ABSTRACTPolyimides are considered as promising packaging materials in multi-layer interconnections and multi-chip modules because of their low dielectric constant and good planarizability. Photosensitive polyimidesiloxane (SIM2000XL) as a newly emerging polyimide is showing not only similar properties as conventional polyimides but also the advantages of process simplification and improved adhesion. Moreover, it is proposed that SIM2000XL can be an oxygen-plasma etching barrier in multi-level lithographic systems because of its high silicon content.We characterized the photosensitivity of SIM2000XL thin films under excimer laser (193 nm) exposure. The sensitivity of SIM2000XL was found to be about 20 mJ/cm². After the SIM2000XL thin films were exposed through a photomask in the contact mode, development gave the usual negative patterns. However, the remained film thickness after exposure reached a maximum of about 65 % of the initial film thickness and decreased with further irradiation. This can be attributed to the competing processes of polymer crosslinkage and chain-scission. This phenomenon is important for applications of polymers in DUV lithography. A detailed study of these two competing processes are presented.