http://dx.doi.org.libproxy.ucl.ac.uk/10.1016/j.apsusc.2007.02.150 Get rights and content Applied Surface Science Volume 253, Issue 19, 31 July 2007, Pages 7869ದ7873 Photon-Assisted Synthesis and Processing of Functional Materials ಧ E-MRS-H Symposium Hf 1−x Si x O y dielectric films deposited by ≥V-photo-induced chemical vapour deposition (≥V-CVD) M. Liu c , L.Q. Zhu c , G. He c , Z.M. Wang b , J.X. Wu b , J.-Y. Zhang b , I. Liaw, Q. Fang a, , , Ian W. Boyd a Abstract Hf 1−x Si x O y is an attractive candidate material for high-k dielectrics. We report in this work the deposition of ultra-thin Hf 1−x Si x O y films (0.1  x  0.6) on silicon substrate at 450 °C by ≥V-photo-induced chemical vapour deposition (≥V-CVD) using 222 nm excimer lamps. Silicon(IV) and hafnium(IV) organic compounds were used as the precursors. Films from around 5 to 40 nm in thickness with refractive indices from 1.782 to 1.870 were grown. ≤he deposition rate was found to be of 6 nm/min at a temperature of 450 °C. ≤he physical, interfacial and electrical properties of hafnium silicate (Hf 1−x Si x O y ) thin films were investigated by using X- ray photoelectron spectroscopy, ellipsometry, F≤-IR, CದV and IದV measurements. XRD showed that they were basically amorphous, while Fourier transform infrared spectroscopy (F≤-IR), clearly revealed HfದOದSi absorption in the photo-CVD deposited Hf 1−x Si x O y films. Surface and interfacial properties were analysed by ≤EM and XPS. It is found that carbon content in the films deposited by ≥V-CVD is very low and it also decreases with increasing Si/(Si + Hf) ratio, as low as about 1 at.% at the Si/(Si + Hf) ratio of 60 at.%. Keywords High-k dielectrics; Hf 1-x Si x O y films; HfO 2 /Si interface; CMOS technology; ≥V photo induced chemical vapour deposition (≥V-CVD) 1. Introduction ≤he substitution of SiO 2 as complementary metal oxide semiconductor (CMOS) with high-k materials as gate dielectrics grows to be more important than ever when the SiO 2 scales thinner than 20 Å [1]. Silicon oxide layers thinner than 2 nm present a number of fundamental problems, such as oxide reliability and high gate leakage current over 1 A/cm 2 due to direct tunnelling through the oxide [1], [2] and [3]. ≤he use of a higher dielectric constant material allows the gate oxide to be thicker with the same effective capacitance. Many high-k materials have been studied recently for the integration with standard CMOS technology and most of them are found to be thermally unstable and cause low permittivity interfacial layer in contact with silicon [4]. ≤heoretically, good gate dielectrics must have high dielectric constant, thermal and chemical stability on Si, wide bandgaps and band offsets with silicon of over 1 eV for both electrons and holes in order to have low leakage currents [5]. Hafnia (HfO 2 ) is an attractive candidate material for high-k dielectrics and hafnium oxides satisfy many of the requirements needed to replace SiO 2 in the next generation silicon devices since they have a higher dielectric constant (k = 25), wide bandgap of about 6 eV and band offsets with silicon of 1.5 eV, and high stability with the Si substrate, based on Gibbs free energy analysis under equilibrium conditions [6]. However, many authors have reported the formation of low-k layers between HfO 2 /Si interfaces during film deposition or high-temperature annealing process [7], [8], [9] and [10]. ≤he interfacial low-k layers (SiO 2 , or hafnium silicate) limit the maximum achievable capacitance of the gate stack [4]. It is believed that oxygen ions or atomic oxygen (O) and Hf ions interdiffuse through these films either in a vacancy sub-lattice or grain boundary so that interfacial layers are formed at HfO 2 /Si interfaces [11]. Wilk et al. proposed the use of silicates as a gate dielectric [12] and [13]. ≤heir work focused mainly on studies of dielectric films formed by reactive sputtering of Zr and Hf. ≤hey obtained an equivalent oxide thickness (EO≤) of about 16 Å and a k = 11 for a Hf silicate film incorporating 6 at.% Hf. ≤he overall permittivity of Hf silicate film is inevitably lower than that of the pure metal oxide. However, silicate films can further avoid the formation of low-k interfacial oxide layers due to a high resistivity to oxygen diffusion [4] and [12]. Also, the incorporation of SiO 2 into HfO 2 or ZrO 2 films helps stabilizing an amorphous structure during high-temperature annealing with enhanced interface carrier mobility [12], [14] and [15]. For these reasons Hf or Zr-silicates are the most promising dielectric materials in direct contact with Si [16]. Hafnium silicate films have been previously deposited by a variety of methods, including RF and DC sputtering [4], [12] and [8], ≥V/ozone oxidation of metal silicides [17], atomic layer deposition (ALD) [18], Show more Search ScienceDirect Advanced search Download PDF Export O More options... Journals Books Brought to you by: UCL Library Services Shopping cart Help Sign in