AVS 46th International Symposium
    Plasma Science and Technology Division Monday Sessions
       Session PS-MoM

Paper PS-MoM4
Investigating Ion Density and Electron Temperature Effects on Plasma Damage during Pulsed and Continuous Wave Metal Etching

Monday, October 25, 1999, 9:20 am, Room 609

Session: Plasma Damage
Presenter: K.H.A. Bogart, Lucent Technologies
Authors: K.H.A. Bogart, Lucent Technologies
J.I. Colonell, Praelux
M.V. Malyshev, Lucent Technologies
V.M. Donnelly, Lucent Technologies
J.T.C. Lee, Lucent Technologies
Correspondent: Click to Email
Plasma induced damage across gate oxides has been shown to decrease with the use of pulsed rf source power, although the basis for the reduction in damage is not yet well understood. During the pulsed plasma off time, positive ion density (n@sub i@@super +@), electron temperature (T@sub e@), and electron density generally decrease, reducing the current flux to the wafer and the potential difference across the substrate sheath. Near the end of the off time, negative ions are thought to cross the diminished sheath and neutralize charge on the wafer surface, and also to be the predominant negative charge carrier in the plasma. Langmuir probe measurements of n@sub i@@super +@ and T@sub e@ were made on a LAM 9600-PTX commercial metal etcher using blanket SiO@sub 2@, Al, and TiN films as well as during etching SiO@sub 2@-masked TiN/Al/Ti/TiN while reactor pressure (5-30 mTorr), rf source power (0-400 W), rf substrate bias power (0-200 W), pulse duty cycle (0.5 - 1), and pulse period (0.100 - 1000 ms) were varied. Plasma induced damage was quantified on wafers with 0.25 µm linewidth technology NMOS and PMOS damage testers etched under the conditions listed above. For a 50% duty cycle, 100 µs pulse period, typical I-V curves (asymmetric about zero current) were collected with substrate bias applied. Without substrate bias, I-V curves characteristic of an ion-ion plasma (symmetric about zero current) were observed from 0-15 µs and from 80-100 µs. I-V curves acquired with only substrate bias power (continuous RIE mode) were similar in shape to I-V curves taken at the end of the pulse off time with bias applied. T@sub e@'s decrease and then increase near the end of the off time, indicating that the substrate rf bias power is sufficient to sustain a plasma during the off time, and that negative ions are not able to cross the sheath. Implications for plasma damage mechanisms will also be discussed.