SILICON ETCH PROCESS WITH TUNABLE SELECTIVITY TO SiO2 AND OTHER MATERIALS

Abstract

A tunable plasma etch process includes generating a plasma in a controlled flow of a source gas including NH 3 and NF 3 to form a stream of plasma products, controlling a flow of un-activated NH 3 that is added to the stream of plasma products to form an etch gas stream; and controlling pressure of the etch gas stream by adjusting at least one of the controlled flow of the source gas and the flow of un-activated NH 3 until the pressure is within a tolerance of a desired pressure. An etch rate of at least one of polysilicon and silicon dioxide by the etch gas stream is adjustable by varying a ratio of the controlled flow of the source gas to the flow of un-activated NH 3 .

1 . A plasma etch processing system that etches silicon and silicon dioxide with tunable selectivity, comprising:
 a first NH 3  flow controller that controls an NH 3  plasma source gas stream;   an NF 3  flow controller that controls an NF 3  plasma source as stream;   a remote plasma source configured to apply RF energy to the NH 3  plasma source gas stream and the NF 3  plasma source gas stream, to generate a plasma product stream therefrom;   a second NH 3  flow controller configured to control an un-activated NH 3  gas stream;   apparatus for adding the un-activated NH 3  gas stream to the plasma product stream to form an etch gas stream; and   a process chamber configured to expose a workpiece to the etch gas stream;   wherein etch rates of at least one of polysilicon and silicon dioxide on the workpiece, by the etch gas stream, are adjustable at least by varying a ratio of the plasma source gas stream to the un-activated NH 3  gas stream.   
     
     
         2 . The plasma etch processing system of  claim 1 , further comprising:
 a controller for adjusting at least the first and second NH 3  flow controllers and the NF 3  flow controller.   
     
     
         3 . The plasma etch processing system of  claim 2 , further comprising:
 a pressure sensor for measuring pressure of the etch gas stream, wherein the controller monitors the pressure of the etch gas stream, and adjusts at least one of the first and second NH 3  flow controllers and the NF 3  flow controller, to control the pressure within a range of about 0.5 Torr to 10 Torr.   
     
     
         4 . The plasma etch processing system of  claim 2 , further comprising a temperature sensor, wherein the controller controls a temperature of the workpiece within a range of 100 C to 125 C. 
     
     
         5 . The plasma etch processing system of  claim 2 , further comprising a vacuum pump for evacuating at least one of the remote plasma source and the process chamber, wherein the controller controls the vacuum pump. 
     
     
         6 . The plasma etch processing system of  claim 2 , further comprising a temperature sensor, wherein the controller controls a temperature of the workpiece within a range of 100 C to 125 C. 
     
     
         7 . A plasma etch processing system, comprising:
 a process chamber configured to expose a workpiece to an etch gas stream;   a plasma source that generates a plasma product stream from a source gas stream that includes NH 3  and NF 3 ;   means for controlling a first NH 3  flow of the source gas stream;   means for controlling an NF 3  flow of the source gas stream;   means for controlling a second NH 3  flow of an un-activated NH 3  gas stream; and   a diffuser plate disposed between the plasma source and the process chamber that allows the plasma product stream to flow through the diffuser plate toward the process chamber, and adds the un-activated NH 3  gas stream only on a process chamber side of the diffuser plate, to form an etch gas stream; and   a controller for controlling at least:
 the plasma source, 
 the means for controlling the first NH 3  flow of the source gas stream, 
 the means for controlling the NF 3  flow of the source gas stream, 
 the means for controlling the second NH 3  flow of the un-activated NH 3  gas stream, and 
 a pressure within the process chamber; 
   such that the controller adjusts etch rates of at least one of polysilicon and silicon dioxide by the etch gas stream on the workpiece by varying at least one of the pressure and a ratio of the un-activated NH 3  gas stream to the source gas stream.   
     
     
         8 . The plasma etch processing system of  claim 2 , wherein:
 the controller is operable to provide a 10:1 ratio of the plasma source gas stream to the un-activated NH 3  gas stream; and   at the 10:1 ratio, the system provides a 20:1 selectivity of an etch rate of the polysilicon over an etch rate of the silicon dioxide.   
     
     
         9 . The plasma etch processing system of  claim 8 , wherein:
 the controller is operable to adjust the ratio of the plasma source gas stream to the un-activated NH3 gas stream from 10:1 to 5:1, and   at the 5:1 ratio, the system reduces the selectivity of the etch rate of the polysilicon over the etch rate of the silicon dioxide from 20:1 to 2:1.   
     
     
         10 . The plasma etch processing system of  claim 9 , wherein the controller is operable to adjust the ratio of the plasma source gas stream to the un-activated NH 3  gas stream from 10:1 in a first etch sequence, to 5:1 in a second etch sequence. 
     
     
         11 . The plasma etch processing system of  claim 9 , wherein the controller is operable to adjust the ratio of the plasma source gas stream to the un-activated NH 3  gas stream from 10:1 at a first time within a etch sequence, to 5:1 at a second time within the etch sequence. 
     
     
         12 . The plasma etch processing system of  claim 9 , wherein adjusting the ratio of the plasma source gas stream to the un-activated NH 3  gas stream from 10:1 to 5:1 reduces a concentration of at least one of F and H radicals in the etch gas stream. 
     
     
         13 . The plasma etch processing system of  claim 3 , wherein:
 the controller is operable to provide a 5:1 ratio of the plasma source gas stream to the un-activated NH3 gas stream;   the controller is operable to control the pressure at about 6 Torr, and   the system provides a 3:1 selectivity of an etch rate of the silicon dioxide over an etch rate of the polysilicon.   
     
     
         14 . The plasma etch processing system of  claim 7 , wherein the means for controlling the first NH 3  flow, the means for controlling the NF 3  flow and the means for controlling the second NH 3  flow comprise mass flow controllers for each of the first NH 3  flow, the NF 3  flow and the second NH 3  flow. 
     
     
         15 . The plasma etch processing system of  claim 7 , further comprising means for controlling a flow of one of He, Ar and oxygen that forms part of the etch gas stream. 
     
     
         16 . The plasma etch processing system of  claim 7 , wherein the controller is operable to adjust a ratio of the second NH 3  flow of the un-activated NH 3  gas stream to a flow of the source gas stream, from a first time to a second time within an etch sequence. 
     
     
         17 . The plasma etch processing system of  claim 7 , wherein:
 the first time precedes the second time;   at the first time, the controller controls the second NH 3  flow of the un-activated NH 3  gas stream such that the un-activated NH 3  gas stream produces an initial nonzero oxide etch rate at the first time; and   at the second time, the controller reduces the second NH 3  flow of the un-activated NH 3  gas stream to reduce the oxide etch rate, as compared to the initial nonzero oxide etch rate at the first time.   
     
     
         18 . The plasma etch processing system of  claim 7 , wherein the plasma source ignites a capacitively coupled plasma from the source gas stream to generate the plasma product stream. 
     
     
         19 . A plasma etch processing system that etches silicon and silicon dioxide with adjustable selectivity, comprising:
 a first flow controller that controls a first source gas stream of a hydrogen-containing source gas;   a second flow controller that controls a second source gas stream of a fluorine-containing source gas;   a remote plasma source configured to apply RF energy to the first and second source gas streams, to generate a plasma product stream therefrom;   a third flow controller that controls an un-activated gas stream;   apparatus for adding the un-activated gas stream to the plasma product stream to form an etch gas stream; and   a process chamber configured to expose a workpiece to the etch gas stream;   wherein etch rates of at least one of silicon and silicon dioxide on the workpiece, by the etch gas stream, are adjustable at least by varying a ratio of the plasma source gas stream to the un-activated gas stream.   
     
     
         20 . The plasma etch processing system of  claim 19 , wherein the un-activated gas stream comprises NH 3 .