Reactively Sputtered Tantalum Resistors and Capacitors for Silicon Networks

The protracted contest between solid-state and thin-film microcircuitry proponents appears to be subsiding, due to the recognition that the two techniques really complement each other. Microcircuit manufacturers and users look to hybrid circuits as a good way to achieve Iow-cost, high-performance circuits. The technique, termed "reactive sputtering" of preparing thin films ranging from conductors to resistive films and even to dielectric films, by sputtering from a tantalum cathode in the presence of an oxygen partial pressure has been developed to deposit resistors and capacitors onto oxidized silicon substrates. Reactively sputtered resistive films of tantalum/tantalum oxide offer sheet resistivities of 27 to 25,400 ohms/square and TCR values of -3 to -1,280 ppm/°C. Their stability during 1000 hours at +125°C and 2 watts/inch²is about ±2 per cent. Dielectric films of reactively sputtered tantalum oxide have been prepared which offer 0.30 to 3.16 pF/mil²and Vbd of 82 to 8 volts respectively, and TCC values of +129 to +269 ppm/°C. Capacitors have been llfe tested for 1000 hours at +125°C at a conservative rating of 60 per cent of Vbd, and show excellent stability. Reactive sputtering variables, including time, current, gas flow, pressure, and substrate temperature and their relation to resistive and dielectric film properties are reported.