Ionizing radiation effects on ULSI device yield and reliability

Summary

In terms of initial device yield, and long-term reliability, process-induced radiation damage represents an area of considerable concern. The processes that need to be examined include ion implantation, X-ray, E-beam and ion beam lithography, electron beam metal evaporation, sputtering, reactive ion etching, and even SEM examination. The paper discusses the effects of synchrotron X-radiation in the energy range 300–1000eV, as well as Al Kα exposures which simulate X-ray lithographic procedures. It describes such effects in the context of preliminary studies dealing with varying rad (SiO₂) exposure levels at a constant gate insulator thickness, as well as the behavior at several rad exposure levels, as a function of gate insulator thickness. Data are presented showing that despite prevailing beliefs, damage in the synchrotron range follows a linear relationship over the thickness range form less than 10nm to 50nm, indicating strongly that damage resides near the interface and is constant with increasing insulator thickness. It is shown that such behavior is consistent with a simple model. Even if such damage can be annealed completely using normal techniques, which is questionable, there are wide-ranging implications concerning the rad hardness of scaled devices.