Plasma-surface kinetics and feature profile evolution in chlorine etching of polysilicon

Abstract

Chlorine-based plasma etching of polysilicon was characterized as a function of the impinging Cl+, Cl–to–Cl+ flux ratio, ion bombardment energy, ion bombardment angle, and the flux of etching by-products (SiCl2) using a multiple beam scattering apparatus. The ion-enhanced etching yield was a strong function of the neutral-to-ion flux ratio, and scaled linearly with the square root of the ion energy. The ion-enhanced etching yield was independent of the ion bombardment angle at near normal ion incidence angles, but decreased almost linearly above 40° off-normal angles. The presence of SiCl2 greatly suppressed the etching of polysilicon by either Cl+ or Cl+ with Cl. A Monte Carlo based profile simulator was constructed which incorporated the dominant reaction mechanisms of surface chlorination under ion bombardment, surface re-emission, and ion reflection. The profile evolution of patterned samples etched by Cl and Cl+ beams were simulated. Quantitatively good agreement was found between the simulated profiles and the measured profiles. A sensitivity analysis of the recombination probability of Cl on photoresist suggested that the recombination of atomic chlorine on the photoresist had a significant impact on the profile evolution.

A Model Analysis of Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 Plasmas

“…13) Note that eq. (3) represents the local etch rate as a function of the ion flux À i 0 and the neutral flux À n 0 , resulting in etched profiles that are varied by changing neutral-to-ion flux ratio À n 0 =À i 0 .…”

Profile simulation model for sub-50 nm cryogenic etching of silicon using SF6/O2 inductively coupled plasma

“…47 The ion-assisted etching yield decreases with off-normal ion incident angles. 40,42,43 This is partially due to the ion reflection phenomenon, which in turn depends on the target surface state. 48 Hence, Eq.…”

“…41 Moreover, the mass of the ion as well as its incident angle and energy also have an impact on the ion reflection number efficiency and the ion reflection energy efficiency. Ion-assisted chemical etching of silicon depends on the ion incident angle, 42,43 where the etching yield curve is fairly flat and decreases monotonically with off-normal angle. In the model, we are taking into account the fact that the effective ion flux decreases with the incident angle (Lambert's cosine law).…”

A plasma etching perspective of patterning novel materials and small structures

“…Amongst various techniques, Direct Simulation Monte Carlo (DSMC) methodology is a robust and accurate one to model the profile evolution of plasma etching. [16] As shown in Figure 3 (a), the discretized simulation domain spans between the centerlines of the photomasks which define the trench to be etched. A two-dimensional simulation was performed within this domain with periodic boundary conditions.…”