Cross-sectional elastic imaging and defect detection in low-k spin-on dielectrics

A novel cross-sectional characterization technique for depth-dependent nanomechanical profiling of low-k dielectrics has been developed based on ultrasonic force microscopy. So-called CS-UFM has been demonstrated on silicon-based, spin-on dielectrics (SOD) used for gap-fill in 0.15 /spl mu/m trenches in an SiO/sub 2/ test structure. The SiO/sub 2/ trench walls were coated with a thin (/spl sim/24 nm) PECVD Si/sub 3/N/sub 4/ layer. CS-UFM imaging clearly differentiated the SOD, SiO/sub 2/ and Si/sub 3/N/sub 4/ on the basis of elastic modulus. Variations in the elastic uniformity of the SOD and Si/sub 3/N/sub 4/ were observed. In addition, mechanical defects were identified within the SOD-filled trenches. Initial HF-etch testing suggested the defects represented localized areas of modified SOD composition or intra-trench voids.