Paper PS1-TuA9
Chemical Mechanisms for Dielectric Product Development

Tuesday, November 1, 2011, 4:40 pm, Room 202

Smaller technology nodes in the semiconductor industry place increased emphasis on etch productivity requirements, such as etch rate and critical dimension. Modeling and simulation is playing a central role in new developments (design of new hardware and exploration of novel processing options) to address the concurrent demand for improved performance and shorter development cycle. Validation against experimental data is a critical step in making these models a mature development tool. Monte Carlo, level set and string based feature scale models have been used to investigate processing issues within nanoscale features. Due to the complexity of surface and sub-surface processes, these models generally use empirically developed mechanisms which fit the model predictions to measured profiles and film characteristics. In this paper, we apply and refine the above method to develop a validated dielectric etch mechanism and feature scale model.

We obtained experimental data for etching of blanket SiO₂ wafers in a c-C₄F₈/O₂/Ar plasma over a wide range of pressures (25-150 mTorr), bias powers (500-1500 W), and c-C₄F₈ and O₂ flows in a dual-frequency capacitively coupled plasma etcher. The etch rate increased with bias power and c-C₄F₈ flow rate, weakly decreased with increasing O₂ flow rate, and moderately increased with pressure. The reactor scale simulations were performed using CRTRS, a 2/3-dimensional fluid plasma model. The plasma simulations provided fluxes of various fluorocarbon polymerizing species, atomic oxygen and atomic fluorine. We also calculated fluxes and energies of the ions impacting the wafer. These values were used to calibrate an etch mechanism, whose main features are (a) a polymer thickness determined by the balance between polymer deposition (by C_xF_y species) and polymer removal (by ion sputter and O etch), (b) an exponential decay in ion energy through the polymer, and (c) reactive ion etching at the polymer-dielectric interface.[1] The etch rates and their trends with bias power, c-C₄F₈ flow rate and O₂ flow rate were captured well in this model. The calculated polymer thicknesses also exhibited the expected trends, decreasing with bias power and O₂ flow rate and increasing with c-C₄F₈ flow rate. Our mechanism was not able to capture the etch rate trends with pressure, which is likely due to deficiencies in our plasma chemistry mechanism for Ar/c-C₄F₈/O₂ gas mixture. Finally, the calibrated mechanism was used in a string based feature profile model to investigate the influence of control parameters on dielectric etch process in a dual-frequency capacitively coupled plasma tool.

[1] Schaepkens et al, JVST A, 17, 26 (1999).