A Method for Effective Work Function Monitoring

Abstract

Monitoring of the effective work function (EWF) is proposed that involves quantification of the flatband voltage early during metal gate fabrication process by a non-contact micro corona-Kelvin, enabling faster feedback than traditional MOS capacitor based measurements. Two key elements are: 1. corona charging and 2. Kelvin probe force microscopy, KPFM. The surface voltage decay after corona charging is measured with KPFM under modulated light enabling parameter free extraction of the flatband voltage, VFB and EWF. Results for n- and p-type metals show excellent correlation with end of line CV measurements. The micro corona-Kelvin method allows quantification of two more EWF sensitive parameters: silicon surface potential barrier and the tunneling barrier at the metal / high-k dielectric interface. Results for n- and p-type metals are consistent with the expected behavior.