Group IVB Oxides as High Permittivity Gate Insulators

Abstract

Increasing MOSFET performance requires scaling, the systematic reduction in device dimensions. Tunneling leakage, however, provides an absolute scaling limit for SiO2of about 1.5 nm. Power limitations and device reliability are likely to pose softer limits slightly above 2 nm. We have investigated the use of high permittivity materials such as TiO2, ZrO2, and their silicates as potential replacements for SiO2. We have synthesized titanium nitrate (Ti(NO3)4or TN), zirconium nitrate (Zr(NO3)4or ZrN), and hafnium nitrate (Hf(NO3)4or HfN) as hydrogen and carbon free deposition precursors. Several problems arise in the use of these films including the formation of an amorphous low permittivity interfacial layer. For TiO2this layer is formed by silicon up diffusion. Surface nitridation retards the formation of the interfacial layer. We discuss the effects of both thermal and remote plasma surface nitridation treatments on the properties of the film stack. ZrO2and HfO2appear to form a thermal layer of silicon oxide between the high permittivity film and the silicon and have excess oxygen in the bulk of the film.

Characterization of hafnium silicate thin films grown by MOCVD using a new combination of precursors

“…The chlorine and nitrogen contaminations were less than 0.1 at% (below detection limits). Our preliminary experiments showed that Hf(NEt 2 ) 4 easily decomposes on Si(1 0 0) even below 300 C but Si(O n Bu) 4 does not decompose at 400 C. However, Si(O n Bu) 4 was reacted to grow silicate films in the presence of small amounts of Hf(NEt 2 ) 4 . From these results, we believe that Hf metal catalyzes the C-O bond scission of Si(O n Bu) 4 , These reactivity differences of precursors and catalytic effects might induce Hf-rich phases in the initial growth steps.…”

“…During deposition, the pressure in the reactor was maintained at 0.1 Torr. The temperatures (vapor pressures) of Hf(NEt 2 ) 4 and Si(O nBu) 4 bubblers were fixed at 70 C (0.7 Torr) and 95 C (2 Torr), respectively. The transport lines were kept at 100 C to avoid condensation of precursors.…”

“…Among high-k materials, HfO 2 and ZrO 2 are attractive candidates due to high stability with the Si substrate, based on Gibbs free energy analysis under equilibrium conditions [3]. In practice, however, during film deposition or high-temperature annealing process, atomic oxygen (O) very fast diffuses through these films either in a vacancy sub-lattice or grain boundary so that interfacial layers are formed at HfO 2 /Si and ZrO 2 /Si interfaces [4]. The interfacial silicon oxide layer limits the maximum achievable capacitance of the gate stack, or equivalently, the minimum achievable t eq value, where t eq is an electrical thickness equivalent for pure SiO 2 [5].…”

“…High-resolution TEM image of an interface between silicon substrate and hafnium silicate film grown by MOCVD using Hf(NEt 2 )4 and Si(O n Bu)4 precursors at 400 C. Due to edge effects, the substrate in interfacial edges looks bright.…”

An MOCVD Approach to High‐k Praseodymium‐Based Films

“…They introduce considerable uncertainties such as, the variability in the composition of interfacial layers beneath the deposited oxide dielectric layers that leads to the conclusion that the growth of such layers might have severe drawbacks in terms of an accurate control. [50,51] …”