Investigation of the influence of hardmask morphology on bowing effect in nano-scale silicon plasma etching process

Bowing is one of plasma etching effects that negatively impact device performance. Although there has been plenty of research work on micro-feature surface etch modeling to investigate bowing effect, limited research has been reported on the influence of hardmask morphology on bowing effect. In this paper, we present a plasma etching model based on Monte Carlo simulation with cellular method in order to simulate the feature profile evolution of etching process in nano-scale. The relationship among hardmask angle, open CD and distribution of reflected ion flux on the sidewall from the opposite hardmask was calculated. The reflected ion flux was heavily concentrated in the upper part of the sidewall in the case of a tapered hardmask, and this was the main mechanism of the bowing formation. This model considers chemical reactions and a novel particle reflection algorithm which is a prominent mechanism. This model is capable of reproducing the feature in periodic dense trenches with dimension of tens of nanometers. The hardmask morphology considered in our study includes hardmask angle (θ) and pattern (CD and pitch). As the hardmask angle decreases, the bowing becomes severe, when CD equals to 90nm and θ equals to 70°, the bowing deviation (D=(W-CD)/2) and relative deviation (Δ D=D/CD×100 %) are 23.86nm (26.51 %). In contrast, as the CD increases, the bowing becomes slight. However, bowing moves toward the bottom of the hole as the CD increases. When CD equals to 150nm and θ equals to 70°, the bowing deviation is 18.95nm (12.63 %). Accordingly, a vertical hardmask is very important for a small CD trench.