Nanomechanical defect imaging in premetal dielectrics for integrated circuits

Ultrasonic force microscopy (UFM) has been used for cross-sectional nanomechanical imaging of integrated circuit trenches filled with hydrogen silsesquioxane (HSQ) premetal dielectric. Fully cured HSQ exhibits a local Young's modulus of 55+/-2 GPa calibrated against SiO2. UFM reveals local areas within the HSQ with dramatically reduced modulus exhibiting poor resistance to hydrofluoric acid etching, indicative of incomplete densification during curing. Quantitative UFM analysis reveals a modulus of 28+/-2 GPa at the defect centers. This agrees quantitatively with predictions from recent finite element models of siloxane-based dielectrics in conjunction with relative density measurements of similar defects via transmission electron microscopy. (C) 2004 American Institute of Physics.