Contents I. Introduction
The need for a gate electrode material with lower resistivity than polysilicon arose due to the demand for faster and smaller geometries in integrated circuits. This need has been satisfied by using refractory metal silicide such as tungsten silicide, cobalt silicide, and titanium silicide. Among the various metal silicide materials, tungsten silicide has been used most frequently in integrated circuits using the around 1 technology. can withstand additional high-temperature deposition steps, will oxidize only slightly in an oxidizing ambience, and will not be destroyed as other silicide films might [1], [2]. As integrated circuit manufacturing moves to 0.18 technology and beyond, a further decrease in gate resistance is required, and this can be achieved by using cobalt silicide whose resistivity is around 17 with excellent thermal stability [3]–[5]. It is known that the use of metal silicide over polycrystalline–silicon (referred to as polycide) as a gate electrode material, in order to reduce resisitive loss in interconnection networks, as used by some um and submicron feature size integrated circuits, may increase the radiation sensitivity in MOS circuits due to dose-enhancement effects [6], [7]. While most of the considerations for using polycides are focused on resistance reduction, thermal stability and manufacturability, rarely have been discussed in the literature regarding the radiation hardness in MOS devices with different polycide gate materials. In this letter, we have compared the radiation hardness of MOS capacitors with tungsten polycide and those with cobalt polycide . Interestingly enough, we found that MOS capacitors with as a gate electrode material exhibited better radiation hardness even though has been extensively used in MOS integrated circuits below 0.18 . A reconsideration of using gate materials other than might be needed in order if the circuit is operating under an irradiation environment.
