Characteristics of in_0.7Ga_0.3as MOS capacitors obtained using hydrochloric acid treatment, ammonium sulfide passivation, methanol treatment, and forming gas annealing

This paper proposes a chemical pre-treatment process to reduce sulfate prior to atomic layer deposition of Al₂O₃ gate dielectrics on n-doped In_0.7Ga_0.3As layers to form metal oxide semiconductor capacitors (MOSCAPs). Cleaning with methanol was done after hydrogen chloride etching and ammonium sulfide passivation. X-ray photoelectron spectroscopy performed on the sample with methanol cleaning indicated that its native oxide regrowth was effectively prevented on the sulfur-passivated In_0.7Ga_0.3As surface under air exposure. By analysis using atomic force microscopy of the sample cleaned using methanol, no further increase of surface roughness was observed after 5 months of air exposure. In addition, a mid-gap interface defect density (Dit) of 1.3 × 10¹² cm⁻² eV−¹ was obtained from this sample. After forming gas annealing (FGA), the D_it was improved significantly, to a value below 10¹² cm⁻² eV−¹. The obtained data indicate that the combination of chemical pre-treatment and FGA is advantageous to passivating the trap states on In_0.7Ga_0.3As MOSCAPs.