Paper PS-MoA10
Predictive Etch Profile under Competition Among Deposition, Etching, and Charging on Dielectrics in a Low Temperature Plasma

Monday, October 20, 2008, 5:00 pm, Room 304

A dielectric surface exposed to plasma irradiation keeps competitive, physical and chemical processes among etching, deposition, and charging on the local pattern.¹ Top down plasma nano-etching is a technology assisted by a directional and energetic positive ion onto a surface saturated by adsorbed chemical molecules. The ion flux to the wafer has a magnitude of 10¹⁵cm^-2s^-1. It means that the ion incident on the surface transfers the kinetic energy to the lattice with a relaxation time shorter than the surface collision interval. We have no way to protect the surface from the charging damage, particularly on the dielectric, in a periodically steady state radio frequency (rf) plasma, which always forms the positive ion sheath in front of the biased wafer to be etched. We have demonstrated a technique to inject negative charges having a relatively high energy in a synchronized mode between an rf plasma source with on/off period and a LF bias pulse in order to develop a charging free plasma etching. It is realized by an artificial formation of a double layer close to the wafer.^2,3 The synchronized pulsed operation will enable us to develop a charging free plasma etching. The time constant of local charging, caused by the great difference in the velocity distribution between ions and electrons incident on a topographical surface, is approximately two orders of magnitude shorter than the time for the effective monolayer etching in SiO₂. This difference enables us to estimate the etching profile by the two-step evaluation, i.e., surface charging followed by etching. Even in a controlled wafer exposed to a plasma etching, the surface is the competitive processes between etching and deposition, where two-layer model will be efficient in order to predict the feature profile evolution by using Level set method³. Predictive images are shown and discussed for the feature profile evolution of dielectric.

¹ T. Makabe and Z. Petrovic, “Plasma Electronics: Applications in Microelectronic Device Fabrication”, Taylor & Francis (2006).
² T. Ohmori, T. Goto, T. Kitajima, and T. Makabe, Appl. Phys. Lett. 83, 4637-9 (2003); T. Ohmori and T. Makabe, Appl. Surf. Sci. 254, 3696-3709 (2008).
³ T. Shimada, T. Yagisawa, and T. Makabe, Japan J. Appl. Phys. 45, L132-4 (2006); Ibid. 45, 8876-82 (2006); T. Makabe, T. Shimada, and T. Yagisawa, Comp. Phys. Commun. 177, 64-7 (2007).