EFFECT OF ETCH HOLES ON THE MECHANICAL-PROPERTIES OF POLYSILICON

For large movable parts in the microelectromechanical systems, etch ho les are needed to facilitate the releasing process. These etch holes o bviously weaken the structure and affect its mechanical properties. Ne w techniques and structures have been developed to measure the mechani cal properties of very thin microelectromechanical systems (MEMS) mate rials. A dog-bone shaped tensile specimen is imposed with a uniaxial s tress field and strain is directly measured on the specimen with the i nterferometric strain/displacement gage. This testing approach has bee n used to study the effect of etch holes on the mechanical properties of polysilicon thin film. The material is phosphorus doped, low pressu re chemical vapor deposited polysilicon deposited at MCNC the multi-us er MEMS processes. The specimen is 3.5 mu m thick and 0.6 mm wide at i ts narrowest point. The etch holes are about 5 mu m in diameter and 30 mu m apart. Compared with the mechanical properties of the specimens without etch holes, the tensile strength has dropped by 50% and the Yo ung's modulus decreases only about 18% due to the existence of the etc h holes. Finite element modeling is applied to the specimens with etch holes and in agreement with the test results. (C) 1997 American Vacuu m Society. [S0734-211X(97)04705-7].