BCl 3 /N 2 Plasma for Advanced non-Si Gate Patterning
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0913-D03-12
BCl3/N2 Plasma for Advanced Non-Si Gate Patterning Denis Shamiryan1, Vasile Paraschiv1, Salvador Eslava-Fernandez1,2, Marc Demand1, Mikhail Baklanov1, and Werner Boullart1 1 AMPS, IMEC, Kapeldreef 75, Leuven, 3001, Belgium 2 Catholic University of Leuven, Leuven, 3001, Belgium
ABSTRACT A BN-like film can be deposited from a BCl3/N2 based plasma in a standard etch chamber at temperatures as low as 60°C. Deposition rate can be varied from 10 nm/min to more than 100 nm/min. The film contains hexagonal BN, but is very unlikely to be a stoichiometric BN. It decomposes at elevated temperatures and is water soluble. The latter property makes the post etch clean easy. The film can be used for sidewall passivation during the patterning of advanced non-Si gates. We are presenting as an example the use of BCl3/N2 plasma for patterning of Ge gates. The Ge gate profile is damaged by pure BCl3 plasma during HfO2 removal after the gate patterning. However, BCl3/N2 plasma with 10% N2 preserve the gate profile while removing the high-k.
INTRODUCTION As conventional materials in CMOS manufacturing (Si as a gate material and SiO2 as a gate dielectric) approach their performance limit, the search for new materials becomes key point. Patterning of the stacks containing these new materials require both new plasma etch chemistries and new approaches. Metal gates are seen as a replacement of conventional poly-Si gates since metals can alleviate issues inherent in Si gates such us poly depletion and boron penetration into the channel region. There is a wide variety of potential candidates for metal gates. Often their implementation requires adaptation of existing processing steps, in particular, gate patterning. In most cases the existing chemistries developed for poly-Si gate etch are not producing the required results if applied to metal gates. Investigation of new chemistries is needed. One promising chemistry used for metal gate etch is based on BCl3 [1]. It produces chlorine species that form volatile compounds with the etched metal; it forms passivating Si-B bonds with a silicon substrate [1]; it can etch metal oxides (in contrary to Cl2) by formation of BOClx [2,3] compound eliminating the need of a breakthrough step if the metal to be etched is oxidized. The two latter properties point out BCl3 as a good candidate for high-k (which are mostly metal oxides) removal (where metal oxides should be removed selectively to Si substrate) [4]. However, in some cases BCl3 might be too aggressive and produce profile distortion due to lateral etch of the gate. As will be shown below, we observed this distortion when BCl3 was used for etching Ge gates. In order to preserve the gate profile, the lateral etch rate with BCl3
should be reduced. One way to diminish this isotropic effect is to passivate side walls during the etch. The sidewall passivation was achieved by adding N2 to BCl3 plasma. It is known that BCl3/N2 gas mixture can be used for chemical vapor deposition (CVD) [5] of plasma-enhanced CVD BN films [6]. It should be n
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