AVS 52nd International Symposium
    MEMS and NEMS Monday Sessions
       Session MN-MoP

Paper MN-MoP2
Plasma Enhanced Chemical Vapor Deposition of Low Stress Silicon Nitride Using Diethylsilane as Precursor

Monday, October 31, 2005, 5:00 pm, Room Exhibit Hall C&D

Session: General Aspects of MEMS and NEMS Poster Session
Presenter: L.M. Fischer, University of Alberta, Canada
Authors: L.M. Fischer, University of Alberta, Canada
S. McColman, University of Alberta, Canada
B. Szeto, University of Alberta, Canada
K. Westra, University of Alberta, Canada
S. Evoy, University of Alberta, Canada
Correspondent: Click to Email
The stable surface and high stiffness-to-density ratio of silicon nitride offer interesting advantages over regular silicon for the production of high-frequency and high-quality nanoelectromechanical (NEMS) resonators. Such machining however requires a mechanical material possessing very low residual stress. Silicon-rich low-stress silicon nitride is typically produced using silane/nitrogen or silane/ammonia as precursors. Silane is however highly flammable and thus poses significant safety hazard. In addition, typical low-stress films produced by these methods may still contain residual stress levels exceeding 100 MPa. We here report the PECVD of silicon nitride using the relatively safer diethylsilane (DES) as precursor. We also report the control and reduction of residual stress in the films through post-deposition anneal. Compressive residual stress in the as-deposited material ranged from 555 MPa to 1GPa as the NH3:DES ratio varied from 1:1 to 16:1, while nitrogen content increased and carbon content decreased over the same range. This correlation is related to the increased formation of N-H radicals within the films. Compressive residual stress also increased from 558 MPa to 849 MPa as the deposition temperature was varied from 240 C to 315 C. Such temperature dependence is in turn attributed to an increased densification of the deposited films. A post-deposition anneal in inert nitrogen at temperatures of 500 to 600 C however relieves the stress and enables its control from the compressive to the tensile range. Tensile stresses as low as 50 MPa have been achieved. While hydrogen desorption is believed to be responsible for this change, XPS analysis also provided evidence of the formation C-N bonds in the annealed films. We will report a complete analysis of the formation, stochiometry, and stress relief in these films. We will also present the machining and characterization of NEMS resonators in this low-stress material.