AVS 47th International Symposium
    MEMS Wednesday Sessions
       Session MM-WeA

Paper MM-WeA8
Control of Residual Stress in Thick Sputtered Metal Films

Wednesday, October 4, 2000, 4:20 pm, Room 309

Session: MEMS Processing
Presenter: J.M. Melzak, Case Western Reserve University
Authors: J.M. Melzak, Case Western Reserve University
D.A. Greer, Case Western Reserve University
S. Rajgopal, XACTIX, Inc.
K.S. Lebouitz, XACTIX, Inc.
M. Mehregany, Case Western Reserve University
Correspondent: Click to Email
Metals are the structural material of choice for a growing number of MEMS applications (e.g., optical elements, relays) because of their high reflectivity and low resistivity. This paper investigates the relationship between the parameters used to deposit such thick (1µm) films by DC magnetron sputtering and the resulting residual stress values. The materials of interest-aluminum, tungsten, and a ternary alloy of aluminum/silicon/copper-exhibit quite different residual stresses for a given set of deposition parameters, as well as reacting quite differently to changes in deposition parameters. For example, 1µm-thick tungsten films deposited on silicon at a pressure of 5 mTorr exhibit a compressive stress of 253 MPa while aluminum films deposited under the same conditions have a tensile stress of 73 MPa. Increasing the deposition pressure to 15 mTorr results in a highly tensile tungsten film, whereas the effect on aluminum's residual stress is minimal. As-deposited thick films of these materials have been characterized using wafer curvature, surface profilometry, and TEM analysis. Furthermore, a one-mask surface micromachining process that selectively etches the underlying silicon with xenon difluoride (XeF@sub 2@) has been used to fabricate metal cantilever beams, in order to qualitatively examine residual stress gradient.