|AVS 55th International Symposium & Exhibition|
|Plasma Science and Technology||Friday Sessions|
|Session:||Plasma-Surface Interactions in Materials Processing II|
|Presenter:||J. Pereira, GREMI, France|
|Authors:||J. Pereira, GREMI, France
L.E. Pichon, GREMI, France
R. Dussart, GREMI, France
C.Y. Duluard, GREMI, France
E.H. Oubensaid, GREMI, France
H. Jiang, GREMI, France
P. Lefaucheux, GREMI, France
M. Boufnichel, ST Microelectronics, France
P. Ranson, GREMI, France
|Correspondent:||Click to Email|
Silicon dry etching is widely used in microelectronics and microsystems industries in order to elaborate high aspect ratio structures [Micro-ElectroMechanical Systems (MEMS), Micro-OptoElectroMechanical systems (MOEMS) or integrated components]. In order to elaborate such deep structures, industry mainly uses the Bosch process, consisting of an alternation of isotropic etching (SF6 plasma) and deposition (C4F8 polymerizing plasma) steps at ambient temperature. Even if this process can be well controlled, it presents many drawbacks such as sidewall roughness due to scalloping effect, or low etch rate. Thus, a new robust process used to form high aspect ratio structures into silicon bulk, called alternated cryogenic process (STiGer) is investigated.1 Its principle consists of etching a silicon wafer cooled at cryogenic temperature (T~-80°C) by the alternation of isotropic (SF6) etching steps and plasma deposition steps in SiF4/O2 gas mixture. The deposition step leads to the formation of a SiOxFy passivation layer used to protect the sidewalls and enhanced the anisotropic etching.2 The formation of this passivation layer is not yet well understood, and its study is crucial for improving the cryogenic process. Moreover, fluorine-doped silicon dioxide films deposited by plasma have gained considerable importance for applications as low dielectric constant layers for reducing the capacitance between metallic lines in silicon based high-speed integrated circuits.3 In this presentation, SiOxFy thin films deposited in ICP reactor are analysed in order to understand their formation and evaluate the effect of various parameters: SiF4/O2 gas mixture, substrate temperature, negative bias voltage or source power. The chemical structure and composition of the passivation layer is particularly studied. Fourier-Transformed InfraRed spectroscopy (FTIR) is used in order to determine the molecular groups constituting the coating and particularly the fluorine incorporation within the SiO2 network and its consequences. Ellipsometric measurements give us informations on deposition rate and films characteristics such as refractive index, n.
1 T. Tillocher and al., J. Electrochem. Soc., Volume 155, Issue 3 (2008) pp. D187-D191.
2 X. Mellhaoui and al., J. Appl. Phys., 98 (2005) 104901.
3 T. Homma, Mater. Sci. Eng., R Rep. 23 (1998) 243.