Nanoindentation analysis of mechanical properties of low to ultra-low dielectric constant SiCOH films

Copyright © (2005) by MRS. Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distrubuted for profit. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior specific permission and/or a fee.

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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