Characterization of Ultra-Thin Ni Silicide Film by Two-Step Low Temperature Microwave Anneal

NiSi,atransitionmetalsilicide,hasbeenincreasinglyusedforcontacts in the latest complementary metal oxide semiconductor (CMOS) devices, owing to its low temperature of formation and low Si consumption during silicidation, low sheet resistance (RS) and lower leakage current. 1,2 The use of NiSi currently faces a difficult trade-off between thickness and sheet resistance. The contact junction depth must still scale with gate length. To avoid high contact resistance and high contact leakage, no more than half the contact junction depth can be consumed in the formation of the silicide. Therefore, the silicide must become progressively thinner to accommodate the more shallow contact junction for scaled contacts. The rapid thermal annealing (RTA) has been widely used for silicidation and exhibits difficult thinthickness and phase control. Microwave annealing (MWA) 3 has been realized to activate implanted dopants through solid phase epitaxial regrowth at low temperature. 4 It is promising for achieving advanced Si or Ge CMOS because of its unique volumetric heating and low temperature due to apparent non-thermal energy transfer. 5 The advantages of replacing rapid thermal annealing (RTA) with MWA are ultra-thin NiSi formation, diffusion-less junction, improved capacity of gate oxide and lower gate leakage. In this work, a novel two-step low temperature MWA process is used to form homogeneous NiSi contact films with low sheet resistance while not sacrificing thickness and quality. During silicidation, many kinds of nickel silicide phases may appearsimultaneously. 6 Ithasbeenreportedthatthepredominantphases are Ni2Si, NiSi and NiSi2, form in the ranges 200‐350, 350‐750, and 750‐1000 ◦ C, respectively. 7 The NiSi has the lowest resistivity among three different phases and other metal silicides. Furthermore, the Ni atoms are the primary moving species during the formation of NiSi phase. It could prevent the bridging effect which results in short circuit area between gate and source/drain. 8 It is well recognized that identification of nickel silicide phases after annealing is of crucial importance to its performance, especially, while these phases are formed innano-polycrystallinelayer.Inthisstudy,weuseelectronenergy-loss spectroscopy 9‐13 andenergydispersiveX-rayspectroscopy 13,14 inconjunction with scanning transmission electron microscopy 14 (STEMEELS/EDS) in order to identify the nickel silicide phases concentrating primarily on the Z-contrast image with atomic spatial resolution, elemental analysis, bulk plasmon excitaions and the chemical bonding.