COMPARISON OF ADVANCED PLASMA SOURCES FOR ETCHING APPLICATIONS .2. LANGMUIR PROBE STUDIES OF A HELICON AND A MULTIPOLE ELECTRON-CYCLOTRON-RESONANCE SOURCE

Radial profiles of electron temperature, electron density, and ion cur rent density near the wafer surface are presented for a rf-inductively coupled helicon and a multipole electron cyclotron resonance source a s a function of applied source power, applied rf-bias power, and react or pressure. Both sources show similar trends with respect to changing process conditions, with electron densities in the mid 10(11) cm-3 ra nge and electron temperatures between 5.5 and 6.5 eV. An increase in a pplied source power results in an increase in both electron density an d ion current density as expected. An increase in applied rf-bias powe r results in a 10% change in the measured electron density and ion cur rent density; however, the electron temperature shows a much stronger dependence, indicating that ion flux and ion energy are not completely independent. Radial uniformity is similar in both sources, with the h elicon exhibiting better uniformity at the conditions explored. Neithe r applied source power nor rf-bias power significantly affect radial p lasma uniformity above the wafer in both sources, but higher reactor p ressure does degrade uniformity in the helicon. We attribute this to t he 2:1 geometric expansion between the upper antenna section and the l ower plasma confinement section where the measurements are taken. The conditions resulting in optimum radial uniformity of electron temperat ure, electron density, and ion current density are similar to those fo r the optimum etching rate uniformity measured in previous studies; ye t the uniformity obtained from the Langmuir probe diagnostic is not af fected by changing process conditions to the degree that etching unifo rmity is affected. This can be a result of the difference in chemistry between the two studies since hydrogen bromide was used for etching a nd argon was used for Langmuir probe measurements. It may also indicat e that the correlation between plasma uniformity and etching uniformit y is relatively weak or second order compared to other variables affec ting uniformity such as rf bias of the wafer.