Kazuaki Kondo

Comparing Effects of Vacuum Annealing and Dry Oxidationon the Photoluminescence of Porous Si

Effects of vacuum annealing and dry oxidation on the photoluminescence properties of porous Si are reported. Anodized porous Si is formed by electrochemical etching in an aqueous HF solution of 16 to 48 wt% with a current density of 10 to 70 mA/cm2. A subsequent vacuum annealing (from 400°C to 800°C) weakens the intensity of the photoluminescence, whereas, oxidation using dry oxygen at 5 Torr above 800°C increases the intensity remarkably in addition to providing blue shifts as large as 100 nm. This study suggests that the visible photoluminescence is due to the modified quasi-direct band-gap structure of Si by the quantum confinement of electrons and holes.

Hysteresis variations of (Pb, La)(Zr, Ti)O3 capacitors baked in a hydrogen atmosphere

Baking (Pb, La)(Zr, Ti)O3 capacitors in a hydrogen atmosphere causes a significant loss of remanent polarization even at 150 °C. The hysteresis variations depend on the polarization states during baking. The hysteresis loop showed voltage shifts when the capacitor was polarized before baking, whereas it became a cramped shape when the baking was carried out on a virgin capacitor. Although remanent polarization diminished in all cases, saturation polarization was not suppressed. The clamped hysteresis loop can be described as an average of two loops shifted to positive and negative voltages. The results indicate that the loss of remanent polarization is not due to the suppression of switching, but due to the shift of the hysteresis of each domain larger than the coercive voltage.

Gain analysis for surface emission by optical pumping of wurtzite GaN

We analyzed optically pumped surface emissions by calculating the optical gain in bulk GaN. We found that GaN has a large gain of over 104 cm−1 and no gain saturation up to 25 000 cm−1 . This high optical gain is generated by the high joint‐density of states due to the three valence bands close to band edge and the large effective mass of the conduction band. As a result, although the gain required for lasing in the vertical direction is very high, the high excitation of carriers can achieve this without an intentional high reflection structure.

Nanoscale investigation of hydrogen-induced degradation mechanism in Pt/(Pb, La)(Zr, Ti)O3/Pt capacitors

The effects of hydrogen on Pt/(Pb, La)(Zr, Ti)O3(PLZT)/Pt capacitors have been investigated using atomic force microscopy piezoelectric measurements. The study revealed that the capacitors consist of submicron-sized ferroelectric domains, which were randomly distributed at positive or negative remanent states. After hydrogen annealing, it was observed that the local piezoelectric hysteresis loops of each domain shifted along both the voltage axis and the polarization axis. The degradation of remanent polarization can be explained by the shifted hysteresis of each domain. The degradation of saturation polarization can be understood to have been caused by the nonswitching portion within the capacitor.

Stress stabilization of β‐tantalum and its crystal structure

We studied the relationship between Ta crystal structures and the stress stability of Ta under heating. The stress in Ta which was sputter deposited on SiC was unstable and changed more than 2×109 dyn/cm2 to the compressive side during heating at 200 °C for 30 min in air. In contrast, the stress in Ta which was sputter deposited on SiC whose surface was modified by Ar sputtering was very stable, and the stress change was less than 1.5×108 dyn/cm2 even after 6 h of heating at 200 °C. The x‐ray diffraction patterns of the Ta revealed that stable Ta was strongly (002) oriented β‐Ta, and that unstable Ta was randomly oriented β‐Ta with some α‐Ta. We found that amorphizing the SiC surface or inserting a thin amorphous interlayer enhanced growth of strongly (002) oriented β‐Ta.

Effects of X-ray mask structures and processes on X-ray mask distortion

Abstract We measured the distortion of 0.8 μm thick Ta absorbers patterned on 2 μm thick SiC membranes. The maximum membrane diameter was 60 mm, and the largest field-window was 40 × 40 mm. This paper describes the relationship between the distortion and the shape of the blocker pattern. We got a distortion less than 0.10 μm using a parallel-cross blocker and filling the area outside the blocker pattern with dummy patterns with the same pattern density as the cell region.

Stress stabilization of tantalum absorbers on x-ray masks

Abstract We developed a new technique for stabilizing the stress in Ta sputter deposited over epitaxially grown SiC. The technique is to modify the SiC surface before deposition by bombardment with Ar ions. The stress in the Ta deposited over the SiC treated in Ar plasma was much more stable than that of Ta deposited on as-prepared SiC, and its change due to heating for 6.5 hours at 200°C in air was less than 1.5 × 10 8 dyn/cm 2 . Structure analysis of Ta using X-ray diffraction revealed that the more stable Ta has a β -phase structure with strong (002) orientation.

0.35-um rule, high-density, full-chip x-ray mask patterning

We study the dimensional and placement accuracies of masks for X-ray lithography, using a 64 Mbit DRAM as an example. We describe a way to stabilize and control X-ray absorber, and reduce stress induced distortion to within 0.03 micrometers . We improve the accuracy of e- beam writing which takes several hours by automatically calibrating the e-beam deflector periodically and by using a ceramic mask-holder. Placement accuracy was within 0.1 micrometers over a 40 mm square with a 2 hour exposure. We demonstrated that in chip areas with highly regular size and periodicity, we can correct for the proximity effect using only size shifts. In chip areas without high regularity, we used dose correction based on a double-gaussian proximity effect function and improved dimensional accuracy.

Effects of Surface Treatments on the Photoluminescence of Porous Si and a Suggested Mechanism for the Photoluminescence

We report how vacuum annealing and dry oxidation affect the photoluminescence (PL) properties of porous Si. Vacuum annealing weakens the intensity of as-prepared porous Si, whereas, oxidation using dry oxygen at 5 Torr increases the intensity remarkably above 800 °c. Blue shifts as large as 100 nm are also observed for temperatures between 800 °C and 1000 °c. The photoluminescence decay patterns of both as-prepared and dry-oxidized porous Si excited by a nitrogen laser pulse are not exponential, but are fitted well by two exponential decays with lifetimes ranging from a few nanoseconds to over 100 nanoseconds. Further, those decay patterns do not change with changing excitation power by more than three orders of magnitude. These studies suggest that (l) hydrogen termination (with some fluorine termination) on the porous Si surface is not always necessary to get photoluminescence, (2) low surface defect densities are essential to increase the photoluminescence intensity, and (3) the radiative recombination path is not a direct interband transition, but, due to quantum size effects, it may go through some luminescence centers lying In the widened band gap.

Anomalous Etching Residues of Sputter-Deposited Ta upon Reactive Ion Etching Using Chlorine-Based Plasmas

Anomalous etching of Ta which is sputter-deposited on silicon carbide (SiC) films is observed upon reactive ion etching (RIE) using a gas mixture of chlorine and chloroform. We find that α-Ta is hardly etched off by either chlorine-based plasmas or aqueous hydrofluoric acids (HF), while β-Ta is easily etched off by the same methods. The extent of α-Ta depends on the surface treatment of SiC. The difference in chemical reactivity between the α phase and β phase is discussed using photoemission spectroscopy.