Electrical stability of metal/low dielectric constant material systems.

摘要

In order to boost the performance of future generation silicon integrated circuits, new materials with lower dielectric constant (κ) are under evaluation to replace traditional SiO₂ as on-chip inter-layer dielectrics (ILDs). The goal of this thesis has been to investigate the intrinsic electrical stability and metal penetration resistance of a variety of low κ materials: fluorinated silica glass (FSG), polyparaxylylene-N (parylene-N), polyarylether (PAE) and hybrid organosiloxane polymer (HOSP). Emphasis was placed on fundamental understanding of the factors controlling the electrical properties of different metal/low κ dielectric systems.; Traditionally, metal ion penetration is studied using Bias Temperature Stressing (BTS) with Capacitance-Voltage (C-V) measurement. In this work, an alternative technique, Triangular Voltage Sweep (TVS), was also adopted to provide insight into metal penetration behavior. Surprisingly, aluminum ion penetration into oxygen containing polymers such as PAE and HOSP was detected, and was in contrast to the stability of the Al/SiO₂ system. Platinum was demonstrated as a viable control for metal drift studies in such polymers, as no platinum ion penetration was detected.; Among the blanket dielectrics, the number of copper ions detected was lowest in HOSP, demonstrating its promise for ILD applications. Experimentation with a variety of metals led to the result that ion penetration behavior in HOSP showed the trend Pt Cu Ta Al. This trend indicated that metal penetration increases with metal ionization and oxidation tendency. Plasma modification of HOSP by converting its surface to a thin intrinsic dielectric barrier resembling SiO₂ dramatically reduced aluminum ion penetration in HOSP. Surface modification is therefore a powerful strategy to realize the future requirement of ultra-thin barriers.; The impact of on-chip integration on electrical stability was also studied. Copper ions were detected along fast diffusion paths in an integrated FSG due to barrier failure and processing-related copper contamination.; The results from all the various novel dielectrics clearly establish that metal/dielectric interactions induced by thermal and electrical treatments are very unlike those observed in metal/SiO₂ systems. Careful evaluation is required to elucidate the metal penetration mechanism as it is influenced by surface chemistry, metal ionization and chemical reactivity, and bulk dielectric structure or composition.