The annealing effect on work function variation of WN_xC_y films deposited by remote plasma atomic layer deposition

Abstract

Phone: þ82 10 4608 1464, Fax: þ82 2 2292 5957 Tungsten-nitrogen-carbide (WN x C y ) thin films were investigated as the metal gate of complementary metal-oxide-semiconductor (CMOS) devices. WN x C y thin films were deposited by employing the remote plasma atomic layer deposition (RPALD) using a bis(tert-butylimido) bis (dimethylamido) tungsten (BTBMW) precursor and hydrogen plasma as a reactant. The growth rate of the WN x C y films was about 0.12 nm/cycle. X-ray diffraction (XRD) analysis indicated that the films consisted of a mixture of tungsten carbide and tungsten nitride phases. The atomic force microscope (AFM) analysis further confirmed that the WN x C y film surfaces deposited by RPALD were smooth. In addition, the chemical bonding state analysis showed that the WN x C y films consisted of WN, WC, and WO phases. To measure the work function of the WN x C y film, a MOSCAP (metal oxide semiconductor capacitor) stack was fabricated and the flat band voltage was measured by current-voltage (C-V) measurements.A WN x C y work function value of 4.91 eV was suitable for p-MOS and the work function of the WN x C y films varied depending on the annealing treatment, and was higher than the work function of the as-deposited WN x C y film.1 Introduction As the feature size of the integrated circuits has continuously decreased, the complementary metal-oxide-semiconductor (CMOS) is affected by several critical properties such as boron penetration from the poly silicon gate to the gate oxide, polycrystalline silicon gate depletion, and high gate resistance, which causes resistance capacitance (RC) interconnection delay [1]. Various metal gate materials such as metals, metal nitrides, metal carbides, and metal silicide are candidates to replace the current use of the poly-Si gate electrode [2]. Among the materials considered for metallic gate electrodes, there are the elemental metal gates but they have several drawbacks. Elemental refractory metals such as Ni, Pt, and Ir for the p-MOS metal gate exhibit poor adhesion to the dielectric layer, are incompatible with the conventional plasma etch processes, and the materials are not cost effective [3]. Another problem with the elemental refractory metal gates is that their work function is difficult to fine-tune. As the