The effect of the Si-SiO2 interface microroughness on the electron channel mobility of n-MOSFET's was investigated. In this experiment, the surface microroughness was controlled by changing the mixing ratio of NH4OH in the NH4OH-H2O2-H2O solution in the RCA cleaning procedure. The gate oxide was etched, following the evaluation of the electrical characteristics of MOS transistors, to measure the microroughness of the Si-SiO2 interface with scanning tunneling microscope (STM). As the interface microroughness increases, the electron channel mobility, which can be obtained from the current-voltage characteristics of the MOSFET, gets lowered. The channel mobility is around 360 cm2/V – s when the average interface microroughness (Ra) is 0.2 nm. where the substrate impurity concentration is 4.5 x 1017 cm-3, i.e., the electron bulk mobility of 400 cm2/Vs. It goes down to 100 cm2/Vs when the interface microroughness (Ra) exceeds 1 nm. This series of studies has made it clear that the microroughness of the Si-SiO2 interface must be improved in order to increase the transconductance of MOS transistors to get better speed performance as well as the reliability of thin gate oxides.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Electrical and Electronic Engineering