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Carbon-doped oxide SiCOH films with low to ultralow dielectric constants have been prepared on a Si substrate by plasma-enhanced chemical vapor deposition (PECVD) from mixtures of SiCOH precursors with organic materials. The mechanical properties of the films have been characterized by continuous-stiffness nanoindentation measurements. To study the film thickness effect, each group of samples with the same dielectric constant comprised samples prepared with different film thicknesses. It is shown that the effective hardness and modulus of the film/substrate system significantly depend on indentation depth due to surface gradient plasticity and the substrate constraint effects. The “true” film properties were determined using both an empirical formulation of the effective modulus and direct inversion based on a finite element model. The hardness and modulus of three groups of samples with different degree of dielectric constants have been measured. The hardness increases from 0.7 to 2.7 GPa and modulus from 3.6 to 17.0 GPa as the dielectric constants change from 2.4 to 3.0. While for stiffer films the modulus measured at an indentation depth of 10% of film thickness is close to the “true” value for films thicker than 0.5 micron, the measured value can give an overestimate up to 35% for softer films.
By: Lugen Wang; M. Ganor; S. I. Rokhlin; Alfred Grill
Published in: Journal of Materials Research, volume 20, (no 8), pages 2080-93 in 2005
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