Improved gate-edge profile of metal/high-k gate stack using an NH3 ashing process in gate-first CMOSFETs

This study analyzed an alternative ashing technology for removing photoresist in the production of gate-first complementary metal oxide semiconductor field effect transistors (CMOSFETs) with a high-k metal gate stack. NH3 ashing is proposed as an alternative to O-2 ashing to improve the gate-edge profile. It was found that NH3 ashing suppresses bottom oxide growth below the thin HfO2 layer, reducing Si recesses in the source/drain active area, and eliminating bottom oxide encroachment into the gate edge. The NH3 ashing process also makes the HfO2 film more resistant to the wet chemistry, which reduces the high-k undercut beneath the metal gate during the high-k removal process. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.2131243] All rights reserved.