Acid-Based Etching of Silicon Wafers: Mass-Transfer and Kinetic Effects

Abstract

A study to understand the transport and kinetic effects in three‐phase, acid‐based wet etching of silicon has been accomplished. Reactants overcome the liquid‐phase mass‐transfer resistance and the kinetic resistance to complete the reaction. The gaseous bubbles formed by the reaction adhere to random sites on the surface and thus, mask a fraction of the surface from the reactants. This bubble masking effect is modeled as the bubble transport resistance that acts in parallel with the liquid‐phase mass‐transfer resistance. These transport effects are lumped into an effective mass‐transport resistance, which acts in series with the kinetic resistance. It is shown that the etched surface morphology is a function of the ratio of the effective mass‐transport resistance to the kinetic resistance. A rough surface is a field of peaks and valleys. It is theorized that under mass‐transfer influence, etch rates at peaks are higher than etch rates at valleys. Hence, the surface is chemically polished. It is shown that the polishing efficiency increases with increasing ratio of mass‐transfer resistance to the kinetic resistance, reaches a maximum, and then decreases. Effects of mass‐transfer and kinetics on the surface roughness and gloss are explained by both the developed phenomenological model and experimental data. © 2000 The Electrochemical Society. All rights reserved.