
     
     
         16 . The processor of  claim 15  wherein the controller is arranged for (a) controlling (i) a gas species adapted to flow into the chamber, (ii) the pressure in the vacuum chamber, and (iii) the flow rates of the gas species, and (b) maintaining the constant (I) the gas species, (ii) the gas species flow rate and (iii) the chamber pressure while the plasma power is gradually changing on the preprogrammed basis.  
     
     
         17 . A computer program for controlling a computer for controlling processing of a workpiece in a vacuum plasma processor chamber wherein a gas species is converted into an AC plasma, the computer program storing signals causing (a) the vacuum chamber to operate at different pressures while the workpiece is being processed, (b) control of the gas species type and the flow rates thereof into the chamber while the workpiece is being processed, (c) the amount of AC power applied to the plasma while the workpiece is being processed; the stored signal for the amount of applied AC power causing gradual preprogrammed changes in the amount of AC power supplied to the plasma during processing of the workpiece.  
     
     
         18 . The program of  claim 17  wherein the stored signal causes the gradual power change to occur while no change is made in (a) the species, (b) the pressure or (c) the flow rate.  
     
     
         19 . The program of  claim 17  wherein the stored signal causing gradual power change causes a gradual transition in the shape of material in the workpiece being processed in response to the gradual power change.  
     
     
         20 . The program of  claim 19  wherein the stored signal controls etchant species supplied to the chamber while the workpiece is being processed and the gradual power transition so as to cause the workpiece to be etched to have a rounded corner.  
     
     
         21 . The program of  claim 20  wherein the stored signal controls etchant species supplied to the chamber while the workpiece is being processed and the gradual power transition so as to cause the workpiece to be etched to have a trench wall including the rounded corner.  
     
     
         22 . The program of  claim 21  wherein the rounded corner is at an intersection of a wall and a base of a trench.