Two-step cycling process alternating implantation and remote plasma etching for topographically selective etching: Application to Si₃N₄ spacer etching

This article proposes an original method to achieve topographically selective etching. It relies on cycling a two-step process comprising a plasma implantation step and a removal etching step using remote plasma source process. Both steps can be achieved in the same reactor prototype chamber, which has the capability to produce both capacitively coupled plasma and remote plasma (RP) discharges. It is shown that in RP processes, an incubation time exists before the etching starts. The introduction of a plasma implantation step prior to the RP step allows us to selectively functionalize the horizontal surfaces of the material with respect to the vertical surfaces, thanks to the ion directionality. The modifications induced by the implantation allow us to modify the incubation time between an implanted and a nonimplanted material offering a process window with infinite etch selectivity between horizontal and vertical surfaces. This approach has been demonstrated on Si3N4 blanket films with the perspective to be applied to the Si3N4 spacer etching process in which etch selectivity is a key issue. For this particular application, a cycling process comprising an H2 plasma implantation and a He/NH3/NF3 remote plasma process has been developed. The H2 implantation modifies the Si3N4 surface state by incorporating oxygen contaminants coming from the reactor wall and creating dangling bonds. This surface functionalization considerably reduces the incubation time. New insights into the etching mechanisms of Si3N4 films exposed to NH3/NF3 remote plasma are proposed and explain why the presence of Si–O bonds is mandatory for the initiation of the etching.