Substrate bombardment with ions having targeted mass using pulsed bias phase control
A method of plasma processing includes generating plasma by coupling a source power pulse to a plasma processing chamber containing a substrate holder configured to support a substrate. The plasma includes first ions having a first mass and second ions having a second mass greater than the first mass. The ion density ratio of the second ions to the first ions is a first ratio. The method further includes delivering an energetic ion flux of second ions to the substrate by applying a delayed bias power pulse to the substrate holder after a delay between the source power pulse and the delayed bias power pulse. The delay is chosen based on the diffusion time constants of the first ions and the second ions so that the ion density ratio of the second ions to the first ions is a second ratio that is greater than the first ratio.
1 . A method of plasma processing comprising:
generating plasma by coupling a source power pulse to a plasma processing chamber containing a substrate holder configured to support a substrate, the plasma being contained in the plasma processing chamber and comprising first ions having a first mass and second ions having a second mass greater than the first mass, an ion density ratio of the second ions to the first ions being a first ratio; and
delivering an energetic ion flux of the second ions to the substrate by applying a delayed bias power pulse to the substrate holder after a delay between the source power pulse and the delayed bias power pulse, the delay being chosen based on a diffusion time constant of the first ions and a diffusion time constant of the second ions so that the ion density ratio of the second ions to the first ions is a second ratio greater than the first ratio.
2 . The method of claim 1 , further comprising:
cyclically repeating generating the plasma and delivering the energetic ion flux of the second ions.
3 . The method of claim 1 , wherein the delay is greater than about 20 μs and less than about 200 μs.
4 . The method of claim 1 , wherein a threshold ion energy of the first ions to etch a mask of the substrate is lower than a threshold ion energy of the second ions to etch a target material of the substrate.
5 . The method of claim 1 , wherein the second ions are ions of an inert species.
6 . The method of claim 5 , wherein the second ions comprise krypton (Kr).
7 . The method of claim 1 , wherein the first ions are ions of a reactive species.
8 . The method of claim 7 , wherein the first ions comprise a halogen.
9 . The method of claim 1 , further comprising:
while generating the plasma, delivering a glow phase energetic ion flux comprising the first ions and the second ions to the substrate by applying a glow phase bias power pulse to the substrate holder.
10 . The method of claim 1 , further comprising:
after generating the plasma and before delivering the energetic ion flux of the second ions, delivering an early afterglow energetic ion flux comprising the first ions and the second ions to the substrate by applying an early afterglow bias power pulse to the substrate holder.
11 . A method of plasma processing comprising:
generating plasma by coupling a first source power pulse to a plasma processing chamber containing a substrate holder configured to support a substrate, the plasma being contained in the plasma processing chamber and comprising first ions having a first mass and second ions having a second mass greater than the first mass;
collecting measurements indicative of ion density in the plasma;
calculating a delay according to ion diffusion time constants determined from the measurements, the delay being between a second source power pulse and a bias power pulse;
generating plasma comprising the first ions and the second ions by coupling the second source power pulse to the plasma processing chamber; and
delivering an energetic ion flux comprising the second ions to the substrate by applying the bias power pulse to the substrate holder after the delay.
12 . The method of claim 11 , wherein collecting the measurements comprises
applying a plurality of bias power test pulses to the substrate holder, each of the plurality of bias power test pulses causing a voltage response from the plasma, and
measuring the voltage response from each of the plurality of bias power test pulses.
13 . The method of claim 12 , further comprising:
generating plasma comprising the first ions and the second ions by coupling a plurality of source power pulses to the plasma processing chamber, the plurality of source power pulses comprising the first source power pulse; and
wherein applying the plurality of bias power test pulses to the substrate comprises
applying each bias power test pulse of the plurality of bias power test pulses after a corresponding time interval between the bias power test pulse and a corresponding source power pulse of the plurality of source power pulses.
14 . The method of claim 11 , wherein calculating the delay comprises
determining an ion diffusion time constant of the first ions and an ion diffusion time constant of the second ions by comparing the measurements to diffusion time constants predicted by the first mass and the second mass, respectively, and
selecting a delay that is greater than the ion diffusion time constant of the first ions so that the energetic ion flux comprises a ratio of the second ions to the first ions that is greater than a predetermined value.
15 . The method of claim 14 , wherein comparing the measurements to the diffusion time constants predicted by the first mass and the second mass respectively comprises comparing the measurements to the diffusion time constants predicted by the radius of the plasma processing chamber divided by the square root of the electron temperature of the plasma and multiplied by the square root of the first mass and the second mass, respectively.
16 . A method of plasma processing comprising:
generating plasma by coupling a source power pulse to a plasma processing chamber containing a substrate holder configured to support a substrate, the plasma being contained in the plasma processing chamber and comprising first ions of a reactive species having a first mass and second ions of an inert species having a second mass greater than the first mass, an ion density ratio of the second ions to the first ions being a first ratio; and
delivering an energetic ion flux of the second ions to the substrate by applying a delayed bias power pulse to the substrate holder after a delay between the source power pulse and the delayed bias power pulse, the delay being chosen based on a diffusion time constant of the first ions and a diffusion time constant of the second ions so that the ion density ratio of the second ions to the first ions is a second ratio greater than the first ratio.
17 . The method of claim 16 , further comprising:
generating plasma comprising the first ions and the second ions by coupling a previous source power pulse to the plasma processing chamber;
collecting measurements indicative of ion density in the plasma by
applying a plurality of bias power test pulses to the substrate holder, each of the plurality of bias power test pulses causing a voltage response from the plasma, and
measuring the voltage response from each of the plurality of bias power test pulses; and
calculating the delay according to the ion diffusion time constants as determined from the measurements.
18 . The method of claim 16 , wherein the first ions comprise a halogen and the second ions comprise krypton (Kr).
19 . The method of claim 16 , further comprising:
while generating the plasma, delivering a glow phase energetic ion flux comprising the first ions and the second ions to the substrate by applying a glow phase bias power pulse to the substrate holder.
20 . The method of claim 16 , further comprising:
after generating the plasma and before delivering the energetic ion flux of the second ions, delivering an early afterglow energetic ion flux comprising the first ions and the second ions to the substrate by applying an early afterglow bias power pulse to the substrate holder.