A novel degradation mechanism in SiCr-O based thin film resistors under temperature and current stress

The degradation mechanism during current and temperature stress of SiCr-O thin film resistors in integrated circuits is investigated closely by experiments with the use of various characterization techniques. It is found that the degradation in SiCr-O resistors is dominated by the migration of Si in the resistor from the anode electrode to the cathode electrode. The direction of material migration is contrary to EM process in metal interconnect lines. It is shown that only excess Si in the SiCr-O resistive film besides a stable phase of the material migrates while the material of the stable phase does not migrate nor degrade during further stress, which explains why voiding is never observed at the anode electrode of the resistor. The new understanding on the degradation mechanism points to a way to eliminate the degradation process in SiCr-O based devices (resistors or heating elements) by optimization of the material composition. In addition, the degradation is found to be strongly dependent on the length of the resistor - the shorter the resistor, the faster the drift of the resistance value in percentage, which is in contrast to the well-known Blech effect of EM process in metal lines. Such a length dependency of degradation rate suggests that the driving force for the migration process in SiCr-O is much stronger than for EM in metal lines.