A novel method to eliminate the toppling issue for small CD/high AR/dense structures

Toppling during clean process is a general structure issue when we scale down critical dimension (CD)/increase aspect ratio (AR) and density of the nano structures. In this paper, we demonstrated a novel process with CH₄ PLAD (plasma doping) conformal process to eliminate the toppling issue. A uniform C deposition layer from CH₄ PLAD process wrapped the whole structure on the top/bottom/sidewall and made structure more robust during clean process. As a result, the toppling issue could be eliminated. The PLAD condition should be chosen in the “highly collisional case” in order to maximize deposition and minimize implant. ARXPS (angle resolved X-ray photoelectron spectroscopy) and PDP1 (plasma device planar 1D) simulation were applied to define the “highly collisional case”. There was a strong correlation between implant dose and toppling reduction rate. Besides CH₄ PLAD, other neutral species such as GeH₄ PLAD may also be used for this process. The advantages of this process include no thermal Dt, fast throughput and low cost. It may help us to continue scaling down the structures with higher AR/smaller CD/higher density.