AVS 50th International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS2-ThM

Paper PS2-ThM7
Etching of a Porous SiOC with Varied Porosity in Fluorocarbon Based-plasma

Thursday, November 6, 2003, 10:20 am, Room 315

Session: Low k Dielectric Etch
Presenter: N. Posseme, STMicroelectonics, France
Authors: N. Posseme, STMicroelectonics, France
T. Chevolleau, CNRS/LTM, France
L. Vallier, CNRS/LTM, France
O. Joubert, CNRS/LTM, France
I. Thomas-Boutherin, STMicroelectronics, France
Correspondent: Click to Email
In CMOS technology, the traditional SiO@sub2@ is being replaced by Low-k materials in order to reduce the total resistance capacitance delay in the interconnect levels. Before Low-k materials can be implemented successfully, many problems must be solved such as the materials stability during etch and stripping processes. This work focuses on the etching of porous methylsilsesquioxane (MSQ) materials (spin on SiOC, k = 2.2) with different porosity ( 30%, 40% and 50%) in fluorocarbon based plasmas (CF@sub4/Ar). The surface and bulk modification after partial etching is studied using different surface analysis techniques such as quasi in-situ X-Ray Photoelectron Spectroscopy (XPS), Infrared Spectroscopy (FTIR), mercury probe capacitance measurement (C-V) and spectroscopic ellipsometry. The etching of these materials is performed on blanket wafers in a Magnetically Enhanced Reactive Ion Etcher. Similarly to non porous SiOC materials, a decrease in etch rate of porous SiOC films is observed with either increasing Ar dilution or polymerizing gas addition (CH@sub2@F@sub2@) leading in this last case to an etch stop phenomenon. The etch rate increases with higher porosity in the SiOC film, since less material per unit thickness need to be removed as the porosity increases. After partial etching, FTIR analysis indicate that the remaining film is altered by the direct impact of ion bombardment that induces a physical degradation of porous SiOC. This film modification increases with the amount of porosity in the film. The XPS results indicate that the interaction layer formed at the film surface has almost the same composition whatever the porosity of the films studied. Complementary study, from angle resolved XPS analyses reveals also that the C and F atoms diffuse inside the pores of the different films and induce bulk modification observed on FTIR spectra. XPS analysis are also conducted on the porous SiOC sidewalls using the chemical topography analysis technique.