A Versatile Ta2N-W-Au/SiO2/Al/SiO2Thin Film Hybrid Microcircuit Metallization System

A versatile thin film metallization technique in which both gold and aluminum can be incorporated on sapphire or fine grained alumina substrates in a two level metallization system with thin film resistors is described. Tungsten is used as a lateral transition metal permitting electrical contact between the gold and aluminum without the two metals coming in physical contact. Silicon dioxide serves as an insulator between the tungsten and aluminum for crossover purposes and vias through the silicon dioxide permit interconnections where desired. Tantalum nitride is deposited first and serves as the resistor film. Sheet resistance of the film is typically 100 ohms per square. Tungsten-gold is the first level conductor except at crossovers where tungsten only is used. Aluminum is the second level conductor. Sheet resistances of the two conductor levels can be as Iow as 0.01 ohm/square. I inewidths and spaces as small as 0.025 mm can be attained. A second layer of silicon dioxide is deposited over the metallization and opened for all gold and aluminum bonding areas. The metallization system permits effective interconnection of a mixture of devices having both gold and aluminum terminations without creating undesirable gold-aluminum interfaces. Devices can be attached by epoxy or silicone directly on the circuitry. Processing temperatures up to 400°C can be tolerated for short times without effect on bondability, resistor, conductor, and insulator characteristics, thus permitting silicon-gold eutectic die attachment, component soldering, and higher temperatures during gold lead bonding. Tests conducted on special test pattern circuits indicate good stability over the temperature range--55°C to +150°C. Aging studies showed no degradation in characteristics in tests of 500 hours duration at 150°C.