Formation of cobalt silicide under a passivating film of molybdenum or tungsten

Abstract

A very simple and reproducible cobalt silicide process with Mo/Co or W /Co bilayer metallization to overcome the oxidizing liability of Co annealed in a normal flowing-nitrogen furnace has been developed. Cobalt is deposited on blank and patterned silicon wafers in an electron-beam evaporation system followed by Mo (or W) deposition without breaking the vacuum. The cobalt silicidation is carried out using a two-step annealing process. The first annealing is performed at a temperature ranging from 400 to 600 °C, during which the role of the upper layer ofMo (or W) is to protect the underlying Co layer from being oxidized while not disturbing the cobalt's silicidation process. Perfect selective etching of Mo (or W) can be accomplished by a NR 4 0H + Hz O 2 + (2-3) H2 0 solution. The second annealing is performed at a higher temperature of7S0"C to completely transform the CoSi obtained in the first annealing into CoSi z and induce grain growth of CoSi 2 , thus lowering the resistivity. X-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, and sheet resistance measurement are used to characterize the silicide phase and microstructure.

Phase Transformation of Mo and W over Co OR Its Alloy in Contact with Si

“…In our previous study for cobalt silicide, Mo or W overlying Co was employed as a passivating layer [6]; both metals were deposited using an e-beam evaporator at a base pressure of 4.0 x 10-6 torr. It was found that in normal flowing-nitrogen (N2 furnace, the Co was transformed into silicide, while the Mo or W did not become silicide but was either inert or oxidized at 400-600 *C. However, both Co and Mo (or W) were well transformed into silicides at 900 *C. On the other hand, Mo or W cannot react with Si to form silicide if it is deposited directly on Si substrate on the same depositing conditions, followed by either N 2 or H 2 furnace annealing.…”