The effects of nitrogen concentration on the thermal stability and electric properties of the WN x film as the gate electrode are investigated. WN x is deposited by using reactive radio frequency sputtering, and films with composition of WN 0.6 , WN 0.8 , and WN 1.5 are obtained at 10, 25, and 40% of N 2 partial flow ratio, respectively. The crystal structure of the WN 0.6 film indicates that this film is a mixture of W + W 2 N, while WN 0.8 and WN 1.5 films both show the W 2 N phase. After annealing in N 2 + H 2 ͑N 2 /H 2 = 9:1͒ ambient at 500°C, the surface of the WN 0.6 film reveals only the W-O bonding but no W-N bonding. In addition, oxygen diffuses from SiO 2 into WN 0.6 and leads to the formation of a mixing layer. Subsequently, flatband voltage ͑V FB ͒ of the metal oxide semiconductor capacitor shifts positively after annealing at 500°C. After annealing at 500°C, WN 0.8 and WN 1.5 films exhibit better resistance to oxidation than the WN 0.6 film, regardless of the surface of the WN x film or the interface between WN x and SiO 2 . Resistivity of all WN x films increases after annealing and also increases with increasing nitrogen content in the WN x films. However, neither the nitrogen content in the WN x nor the postmetal annealing affect the leakage current of WN x /SiO 2 /Si capacitors at both positive and negative biases.The dimension of complementary metal oxide semiconductor ͑CMOS͒ devices shrinks continuously in order to improve the electrical performance. At the same time, the choice of the gate electrode materials becomes an important issue. The conventional polysilicon gate electrode of CMOS devices suffers several problems, such as gate depletion and boron penetration into the channel region. 1-4 Gate depletion decreases the capacitance of the device and degrades the driving capability of the channel current. 1,2 Boron penetration in the p-channel metal oxide semiconductor field effect transistor ͑PMOSFET͒ reduces the control of threshold voltage and gate oxide reliability. 3,4 Therefore, metals or metal nitrides are interesting materials for gate electrode applications.Gate electrode work functions, resistivity, and compatibility with CMOS technology are key parameters. 5 Nitrogen-implanted Mo ͑Ref. 6͒ and thin films of Ti 1−x Al x N y , 7 Ta-Pt, 8 Ta-Ti, 8 and Ti-Ni ͑Ref. 9͒ have been investigated as gate electrodes. By varying their atomic composition, these materials may possess a suitable work function for gate-electrode applications. The thermal stability of TiN, [10][11][12][13]13,14 TaN, 15 Ta,16 TaSi x N y , 17 and WSi x ͑Ref. 18͒ has been discussed to see their compatibility with the gate-electrode process. Unfortunately, metal nitrides generally exhibit high resistivity. However, resistivity of gate electrodes can be reduced by the stacking structure, such as W/TiN, 19-21 W/WN x , 20 and Ta/TaN x . 22 Therefore, the literature suggests that metal nitrides are approved materials for gate electrodes. Nevertheless, the nitrogen concentration and structure of metal nitride gate electrodes ...
