CMOS gate oxide defects induced by pre-gate plasma process

Plasma processes used for strip resist and etch oxide in CMOS technologies may degrade the quality of the silicon surface if it is protected of the plasma by a too thin oxide capping. Using AFM measurements, we have identified this degradation as a silicon roughness increase. The degradation mechanism can be understood like an uncontrolled plasma oxidation of the silicon. Next, if gate oxidation is performed after such plasma treatments, the gate oxide will show defects at the oxide/silicon interface. The consequence will be a poor reliability when negative electrical bias is applied on CMOS gate. Finally, the damaged silicon layer can also be efficiently removed by performing a sacrificial oxidation.