| AVS 62nd International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS-TuM |
| Session: | Advanced BEOL/Interconnect Etching |
| Presenter: | Floriane Leroy, GREMI CNRS/Université d'Orléans, France |
| Authors: | F. Leroy, GREMI CNRS/Université d'Orléans, France T. Tillocher, GREMI CNRS/Université d'Orléans, France L. Zhang, IMEC, KU Leuven, Belgium P. Lefaucheux, GREMI CNRS/Université d'Orléans, France K. Yatsuda, TEL, Japan K. Maekawa, TEL Technology Center, America, LLC J.-F. de Marneffe, IMEC, Belgium M. Baklanov, IMEC, Belgium R. Dussart, GREMI CNRS/Université d'Orléans, France |
| Correspondent: | Click to Email |
Porous Organosilicate (OSG) low-k materials were introduced as inter-metal dielectrics, in order to reduce RC signal delay and energy dissipation. Low-k value is achieved by enlarged open porosity and pore size, but integration of porous low-k is impeded by plasma induced plasma (PID). Several low-damage processes have been reported in the literature. Recently, cryogenic etch, using SF6-based plasma, was studied as an alternative approach [1]. It was observed that the PID is reduced by decreasing the wafer temperature to cryogenic region (-120°C). At such a low temperature, a passivation layer forms on the pore sidewalls in the low-k bulk, and minimize reaction with damaging radicals.
In this work, we investigate the mechanisms behind this cryogenic low damage process on blanket sample glued on a SiO2 carrier wafer. The etch rate and the refractive index were measured by in-situ ellipsometry and ex-situ FTIR was used to evaluate methyl group depletion. Species desorbed during the warm-up of the cooled OSG films were detected by a mass spectrometer mounted on the diffusion chamber. In the case of a pure SF6 plasma, the main desorbed species are CxFy, SFx, SOxFy and SiFx. SOF2+ increases first from -120°C to -80°C and decreases from -80°C to 20°C, which shows that a strong desorption of SOF4 occurs in this range of temperature and play a major role in SF6 silicon etching [2]. SiF3+ and C2F4+ mainly desorb at -60°C. It is known that SiF4 is involved in passivation mechanisms for cryogenic etching, but this result suggests that fluorocarbon species also play a significant role. This is why it was proposed to add C4F8 to further protect the low-k material. This new SF6/C4F8 chemistry was studied for various temperatures (from -120°C to +20°C). PID were minimized at -120°C and lower than with pure SF6. In addition, the increase of the refractive index during the etching process reveals that C4F8 condenses into the pores, which is believed to enhance the protection of the material. The desorption of the CxFy, SFx, and SiFx species is still observed by mass spectrometry. It appears that SiF3+ and C2F4+ peaks intensity exhibit two local maxima: -120°C, due to desorption of condensed C4F8, and -60°C, due to the desorption of the passivation layer. In addition, in-situ XPS experiments was carried out to determine the fluorine based stoichiometry of the passivation layer [3]. Finally, profiles etched with SF6/C4F8 chemistry at -120°C will be presented.
[1] L. Zhang et al., ECS J. Solid State Sci. Technol. 2(6), N131-N139 (2013)
[2] X. Melhaoui et al., J. Appl. Phys 98, 104901 (2005)
[3] J. Pereira et al., Appl. Phys. Lett. 94, 071501 (2009)