Characterization of Plasma Etch Processes for Wide Bandgap Semiconductors.

摘要

We have completed etch rate determination and plasma diagnostics using optical emission spectroscopy, mass spectrometry, and microwave measurements of average electron densities. The previous diagnostics indicate that the observed etch rate enhancement might be due to in part to an increase in the overall electron density (but not enough to account for the entire etc rate enhancement) and a probable increase in the average electron temperature (energy), both of which lead to increased dissociation of SF6 and the creation of more etch species. We have finally obtained reproducible Langmuir probe results, which show that the electron temperature does indeed increase with the addition of helium to SF6. The design of the Langmuir probe and the measurement technique have been discussed in detail in previous reports. We have found that the key to obtaining reproducible measurements ties with the cleaning procedure used between measurements. This cleaning . procedure removes any impurities that may have collected on the probe tip. This procedure consists of driving the probe tip to carry a high current in inert plasmas (e.g., argon or helium) in order to heat the probe tip to induce refractory cleaning. Plasma chemistries containing SF6 are notorious for contaminating probe tips. The cleaning procedure we have developed which gives reproducible results is given, on the next page.