An optimized layout for a trench-gate SiC-MOSFET with a self-aligned Bottom P-Well (BPW) was investigated for reduction of the specific on-resistance and switching loss. The static and dynamic characteristics of trench-gate MOSFETs with lattice and stripe in-plane structures were evaluated by varying the distance between neighboring BPWs (dBPWs). For the stripe structure, more significant improvements on the specific on-resistance (Ron,sp), gate-source threshold voltage (Vth) were achieved compared with the lattice structure, which was found to be due to the difference in the spread of the depletion layer and the channel planes in the device.

This paper investigates thereduction of parasitic resistance (JFET resistance) betweenthe p-well and the grounded p-type gate-oxide protection layer (BPW)of a trench-gate SiC-MOSFET. Forming a deeptrench is a way to reducethe JFET resistance, but this consequently leads to high electric field at thebottom oxide. In order to improve the trade-off between the specific on-resistance (Ron,sp) and the maximum bottom oxide electric field (Eox), wenewly developed a trench-gate SiC-MOSFET with an n-type region, named DepletionStopper (DS), formed under the entire p-welllayer. As aresult of fabrication, Ron,sp of the trench-gate SiC-MOSFET with DS is70 % lower than that without DS at a trench depth (dt) of about 1.5 mm. The dtof the trench-gate SiC-MOSFET with DS can be designed 25 % shallower than thatwithout DS at a Ron,sp of about 3.0 mWcm2.Therefore, it can reduce the JFET resistance and allow to shrinkthe trench depth. Optimizing the parametersof DS, the structure having DS is an effective means of reducing the JFETresistance, while reducing Eox by minimizing the depth of the trench.

This paper investigates the effects of grounding the p-type gate-oxide protection layer called bottom p-well (BPW) of a trench-gate SiC-MOSFET on the short-circuit ruggedness of the device. The BPW is grounded by forming ground contacts in various cell layouts, and the layout of the contact cells is found to be a significant factor that determines the short-circuit safe operation area (SCSOA) of a device. By grounding the BPW in an optimized cell layout, an SCSOA of over 10 μs is obtained at room temperature. Further investigation revealed that minimizing the distance between the ground contacts for the BPW is a key to developing a highly-robust, high-performance power device.

Ensuring gate oxide reliability and low switching loss is required for a trench gate SiC-MOSFET. We developed a trench gate SiC-MOSFET with a p-type region, named Bottom P-Well (BPW), formed at the bottom of the trench gate for bottom oxide protection. We can see an effective reduction in the maximum bottom oxide electric field (Eox) and a significant improvement in dynamic characteristics with a grounded BPW, whose dV/dt is 76 % larger than that with a floating BPW due to reduction in gate-drain capacitance (Cgd). The grounded BPW is found to be an effective means of both suppressing Eox and reducing switching loss.

We report an optical waveguide sensor using ring resonator. A refractive index sensor using resonator with vertical light input will be described. A grating coupler is used to couple the light beam to waveguide and output the light beam. The device has diameter of 40 μm with 500 nm wide waveguide, and fabricated in silicon on insulator (SOI). Experiments show that it has 313 nm/RIU sensitivity and detection limit of 1.5×10-3 RIU for changes in the refractive index of the sample.

We report a waveguide optical sensor using wire waveguide array. A grating coupler is used to couple waveguide modes with input and output light beam. A resonant cavity is formed by Bragg grating or ring waveguide to enhance the sensitivity. A high reflectivity is also realized by high-order modes at the abrupt waveguide end in the array waveguide structure.

High speed trains in the northern area of Japan use alloyed cast iron brake blocks including nickel (Ni) and molybdenum (Mo). Reducing the Ni and Mo contents of the alloyed cast iron brake blocks would be beneficial because they are rare metals with variable prices. Ni and Mo play important roles in increasing the friction coefficient and decreasing the wear of brake blocks at high speeds. Brake blocks with reduced contents of these metals must maintain a sufficient friction coefficient and wear characteristics at high speeds. Cast iron composite brake blocks with reduced Ni and Mo contents were prepared using two types of alumina: aluminum titanate and silicon carbide foams to maintain the friction coefficient and decrease the wear characteristics at high speeds. These blocks were tested on a full-scale dynamometer, and the friction and wear performance of one of the best performing blocks were tested under real operating conditions. The friction coefficients of all reduced Ni, Mo cast iron composite brake blocks were higher than those of conventional blocks at high speeds. The wear of the reduced Ni, Mo cast iron composite brake blocks containing alumina blended with aluminum phosphate (AlPO4) foam was significantly decreased as compared with that of conventional blocks. Under real operation, the friction coefficients of conventional and reduced Ni, Mo brake blocks were similar under normal braking conditions, but those of conventional brake blocks were lower than those of the reduced Ni, Mo blocks under emergency braking conditions. The lower friction coefficient of conventional brake blocks under emergency braking conditions is likely caused by the adhesion of wear particles to the wheel tread. While the wheel tread was not worn by conventional brake blocks, it was worn by the reduced Ni, Mo blocks under emergency braking conditions.

In this article, the authors focus on the profiles formed by high-aspect-ratio deep Si etching with SF6/O2 plasma mixtures. One of the most serious problems for deep Si etching processes is lateral etching in the upper regions of sidewalls. This lateral etching seems to depend on time (or etched depth) rather than aspect ratio (depth/width). Reducing the SF6:O2 ratio and lowering the temperature not only reduced the scope of lateral etching but also produced features that were more strongly tapered with depth. Results of simulation indicated that the distribution of radicals during the formation of a hole plays a significant role in determining the characteristics of the hole. In fact, the addition of SiFx radicals from the top of the hole is markedly effective in reducing lateral etching without sacrificing shape in the vicinity of the bottom of the hole. However, the distribution of radicals alone cannot explain the time dependence of lateral etching. The results of experiments with masks having various shapes shows that scattered ions at the facets of the mask are mainly responsible for lateral etching. The time dependence of lateral etching is due to expansion of the mask facets over time.

This article presents a study of the characteristics of radicals in high-aspect-ratio deep Si etching by continuous-type SF6/O2 plasmas. A parametric study of etched depths clearly shows that the Si etch rates are dependent on concentrations of F atoms but independent of ion energy and substrate temperature. Results of Monte Carlo simulation based on a Knudsen transport model provide a remarkably good fit for experimental results on aspect-ratio-dependent etching. Comparison of the experimental data and results of simulation shows that the probability of a F atom reacting with the Si surface is 0.4–0.45 if the probability of loss at sidewall surfaces for F atoms is negligible. Results also indicate that the latter probability is, in fact, extremely small (<0.005).

温室効果ガスの主要な構成要素であるCO2 を減らすためには,排出量を減らすことと併せて,植物による吸収・固定を推進させることが必要である。都市緑化等の推進は,その対策の一つとして重要な役割を担っており,その効果を定量的に明らかにし,京都議定書の報告等にも活用可能な算出手法の開発が求められている。本研究では,木質部重量の増加量からCO2 の固定量が算定できることに着目し,我が国の街路樹や都市公園などに多用されている樹木の部位毎の乾燥重量測定・樹齢判読等を行い,胸高直径を基にした樹木1 本当たりの年間CO2 固定量の算定式の作成を試みることとした。これまでに,樹齢20 年前後の6 樹種を対象に同様の手法で研究・報告を行っているが,今回はその内の5 種に新たな1 種を加え,樹齢30 年から50 年前後の樹木を調査対象とし,先行研究のデータと合わせて解析した。その結果,樹齢50 年前後までを適応範囲とする年間木質部乾重成長量の算定式とそれを基にした年間CO2 固定量算定式を作成した。今後さらなる研究を進め,都市緑化樹木のCO2 吸収・固定効果を明らかにすることで,都市緑化の促進に貢献するものと考えられる。

The gate critical dimension (CD) variation of ultra-large-scale integrated circuit (ULSI) devices should be reduced to improve the production yield. An examination of the formulation of a gate-CD model for the transistor area, including the static random access memory (SRAM), was conducted taking the topographical and layout effects into account. It was found that the formulation of a gate CD for transistor areas with a root-mean-square error (RMSE) of less than 1 nm was efficient. The coefficients of the shallow-trench-isolation (STI) step height and polycrystalline-silicon (poly-Si) thickness were found to be inversely proportional to the distance between the gate electrodes. It was found that this dependence is related to the reactive-ion-etching (RIE) lag in the etching process.

We conducted a survey on vegetation change and performed a germination test for the topsoil seed bank after vegetation management of the herbaceous community dominated by the invasive alien species Coreopsis lanceolata on the riverbed of the Kiso River. We observed that although a large number of C. lanceolata seedlings were established, few flowering shoots emerged in the year following vegetation management (removal). The extended summed dominance ratio of C. lanceolata decreased, while that of Potentilla chinensis and Galium verum-domestic species growing on the gravelly riverbed-increased. However, the number of alien species of annual and biennial plants markedly increased after the removal. The germination test showed that this increase was caused by germination and establishment from the seed bank in the disturbed area after the removal. The test also showed that the seed supply of Artemisia capillaris and Dianthus superbus var. longicalycinus-domestic species growing on the gravelly riverbed and, in small numbers, in the surveyed and surrounding areas-was low. In this study, the removal proved effective in controlling the flowering of C. lanceolata; however, the problem of increase in the number of alien species of annual and biennial plants remains to be resolved.

The H2 plasma treatment for spin-on carbon (SOC) hard mask in the trilayer resist process is expected to serve as a reliable alternative to single layer resist process for 45nm nodes and beyond. The authors have investigated this treatment with a view to suppress the deformation of SOC by oxide etching. The wiggling profile of SOC drastically improves due to the formation of a thicker diamondlike amorphous carbon structure by the H2 plasma treatment with higher-energy hydrogen ions.

Suppression of 193-nm photoresist deformation by H2 addition to fluorocarbon plasmas in via-hole etching is investigated for sub-65-nm-node dual-damascene patterning. Photoresist deformation causes profile distortion and results in degradation of reliability, such as the line-to-line time dependent dielectric breakdown. To prevent profile distortion, H2 addition to fluorocarbon plasma is investigated in terms of fluorocarbon polymer and photoresist modification. XPS, FT-IR, and highlight etching investigations reveal that the H2 plasma treatment extracts oxygen from the photoresist and modifies it. This modification suppresses the photoresist deformation and H2 addition to fluorocarbon plasmas can have the same effects as the H2 plasma treatment. Finally, a highly reliable damascene interconnection is successfully achieved.

The oxidation on nickel silicide (NiSix) during plasma etching and oxygen ashing is investigated for stable contact resistance on NiSix. NiSix exposed by various processes is observed by X-ray photoelectron spectroscopy. The oxidation on NiSix is promoted by the fluorine that remains during etching and the oxide thickness on n+ NiSix is greater than that on p+ NiSix. The remaining fluorine after etching can be decreased by in-situ nitrogen plasma treatment during the post-etching process. Therefore, the oxidation progress with exposure to air and the difference in oxidation on NiSix between n+ and p+ can be suppressed.

We have developed a fab-wide APC system to control critical dimension (CD) of gate electrode length. We have also developed a model equation to predict gate CD by considering the structures of gate electrode and STI. This prediction model was also used to do factor analysis of gate CD variation. Effectiveness of the prediction model for feedforward control was evaluated by both simulation and experiment.

Nesting locations of the Northern Goshawks (Accipiter gentilis) were investigated in two areas of about 390km2 in Tochigi prefecture, about 50km north of Tokyo. A total of 22 nesting locations were found in the area. Their food items were also monitored. A multiple regression model was constructed to predict the breeding density (measured as the total area covered by 1.8km buffers generated from the location of each nests within a 3x3km grid) from several environmental factors such as vegetation and human population size. The resulted model could explain about 63% of the variation in the breeding density (r2=0.63). Factors used in the model were: length of forest edge facing grassland (positive factor), area of bare land, construction sites etc. and human population size within each grid (negative factors). In this area, Goshawks were feeding mainly on small or medium sized birds, but the abundance, or biomass, of the birds was not an important factor that affected the breeding density of the Goshawks. The reason for this might be either that the food (amount of birds) is generally abundant in the area and therefore not an important limiting factor, or that availability of the suitable hunting area such as the forest edge facing the grassland is more important than the availability of the food itself.