Effects of various Co/TiN and Co/Ti layer stacks and the salicide rapid thermal process conditions on cobalt silicide formation

Abstract

The effects of cap layer type (Ti or TiN) and its thickness, Co thickness and rapid thermal processing (RTP) temperature on cobalt silicide formation are investigated by a combination of electrical and optical measurements. Various Co/TiN and Co/Ti layer stacks (thicknesses 8–20 nm per layer) were deposited on (100) Si substrates. The first RTP step (RTP1) was performed by isochronal annealing at various temperatures between 400 and 600 °C for 30 s. It was observed that the temperature range for constant sheet resistance (Rs) values after the first RTP step (RTP1 process window) is smaller for the Co/TiN layer stacks than it is for the Co/Ti layer stacks. After the subsequent selective etch step the second RTP step (RTP2) was performed at 800 °C for 30 s. Rs after RTP2 strongly depends on the initial Co thickness and its uniformity for both systems if the RTP1 temperature was above 470 °C. For the Co/TiN layer stacks the final Rs results are not influenced by the RTP1 temperature or its uniformity (above 470 °C). In this case silicidation is independent of the cap thickness. But in the Co/Ti system the reactive Ti influences the silicidation process by reducing the amount of available Co in a manner that depends on the RTP1 temperature and the Ti cap thickness.