Characterization of the Young's Modulus of CMOS Thin Films

We have developed a technique to determine the local Young's moduli of the thin films within a composite stack of CMOS films, without accessing the individual layers during processing. By fabricating cantilevers of various combinations of field oxide, polysilicon 1, gate oxide, polysilicon 2, oxide 1, metal 1, oxide 2, metal 2, and overglass, measuring the thicknesses of each layer in a cross-section SEM, and deflecting the cantilevers with a Tencor Alpha Step profilometer, we were able to determine the Young's modulus for each film from elastic beam theory. The values we determined for the field oxide, polysilicon, and metal layers were in close agreement with published data on similar but isolated pure films. Values were also determined for the proprietary interlayer dielectrics and passivation overglass layers whose compositions are unknown and thus not available in the literature. These results are of use to MEMS designers utilizing CMOS processes since they do not have control over the mechanical properties of the films in the process nor are they able to directly measure them.