High Contact Resistance from Preferential Oxidation of Silane Gas

Abstract High resistance failures in P+ and N+ contact chains were traced to contacts partially filled with silicon dioxide (SiO2) instead of the intended tungsten. Investigation revealed that oxygen (O2) entered the deposition chamber through a faulty valve during silane gas (SiH4) flow for tungsten seed deposition. This contamination triggered a gas-phase reaction producing SiO2 particles that partially filled the contacts. Analysis of reaction kinetics explained the predominance of SiO2 formation over tungsten deposition: the bond dissociation energy for SiO2 formation is lower than that for tungsten, and SiO2-producing molecular collisions occur more frequently than tungsten-producing ones. The issue was resolved by replacing the leaking valve.