Investigation of Molybdenum Nitride Gate on SiO[sub 2] and HfO[sub 2] for MOSFET Application

Abstract

It has been reported that the work function of nitrided molybdenum ͑MoN͒ can be modulated by the atomic ratio of N/Mo and is suitable for gate material of complementary metal oxide semiconductor devices. In this work, we investigated the characteristics of MoN x prepared by reactively sputtering deposition from the gate electrode point of view. The main phase of the MoN x films is MoN͑200͒. As the N/Mo ratio increases, the microstructure of MoN x film tends to be amorphous-like and the resistivity increases. After high-temperature annealing, the phase remains stable and grain size increases slightly. The HfO 2 film has better immunity to sputtering damage than SiO 2 film; therefore, the sputtering deposition method could be a choice of metal gate deposition as HfO 2 -based dielectric is used. The work function of MoN x increases with the increase of nitrogen content and tends to saturate at the valence band of Si. No Fermi-pinning effect is observed on HfO 2 film. The work function and thermal stability of MoN x show good thermal stability on both SiO 2 and HfO 2 films up to 800°C at least. All of these results indicate that MoN is a good candidate of gate electrode for p-type metal oxide semiconductor field effect transistors ͑pMOSFETs͒ or fully depleted SOI devices.Metal gates are expected to replace polysilicon gates beyond the 45-nm technology node, according to the ITRS roadmap. 1 Suitable work function ͑⌽ m ͒ and chemical inertia of metal gates are the two main criteria for proper threshold voltage and easy device integration, respectively. The work function of metal gates should be 4.1-4.4 eV for bulk n-type metal oxide semiconductor field effect transistors ͑nMOSFETs͒ and 4.8-5.1 eV for bulk p-type MOSFETs ͑pMOSFETs͒. 2,3 The chemical inert metal gates should be thermally stable enough to avoid chemical reaction with gate dielectric and the surrounding insulators during source/drain dopant activation. With these properties, metal gates could be suitable for the conventional gate process, which is much simpler than the replacement gate process. 4-10 Actually, for the complementary metal oxide semiconductor ͑CMOS͒ fabricated with conventional gate process, dualwork-function metal gates would still be crucial if two different metal gate materials are required. 11,12 The significant challenges are removing the gate materials without damaging the underlying dielectric and simultaneous patterning different gate electrodes.Molybdenum ͑Mo͒ films have drawn a lot of attention as a single metal gate electrode of CMOS devices because the work function of Mo on SiO 2 can be adjusted from 4.36 to 4.95 eV. 13-18 Moreover, molybdenum has low resistivity, good thermal stability, and high density, which is a benefit for ion-implantation mask. 15,16 The work function of molybdenum varies with the bulk microstructure, which depends on the deposition and annealing conditions. 17,18 It can also be modulated by the implantation of nitrogen or argon. 2,18-21 The work function of the ͑110͒-oriented Mo film is 4.95 eV. After nitr...

Effect of Nitrogen on the Physical Properties and Work Function of MoNxCap Layers on HfO2Gate Dielectrics

“…The effective work function increases significantly with the addition of nitrogen and then gradually saturates with increasing nitrogen concentration. Our results show a similar trend to the work reported by Tsui et al 29 and Tewg et al 30 Hinkle et al demonstrated that when the O atoms at the interface are replaced by N atoms, the effective work function will increase due to a balance of two opposing dipoles associated with the Ti and Hf atoms at the interface, i.e. the sequence O-Hf-O-Ti-N is being replaced by O-Hf-N-Ti-N. 46 In our case, the polarizability of Hf is also larger than that of Mo, and the sequence O-Hf-O-Mo-N is partially substituted by O-Hf-N-Mo-N. As a result, the increase in the effective work function of MoN x gates is possibly due to the increase of nitrogen atoms at the gate/dielectric interface, which in turn creates a net increase of the work function.…”

“…In previous studies, the work function of MoN x gate electrodes on SiO 2 and on HfO 2 has been demonstrated. [27][28][29][30] Nevertheless, the effect of nitrogen concentration on the structure and work function of bilayer Mo/MoN x on HfO 2 are not fully explored. In this study, Mo/MoN x stacks are employed as gate electrodes and HfO 2 is chosen as the gate dielectrics of metal-oxide-semiconductor (MOS) capacitors.…”

Adaptive Mo2N/MoS2/Ag Tribological Nanocomposite Coatings for Aerospace Applications

“…In the last decade, thin layers of molybdenum nitride (Mo-N) have been investigated as materials with a wide variety of potential applications that include catalysis [1,2], superconductivity [3,4], diffusion barriers for copper interconnects [5], gate electrode materials for high-k gate dielectrics [6,7], and as corrosion-and wear-resistant coatings [8,9]. The Mo-N system was reported to crystallize in three possible phases, namely, face-centered cubic Mo 2 N, tetragonal Mo 2 N, and hexagonal MoN [8].…”

Dependence of crystal structure and work function of WNx films on the nitrogen content

“…The advantage of using transition metal nitrides as gate electrode is due to not only their thermal stability but also their tunable ⌽ m . Therefore, ⌽ m of the TiN x , TaN x , 5 MoN x , 6 and HfN ͑Ref. 7͒ have been studied.…”