Methods and Systems for Independent Control of Radical Density, Ion Density, and Ion Energy in Pulsed Plasma Semiconductor Device Fabrication

Abstract

For a first period of time, a higher radiofrequency power is applied to generate a plasma in exposure to a substrate, while applying low bias voltage at the substrate level. For a second period of time, a lower radiofrequency power is applied to generate the plasma, while applying high bias voltage at the substrate level. The first and second periods of time are repeated in an alternating and successive manner for an overall period of time necessary to produce a desired effect on the substrate. In some embodiments, the first period of time is shorter than the second period of time such that on a time-averaged basis the plasma has a greater ion density than radical density. In some embodiments, the first period of time is greater than the second period of time such that on a time-averaged basis the plasma has a lower ion density than radical density.

What is claimed is: 
     
         1 . A method for controlling a plasma in a semiconductor fabrication process, comprising:
 (a) supplying a process gas composition to a plasma generation region overlying a substrate holder on which a substrate is present;   (b) for a first period of time, applying a first radiofrequency power to the process gas composition within the plasma generation region to generate a plasma, the first radiofrequency power corresponding to a high radiofrequency power level, and applying bias voltage at the substrate holder at a first bias voltage setting corresponding to a low bias voltage level that is below a threshold voltage required for removal of a material from the substrate through interaction of ions from the plasma with the material on the substrate;   (c) for a second period of time, after completion of the first period of time, applying a second radiofrequency power to the process gas composition within the plasma generation region to generate the plasma, wherein the second radiofrequency power is applied instead of the first radiofrequency power, the second radiofrequency power corresponding to a low radiofrequency power level, and applying bias voltage at the substrate holder at a second bias voltage setting corresponding to a high bias voltage level; and   (d) repeating operations (b) and (c) in an alternating and successive manner for an overall period of time.   
     
     
         2 . The method as recited in  claim 1 , wherein the first radiofrequency power corresponding to the high radiofrequency power level is within a range extending from about 500 Watts to about 6000 Watts, or within a range extending from about 1000 W to about 4000 W. 
     
     
         3 . The method as recited in  claim 1 , wherein the second radiofrequency power corresponding to the low radiofrequency power level is within a range extending from about 20 Watts to about 1000 Watts, or within a range extending from about 100 Watts to about 600 Watts. 
     
     
         4 . The method as recited in  claim 1 , wherein the first bias voltage setting corresponding to the low bias voltage level is zero. 
     
     
         5 . The method as recited in  claim 1 , wherein the second bias voltage setting corresponding to the high bias voltage level is within a range extending up to about 5000 volts, or within a range extending up to about 3000 volts, or within a range extending from about 100 volts to about 5000 volts, or within a range extending from about 200 volts to about 3000 volts. 
     
     
         6 . The method as recited in  claim 1 , wherein a duration of the first period of time of operation (b) is within a range extending from about 0.001 millisecond to about 1 millisecond, and wherein a duration of the second period of time of operation (c) is within a range extending from about 0.009 millisecond to about 100 milliseconds. 
     
     
         7 . The method as recited in  claim 1 , wherein a sum of a duration of the first period of time of operation (b) and a duration of the second period of time of operation (c) is within a range extending from about 0.01 milliseconds to about 100 milliseconds. 
     
     
         8 . The method as recited in  claim 1 , wherein a duration of the first period of time of operation (b) is less than or equal to about ten percent of a sum of the duration of the first period of time of operation (b) and a duration of the second period of time of operation (c). 
     
     
         9 . The method as recited in  claim 1 , wherein the plasma is generated such that a mean-lifetime of radicals with the plasma is about three orders of magnitude greater than a mean-lifetime of ions within the plasma. 
     
     
         10 . The method as recited in  claim 1 , further comprising:
 managing a duration of the first period of time of operation (b) and a duration of the second period of time of operation (c) to increase a time-averaged ion density within the plasma relative to a time-averaged radical density within the plasma.   
     
     
         11 . The method as recited in  claim 1 , further comprising:
 managing a duration of the first period of time of operation (b) and a duration of the second period of time of operation (c) to decrease a time-averaged ion density within the plasma relative to a time-averaged radical density within the plasma.   
     
     
         12 . The method as recited in  claim 1 , wherein a duration of the first period of time of operation (b) is within a range extending from about 0.009 millisecond to about 100 milliseconds, and wherein a duration of the second period of time of operation (c) is within a range extending from about 0.001 millisecond to about 1 millisecond. 
     
     
         13 . The method as recited in  claim 1 , wherein a duration of the second period of time of operation (c) is less than or equal to about ten percent of a sum of a duration of the first period of time of operation (b) and the duration of the second period of time of operation (c). 
     
     
         14 . An apparatus for semiconductor fabrication, comprising:
 a substrate holder configured to hold a substrate in exposure to a plasma generation region;   a process gas input configured to supply a process gas to the plasma generation region;   a radiofrequency power supply configured to supply radiofrequency power to the plasma generation region;   a bias voltage supply configured to supply bias voltage to the substrate holder; and   a control system configured to direct supply of the process gas through the process gas input to the plasma generation region,   the control system configured to direct performance of a first operation for a first period of time during which the radiofrequency power supply is controlled to apply a first radiofrequency power to the process gas within the plasma generation region to generate a plasma, and during which the bias voltage supply is controlled to apply bias voltage at the substrate holder at a first bias voltage setting corresponding to a low bias voltage level that is below a threshold voltage required for removal of a material from the substrate through interaction of ions from the plasma with the material on the substrate, the first radiofrequency power corresponding to a high radiofrequency power level,   the control system configured to direct performance of a second operation for a second period of time, after completion of the first period of time, during which the radiofrequency power supply is controlled to apply a second radiofrequency power to the process gas within the plasma generation region to generate the plasma, and during which the bias voltage supply is controlled to apply bias voltage at the substrate holder at a second bias voltage setting corresponding to a high bias voltage level, the second radiofrequency power being applied instead of the first radiofrequency power, the second radiofrequency power corresponding to a low radiofrequency power level,   the control system configured to direct repeated performance of the first operation and the second operation in an alternating and successive manner for an overall period of time.   
     
     
         15 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to manage a duration of the first period of time of the first operation and a duration of the second period of time of the second operation to achieve a prescribed relationship between a time-averaged ion density within the plasma and a time-averaged radical density within the plasma. 
     
     
         16 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct the duration of the first period of time of the first operation to be shorter than the duration of the second period of time of the second operation to increase the time-averaged ion density within the plasma relative to the time-averaged radical density within the plasma. 
     
     
         17 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct the duration of the first period of time of the first operation to be longer than the duration of the second period of time of the second operation to decrease the time-averaged ion density within the plasma relative to the time-averaged radical density within the plasma. 
     
     
         18 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct the first radiofrequency power corresponding to the high radiofrequency power level to be within a range extending from about 500 Watts to about 6000 Watts, or within a range extending from about 1000 W to about 4000 W. 
     
     
         19 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct the second radiofrequency power corresponding to the low radiofrequency power level to be within a range extending from about 20 Watts to about 1000 Watts, or within a range extending from about 100 Watts to about 600 Watts. 
     
     
         20 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct the first bias voltage setting corresponding to the low bias voltage level to be zero. 
     
     
         21 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct the second bias voltage setting corresponding to the high bias voltage level to be within a range extending up to about 5000 volts, or within a range extending up to about 3000 volts, or within a range extending from about 100 volts to about 5000 volts, or within a range extending from about 200 volts to about 3000 volts. 
     
     
         22 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct a duration of the first period of time of the first operation to be within a range extending from about 0.001 millisecond to about 1 millisecond, and wherein the control system is configured to direct a duration of the second period of time of the second operation to be within a range extending from about 0.009 millisecond to about 100 milliseconds. 
     
     
         23 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct a sum of a duration of the first period of time of the first operation and a duration of the second period of time of the second operation to be within a range extending from about 0.01 milliseconds to about 100 milliseconds. 
     
     
         24 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct a duration of the first period of time of the first operation to be less than or equal to about ten percent of a sum of the duration of the first period of time of the first operation and a duration of the second period of time of the second operation. 
     
     
         25 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct generation of the plasma such that a mean-lifetime of radicals with the plasma is about three orders of magnitude greater than a mean-lifetime of ions within the plasma. 
     
     
         26 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to manage a duration of the first period of time of the first operation and a duration of the second period of time of the second operation to increase a time-averaged ion density within the plasma relative to a time-averaged radical density within the plasma. 
     
     
         27 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to manage a duration of the first period of time of the first operation and a duration of the second period of time of the second operation to decrease a time-averaged ion density within the plasma relative to a time-averaged radical density within the plasma. 
     
     
         28 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct a duration of the first period of time of the first operation to be within a range extending from about 0.009 millisecond to about 100 milliseconds, and wherein the control system is configured to direct a duration of the second period of time of the second operation to be within a range extending from about 0.001 millisecond to about 1 millisecond. 
     
     
         29 . The apparatus for semiconductor fabrication as recited in  claim 14 , wherein the control system is configured to direct a duration of the second period of time of the second operation to be less than or equal to about ten percent of a sum of a duration of the first period of time of the first operation and the duration of the second period of time of the second operation.