Chemical states and electrical properties of a high-k metal oxide/silicon interface with oxygen-gettering titaniummetal-overlayer Appl.We present theoretical and experimental results regarding the thermodynamic stability of the high-k dielectrics ZrO 2 and HfO 2 in contact with Si and SiO 2 . The HfO 2 /Si interface is found to be stable with respect to formation of silicides whereas the ZrO 2 /Si interface is not. The metal-oxide/SiO 2 interface is marginally unstable with respect to formation of silicates. Cross-sectional transmission electron micrographs expose formation of nodules, identified as silicides, across the polycrystalline silicon/ZrO 2 /Si interfaces but not for the interfaces with HfO 2 . For both ZrO 2 and HfO 2 , the x-ray photoemission spectra illustrate formation of silicate-like compounds in the MO 2 /SiO 2 interface.

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.

.66. Dk, 68.37.Lp Crystallization of hafnia and zirconia and their alloys with silica and lanthana was studied in bulk and thin film samples by thermal analysis, X-ray diffraction and electron microscopy. Crystallization temperatures of hafnia and zirconia increase by more than 300 °C with increase of surface/interface area of the amorphous phase. Crystallization temperatures of zirconia and hafnia alloys with silica and lanthana increase with dopant content and exceed 900 °C for 50 mol% SiO 2 and LaO 1.5 . Energies for tetragonal HfO 2 and ZrO 2 interfaces with amorphous silica were derived from their crystallization enthalpies from silicates as 0.25 ± 0.08 and 0.13 ± 0.07 J/m 2 , respectively. The crystallization pathways in bulk powders and films of zirconia and hafnia can be interpreted as resulting from thermodynamic stabilization by the surface energy term of tetragonal and amorphous phases over monoclinic.

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...

Two autolysis-defective mutants (Lyt-1 and Lyt-2) of Staphylococcus aureus have been isolated by transposon Tn917-lacZ mutagenesis. The mutants exhibited normal growth rate, cell division, cell size, and adaptive responses to environmental changes. No autolytic activities were detected in a crude autolytic enzyme preparation from the Lyt- mutants. The rate of autolysis of whole cells and cell walls in the mutants were negligible, but mutant cell wall preparations were degraded by crude enzyme preparations from the wild-type strain. Zymographic analyses of enzyme extracts from the mutants showed a single autolytic enzyme band, compared with more than 10 autolytic enzyme bands from the parent strain. Analyses of intracellular and exoprotein fractions gave results similar to those in experiments with total-cell extracts. Southern blot analysis indicated the insertion of a single copy of the transposon into the chromosome of Lyt mutants. Isogenic Lyt mutants constructed by phage phi 11 transduction showed similar phenotypes. Because both Lyt- mutants had Tn917-lacZ inserted in the appropriate orientation, it was possible to determine gene activity under various conditions by measuring beta-galactosidase activity. The gene activity was found to be induced by low pH, low temperature, and high sucrose and high sodium chloride concentrations. From these data, we propose that the mutation lies in either a master regulatory gene or a structural gene which is responsible for the synthesis or processing of a majority of the autolytic enzyme bands.