Paper PS1-TuM3
Synchronously Pulsed Capacitively Coupled Plasma Sources for Dielectric Etching

Tuesday, November 10, 2009, 8:40 am, Room A1

Plasma etching processes for microelectronics fabrication at future technological nodes are extremely challenging. The requirements regarding the uniformity (both etch rate and critical dimensions) are also more stringent than ever. One particular challenge in plasma etching of extremely high aspect ratio features (aspect ratio > 40) is minimizing plasma induced damage, both physical and electrical. The via-like features may physically twist/turn due to the stochastic nature of fluxes entering the feature as the size of the opening shrinks.[1] Charge trapped by the polymer on the sidewalls exaggerates this phenomenon. Alternately, charge retention at the bottom of trenches may lead to breakdown as the material stresses under the accumulated charge creating a weak path for the injected current.[2] Pulsed plasma operation has been shown to be a promising approach to improving uniformity while reducing charge damage.[3] Although pulsing of both capacitively and inductively coupled plasma sources has been investigated before, novel pulsing schemes such as synchronous pulsing in multi-frequency capacitively coupled plasmas (CCP) may allow for expanded operating regime for damage-free etching of high aspect ratio features.

In this paper, pulsed and continuous plasma operation of a multiple frequency capacitive coupled plasma reactor in electronegative gas mixtures will be discussed using results from a computational investigation. A 2/3-dimensional plasma equipment model (CRTRS) [4] has been linked to a Monte Carlo feature profile model [5] to assess the consequences of pulsed plasma operation on etching of dielectric features. Results will be discussed for impact of pulse characteristics such as duty cycle, pulse excitation frequency, phase lag between source and bias pulses on dielectric etching in a multi-frequency CCP chamber. Careful tailoring of pulsing at both source and bias frequencies enables negative charge acceleration in the features and helps negate charge buildup. The impact of varying plasma electronegativity at different gas pressures will also be discussed. If strongly electronegative gas mixtures are used, sustaining a steady pulsed plasma can however be complicated as the plasma may not re-ignite after power is turned-off.

¹ A. Agarwal, M.M. Wang, and M.J. Kushner, 54^th AVS Symposium 2007.

² T. Ohmori and T. Makabe, Appl. Surf. Sci. 254, 3696 (2008).

³ S. Banna, et al., 55^th AVS Symposium 2008.

⁴ A. Agarwal, P.J. Stout, S. Rauf and K. Collins, 61^st Gaseous Electronics Conference 2008.

⁵ P. Stout, 60^th Gaseous Electronics Conference 2007.