Plasma etch selectivity study and material screening for Self-Aligned Gate Contact (SAGC)

Self-Aligned Gate Contact (SAGC) integration is design based on formation of the two separate contacts to the source/drain (S/D) and to the gate (G), which are realized in two separate plasma etch steps. Essentially, the first one is the contact plug (CP) etch over S/D contact selective to the gate plug (GP) and sidewall spacer (SWS), and the second one is the gate plug (GP) etch selective to the contact plug (CP) and the sidewall spacer (SWS). Therefore, the high selectivity plasma etch processing for the CP and GP towards the other two relevant, neighboring films is a key requirement for successful SAGC integration. In this paper we present plasma etch process development required for SAGC implementation, primarily focusing on the multi-color selectivity studies, i.e., selective CP (towards GP and SWS) as well as selective GP (towards CP and SWS) at contacted poly pitch (CPP) 42nm. The primary ('standard') integration scheme uses SiO2 CP, Si3N4 GP and SiCO SWS. Furthermore, we investigate the " alternative' integration scheme with SiCxNy films as replacement of the traditionally used SiO2 CP material aiming to simplify the patterning sequence and ease high selectivity requirements. We report the selectivity values obtained on the CP/GP/SWS multi-color stack for the CP plasma processing (SiO2 or SiCxNy) towards Si3N4 and SiCO; as well as for GP (Si3N4) plasma dry etch process towards SiO2 or SiCxNy and SiCO. Using a Quasi-ALE (Q-ALE) approach for selective SiO2 etch process is developed with a selectivity of 8 to 1 towards Si3N4 and SiCO. For the selective Si3N4 etch continuous wave plasma CH3F-based process is developed and selectivity of 9 to 1 towards SiO2 and SiCO achieved. In the case of the integration scheme with SiCxNy CP, the selectivity for SiCxNy etch towards Si3N4 GP and SiCO SWS higher than 20 to 1 is accomplished using continuous RF source NF3/O-2-based process. As for the Si3N4 plasma etch in the 'alternative' scheme using CH3F/O-2-based process, the selectivity towards SiCxNy of higher than 20 to 1 and selectivity to SiCO of around 10 to1 is achieved.