NANO.IL.

Modification of the Effective Work Function of Titanium Nitride by the Reactive Gas Choice in Plasma Enhanced Atomic Layer Deposition Process

Ekaterina Zoubenko Materials Science and Engineering Department, Technion, Israel Institute of Technology, Haifa, Israel

The persistent race to sustain Moore`s law requires the introduction of novel materials, 3D devices, and versatile deposition techniques that allow a precise compositional control and a good step coverage. Refractory metal nitrides are promising candidates for metal gate in complementary metal-oxide-semiconductor field effect transistors (CMOSFET). One of the most important device performance parameters, the transistor`s threshold voltage, is determined by the effective work function (EWF) of the metal. Therefore, EWF modification is an important challenge. The plasma enhanced atomic layer deposition (PEALD) technique enables the deposition of thin and conformal films of various metals and their nitrides or carbides, and provides diverse parameters for EWF engineering.

The current work demonstrates the ability to modify the EWF of TiN deposited by PEALD using various reactive gases: N2, H2, NH3. X-ray reflectivity (XRR) is used for the films thickness determination, four-point probe for electrical resistivity, X-ray diffraction (XRD) for preferred orientation comparison, transmission electron microscopy (TEM) for microstructure study and X-ray photoelectron spectroscopy (XPS) for compositional depth profiling. The EWF of TiN on SiO2 is determined by capacitance-voltage measurements followed by plotting the flat-band voltage versus the oxide thickness.

TiN films, with a thickness of 25±1[nm] are polycrystalline and have low resistivity values of 242±15, 134±3, 207±8 [μΩ∙cm] for N2, NH3, H2 reactive gases, respectively. The choice of reactive gas determines the preferred orientation of the films: TiN deposited by N2 plasma is (100) oriented, (111) oriented in an H2 plasma process, and NH3-produced TiN presents an intermediate state. The microstructure, oxygen concentration and Ti:N ratio of the TiN films vary with the reactive gas as well. The obtained EWF values are 4.5±0.1, 4.85±0.05, 5.2±0.1 [eV] for N2, NH3, H2 reactive gases, respectively. A correlation between the structural and electrical properties of TiN/SiO2 interface is presented in the current work.









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