Nanoscale Roughness Effects at the Interface of Lithography and Plasma Etching: Modeling of Line-Edge-Roughness Transfer During Plasma Etching

We present 3-D modeling results on resist line-edge-roughness (LER) transfer to underlying films during plasma etching. After generating random fractal resist sidewalls with controlled roughness parameters, we model and contrast the nanoscale roughness phenomena for both resist and underlayer sidewalls in a two-layer stack using two different plasma processes in three scenarios: (1) pattern transfer; (2) resist trimming; and (3) resist trimming followed by pattern transfer. In the pattern transfer process, etching is considered ion driven and anisotropic. The protrusions of the rough, trimmed or nontrimmed, resist sidewall act as a shadowing mask for the incident ions. It is found that shadowing of ions is enough to induce the, well known by experiments, striations at the sidewalls of both the underlayer and the resist. Pattern transfer induces a decrease of rms roughness but has no important effects on the correlation length. In the trimming process, the evolution of the resist sidewall is modeled with an isotropic etching process not affecting the underlayer. The trimming process causes a decrease of the rms value of the resist sidewall and an increase of its correlation length and roughness exponent. For sufficiently long trimming times, the change of LER parameters becomes less intense. In the case of trimming followed by pattern transfer, the striations of the underlayer widen with trimming time, and pattern transfer further reduces all LER parameters. The effect of trimming on the rms roughness of the underlayer is important in the case of initially anisotropic resist sidewall. For both trimming and pattern transfer, a stronger relative reduction on rms roughness of both the resist and the underlayer sidewalls is obtained for smaller correlation length and larger rms roughness of the initial resist.