Effect of chemical treatment on III-nitride surface characteristics

Surface cleaning has a significant influence on the overall performance and reliability of semiconductor devices. Like other advanced semiconductor device technologies, III-nitride device technology, most likely will require multiple processing/regrowth steps and several photolithography/dry etching steps to define active device areas. The surface used for epitaxial regrowth, deposition of gate dielectrics, or Ohmic/Schottky metal deposition must be clean and smooth for the fabrication of high quality electronic and photonic devices. This surface cleaning will include the removal of native oxides, organic contaminants, metallic impurities, particulates and chemical residuals.; In this study, various surface-cleaning techniques for the removal of carbon (C) and oxygen (O) from AlN and GaN were investigated. The utility of various cleaning techniques was assessed by chemical, structural and electrical characterization. Auger electron spectroscopy (AES) analysis showed that ex-situ UV/O₃ and wet chemical treatments based on HF and HCl were very effective in removing surface C and reducing the native oxide on both AlN and GaN. After H₂ and N₂ plasma treatments in ultra high vacuum (UHV) at temperatures of 750°C and 900°C, clean GaN surfaces could be achieved within the detection limits of AES. However, secondary ion mass spectroscopy (SIMS) analysis showed that significant concentrations of surface C and O still exist on plasma treated GaN. Further in-situ cleaning methods were performed to obtain clean GaN and AIN surfaces using chemical beam-etching techniques at various temperatures. SIMS and current-voltage (I-V) results showed that PCl₃ chemical beam treatment at 500°C on GaN surface was the most successful in removing the interfacial oxide. This removal of the surface oxide from the GaN substrate may improve the quality of the regrown GaN and allow better quality growth of AlN gate dielectrics.; Also, the effect of annealing on the behavior of GaN Schottky diodes was investigated. Rapid thermal annealing experiments were performed in N ₂ ambients for 30 sec at temperatures of 500 to 1000°C. Only annealing at temperatures ≥900°C significantly degraded the Schottky diode characteristics. This degradation is believed to be due to the preferential loss of surface nitrogen. Ozone/HCl surface chemical treatments were only partially successful in repairing the thermal damage. The sample exposed to N₂ plasma at 750°C after being thermally damaged showed the worst Schottky diode characteristics due to the highly increased surface nitrogen vacancies, while PCl₃ exposure removed the thermally damaged surface.