Oxidation of the Pt∕HfO2 interface: The role of the oxygen chemical potential

Abstract

Using first-principles calculations we investigated the oxidation properties of model Pt∕HfO2 interfaces as a function of oxygen partial pressure. A wide range of interfacial oxygen concentrations were explored, varying from an oxygen-free interface to the case of 1 oxygen ML separating the Pt(111) slab from the first Hf plane in the monoclinic HfO2(001) slab. In all cases the interfaces were optimized using ab initio molecular dynamics. It was found that 1 ML of oxygen at the Pt∕HfO2 interface is only possible for chemical potentials equivalent to an oxygen pressure of tens of bars. With respect to silicon oxidation only the oxygen-free interface is stable. Depending on the anneal conditions, intermediate concentrations of ~0.25 or ∼0.75 ML of oxygen at the interface are possible, while the concentration of 0.5 ML is only stable over a narrow range of conditions. The band offset and work of separation were calculated for Pt∕HfO2 interfaces as a function of the oxygen concentration at the interface. The valence band offset drops sharply with increasing oxygen chemical potential, from ∼3.0 to ∼1.0 eV. The same trend is observed for the work of separation, which decreases from ∼6 J∕m2 for an oxygen-free interface to ∼1 J∕m2 for one oxygen monolayer. These findings may shed new light into recent experimental data reporting exceedingly small values for the effective work function of Pt on HfO2 and its dependence on the oxygen partial pressure during high temperature annealing.

Metal gate work function tuning by Al incorporation in TiN

“…The EWF values obtained were 5.60 eV and 5.05 eV, respectively, in good correspondence which values reported in the literature. 8,17 From Al dif. devices (see Table I) the extracted TiN EWF value was about 4.68 eV.…”

Environment-dependent interfacial strength using first principles thermodynamics: The example of the Pt-HfO2 interface

“…A previous DFT study calculated the W sep of the Pt-HfO 2 heterostructure for the same O coverages studied here. 8 However, only the interfacial plane of each heterostructure was considered. 8 The values and the tendency obtained here for W sep are consistent with the ones reported in this past work.…”

“…Nevertheless, the interfacial strength has defied a quantitative and universal understanding, primarily because it is not an intrinsic property of the system, but a result of the interplay between factors such as interfacial composition, 4 the atomic-level structure at the interface, 5,6 and the environment (temperature, pressure, and chemical potentials). 7,8 On the experimental side, several well known methods are available to quantitatively understand the linkages between such extrinsic factors and interfacial adhesion, also referred as the work of separation (W sep ). These include the four-point bending fracture test 9 and the contact angle measurement.…”

“…10 On the computational side, first-principles density functional theory (DFT) computations have been instrumental in determining and understanding W sep for a plethora of important metal-insulator interfaces. [3][4][5][6][7][8][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] However, a major drawback of past DFT work is that they apply strictly to 0 K situations. Since the interface atomic configuration appropriate for a given set of experimental measurement conditions (temperature and pressure) is a priori not known, the general practice has been to compute W sep for a variety of different interfacial atomic configurations.…”

Impact of nitrogen on effective work function of metal/oxide stack: A first-principles study of the Pt/HfO2 interface

“…The Pt/HfO 2 interface stack is usually annealed in forming gas or ambient atmosphere which contains N 2 , especially in the post metallization anneal (PMA) process of gate-first CMOS integration scheme [11]. The role of oxygen at the Pt/HfO 2 interface has been researched extensively [12], but how nitrogen impacts the metal/ metal oxide interface remains unknown.…”