Stability of contacts in shallow junction devices against high current density is a reliability issue for very large scale integration technology. We have observed a strong polarity effect on failure at nickel and nickel silicide contacts on bothn-andp-type Si under high stress conditions. In a pair of cathode and anode contacts theNi/n+-Sicontact pair fails at the anode, while theNi/p+-Sipair fails at the cathode. TheNi/Ni2Si/n+-Si andNi/Ni2Si/p+-Siwere found to fail preferentially at the cathode. Microbeam Rutherford backscattering spectrometry and Auger electron spectroscopy depth profiles show that a silicide reaction occurs between Ni and Si during current stressing, especially at the failed contacts.In situresistance data indicate that the resistance of the failed contact increases with time while that of the other contact in the pair remains constant. Transmission electron microscopy shows that the silicide formation is not uniform at the damaged contacts. A mixture of dominant epitaxialNiSi2and a minor amount of polycrystallineNiSi2phases was identified. We have proposed mechanisms to explain the polarity effect on failure: wear-out mechanism for the damaged positive contacts ofNi/n+-Si,electromigration enhanced silicide formation for the damaged negative contacts ofNi/Ni2Si/n+-Siand electron-hole recombination mechanism for the damaged negative contacts ofNi/p+-SiandNi/Ni2Si/p+-Si.©1997 American Institute of Physics.