Plasma doping with enhanced charge neutralization

Abstract

A plasma doping apparatus includes a pulsed power supply that generates a pulsed waveform having a first period with a first power level and a second period with a second power level. A plasma source generates a pulsed plasma with the first power level during the first period and with the second power level during the second period. A bias voltage power supply generates a bias voltage waveform at an output that is electrically connected to a platen which supports a substrate. The bias voltage waveform having a first voltage during a first period and second voltage with a negative potential that attract ions in the plasma to the substrate for plasma doping during a second period. At least one of the first and second power levels of the RF waveform is chosen to at least partially neutralize charge accumulating on the substrate.

1 . A plasma doping apparatus comprising:
 a. a pulsed power supply that generates a pulsed waveform at an output, the pulsed waveform having at least a first period with a first power level and a second period with a second power level;   b. a plasma source having an electrical input that is electrically connected to the output of the pulsed power supply, the plasma source generating a pulsed plasma with the first power level during the first period and with the second power level during the second period;   c. a platen that supports a substrate for plasma doping; and   d. a bias voltage power supply having an output that is electrically connected to the platen, the bias voltage power supply generating a bias voltage waveform having a first voltage during a first period and a second voltage with a negative potential that attract ions in the plasma to the substrate for plasma doping during a second period, at least one of the first and second power levels of the RF waveform being chosen to at least partially neutralize charge accumulating on the substrate.   
   
   
       2 . The plasma doping apparatus of  claim 1  wherein the first voltage in the bias voltage waveform is at ground potential. 
   
   
       3 . The plasma doping apparatus of  claim 1  wherein the first voltage in the bias voltage waveform has a positive potential that at least partially neutralize charge accumulating on the substrate. 
   
   
       4 . The plasma doping apparatus of  claim 1  wherein the first and second periods of the pulsed waveform generated by the pulsed power supply are substantially the same as the first and second periods of the bias voltage waveform generated by the bias voltage power supply. 
   
   
       5 . The plasma doping apparatus of  claim 1  wherein the pulsed waveform generated by the pulsed power supply is synchronized to the bias voltage waveform generated by the bias voltage power supply. 
   
   
       6 . The plasma doping apparatus of  claim 1  wherein the pulsed waveform generated by the pulsed power supply includes a third period having a third power level. 
   
   
       7 . The plasma doping apparatus of  claim 6  wherein the third power level is a zero power level. 
   
   
       8 . The plasma doping apparatus of  claim 1  wherein a relative timing of the pulsed waveform generated by the pulsed power supply and the bias voltage waveform generated by the bias voltage power supply is chosen to at least partially neutralize charge accumulating on the substrate. 
   
   
       9 . The plasma doping apparatus of  claim 1  wherein a relative timing of the pulsed waveform generated by the pulsed power supply and the bias voltage waveform generated by the bias voltage power supply is chosen so that the pulsed waveform generated by the pulsed power supply changes from the first power level to the second power level during the second period of the bias voltage waveform where the bias voltage waveform has the negative potential that attracts ions in the plasma to the substrate for plasma doping. 
   
   
       10 . The plasma doping apparatus of  claim 1  wherein the first and second power levels are chosen to increase retained dose in the substrate. 
   
   
       11 . The plasma doping apparatus of  claim 1  wherein a relative timing of the pulsed waveform generated by the pulsed power supply and the bias voltage waveform generated by the bias voltage power supply is chosen to increase retained dose in the substrate. 
   
   
       12 . The plasma doping apparatus of  claim 1  wherein the first and second power levels are chosen to enhance knock-on type implant mechanisms so as to produce a more conformal doping profile. 
   
   
       13 . The plasma doping apparatus of  claim 1  wherein a relative timing of the pulsed waveform generated by the pulsed power supply and the bias voltage waveform generated by the bias voltage power supply is chosen to enhance knock-on type implant mechanisms so as to produce a more conformal doping profile. 
   
   
       14 . The plasma doping apparatus of  claim 1  wherein a frequency of the pulsed waveform in the first period is different from a frequency of the pulsed waveform in the second period. 
   
   
       15 . A plasma doping apparatus comprising:
 a. a chamber that contains a process gas, the chamber comprising a dielectric window that passes electromagnetic radiation;   b. a RF source that generates a RF waveform at an output, the RF waveform having at least a first and a second power level;   c. at least one RF antenna having an input that is electrically connected to the output of the RF power supply, the at least one RF antenna being positioned proximate to the dielectric window so that the RF waveform electromagnetically couples into the chamber to excite and ionize the process gas, thereby forming a plasma in the chamber;   d. a platen that supports a substrate for plasma doping; and   e. a bias voltage power supply having an output that is electrically connected to the platen, the bias voltage power supply generating a bias voltage waveform at the output that includes negative potential pulses that attract ions in the plasma to the substrate for plasma doping, at least one of the first and second power levels of the RF waveform and a relative timing of the RF waveform and the bias voltage waveform being chosen to at least partially neutralize charge accumulating on the substrate.   
   
   
       16 . The plasma doping apparatus of  claim 15  wherein the at least one RF antenna comprises a vertical and a horizontal antenna. 
   
   
       17 . The plasma doping apparatus of  claim 15  wherein the at least one RF antenna comprises an active antenna and a passive antenna. 
   
   
       18 . The plasma doping apparatus of  claim 15  wherein the bias voltage waveform periodically returns to ground potential. 
   
   
       19 . The plasma doping apparatus of  claim 15  wherein the bias voltage waveform periodically returns to a positive potential that at least partially neutralize charge accumulating on the substrate. 
   
   
       20 . The plasma doping apparatus of  claim 15  wherein the relative timing of the RF waveform and the bias voltage waveform is chosen so that the RF waveform has both the first and second power levels while the bias voltage waveform is at a negative potential that attract ions in the plasma to the substrate for plasma doping. 
   
   
       21 . The plasma doping apparatus of  claim 15  wherein the first and second power levels are chosen to increase retained dose in the substrate. 
   
   
       22 . The plasma doping apparatus of  claim 15  wherein the relative timing of the RF waveform and the bias voltage waveform is chosen to increase retained dose in the substrate. 
   
   
       23 . The plasma doping apparatus of  claim 15  wherein the first and second power levels are chosen to enhance knock-on type implant mechanisms so as to produce a more conformal doping profile. 
   
   
       24 . The plasma doping apparatus of  claim 15  wherein the relative timing of the RF waveform and the bias voltage waveform is chosen to enhance knock-on type implant mechanisms. 
   
   
       25 . The plasma doping apparatus of  claim 15  wherein the at least one RF antenna comprises a vertical and a horizontal antenna. 
   
   
       26 . The plasma doping apparatus of  claim 25  wherein the RF source applies the RF waveform having the first power level to the vertical antenna and applies the RF waveform having the second power level to the horizontal antenna. 
   
   
       27 . A method of plasma doping comprising:
 a. generating a pulsed waveform having at least a first period with a first power level and a second period with a second power level;   b. generating a plasma from the pulsed waveform;   c. generating a bias voltage waveform having a first voltage during a first period and second voltage with a negative potential during a second period; and   d. applying the bias voltage waveform to a substrate exposed to the plasma so that ions in the plasma are attracted to the substrate for plasma doping during the second period where the bias voltage waveform has a negative potential, at least one of the first and second power levels of the RF waveform being chosen to at least partially neutralize charge accumulating on the substrate.   
   
   
       28 . The method of  claim 27  wherein the generating the bias voltage waveform having the first voltage during the first period comprises generating a positive voltage that at least partially neutralize charge accumulating on the substrate. 
   
   
       29 . The method of  claim 27  further comprising adjusting a relative timing of the pulsed waveform and the bias voltage waveform so that the RF waveform has both the first and the second power level during the second period where the bias voltage waveform has a negative potential. 
   
   
       30 . The method of  claim 27  further comprising adjusting a relative timing of the pulsed waveform and the bias voltage waveform so as to increase a retained dose in the substrate. 
   
   
       31 . The method of  claim 27  further comprising selecting at least one of the first and the second power levels so as to increase a retained dose in the substrate. 
   
   
       32 . The method of  claim 27  further comprising adjusting a relative timing of the pulsed waveform and the bias voltage waveform so as to enhance knock-on type implant mechanisms to produce a more conformal doping profile. 
   
   
       33 . The method of  claim 27  further comprising selecting at least one of the first and the second power levels so as to enhance knock-on type implant mechanisms to produce a more conformal doping profile. 
   
   
       34 . The method of  claim 27  wherein the pulsed waveform includes a third power level having a third period. 
   
   
       35 . The method of  claim 34  wherein the third power level is zero. 
   
   
       36 . A method of plasma doping comprising:
 a. generating a pulsed waveform having a first period and a second period;   b. generating a plasma from the pulsed waveform;   c. generating a bias voltage waveform having a first voltage during a first period and second voltage with a negative potential during a second period; and   d. applying the bias voltage waveform to a substrate exposed to the plasma so that ions in the plasma are attracted to the substrate for plasma doping during the second period where the bias voltage waveform has a negative potential, the RF waveform being chosen to at least partially neutralize charge accumulating on the substrate.   
   
   
       37 . The method of  claim 36  wherein the pulse waveform has at least two different power levels. 
   
   
       38 . The method of  claim 36  wherein the pulse waveform has at least two different frequencies.