HF Based Solutions for HfO2 Removal; Effect of pH and Temperature on HfO2:SiO2 Etch Selectivity

摘要

High-k gate material (HIK) like hafnium oxide (HfO2) and its combination with aluminum (Al) or silicon (Si) emerged as promising candidates for replacing silicon dioxide (SiO_2) in the gate structure. Patterning is one key point on this long way from theoretical idea till practical implementation into an integration device. Specification imposed on silicon substrate recess, under 1 nm, is enough to explain the importance of this step. Conventional dry etch processes lacks the adequate selectivity, mostly due to the physical sputtering component required to remove a metal oxide. Also wet approaches only, performed on annealed HfO2 layer, do not bring viable solutions to be transferred into production. The preferred route, to pattern the HIK layer selectively towards SiCb, is a combination of both approaches [1, 2]. As such, the wet removal is not applied on a polycrystaline surface but on a damaged and/or thinned amorphous HfO2 one. Among few chemistries proposed to etch the HIK-layer, the HF based solutions are the preferred candidates [3, 4], We are reporting here our approach to develop a HF solution highly selective towards a SiOi layer. This has been done based on identification and control of the active species responsible for removal.