The Reactivity of Thin Titanium Films Towards Aluminum and the N-O-N Insulator Stack, and its Effects on the Composition and Properties of Voltage Programmable Links

A metal-insulator-metal (MIM) voltage programmable link (VPL) has been fabricated that relies on the breakdown of a thin nitride - oxide - nitride (N-O-N) plasma deposited insulator stack. The metal electrodes were prepared by depositing a titanium layer (400 A) on top (or bottom) of 7500 A Al ( 1% Si). The resulting metallization resists hillock formation during thermal anneal steps and thus preserves the integrity of the thin link dielectric. The breakdown voltage is typically 10 volts for a 100 A-150 A-100 A NON stack. Sintering at temperatures up to 425°C results in a negligible increase in breakdown voltage. After sinter at 455°C, the breakdown voltage drops to 6 volts and continues to decrease with further sintering. Auger depth profiles of the as-deposited sample indicate the N-O-N stack is intact and the titanium has also not reacted with the aluminum film. After sinter at 455°C no distinct interfaces are observed in the auger depth profile. Angle-resolved x-ray photoelectron spectroscopy (ARXPS) of the nitride film after deposition and sinter indicate that the nitride film reacts with the titanium to form titanium nitride or titanium silicide. Angle resolved measurements indicate the titanium concentration has increased by a factor of 5 throughout the film as compared to the as-deposited sample. These results explain the observed drop in breakdown voltage since the insulator is being consumed and being converted into conducting titanium nitride or titanium silicide.