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

Abstract

Articles you may be interested inInfluence of ion mixing on the energy dependence of the ion-assisted chemical etch rate in reactive plasmas An ion beam etching study, designed to characterize the important kinetic and transport processes involved in the ion-assisted etching of silicon in both molecular and atomic chlorine, was performed. Monoenergetic argon ions were directed normal to a silicon wafer that was simultaneously exposed to a neutral molecular and/or atomic chlorine beam. Dissociation of the beam was induced by thermally heating the graphite tip of an effusive source via electron impact. Beam composition was characterized using a quadrupole mass spectrometer and was found to be in excellent agreement with a thermodynamic equilibrium model at the source pressure and tip temperature. Unpatterned polysilicon wafers were etched to determine the ion-induced etching yields as a function of ion energy, ion to neutral flux ratio, and neutral flux composition. A physically based kinetic model was developed to represent the yield data, incorporating chlorine adsorption, atomic to molecular chlorine surface recombination, and the ion-induced desorption of adsorbed chlorine and silicon chloride products. Feature profile etching experiments using patterned silicon wafers were also performed under ion and neutral-limited conditions of varying neutral composition. Resulting profiles were examined for aspect ratio dependent etching effects, where traditional lag was observed for features etched using an isotropically distributed background chlorine flux and inverse lag was observed for features etched with a molecular and atomic chlorine flux arriving directly from the effusive source. Microtrenching was also present in the etched features. 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. The dependence of the yield on the ion angle of incidence was also incorporated into a simulation for an isotropically distributed molecular chlorine flux and was found to have a significant impact on profile evolution as a function of the ion to neutral flux ratio. Using the simulation, atomic to molecular chlorine recombination effects were also explored as a function of the surface recombination coefficient. Predictions of the simulations were compared to experimentally derived profiles and were found to be in good agreement.

Si etching rate calculation for low pressure high density plasma source using Cl2 gas

“…Most of these experiments, however, are performed with an ion beam source and the results are also employed in etching profile simulations. [7][8][9] Thus, the ions bombarding a Si wafer is monoenergetic single ion beam ͑MSIB͒ approach. But, in a practical processing plasma source, the bombarding ion flux distribution function features a bimodal shape spreading over a wide energy range.…”

Energy dependence of ion-assisted chemical etch rates in reactive plasmas

“…These models have been found to adequately describe the dependence of the etch rate on the ion and reactive neutral fluxes for various materials etched in a wide variety of etch tools. [4][5][6] However, the question of ion energy is not explicitly addressed in these works. It is usually assumed in the literature that the etch rate varies similarly to the etch yield, e.g., according to the square root of the ion energy in the sub-keV region.…”

“…k sat Ӷ J + Y sat ͒, the dependence of ER on ion and reactive neutral fluxes is comparable to that obtained by Gottscho et al 1 This specific dependence of the etch rate on J + and J n was observed by many authors for a wide variety of materials using various type of etch tools. [4][5][6] As for the dependence of the etch rate on the ion energy, recall that, according to Steinbrüchel, 2 Y sat varies linearly with the square root of the ion energy in the sub-keV region. Therefore, Eq.…”

Numerical investigation on plasma and poly-Si etching uniformity control over a large area in a resonant inductively coupled plasma source

“…35,37 Chang and Sawin 35 measured the ionenhanced etch yield for Cl ϩ ions with background Cl or Cl 2 and observed that the etch yield increases sharply at low neutral-to-ion flux ratios ͑i.e., the neutral-limited regime͒ but gradually saturates at high flux ratios ͑i.e., the ion-limited regime͒. Levinson et al 37 reported similar results for etching by Ar ϩ /Cl 2 . In our simulations presented in the next section, the minimum ratio of neutral to ion fluxes on the substrate is beyond 100 and therefore the etching processes are in the ion-limited regime.…”