AVS 56th International Symposium & Exhibition
    MEMS and NEMS Friday Sessions
       Session MN-FrM

Paper MN-FrM5
Determination of Young Modulus and Density of Thin Films using Nanomechanics

Friday, November 13, 2009, 9:40 am, Room B3

Session: Multi-scale Interactions of Materials and Fabrication at the Micro- and Nano-scale
Presenter: B.R. Ilic, Cornell University
Authors: B.R. Ilic, Cornell University
S.L. Krylov, Tel Aviv University, Israel
H. Craighead, Cornell University
Correspondent: Click to Email
Material properties of atomic layer deposited (ALD) thin films are of considerable interest to proposed applications ranging from wear resistance to high k-dielectrics in electronic circuits. We demonstrate the ability to simultaneously measure Young's modulus (E) and density (ρ) of 212-215Å ALD hafnia , alumina and aluminum nitride ultrathin films from vibrations ofnanomechanical cantilever beams. The nanomechanical structures were fabricated from a 250nm thick single crystal silicon layer with with varying length and width ranging from 6 to 10μm and 40nm to 1μm, respectively. Our approach is based on an optical excitation and interferrometric detection of in-plane and out-of plane vibrational spectra of single crystal silicon cantilevers before and after a conformal deposition of an ALD thin film. Due to the high degree of conformality, uniform thickness and composition of ALD films, fundamental mode eigenvalues depending on uncertainties in geometrical parameters and clamping compliances of the nanomechanical structures were filtered out. In conjunction with three-dimensional numerical finite element analysis, baseline measurements carried out prior the deposition revealed that while the influence of clamping compliances arising due to the undercut of the sacrificial layer is significant for wider beams, the effect is less pronounced for both, narrower cantilevers and the in-plane vibrational responses. Following the deposition, higher stiffness alumina films (E>ESi) showed an increase in the resonant frequency whereas lower stiffness (E<ESi) hafnia and aluminum nitride films decreased the natural frequency. From the measured spectral response, material properties were extracted using simple expressions for E and ρ in terms of measured in-plane and out-of-plane frequencies shifts were derived from a model based on an ideally clamped Euler-Bernoulli beam with effective bending stiffness and effective mass per unit length. In-plane and out-of-plane frequency measurements provided two equations required for the extraction of E and ρ without the necessity of knowing material density prior to experiment. Our theoretical and experimental results are in good agreement with the data available in literature and indicate that the suggested approach can be efficiently used for the in-situ material parameters extraction of very thin films incorporated in nano-scale oscillators as well as for combined stiffness-density based material identification and comparative quantitative characterization of the film quality.