AVS 51st International Symposium
    Manufacturing Science and Technology Wednesday Sessions
       Session MS+AS-WeA

Paper MS+AS-WeA5
Optical Properties (IR to VUV) and Birefringence of Graphite-like Amorphous Carbon

Wednesday, November 17, 2004, 3:20 pm, Room 303B

Session: Non-Destructive Analysis and Metrology for Advanced Manufacturing
Presenter: S. Zollner, Motorola
Authors: S. Zollner, Motorola
R. Liu, Motorola
R.B. Gregory, Motorola
W. Qin, Motorola
J. Kulik, Motorola
N.V. Edwards, Motorola
K. Junker, Motorola
T.E. Tiwald, J.A. Woollam Co.
Correspondent: Click to Email
Amorphous carbon films of 50 nm thickness, low surface roughness, and low densities (1.5-1.7 g/cm@super 3@) were deposited on Si using plasma-enhanced chemical vapor deposition (PECVD) between 300 and 550°C. With increasing deposition temperature, the hydrogen content (determined with elastic recoil detection) is reduced from 35% to 15%. For films grown at lower temperatures, ellipsometry data (0.7 to 9.5 eV photon-energy range, taken at 35-75° angle of incidence on a rotating-analyzer ellipsometer with a computer-controlled Berek waveplate) can be fitted very well by a single optically isotropic layer with low visible absorption (@epsilon@@sub 2@<1 below 4 eV) and two broad absorption peaks at 4.5 and 6.5 eV, a pronounced absorption minimum between 7 and 8 eV, and another strong rise of the absorption above 9 eV. At higher growth temperature, the visible absorption rises, the absorption peaks sharpen and red-shift, and the film becomes birefringent with the optical axis oriented normal to the substrate. The extraordinary absorption also shows two peaks at 3 and 4.5 eV, but the magnitude is much larger than the ordinary absorption peaks. The amorphous character of the films was confirmed by high-power powder x-ray diffraction. At our growth pressure (>1 Torr), the ion energy is expected to be very low, which leads to dominant sp@super 2@ character of our films@footnote 1@ (verified by electron energy loss spectrometry) and low density (<1.8 g/cm@super 3@). The birefringence is thus explained by alignment of the amorphous sp@super 2@ clusters along or perpendicular to the Si substrate. Birefringence and a double-peak absorption structure has not previously been reported for amorphous carbon. Vibrational properties of the films will also be discussed. Proper consideration of the birefringence is crucial to determine the thickness and optical constants of such layers. @FootnoteText@ @footnote 1@J. Robertson, Mat. Sci. Eng. R 37, 129 (2002).