The effect of nitrogen content on crystal structure ͑phase and grain size͒ and work function ͑⌽ m ͒ of WN x films is investigated. The ⌽ m of WN x films is extracted from the plot of flatband voltage versus SiO 2 thickness. For W and WN 0.4 films, the ⌽ m are 4.67 and 4.39 V, and their crystal phases are both body-centered-cubic W. For WN 0.6 film, it contains W + W 2 N mixed phases and the ⌽ m is 4.50 V. On the other hand, the ⌽ m of WN 0.8 and WN 1.5 films are 5.01 and 4.49 V, and their crystal phases are both face-centered-cubic W 2 N. The grain size of W and W 2 N phases decreases with the increase of the nitrogen content in WN x. It is concluded that the ⌽ m is affected by the crystal phase as well as the grain size of WN x film.

Articles you may be interested inStructural and electrical characteristics of high quality (100) orientated-Zn 3 N 2 thin films grown by radiofrequency magnetron sputtering Epitaxial Ti 1-x W x N alloys grown on MgO(001) by ultrahigh vacuum reactive magnetron sputtering: Electronic properties and long-range cation orderingThe crystal structure, chemical bonding state, composition, and electrical resistivity of W-N films deposited by reactive rf sputtering are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, and four-point probe. Using 150 W of sputtering power and 25% of N 2 partial flow rate, the deposition rate and resistivity of W-N films decrease with increasing negative substrate bias. When the substrate bias is set at Ϫ100 V, resistivity of W-N films increases while the deposition rate decreases with increasing N 2 partial flow rate. WϩW 2 N mix phase, W 2 N phase, and W 2 NϩWN mix phase are obtained at 10%, 15%-25%, and 40% of N 2 partial flow rate, respectively. When the N 2 partial flow rate is greater than 40%, the films become amorphous like. Nitrogen concentration in the W-N films increases continuously with increasing N 2 partial flow rate, and the W 4 f core-level electrons change gradually from metallic W bondings to WN bondings. By reducing the sputtering power to 50 W, we have found that film resistivity also rises with increasing N 2 partial flow rate but crystalline W 2 N phase can be obtained with 10%-50% of N 2 partial flow rate. The connection between the process conditions, structural change and electrical resistivity of the sputtered W-N thin films is discussed.

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 ...

The thermal stability and electrical properties of W 2 N/Ta 2 O 5 /Si metal oxide semiconductor ͑MOS͒ capacitors upon post-metal annealing in H 2 or N 2 ϩ H 2 ambient at 400-600°C for 30 min are investigated. After annealing at 400-500°C, the W 2 N gate remains intact but, due to loss of nitrogen, partly transforms to WO 3 after annealing at 600°C. The partial oxidation of W 2 N is more noticeable when annealing in H 2 ambient than in N 2 ϩ H 2 , and also induces greatly increased resistivity. However, the capacitance-voltage ͑C-V͒ curves of the W 2 N/Ta 2 O 5 /Si MOS capacitors are similar before and after post-metal annealing. C-V hysteresis measurements showed that charges within the Ta 2 O 5 layer of the as-fabricated MOS structure are positive, and the density is 4.94 ϫ 10 12 cm Ϫ2 . After annealing in H 2 , the charge density decreased with increasing annealing temperature, and the charge polarity became negative after annealing at 600°C. In N 2 ϩ H 2 , the charge polarity became negative right after annealing at 400°C, and the density was below 10 12 cm Ϫ2 . For the I-V curves, the leakage current decreases with increasing annealing temperature at positive bias, and H 2 annealing results in lower leakage currents than N 2 ϩ H 2 annealing. In contrast, the leakage currents are all similar when the samples are stressed at negative bias, regardless of the annealing temperature and ambient.Poly-Si/SiO 2 stacks have been utilized as the gate structure of metal oxide semiconductor field effect transistors ͑MOSFETs͒ for decades. The high direct tunneling currents and boron penetration preclude the use of SiO 2 as gate dielectrics when its thickness decreases to below 2 nm in the sub-100 nm generation. To solve this problem, high dielectric constant ͑high k͒ materials are employed as gate oxides. At the same capacitance, high k materials have a greater physical thickness to prevent direct tunneling currents. Among the high k materials, tantalum pentoxide (Ta 2 O 5 ) 1,2 has been widely investigated as the capacitance film in dynamic random access memories. 3,4 Accompanied by the exploration of high k gate oxides, researchers also attempted to find new materials for gate electrodes. The key parameters for new gate electrode materials included work function, resistivity, and compatibility with the existing semiconductor processes. Metals and metal alloys are attractive candidates for alternate gate electrode materials because, unlike poly-Si, they do not suffer from the depletion effect. Therefore, a metal ͑or metal nitride͒/high k oxide stack is an interesting structure for gate application.The electrical properties of W, 5 W/TiN, 6,7 W/WN x , 6,8 TiN, 5,9-11 WN x , 5,11 and TaN 12 have been investigated for gate electrode applications in MOS systems. WN x is considered as a promising gate electrode because of its high melting point and low electrical resistivity ͑Ͻ1000 ⍀-cm for thin films͒. Comparable studies on WN x and TiN electrodes for Ta 2 O 5 gate oxides demonstrated that after post-metal annealing, the WN x...

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