Yohei Otani

Low-Temperature Formation of High-Quality

We have fabricated an Al2O3/GeO2 gate-dielectric stack on p-type Ge by electron-cyclotron-resonance plasma oxidation and sputtering without external substrate heating. We show that the midgap interface state density at the GeO2/Ge interface is 4.5 × 1010 cm-2 · eV-1. The hysteresis observed in capacitance-voltage measurements is reduced to 50 mV when the gate bias is swept from accumulation to inversion and back to accumulation or after a single dummy sweep from inversion to accumulation, indicating the possibility that the bulk oxide traps causing the hysteresis are deactivated by the injected holes. The band gap of GeO2 was determined by internal photoemission measurements to be 4.7 eV. The conduction- and valence-band offsets at the GeO2/Ge interface are moderately symmetric and large with values of 1.8 and 2.2 eV, respectively. These promising results suggest that low-temperature plasma-grown GeO2 is a suitable interlayer between high-dielectric-constant dielectrics and Ge.

\hbox{GeO}_{2}

Epitaxially grown lanthanum-modified lead zirconate titanate (PLZT) thin films were deposited on r-cut sapphire substrates using an advanced sol–gel method. The methanol addition into sol–gel solutions brought high quality epitaxial growth of PLZT thin films. This film showed high electro-optic (EO) coefficients that were almost comparable to those of bulk PLZTs. We believe this PLZT deposition technique will open the door for the future data communication systems with integrated EO devices.

Interlayer for High-

Three kinds of TiO2 layers were formed on SiO2/Si substrates: (200)-oriented TiO2 with rutile structure, (103)-oriented TiO2 with anatase structure and randomly oriented TiO2. All the Pt films deposited on the TiO2 layers had (111) orientation. Pt films deposited on the rutile TiO2 had a columnar structure and the full-width at half maximum (FWHM) of the rocking curve of the Pt(111) plane was estimated to be 0.88°. The diffusion of TiO2 to the surface of the Pt films hardly occurred in the case of rutile TiO2. The FWHM of the rocking curve of Pt(111) formed on anatase TiO2 was estimated to be 1.55°. The rocking curve of Pt(111) formed on randomly oriented TiO2 consisted of two peaks with centers separated by 6.25°. The diffusion of TiO2 to the surface was observed in the cases of anatase and randomly oriented TiO2. From these results, we concluded rutile TiO2 fabricated by metal deposition and subsequent oxidation was the best material for high-quality bottom Pt electrodes.

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Ferroelectric Pb(Zr,Ti)O3 (PZT) thin films were deposited on trenched SiO2/Si substrates at various substrate temperatures by liquid delivery metalorganic chemical vapor deposition (MOCVD) using Pb(DPM)2, Zr(DIBM)4 and Ti(OiPr)2(DPM)2 as precursors. Their step coverage increased from 38 to 80%, while their deposition rate decreased with decreasing the substrate temperature from 600 to 400°C. In the deposition on planar Pt/Ti/SiO2/Si substrates, the as-grown PZT films deposited under the substrate temperature of 450°C were confirmed to be amorphous; they crystallized into perovskite PZT single phase and showed ferroelectric properties after post annealing at 600°C in air for 15 min. From these results, we concluded that the combination of low-temperature deposition and post annealing is effective in improving the step coverage of PZT thin films deposited by liquid delivery MOCVD although composition control is severe in such a case because the self-regulation of lead atoms is not realized at low temperatures.

Gate Dielectrics/Ge by Electron-Cyclotron-Resonance Plasma Techniques

The variation in 111 d-space of Pt thin-film electrodes during heat treatment was precisely measured by an X-ray diffraction system with a heating stage. The 111 d-space of Pt films deposited at 200°C linearly increased as the temperature was increased to 450°C and was almost constant over the temperatures range from 450 to 600°C due to stress relaxation. The generation of hillocks was observed in the Pt films which were relaxed in this way. On the other hand, in the case of Pt films deposited at temperatures higher than 500°C, the d-space linearly increased and then linearly decreased to almost the same value in the heat treatment at a maximum temperature of 600°C, and no hillocks were observed on the surface after the heat treatment. Furthermore, Pt films prepared at room temperature (RT) at different deposition rates showed different variations in d-space and different sizes of hillocks. These results suggest that knowing the variation in 111 d-space during heat treatment is beneficial for predicting the generation of hillocks in 111-oriented Pt thin films.

Electro-Optic Properties of Lanthanum-Modified Lead Zirconate Titanate Thin Films Epitaxially Grown by the Advanced Sol–Gel Method

Pb(Zr,Ti)O3 (PZT) thin films were deposited onto Pt/TiO2/SiO2/Si substrates with different-types of TiO2 layers by liquid delivery MOCVD at 550°C. Three kinds of TiO2 adhesion layers were examined: 200 oriented TiO2 with rutile structure, 103 oriented TiO2 with anatase structure and randomly oriented TiO2 which consisted of nanocrystals. In the anatase case, the PZT thin film consisted of large tetrapod-like grains with 111 orientation while the PZT film had a 001/100 mixed orientation and consisted of fine columnar grains in the rutile cases. In the nanocrystal case, the orientation was weak and the film consisted of both types of grains. From these results, we concluded that highly oriented TiO2 formed at higher temperature, the rutile TiO2 in this investigation, is the better material for the under layer. However, the remanent polarization of the PZT capacitor with the rutile TiO2 significantly increased with polarization reversal because the PZT film had a 001/100 mixed orientation. Some seeding layer will be required to obtain 111 oriented PZT thin films on Pt/TiO2/SiO2/Si substrates with rutile TiO2.

Influence of a TiO2 Adhesion Layer on the Structure and the Orientation of a Pt Layer in Pt/TiO2/SiO2/Si Structures

Electron-cyclotron-resonance (ECR) oxygen (O2) plasma was irradiated onto the surface of germanium (Ge) substrates prior to germanium nitride (GeNx) formation. Germanium metal–insulator–semiconductor (Ge-MIS) structures with a 5-nm-thick silicon nitride/2-nm-thick GeNx gate insulator stack fabricated by ECR plasma nitridation and sputtering deposition without substrate heating were electrically and physically characterized. Although ECR O2 plasma irradiation onto the surface of Ge substrates caused no significant difference in the chemical state of GeNx/Ge interfaces in X-ray photoemission spectroscopic measurement, irradiation for an appropriate period improved the state of GeNx/Ge interfaces and the electrical properties of Ge-MIS.

Improvement in Step Coverage of Pb(Zr,Ti)O3 Thin Films Deposited by Liquid Delivery Metalorganic Chemical Vapor Deposition

ABSTRACT High quality PLZT ((Pb, La)(Zr, Ti)O3) thin films were deposited on r-plane sapphire substrates using sol-gel method. The solution concentration affected a film quality a lot and less than 10 wt% concentration is needed for high quality depositions. The PLZT films deposited at 9 wt% solution concentration showed only (101)(011) X-ray reflection peaks with quite high peak intensities. This means that the deposited film was extremely highly oriented, in other words, almost epitaxially grown. This film also showed high EO coefficients that are comparable to those of bulk PLZTs. We believe this PLZT deposition technique will open the door for the future data communication systems with integrated electro-optic devices.

Variation in 111

Ferroelectric Pb(Zr,Ti)O3 (PZT) thin films were fabricated by liquid delivery MOCVD using conventional multi-sources. The deposition rate of 20 nm/min was attained at the reactor pressure of 5 Torr and the substrate temperature of 550°C by using Zr(DIBM)4 as a Zr-source instead of Zr(DPM)4. The step coverage increased from 50 to 100% by decreasing the substrate temperature from 600 to 400°C although the deposition rate decreased to the half. The uniform PZT thin films were successfully formed on 6-inch wafers. The variation in thickness was less than 5% all over the wafers. However, the remanent polarization at the center was half of that at the border. A cocktail source prepared by mixing Pb(METHD)2, Zr(METHD)4 and Ti(MPD)(METHD)2 with ECH was also examined. The cocktail source was stable for 3 months. PZT thin films deposited using the cocktail source exhibited ferroelectric properties. However, strongly oriented PbPtx alloy and oriented PbO were also formed. The improvement in crystallinity, electrical properties and surface morphology remains for future study.

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Ferroelectric PZT thin films were deposited by liquid delivery MOCVD using a cocktail solution. The cocktail solution consisted of Pb(METHD)2, Zr(METHD)4 and Ti(MPD)(METHD)2 diluted with ethylcyclohexane. The films deposited on Pt/Ti/SiO2/Si at a substrate temperature of 500°C consisted of PZT, PbO and PbPtx, and showed poor properties. However, after annealing at 450°C in air for thirty minutes, the PbPtx phase disappeared while the volume of the PbO phase increased. The hysteresis properties were also improved by annealing at 450°C. After annealing at 600°C in air for thirty minutes, the PbPtx and the PbO phases disappeared perfectly and the PZT thin films showed good hysteresis properties with the remanent polarization of 30 μC/cm2 and the coercive field of 88 kV/cm.