AVS 58th Annual International Symposium and Exhibition
    Plasma Science and Technology Division Tuesday Sessions
       Session PS1-TuA

Paper PS1-TuA4
Model for High Aspect Ratio Dielectric Etch Process in a Capacitively-Coupled Plasma

Tuesday, November 1, 2011, 3:00 pm, Room 202

Session: Advanced BEOL / Interconnect Etching II
Presenter: Jason Kenney, Applied Materials, Inc.
Authors: J.A. Kenney, Applied Materials, Inc.
A. Balakrishna, Applied Materials, Inc.
A. Agarwal, Applied Materials, Inc.
N. Misra, Applied Materials, Inc.
S. Rauf, Applied Materials, Inc.
K. Collins, Applied Materials, Inc.
Correspondent: Click to Email

Etching of high aspect ratio (HAR) features in dielectric substrates is a challenging process, growing increasingly difficult with each new device generation. A common approach uses a multi-frequency capacitively-coupled plasma (CCP) reactor with high bias power and a dilute mixture of fluorocarbon and oxygen feed gases. Here, F atoms are the primary etchant, assisted by high energy ions to penetrate the fluorocarbon polymer layer formed by CFx radicals. [1] Oxygen atoms act to suppress excessive polymerization. The high energy ions give directionality to the etch process, with sidewalls remaining protected by the fluorocarbon polymer.

Due to the complexities involved in developing processes for each new application, many efforts have been made to model HAR etch processes (e.g., [2]). These necessarily involve at least two fundamental parts: (1) a plasma model of the CCP, which ideally includes the effects of power, generator frequencies, gas composition and flow, pressure, and reactor geometry, and (2) a model of the surface mechanism, which considers fluxes of relevant species, ion energies, and a simplified description of the competing deposition and etching processes. Complicating matters are the difficulties in obtaining systematic experimental data by which to validate either model so as to gain confidence in their predictive capabilities.

In this paper, we present models of an HAR dielectric etch process in a CCP, where the surface mechanism has been developed using experimental etch rate data generated on blanket oxide wafers. We focus on low pressure processes in an Ar/C4F6/O2 mixture, using a multi-frequency CCP with very high frequency (VHF) source and dual radiofrequency (RF) bias. Experimental data were collected for multiple pressures (15 – 80 mT), source powers (500 – 900 W), bias powers (3500 – 7100 W in different frequency mixtures), and flows of feed gases. The same processes were modeled using CRTRS, Applied Materials’ 2/3D reactor-scale plasma simulation tool, giving fluxes and energies of etch-relevant ion and neutral species. A surface mechanism based on that of Schaepkens et al. [1] was then developed, using the plasma simulation output and experimental etch rate data for calibration of parameters. Finally, this mechanism was used in a string-based feature profile evolution tool to quantify the impacts of varying the above process parameters.

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

[2] Stout et al., AVS 56th International Symposium, San Jose (2009).