Stability of a new polyimide siloxane film as interlayer dielectrics of ULSI multilevel interconnections

Stability of a new polyimide siloxane (PSI) film as interlayer dielectrics of ULSI multilevel interconnections is studied. The PSI films, involving Si-phenyl bonds, are designed to have a three-dimensional polymer structure by crosslinking through Si-O bonds. It has been revealed that the PSI films are more stable than conventional polyimide films in terms of thermal and electrical properties at high temperatures. The PSI film's decomposition temperature is as high as 500°C. The coefficient of thermal expansion is 4 × 10^-5 K^-1 in the temperatures of 25-450°C. The abrupt thermal expansion that usually occurs at around 270°C for conventional polyimide films is eliminated. The residual stress for the PSI films is less than 20 MPa, and is lower than for conventional polyimide films. Leakage currents through the PSI films at temperatures above 100°C are over one order of magnitude lower than those through conventional polyimide films. Good surface planarization characteristics are obtained for the PSI films by decreasing the molecular weight and viscosity of the polyamic acid solutions. No void is observed acid the films formed on 2.4 μm thick silicon dioxide lines with 1.1 μm width and 1.5 μm spacing, using polyamic acid solutions with precursor molecular weights ranging from 2900 to 9600.