Mechanism of Hf-silicide formation at interface between poly-Si electrode and HfO2∕Si gate stacks studied by photoemission and x-ray absorption spectroscopy

Abstract

We have investigated the mechanism for silicidation by chemical reactions at polycrystalline-Si (poly-Si)∕HfO2∕Si gate stacks by annealing in ultrahigh vacuum using photoemission spectroscopy and x-ray absorption spectroscopy. Si 2p, Hf 4f, and O 1s high-resolution photoemission spectra have revealed that a Hf-silicide formation starts at as low temperature as 700°C and that a Hf silicate is also formed at the interface between poly-Si electrodes and HfO2. The metallic Hf silicide is formed at the interface between HfO2 and Si substrates, which changes the band offsets on Si substrates. We have found that poly-Si electrodes promote the interfacial reaction between HfO2 and Si substrates, while the crystallization in a HfO2 layer is independent of the silicide formation. The silicidation mechanism based on photoemission spectra is also confirmed from the thermodynamical analysis considering the Gibbs’ free energy.

Degradation kinetics of ultrathin HfO2 layers on Si(100) during vacuum annealing monitored with in situ XPS/LEIS and ex situ AFM

“…In the case of Si cap layer (no SiO 2 layer at HfO 2 /Si interface), HfO 2 film degradation and Hf silicide formation is found to occur at lower temperature (T % 750-800°C) [15,11]. This observation suggests that the SiO 2 IL can act as a barrier against reaction between HfO 2 and Si(1 0 0) at T ann > 750°C.…”

“…1b and c). Indeed, Si in direct contact with HfO 2 has been found to react at T > 850°C [15,11]. Since Si is found as an ultrathin ($1 ML) surface layer, we believe that Hf silicide does not exist as a stable phase at this stage of annealing, rather these are Hf-Si bonds on HfO 2 surface.…”

“…Since post-oxide-growth annealing is part of the MOS device fabrication process, the issue of HfO 2 thermal stability in contact with Si has recently received significant attention. It is established that upon annealing under reducing conditions, the degradation of HfO 2 occurs in the 800-950°C temperature range (depending on O 2 partial pressure and HfO 2 layer thickness) with the formation of voids in HfO 2 [7,8] and its eventual conversion into silicide [9][10][11]. However, the initial reason which ''ignites'' such degradation is still debated.…”

Control of oxidation and reduction reactions at HfSiO∕Si interfaces through N exposure or incorporation

“…In Fig. 1͑a͒ 9 In Fig. 1͑b͒, broad peaks of Si 2p located at higher binding energy than the substrate components ͑99.2 eV͒ represent Si-oxide components.…”

Structural degradation of thin HfO2 film on Ge during the postdeposition annealing

“…[2][3][4] Since the gate stack structures usually undergo high-temperature processes ͑Ͼ800°C͒ in the device fabrication, thermal stability of thin HfO 2 film on these semiconductor surfaces is a crucial issue. [6][7][8][9][10][11][12] Surface microscopic studies for the annealing of HfO 2 / Si structures in vacuum have revealed that void nucleation initially takes place in HfO 2 films, and leads to the silicidation. Although thermodynamic considerations suggest that the contact of HfO 2 with Si is thermally stable up to 1000°C, 5 the experimental studies have shown that local decomposition accompanied by Hf silicidation takes place at the temperature higher than 700°C.…”