Nanoindentation analysis of mechanical properties of low to ultralow dielectric constant SiCOH films
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Alfred Grill IBM—Thomas J. Watson Research Center, Yorktown Heights, New York 10598 (Received 24 January 2005; accepted 14 April 2005)
Carbon-doped oxide SiCOH films with low to ultralow dielectric constants were prepared on a Si substrate by plasma-enhanced chemical vapor deposition (PECVD) from mixtures of SiCOH precursors with organic materials. The films have different levels of nanoscale porosity resulting in different dielectric constants and mechanical properties. The mechanical properties of the films have been characterized by continuous-stiffness nanoindentation measurements. To study the effect of film thickness, each group of samples with the same dielectric constant was composed of samples prepared with different film thicknesses. It is shown that the effective hardness and modulus of the SiCOH/Si substrate system depends significantly on indentation depth due to 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 degrees 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 10% of the film thickness is close to the “true” value for films thicker than 0.5 m, the measured value can give an overestimate of up to 35% for softer films. Thin film cracking and film–substrate debonding have been observed with scanning electron and atomic force microscopy at the indentation sites in softer films. The damage initiation is indicated by pop-in events in the loading curve and sharp peaks in the normalized contact stiffness curves versus indentation depth.
I. INTRODUCTION
As the dimensions of ultralarge-scale integrated (ULSI) circuits continue to shrink, optimization of the electrical properties of the interconnect dielectric becomes more important in improving the performance of ULSI devices. Such systems require materials of low dielectric constant to reduce propagation delay, crosstalk noise, and power dissipation from resistancecapacitance (RC) coupling.1–3 Amorphous carbon-doped glass materials (SiCOH) deposited by plasma-enhanced chemical vapor deposition (PECVD) have low to ultralow dielectric constants (k from 3.0 to less than 2.1) and are currently considered the most promising and films
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0258 2080
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 8, Aug 2005 Downloaded: 01 Apr 2015
with dielectric constant of 3.0 are currently integrated in ULSI.4 The ultralow dielectric constant of SiCOH materials (k less than ∼2.7) is achieved by introducing porosity in the films.5 The existence of porosity significantly reduces mechanical properties such as modulus and hardness and affects the mechanical robustness of the inte
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