Microwave Plasma-Assisted Reactive HiPIMS of InN Films: Plasma Environment and Material Characterization
A scientific collaboration between Bern University of Applied Sciences (BFH), École Polytechnique Fédérale de Lausanne (EPFL), Swiss Federal Laboratories for Materials Science and Technology (Empa, Thun & Dübendorf) and TOFWERK, focused on development of a low temperature fabrication process for InN thin films via microwave plasma- assisted reactive high power impulse magnetron sputtering (MAR-HiPIMS).
In situ- and ex situ- diagnostics techniques characterized the influence of the microwave plasma on the HiPIMS discharge process at various nitrogen flows and microwave powers. Measurements have shown the microwave plasma enhances the dissociation/activation of nitrogen species and supplies seed electrons to the magnetron discharge plasma.
A TOFWERK TOFMS Process Analyzer combined with a Langmuir probe from Impedans Ltd. were used to simultaneously measure the mass and the energy distribution of all the species present during the MAR-HiPIMS process as well as the plasma potential and current. As such, the identification of the species plasma origin and their temporal behavior in conjunction with the relevant plasma electrical parameters was possible. In addition, use of the TOF analyzer allowed for the determination of origin for the detected species – generation from the HiPIMS discharge or the microwave plasma.
The TOFWERK Process Analyzer detected all process relevant species such as Ar+, Ar2+, N2+, N+ and In+ and allowed classification of their energy distribution into three energy/charge categories: E/Q low, mid, and high.
In the study, it was determined that the low and high E/Q come from HiPMS discharge, where the time profiles show an increase in In+ ions near the end and after the end of the pulse. For low E/Q , an increase in argon and nitrogen species was also observed. The mid E/Q ions were determined to be generated within the microwave plasma.
This work demonstrates integration of a TOFWERK Process Analyzer and a Langmuir probe allows for in-depth characterization of the MAR-HiPIMS sources, permitting time resolved measurements of the plasma properties. In addition the chemistry, energy distribution, and origin of the various process species were characterized.