Method and apparatus for ion energy distribution manipulation for plasma processing chambers that allows ion energy boosting through amplitude modulation

Abstract

Methods and apparatus for boosting ion energies are contemplated herein. In one embodiment, the methods and apparatus comprises a controller, a process chamber with a symmetrical plasma source configured to process a wafer, one or more very high frequency (VHF) sources, coupled to the process chamber, to generate plasma density and two or more frequency generators that generate low frequencies relative to the one or more VHF sources, coupled to a bottom electrode of the process chamber, the two or more low frequency generators configured to dissipate energy in the plasma sheath, wherein the controller controls the one or more VHF sources to generate a VHF signal and the two or more low frequency sources to generate two or more low frequency signals.

1 . A method for plasma processing comprising:
 processing a wafer using a process chamber with a single monolithic top electrode, the single monolithic top electrode positioned centrally within the process chamber;   providing one or more very high frequency (VHF) signals with one or more VHF sources to the single monolithic top electrode of the process chamber via symmetrical conductors;   providing two or more frequency signals having frequencies less than the one or more VHF signals with two or more frequency generators to a bottom electrode of the process chamber, wherein the single monolithic top electrode is DC grounded to the process chamber such that a symmetrical low impedance current return path for the two or more frequency signals is created; and   amplitude modulating a first frequency signal of the two or more frequency signals with a second frequency signal of the two or more frequency signals to produce a higher peak-to-peak voltage on a plasma sheath.   
     
     
         2 . The method of  claim 1 , further comprising:
 amplitude modulating the first frequency signal with the second frequency signal to obtain a modulation depth of approximately 0.2 to approximately 1.   
     
     
         3 . The method of  claim 1 , wherein the second frequency signal has a higher frequency than the first frequency signal. 
     
     
         4 . The method of  claim 1 , wherein the second frequency signal is a harmonic frequency of the first frequency signal. 
     
     
         5 . The method of  claim 1 , further comprising:
 adjusting a phase coherence between the first frequency signal and the second frequency signal to manipulate ion energies.   
     
     
         6 . The method of  claim 1 , further comprising:
 impedance matching the one or more VHF sources and the process chamber using a VHF match; and   impedance matching the bottom electrode and the two or more frequency generators using, respectively, two or more frequency matches.   
     
     
         7 . The method of  claim 6 , further comprising:
 isolating the two or more frequency signals respectively using two or more isolators, each isolator of the two or more isolators is positioned directly between one of the two or more frequency matches and the bottom electrode and removes frequencies not supplied directly to the isolator by one of the two or more frequency generators.   
     
     
         8 . The method of  claim 6 , wherein the process chamber further comprises:
 wherein the symmetrical conductors are coupled to the VHF match; and   an electrostatic chuck configured to support the wafer,   wherein the process chamber is coupled to DC ground.   
     
     
         9 . The method of  claim 8 , wherein the process chamber further comprises:
 wherein the symmetrical conductors are connected to a top edge of a hollow cylinder which has a bottom edge connected to the single monolithic top electrode;   wherein the hollow cylinder is conductive and RF hot; and   an outer hollow cylinder acting as a DC ground, coupled to the single monolithic top electrode.   
     
     
         10 . The method of  claim 1 , wherein the two or more frequency signals have frequencies that are less than 4 MHz. 
     
     
         11 . The method of  claim 1 , further comprising:
 generating a signal with a VHF of approximately greater than 30 MHz; and   generating a first signal with a first frequency of 2 MHz and a second signal with a second frequency of 400 kHz as frequencies of the two or more frequency signals.   
     
     
         12 . An apparatus for plasma processing, comprising:
 a controller;   a process chamber with a symmetrical plasma source configured to process a wafer with a single monolithic top electrode, the single monolithic top electrode positioned centrally within the process chamber opposite a bottom electrode;   one or more very high frequency (VHF) sources, coupled to the single monolithic top electrode via symmetrical conductors connected to a top edge of a hollow cylinder which has a bottom edge connected to the single monolithic top electrode, to generate plasma density; and   two or more frequency generators that generate low frequencies relative to the one or more VHF sources, coupled to a bottom electrode of the process chamber, the two or more frequency generators configured to dissipate energy in a plasma sheath above the bottom electrode,   wherein the controller is configured to control the one or more VHF sources to generate a VHF signal and the two or more frequency generators to generate two or more frequency signals,   wherein the controller is configured to amplitude modulate a first frequency signal of the two or more frequency signals with a second frequency signal of the two or more frequency signals to produce a higher peak-to-peak voltage on a plasma sheath, and   wherein the single monolithic top electrode is DC grounded to the process chamber such that a symmetrical low impedance current return path for the two or more frequency signals is provided by the symmetrical conductors.   
     
     
         13 . The apparatus of  claim 12 , wherein the controller is configured to amplitude modulate the first frequency signal with the second frequency signal to obtain a modulation depth of approximately 0.2 to approximately 1. 
     
     
         14 . The apparatus of  claim 12 , wherein the second frequency signal has a higher frequency than the first frequency signal. 
     
     
         15 . The apparatus of  claim 12 , wherein the second frequency signal is a harmonic frequency of the first frequency signal. 
     
     
         16 . The apparatus of  claim 12 , wherein the controller adjusts a phase coherence between the first frequency signal and the second frequency signal to manipulate ion energies. 
     
     
         17 . An apparatus for plasma processing, comprising:
 a controller;   
       a process chamber with a symmetrical plasma source configured to process a wafer with a single monolithic top electrode, the single monolithic top electrode positioned centrally within the process chamber above a bottom electrode; 
       one or more very high frequency (VHF) sources, coupled to the single monolithic top electrode via symmetrical conductors connected to a top edge of a hollow cylinder which has a bottom edge connected to the single monolithic top electrode, to generate plasma density;
 two or more isolators for isolating particular frequencies coupled to a bottom electrode of the process chamber; 
 two or more frequency matches coupled respectively, to the two or more isolators; and 
 two or more frequency generators that each generate a signal with frequencies less than 4 MHz, coupled respectively to the two or more frequency matches, the two or more frequency generators configured to dissipate energy in a plasma sheath above the bottom electrode, 
 wherein the controller is configured to control the one or more VHF sources to generate a VHF signal with a frequency greater than 30 MHz and control the two or more frequency generators to generate two or more frequency signals, 
 wherein the controller is configured to amplitude modulates a first frequency signal of the two or more frequency signals with a second frequency signal of the two or more frequency signals to produce a higher peak-to-peak voltage on a plasma sheath, and 
 wherein the single monolithic top electrode is DC grounded to the process chamber such that a symmetrical low impedance current return path for the two or more frequency signals is provided by the symmetrical conductors. 
 
     
     
         18 . The apparatus of  claim 17 , wherein the controller is configured to amplitude modulate the first frequency signal with the second frequency signal to obtain a modulation depth of approximately 0.2 to approximately 1. 
     
     
         19 . The apparatus of  claim 17 , wherein the second frequency signal has a higher frequency than the first frequency signal or wherein the second frequency signal is a harmonic frequency of the first frequency signal. 
     
     
         20 . The apparatus of  claim 17 , wherein the controller is configured to adjust a phase coherence between the first frequency signal and the second frequency signal to manipulate ion energies.