AVS 52nd International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS2-MoA

Paper PS2-MoA8
Optimization of Cryogenic Processes with Plasma Diagnostics

Monday, October 31, 2005, 4:20 pm, Room 304

Session: Silicon Etching
Presenter: T. Tillocher, GREMI - Université d'Orléans, France
Authors: T. Tillocher, GREMI - Université d'Orléans, France
R. Dussart, GREMI - Université d'Orléans, France
X. Mellhaoui, GREMI - Université d'Orléans, France
P. Lefaucheux, GREMI - Université d'Orléans, France
N. Mekkakia Maaza, GREMI - Université d'Orléans, France
M. Boufnichel, ST Microlectronics
L.J. Overzet, University of Texas at Dallas
P. Ranson, GREMI - Université d'Orléans, France
Correspondent: Click to Email
The so-called cryogenic process is a good alternative to the Bosch process for the etching of high aspect ratio structures. Indeed, etching and passivation occur simultaneously and anisotropic profiles result from a balance between these two mechanisms. Consequently, high etch rates can be reached with relatively smooth profiles. This equilibrium is put into evidence with mass spectrometry and optical spectroscopy on maskless silicon wafers : an oxidation threshold appears from one oxygen percentage in the SF@sub 6@/O@sub 2@ plasma where the etch rate drops. In such a case an overpassivation regime is reached, which strongly reduces the etching. We have shown that this threshold depends on the substrate temperature, the source power and the chuck self-bias : a lower temperature involves a higher sticking coefficient of oxygen on silicon and a higher energy transmitted to the wafer by the ions can prevent the formation of the layer. We think that these results, which can be characterized with a simple model, can also be correlated to the etching of high aspect ratio patterns. Indeed, the interaction between the surface and the radicals is quite similar on a bulk silicon wafer and on the sidewalls of the patterns. This appears to be a way to find the optimum oxygen flow. Plasma diagnostics, such as mass spectrometry, optical emission spectroscopy and Langmuir probe can also be used to optimize the other plasma parameters, especially the SF@sub 6@ flow and the source power. Finally, we will present performances which can be reached with optimized processes in the case of holes etching for the drilling of 400 µm thick silicon wafers.