Correlation of roughness and device properties for hydrogen plasma cleaning of Si(100) prior to gate oxidation

Hydrogen plasma treatment was used as a cleaning and conditioning step prior to gate oxide deposition in the fabrication of cluster-based MOS field effect transistors. Surface roughness was measured by atomic force microscopy and compared to current-voltage characteristics of the MOSFET devices. The MOSFET devices were evaluated on the basis of threshold voltage, peak mobility, interface scattering, and surface roughness coefficient. Following a 10 minute H-plasma exposure at a substrate temperature of 150°C the rms roughness increased from 1.1±0.3 angstrom to 17±9 angstrom. The rms roughness for samples treated for 10 minutes at 700°C was 4±1 angstrom. Analysis of the MOSFET devices treated in the low temperature range (200°C) show significant degradation due to the H-plasma interaction. Threshold voltage for the devices exposed to a 2 minute H-plasma at a temperature of 200°C was 0.72±0.02 V. In contrast the threshold voltage for the 600°C, 2 minute plasma exposure was 0.86±0.03 V. The peak mobility for those devices was 370 cm ²/V·s. Further device analysis was accomplished from the current-voltage measurements to extract a value of interface scattering and surface roughness scattering for each device. Interface scattering and surface roughness scattering do not increase for H-plasma process temperatures of 450 - 700°C. An H-plasma treatment for 2 minutes at 500°C also resulted in no observable increase in rms roughness, a threshold voltage of 0.92±0.03 V, a peak mobility of 410 cm ²/V·s, and no increase in interface scattering and surface roughness scattering.