Effectiveness of Plasma Nitrided Silicon Oxynitride as a Barrier Layer between High k Materials and Si Substrates
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Effectiveness of Plasma Nitrided Silicon Oxynitride as a Barrier Layer between High k Materials and Si Substrates Yi-Sheng Lai and J. S. Chen Department of Materials Science and Engineering, National Cheng Kung University, Tainan, TAIWAN ABSTRACT In this work, low temperature (300 – 450oC) plasma nitridation was conducted using N2O and NH3 atmosphere to produce an ultrathin SiOxNy layer. The bonding structure, distribution, and quantity of nitrogen and their effects on the growth kinetic of SiOxNy layers are studied by X-ray photoelectron spectroscopy (XPS). It is found that nitrogen atoms pile at the SiOxNy/Si interface at the very beginning of plasma N2O and NH3 nitridation. Due to the lack of additional Si source and low diffusivity of O or N atoms at low temperature, plasma nitridation will form a self-limited growth of SiOxNy layer. Thermal stability of the interlayer between ultrathin Ta2O5 films on bare Si, plasma N2O nitrided Si, and plasma NH3 nitrided Si is also studied. INTRODUCTION The performance of metal-oxide-semiconductor devices depends strongly on the characteristics of the interface between high k materials and Si substrate. In recent reports, even the thermally stable high k materials like HfO2, ZrO2, and metal silicates still generate an interlayer (IL) during the deposition and/or subsequent postannealing process [1-4]. The cause possibly arises from the initial stage of SiOx growth on bare Si or the oxygen species diffusing across the ultrathin high k matrix to react with the Si substrate. Additionally, the interface states density (Dit) of high k materials is still high (1011 - 1012 cm-2eV-1) for the usage of MOSFET devices. As a result, engineering of the interface becomes a very challenging issue on high k gate dielectrics. Silicon oxynitride (SiOxNy), which has good interfacial properties and may act as a diffusion barrier against reaction between Si and high k materials, is a promising candidate for gate dielectric applications [5]. EXPERIMENTAL Bare n-type (100) silicon wafers were used as substrates. The Si surface was cleaned by a modified RCA clean and then dipped in 1% HF solution for 20 s to remove the native oxide. Followed by a DI water rinse and N2 dry, the Si wafer was placed on a 6 inch substrate holder. Nitridation was carried out in a cold-wall, single-wafer plasma-enhanced chemical vapor deposition (PECVD) chamber. N2O or NH3 gas was introduced to the chamber at a flow rate of 100 sccm, respectively. Keeping the total pressure at 0.4 Torr and temperature at 300oC, 350oC, 400oC, and 450oC, capacitively-coupled plasma was generated by a radio-frequency (rf, 13.56 MHz) power supply connected to the showerhead plate with a power of 50 W and the substrate holder was grounded. Chemical bonding states of nitrided Si surfaces were examined by using VG ESCA-210
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X-ray photoelectron spectroscope (XPS) equipped with a 12 kV Al/Mg X-ray source. XPS measurements were performed using Mg and Al Kα emission at 1253.6 eV and 1486.6 eV. Thickness of the overlayer is determi
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