|AVS 54th International Symposium|
|Plasma Science and Technology||Thursday Sessions|
|Session:||Plasma-Surface Interactions II|
|Presenter:||L.E. Pichon, GREMI/CNRS, Université d'Orléans, France|
|Authors:||L.E. Pichon, GREMI/CNRS, Université d'Orléans, France
E.H. Oubensaid, GREMI/CNRS, Université d'Orléans, France
C. Duluard, GREMI/CNRS, Université d'Orléans, France
R. Dussart, GREMI/CNRS, Université d'Orléans, France
P. Lefaucheux, GREMI/CNRS, Université d'Orléans, France
M. Boufnichel, STMicroelectronics Tours, France
P. Ranson, GREMI/CNRS, Université d'Orléans, France
L.J. Overzet, University of Texas at Dallas
|Correspondent:||Click to Email|
The need to scale down integrated circuits can be achieved by reducing transistor dimensions and also by 3D-integration. The latter takes advantage of high aspect ratio features and uses the silicon wafer volume as well as its surface. As a consequence, deep silicon etching is of crucial importance for 3D-integration. At GREMI laboratory, the cryogenic process is investigated for etching high aspect ratio structures in silicon. Generally, an inductively coupled SF6/O2 plasma is used to simultaneously etch silicon and deposit a passivation layer on the sidewalls at low temperature. When the wafer is warmed up to ambient temperature, the passivation film desorbs. Thus, the sidewalls are clean and have a low roughness.1 The standard cryogenic process allows high etch rates but the passivation layer is not robust. This reduces the use of the cryogenic process in industry. To overcome this problem, passivation mechanisms have been investigated. A previous work has shown that SiF4 plays a significant role in passivation layer formation.2 Hence, it is possible to deposit a SiOxFy passivation film in SiF4/O2 plasma when the silicon substrate is cooled down to cryogenic temperatures. Moreover, a study has shown that the robustness of the passivation film is enhanced when it is grown using a SiF4/O2 plasma rather than SF6/O2 plasma2. We will show the use SiF4/O2 plasmas to reinforce the passivation layer during a standard cryogenic process. In brief, the SF6/O2 anisotropic etching plasma is regularly stopped and the silicon substrate is exposed to a SiF4/O2 plasma to strengthen the SiOxFy passivation film. This passivation-enhanced cryogenic process allows to significantly reduce the undercut (e.g. by a factor of 6 for a 10 µmm wide trench). Besides, the undercut can be completely eliminated for submicron trenches with an aspect ratio of 15 while the etch rate dropped only by a factor 1.3. We will present the passivation-enhanced cryogenic process and its performances.
1 R. Dussart et al, J. Micromech. Microeng., 14 (2004) 190-196
2 X. Mellhaoui et al, J. Appl. Phys., 98 (2005) 104901 .