Characteristics of chlorine, transformer-coupled pulsed plasmas are reported. Time dependencies of electron (ne), positive ion (n+ i), and negative ion (n- i) densities and electron temperatures (Te) were measured with a Langmuir probe and microwave interferometry at 240 and 500 W input powers, and pressures between 3 and 20 mTorr. During the OFF portion of the power modulation, ne decreases rapidly as Cl- is formed by dissociative attachment of Cl2. The formation of Cl- is accelerated at high Cl2 densities (at high pressures and low powers). At 10 mTorr and higher pressures, an ion-ion plasma forms near the end of the OFF portion of the cycle, the sheath collapses, and Cl- reaches the wafer. Te decays rapidly in the OFF period and increases with a similar time constant at the beginning of the ON cycle if electrons are present at a sufficiently high level. If ne is very low at the beginning of the ON cycle, such as at high pressure (10 mTorr), then Te exhibits a spike at the beginning of the ON period. In a comparison study, plasma induced damage is reduced when aluminum is etched under similar source power modulation conditions.
ASJC Scopus subject areas
- Physics and Astronomy(all)