AVS 51st International Symposium
    MEMS and NEMS Tuesday Sessions
       Session MN+MS+PS+TF-TuA

Paper MN+MS+PS+TF-TuA8
Characterization of Polycrystalline AlN Film Quality Using Variable Angle Spectroscopic Ellipsometry

Tuesday, November 16, 2004, 3:40 pm, Room 213C

Session: Nano/MEMS Manufacturing and Plasmas
Presenter: L.-P. Wang, Intel Corp
Authors: L.-P. Wang, Intel Corp
D.S. Shim, Intel Corp
Q. Ma, Intel Corp
V.R. Rao, Intel Corp
E. Ginsburg, Intel Corp
A. Talalyevsky, Intel Corp
Correspondent: Click to Email
Aluminum nitride (AlN) thin films have been investigated for piezoelectric, wide band gap, high-k dielectric and other applications. Recently, AlN films for bulk acoustic wave (BAW) resonators and filters have been studied extensively, driven by the fast growth of wireless communications. For this application, AlN films are mostly prepared by reactive sputtering, a technique with the advantage of low deposition temperature, easy process control and low cost when compared to alternatives such as metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). Highly c-axis oriented AlN films are desirable for optimal piezoelectric and crystal properties. Currently, X-ray diffraction (XRD) rocking curve is the predominate method for characterizing the crystal and piezoelectric properties. In this study, optical constants of AlN films, refractive index (n) and extinction coefficient (k), were determined by a variable angle spectroscopic ellipsometry (VASE). The microstructure of the sputtered polycrystalline films is well reflected in the VASE optical model, which includes cylindrical symmetry, effective medium approximation (EMA), index gradient, and surface roughness. For the first time, the film optical constants were correlated to the full width at half maximum (FWHM) of XRD rocking curve. It was found that the films with smaller FWHM, an indication of better crystal and piezoelectric properties, had higher n and lower k. This is consistent with the general observation that higher n and k of polycrystalline films typically have fewer defects and better microstructures. The correlation between the optical parameters and the film quality leads to a simpler and faster method for characterizing sputtered AlN films. Furthermore, such optical tools can be integrated in a sputter deposition system for in-situ monitoring of AlN film thickness and quality simultaneously.