Paper PS1-TuM5
Characterization of Pulsed Plasma Etch Reactors with an Integrated Global Plasma-Feature Scale Model

Tuesday, October 19, 2010, 9:20 am, Room Aztec

Uniformity requirements (both etch rate and critical dimensions) for plasma etching of very small features (< 32 nm) are more stringent than ever. One particular challenge is minimizing feature distortion due to plasma induced damage. If the feature aspect ratio is high, via-like features in dielectric materials may physically twist/turn due to the stochastic nature of fluxes entering the feature as the size of the opening shrinks [1]. Limited quantity of polymer on the sidewalls exaggerates this feature distortion. Pulsed plasma operation is a promising approach to improve uniformity while reducing feature distortion [2]. Although pulsing of both capacitively and inductively coupled plasma (CCP/ICP) sources has been investigated before, novel pulsing schemes such as synchronously pulsed ICPs allow for expanded operating regime for damage-free etching of nanoscale features.

In this paper, pulsed and continuous plasma operation of an ICP reactor in electronegative gas mixtures will be discussed using results from a computational investigation. Earlier investigations [3] have linked a 2-dimensional plasma equipment model (HPEM) to a Monte Carlo feature profile model to assess the consequences of pulsed plasma operation on etching. Long computational times restricted the range of conditions that could be investigated, e.g. more complex chemistries or lower pulse frequencies. We have addressed this constraint by using a global plasma model (Zephyr) combined with analytical expressions for behavior in the sheath. The global plasma model is based on the methods described by Meeks et al [4]. This model calculates all the species (neutrals, ions and electrons) concentrations and their temperatures using time-dependent conservation equations, including both gas and surface reactions. The impact of different surface materials on plasma chemistry is also captured. The global plasma model is validated using more detailed 2-dimensional plasma modeling and experimental diagnostic results for simple chemistries (Ar, O₂). The validated model is then applied to pulsed plasmas of highly electronegative chemistries used for silicon etching (Cl₂ and HBr based). Results will be discussed for impact of pulse characteristics such as duty cycle, pulsing frequency, and phase lag between source and bias pulses on etching in an ICP chamber.

¹ M. Wang and M.J. Kushner, J. Appl. Phys. 107, 023308 (2010).

² S. Banna, et al., Trans. Plasma Sci. 37, 1730 (2009).

³ A. Agarwal et al, J. Appl. Phys. 106, 103305 (2009).

⁴ E. Meeks, H.K. Moffat, J.F. Grcar and R.J. Kee, SAND96-8218 (1996)