Electrical properties of polyimides for interlevel isolation and active device gate isolation

A report is presented on the results of a comparative series of experiments conducted on thin polyimide layers, of thicknesses in the range ~600 A to >1.5 μm, containing intentionally introduced and controlled amounts of Na. The levels of Na ranged from undoped (<0.2 p.p.m.) to 200 p.p.m. in the starting stock. These films were characterized using I/V and C/V measurements on MIS structures fabricated on Si wafers. Although the very best PI films has resistivities of ~10¹⁶ Ω-cm the authors feel that, for use for gate isolation, the Na⁺ contamination level in the polyimide dielectric would need to be less than 0.2 p.p.m. for stable device operation