Atomic Layer Etching of III-Nitride Semiconductor Films

Student’s name: Hajo Johann Wise Home Institution: Rochester Institute of Technology NNCI Site: CNF @ Cornell University REU Principal Investigator: Professor Huili Grace Xing REU Mentor: Dr. Xinwei Wu Abstract: III-nitride semiconductors offer unique advantages in the manufacturing of high-voltage field effect transistors (FETS). However, production of nanoscale III-nitride FETs requires precise etching of III-nitride semiconductor films. We identified atomic layer etching (ALE) as an ideal technique for this application. ALE weakens the bond between a film and its surface layer via a chemical reaction with a reagent gas or plasma. The reagent is then purged, and the surface is bombarded with non-reactive ions. These ions impart enough energy to sputter away the reacted surface layer, but not enough to remove unreacted material underneath. These self-limiting characteristics make it possible to remove just a few atomic layers at a time. To adapt and characterize ALE for the processing of III-nitride films, samples with gallium nitride (GaN), aluminum nitride (AlN), and aluminum-gallium nitride (AlGaN) films were etched in the Cornell Nanoscale Facility’s (CNF) Plasma-Therm Takachi ALE tool. Critical etch metrics such as surface roughness, film thickness, etch rate, and etch selectivity were monitored with various metrological tools. These included CNF’s Veeco Icon Atomic Force Microscope (AFM), Zeiss Ultra Scanning Electron Microscope (SEM), KLA P-7 Profilometer, and Woollam RC2 Ellipsometer. Initially, samples were processed via traditional reactive ion etching (RIE) due to the lack of a functional ALE recipe. Data from these trials matched expected RIE etch rates of 30-40 nm/min, and an expected etched surface roughness of approximately 2 nm root-mean-squared (RMS). When an ALE recipe became available, samples were processed and analyzed. The results of these trials are not available at the time of writing. To give context, typical ALE processing can be expected to remove single-digit nanometer layers of material per etch cycle while producing a surface roughness below 1 nm RMS. With the results of these experiments, researchers will be able to more successfully and consistently produce III-nitride based FETs.