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 SiO 2 CP, Si 3 N 4 GP and SiCO SWS. Furthermore, we investigate the “alternative’ integration scheme with SiCxNy films as replacement of the traditionally used SiO 2 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 (SiO 2 or SiC x N y ) towards Si 3 N 4 and SiCO; as well as for GP (Si 3 N 4 ) plasma dry etch process towards SiO 2 or SiC x N y and SiCO. Using a Quasi-ALE (Q-ALE) approach for selective SiO 2 etch process is developed with a selectivity of 8 to 1 towards Si 3 N 4 and SiCO. For the selective Si 3 N 4 etch continuous wave plasma CH 3 F-based process is developed and selectivity of 9 to 1 towards SiO 2 and SiCO achieved. In the case of the integration scheme with SiC x N y CP, the selectivity for SiC x N y etch towards Si 3 N 4 GP and SiCO SWS higher than 20 to 1 is accomplished using continuous RF source NF 3 /O 2 - based process. As for the Si 3 N 4 plasma etch in the ‘alternative’ scheme using CH 3 F/O 2 -based process, the selectivity towards SiC x N y of higher than 20 to 1 and selectivity to SiCO of around 10 to 1 is achieved.