Nanometer-scale mechanical imaging of aluminum damascene interconnect structures in a low-dielectric-constant polymer

Ultrasonic-force microscopy (UFM) has been employed to carry out nanometer-scale mechanical imaging of integrated circuit (IC) test structures comprised of 0.32-μm-wide aluminum interconnect lines inlaid in a low-dielectric-constant (low-k) polymer film. Such inlaid metal interconnects are typically referred to as damascene structures. UFM clearly differentiates the metal and polymer regions within this damascene IC test structure on the basis of elastic modulus with a spatial resolution≤10nm. In addition, this technique reveals an increase in the polymer elastic modulus at the metal/polymer interface. This nanometer-scale hardening corresponds to compositional modification of the polymer from the reactive ion etch (RIE) process used to form trenches in the polymer film prior to metal deposition. The reported direct, nondestructive nanometer-scale mechanical imaging of RIE-process-induced modifications of low-k polymers in IC test structures offers expanded opportunities for mechanical metrology and reliability evaluation of such materials.