The intrinsic and extrinsic contributions to Fermi level pinning of platinum (Pt) electrodes on hafnium dioxide (HfO2) gate dielectrics are investigated by examining the impact of oxygen and forming gas anneals on the effective work function of Pt-HfO2-silicon capacitors. The effective platinum work function is ∼4.6eV when annealed in forming gas. However, diffusion of oxygen to the Pt∕HfO2 interface increases the platinum work function to a value of ∼4.9eV. Subsequent annealing in forming gas returns the platinum work function to a value comparable to that measured prior to the oxygen anneal. The effective platinum work functions are compared to the prediction of the metal induced gap states (MIGS) model. The presence of interfacial oxygen vacancies or platinum–hafnium bonds is believed to be responsible for a degree of pinning that is stronger than predicted from the MIGS model alone.

and PMOS (AQi is negligible. However, AVfb does not reach OV We report here for the first time that Fermi pinning at the because Si-Hf and Si-0-Hf bonds co-exist at the polySi interface. The polySilmetal oxide interface causes high threshold voltages in AVfb saturation value depends only on the bond number ratio. A MOSFET devices. Results indicate that pinning occurs due to the comparison of AVfb for HfOz (ALD or MOCVD) and HfSixOy interfacial Si-Hf and Si-0-AI bonds for HfO, and AIzO,, respectively. (MOCVD) films deposited with different precursors and dopant This fundamental characteristic also affects the observed polySi activation anneals produce, the universal curve in Fig. 11. The slight depletion. Device data and simulation results will be presented. variation in AVb for Hf02 can be attributed to differences in Keywords: Hf02, AI203, Fermi pinning, polYd, gate dielectric. processing conditions. Our data indicates that the shifts of Vfb(n+) INTRODUCTION and Vfb(pt) from the characteristic values for SiO, NMOS and Scaling MOSFETs to improve performance results in PMOS are a fundamental characteristic of the PolySilMeOx interface. higher gate leakage as the SiOz gate melectic becomes thinner. To These shifts are responsible for the observed high Vts. address this issue, there has been much interest in hafnium-based The impact of the sub-monolayer HfOz on the CETacc is dielectrics as a potential gate dielectric [1-3]. Two major issues shown in Figs. 12 and 13. Although the p+ gate CETacc increases evident in numerous publications [1-3] that must be addressed to with each subsequent cycle, the n+ gate has a CETacc minimum at IO fabricate useful devices for CMOS circuit applications are (1) the cycles, The n+ gate is in depletion and the minimum indicates Si-Hf high threshold voltages and (2) the large CETinv difference between bonds reduce the polySi depletion. To investigate this further, CMOS NMOS and PMOS. To date, a PolySiIMeOx CMOS process with devices were fabricated (Fig. 14). The polySi depletion for ntgate acceptable Vts for both NMOS and PMOS has not been reported. NMOS (p+ gate PMOS) is decreased (increased) when SiOz is capped Defects and charge within the gatestack (Fig. I ) can result with HfO,. This tradeoff in polySi depletion is attributed to Fermi in substantial Vt shifts. At the top interface, Fermi pinning is a pinning near (Fig. 8). Less band bending occurs for n+ polySi mechanism known to cause high Vts for metal gates [41. Considering because the polySi interface is pinned close to the bulk polySi Fermi the polySi/MeOx interface shown in Fig. 2, the question arises, 'Are level. For p+ gates, more band bending occurs because the interface is the metal atoms at the interface part of the dielectric or part of the pinned further away from the bulk. This effect occurs for low and gate electrode?' This raises the issue as to whether the interface bonds high temperame activation anneals (Fig. 15). This effect is the likely affect the Vt. In this work, we examine the role of the polySiIMeOx cause...

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First-principles calculation has become an indispensable methodology in revealing the working principles of nanoscale electronic devices, but ultra-large supercells are usually required in modeling the devices with critical metal/dielectric interfaces. Traditional density functional theory within the generalized gradient approximation (GGA) suffers from the inaccurate band gap problem when metal oxides are present, but they serve as the core component in resistive random access memory (RRAM), which is a promising path for novel high speed non-volatile memories. To obtain improved oxide band gaps, we applied the efficient GGA-1/2 method for self-energy correction, whose computational load is at the same level as standard GGA. In particular, we have investigated the influence of exchange-correlation functional flavors on the GGA-1/2 band structures, taking four important binary oxide RRAM materials (α-Al 2 O 3 , r-TiO 2 , m-ZrO 2 and m-HfO 2 ) as benchmark examples. Five GGA functionals (PBE, PBEsol, PW91, revPBE and AM05) were considered and their band structures were compared in detail. We have found that the performance of GGA-1/2 is comparable to state-ofthe-art GW and generally superior to the HSE06 hybrid functional. Among the five GGA functionals, PBEsol yields the best results in general. In addition, the applicability of a single self-energy potential for various GGA-1/2 flavors is discussed. Our work provides a guide to the GGA flavor selection, when applying the GGA-1/2 method to metal oxides. manifest a transition from a high resistance state (HRS) to a low resistance state (LRS) upon the formation of conductive filaments (CFs) connecting the two electrodes. Yet, at present there are still controversies on the exact composition and geometry of the CFs [19][20][21][22]. Since it is difficult to directly observe and determine experimentally the exact composition of the CFs within the dielectric media, theoretical approaches can be particularly helpful.Among atomistic simulation techniques, ab initio calculations based on density functional theory (DFT) [23] are highly successful in the prediction of total energies, bond lengths, and vibration frequencies. However, DFT within local density approximation (LDA) or generalized gradient approximation (GGA) severely underestimates the band gaps of semiconductors and insulators, which limits its capability of predicting the band alignment in metal/semiconductor contacts, a significant task in understanding charge transmission through CFs [24]. Various theoretical approaches have been proposed to overcome this shortcoming, thus providing more reliable predictions of physical properties that depend on excited states. Hedin's GW approximation is considered to be the state-of-the-art, which is still the most accurate method for electronic structure calculation. It calculates the quasiparticle energies in terms of the perturbation theory [25], and is a beyond-DFT technique. Hybrid functionals [26], which combine standard DFT and Hartree-Fock exchange functionals thro...

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