Characterization of HFO2 Capacitors

Hafnium oxide (HfOn) is a promising dielectric for future microelectronic applications. Hf02 thin films (10-75nm) were deposited on Pt/Si02/Si substrates by pulsed DC magnetron reactive sputtering. Top electrodes of Pt were formed by e-beam evapo- ration through an aperture mask on the samples to create MIM (Metal-Insulator-Metal) capacitors. Various processing conditions (Arloz ratio, DC power and deposition rate) and post-deposition annealing conditions (time and temperature) were investigated. The structure of the Hf02 films was characterized by X-ray diffraction (XRD) and the roughness was measured by a profilometer. The electrical properties were characterized in terms of their relative permittivity (E,(T) and ~,.(f)) and leakage behavior (I-V, I-T and I- time). The electrical measurements were performed over a temperature range from -5 to 200°C. For the samples with best experimental results, the relative permittivity of HfOa was found to be -- 27 after anneal and increased by 0.027%/"C with increasing temperature over the measured temperature range. At 25"C, leakage current density was below lop8 ~ l c m ' at 1 volt. The leakage current increased with temperature above a specific threshold temperature below which the leakage current didn't change much. The leakage current increased with voltage. At voltages below lvolt, it's ohmic; at higher voltages, it follows Schottky model. The breakdown field is - 1 . 8 2 ~ lo6 Vlcm. The optical bandgap was measured with samples deposited on quartz substrates to be 5.4eV after anneal.

Post-Depositional Movement of Methanesulphonic Acid at Law Dome, Antarctica, and the Influence of Accumulation Rate

A series of ice cores from sites with different snow-accumulation rates across Law Dome, East Antarctica, was investigated for methanesulphonic acid (MSA) movement. The precipitation at these sites (up to 35 km apart) is influenced by the same air masses, the principal difference being the accumulation rate. At the low-accumulation-rate W20k site (0.17 in ice equivalent), MSA was completely relocated from the summer to winter layer. Moderate movement was observed at the intermediate-accumulation-rate site (0.7 in ice equivalent), Dome Summit South (DSS), while there was no evidence of movement at the high-accumulation-rate DE08 site (1.4 in ice equivalent). The main DSS record of MSA covered the epoch AD 1727-2000 and was used to investigate temporal post-depositional changes. Co-deposition of MSA and sea-salt ions was observed of the surface layers, outside of the main summer MSA peak, which complicates interpretation of these peaks as evidence of movement in deeper layers. A seasonal study of the 273 year DSS record revealed MSA migration predominantly from summer into autumn (in the up-core direction), but this migration was suppressed during the Tambora (1815) and unknown (1809) volcanic eruption period, and enhanced during an epoch (1770-1800) with high summer nitrate levels. A complex interaction between the gradients in nss-sulphate, nitrate and sea salts (which are influenced by accumulation rate) is believed to control the rate and extent of movement of MSA.