RELIABILITY OF POLYIMIDE/NITRIDE DIELECTRICS FOR MULTILEVEL

In multilevel metallization systems concerning a 3 p metal pitch, polyimides appear as a good solution for the r ealization of the dielectric layers with the advantages of easy coating just by spin on technique and the excellent planarization capability. The main disadvantage of polyimides, their strong tendency to moisture uptake, can be overcome by applying an inorganic barrier layer made of SigNq or even Si02 /6/. In this paper a comparison of combinations of polyimide (PIQ-13) and Si3N4 dielectric layers is presented concerning their resistance against moisture uptake. Conventional oxide dielectrics are taken as a standard. The pressure cooker test (120 OC; 2 x 105 Pa; steam) was chosen to stress the dielectric layers because it is a severe short-time reliability test. Our results show that a passivating Si3N4 layer on top of every polyimide layer results in a dielectric system whose reliability is comparable to conventional oxide dielectrics. On the other hand a special cleaning of the polyimide surfaces l eads to similar results. Extreme low leakage currents of around 1 pA after the pressure cooker test have been achieved and characterize the high level of reliability.