Surface reaction mechanisms in plasma etching processes.

摘要

Plasma etching is an essential process in the fabrication of submicron features in the semiconductor industry. Plasma-surface interactions in plasma etching processes are capable of influencing bulk plasma properties as well as determining etch rates and feature profiles. To address the coupling of plasma and surface processes, the Surface Kinetics Model (SKM) was developed and was linked to the Hybrid Plasma Equipment Model (HPEM), a two-dimensional, modularized simulation tool addressing low temperature plasma processing. The SKM accepts reactive fluxes to the surface from the HPEM and generates the surface species coverages and returning fluxes to the plasma by implementing a modified site-balance algorithm. The integration of the SKM and the HPEM provides a self-consistent simulation of plasma chemistry and surface chemistry.; The integrated plasma-surface model was used to investigate surface reaction mechanisms in fluorocarbon plasma etching. Fluorocarbon plasmas are widely used for silicon and silicon dioxide etching in microelectronics fabrication due to their high etch rates and good selectivity. One characteristic of fluorocarbon plasma processing is that a polymeric passivation layer is deposited on surfaces during etching. Since the passivation layer limits species diffusion and energy transfer from the plasma to the wafer, the etch rate and selectivity are sensitive to the steady state thickness of the passivation. This polymerization process was investigated. The polymer layer grows by CxFy radical deposition and is consumed by ion sputtering and F atom etching. During SiO2 etching, oxygen atoms in the substrate also etch the polymer. The steady state thickness of the polymer is achieved as a result of a balance between its growth and consumption. The polymerization kinetics relies on the plasma properties, such as ion bombarding energy and the ion-to-neutral flux ratio, which are determined by process conditions. Relationships between process parameters, plasma properties, polymer thickness, and etching kinetics were investigated in both silicon and silicon dioxide etching. It was demonstrated that processes with thinner passivation provide higher etch rates. The SiO 2 etching process was also investigated with a feature scale model, the Monte Carlo Feature Profile Model (MCFPM). Tapered profiles were obtained with strong sidewall passivation.; Surface reactions occurring in fluorocarbon plasmas also influence plasma properties by consuming or generating plasma fluxes. Of particular interest is the effect that surfaces have on CF2 densities, as CF2 is a precursor for polymer formation. These processes were investigated with the integrated plasma-surface model. Simulations demonstrated that CF 2 self-sticking is a loss at the surface, while ion sputtering and large ion dissociation can generate CF2 at surfaces. The net effect of the surface depends on the relative magnitudes of the loss and generation reactions.