Ion-assisted etching and profile development of silicon in molecular chlorine

Abstract

Influence of ion mixing on the energy dependence of the ion-assisted chemical etch rate in reactive plasmasAn ion beam etching study designed to characterize the kinetic and transport processes important in the ion-assisted etching of silicon in molecular chlorine was performed. Monoenergetic argon ion beams were directed normal to a silicon wafer that was simultaneously exposed to a background of molecular chlorine, thereby simulating a low temperature rf plasma etching process. The ion-induced etching yield scaled with the square root of the ion energy for a surface saturated with adsorbed chlorine. Moreover, the yield was found to depend strongly on the ion to neutral flux ratio which was varied over two orders of magnitude. A kinetic model in which the dissociative sticking probability and the yield scale linearly with surface coverage was developed and was found to be consistent with the yield data in the ion energy range of 90-300 eV. Its applicability to etching topography was tested with additional experiments where patterned silicon wafers ͑with oxide masks and with a range of features and linewidths͒ were etched at saturation in the apparatus. Minimal lag effects and some microtrenching and sidewall sloping were encountered. The etching selectivity of silicon over oxide at 100 eV was greater than 30. Computer simulations of the etching process and profile development were performed using the kinetic model and a line-of-sight re-emission model for the chlorine transport. Knudsen diffusion was found to be important in the transport of neutrals to the base of the feature, with the aspect ratio dependence of the etch rate becoming significant only at high values of the ion to neutral flux ratio. The agreement between simulation and experiment was good, with the initial sticking probability on a clean surface and the average product stoichiometry as parameters comparing favorably to published results. However, the observed microtrenching and sidewall sloping were not predicted by these simulations.

Photo-assisted etching of silicon in chlorine- and bromine-containing plasmas

“…The ion-assisted etching threshold of E 1 ¼ 28 eV for the Cl 2 /Ar plasma found in this work is between the value of 42 eV reported by Levinson et al, 25 for Ar þ and Cl 2 beams, and the 16 eV threshold found by Chang et al 23 for Ar þ and Cl beams. This could be due to the fact that, in the present work, both Cl and Cl 2 are impinging of the surface.…”

“…Note that there are very few ions with energies above the lowest reported threshold of 16 eV for ion-assisted etching of Si. [23][24][25] Unless otherwise stated, 50% halogen/50% Ar gas mixture plasmas were operated at 400 W rf power and 60 mTorr. When two halogen-containing gases were used, they were mixed in equal amounts (e.g., the HBr/Cl 2 /Ar plasma was 25% HBr, 25% Cl 2 and 50% Ar by volume).…”

Effect of Mask Erosion on Patterning of FePt for Heat-Assisted Magnetic Recording Media Using Embedded Mask Patterning

“…In part III we present the simulation result and discussion showing that how ion sputtering yield, etch selectivity and control of hard mask erosion play important role to the formation of isolated columnar FePt grains. The basic ion-neutral synergy etch model based on Langmuir isotherm adsorption kinetics is widely used to describe the plasma etch mechanism [9,11,12]. Bailey et al also proposed a synergy model with etch inhibition [11] using both neutral coverage and inhibition coverage as independent variables.…”

Model-based etch profile simulation of PSM films

“…3 Levinson applied this model to chlorine etching of Si. 4 Toward the goal of understanding PSM etch, we developed an etch simulation model for photomasks based on these prior efforts.…”