Yoshio Ishihara

Reverse-bias current reduction in low-temperature-annealed silicon pn junctions by ultraclean ion-implantation technology

Reduction in the reverse‐bias current in low‐temperature‐annealed silicon pn junctions has been studied. It has been shown that the transition region existing underneath the ion‐implantation‐generated amorphous layer and the contamination incorporated into this region play a decisive role in determining the reverse current level. In order to minimize the contamination involvement into the transition region, ultraclean ion‐implantation technology has been developed. Ion implantation was carried out under a UHV (5×10−10 Torr) condition in order to minimize the recoil implantation of adsorbed contamination at the surface. The contamination due to the high‐energy ion‐beam sputtering of component parts in the ion implanter has also been suppressed. As a result, a low reverse‐bias current level of about 1.2×10−7 A/cm2 has been obtained for arsenic‐implanted n+p junctions annealed at 550 °C, which is more than two orders of magnitude smaller than that previously reported. The stress compensation technology emplo...

Economical clean dry air system for closed manufacturing system

We demonstrated that the organic carbon contaminants influenced the J-E characteristics of a gate oxide. Molecular-contamination-free clean dry air (CDA) is a choice for the atmosphere control in a closed manufacturing system. The adsorption and desorption characteristics, which are important items for the design and operation of CDA production plants, were confirmed with both a dynamic simulation and a pilot column. Based on the results, we built a CDA plant with a capacity of 4000 m/sup 3//h, and confirmed that each contamination concentration was less than 10 ppb. We also proposed the economical CDA system using a power recycle device which has been newly developed. Using this CDA system, it is possible to reduce the power consumption in the CDA plant. Also, it is possible to realize the circulation of the used CDA without generating more contamination or power consumption.

Electrical Conductivity Measurement in Liquified Hydrogen Chloride

A measurement technology for trace impurities in hydrogen chloride (HCl) was developed in relation to future ultralarge scale integration (ULSI). We developed an electrical conductivity measurement system for analyzing liquified HCl with an in-line high pressure cell. The detection limit of this measurement system is 1.0×10 -11 S/cm, and the external leak rate of the cell is below 1.5×10 -11 Torr-liter/s. The apparent temperature coefficient of the electrical conductivity is negative in the range from - 12 to 20 o C at constant pressure, which is caused by a decrease of the density of HCl with increasing temperature. The real temperature coefficient of the electrical conductivity is positive at constant density

Development of Nitrogen Gas Bubbling Deaerator Made of Polyvinyliden Fluoride

It is essentially important to remove the dissolved oxygen (I)O) in the ultrapure water for the future ultralarge scale integration (ULSI). We have found the existence of the big driving force for the oxygen diffusion through tube materials that increases the DO concentration. The DO concentration through the perfluoro alkoxide (PFA) tube rapidly increased with decreasing the flow rate of the ultrapure water. On the other hand, the DO concentration through the polyvinyliden fluoride (PVDF) tube that is a low oxygen permeability material did not increase with decreasing the flow rate. Based on this finding, we have developed the nitrogen gas bubbling deaerator made of PVDF as a point of use purifier. In this system, the residual DO concentration reached 0.2 ppb at a gas-liquid ratio of 1.2 m 3 /m 3 at each bubbling tower that is ten times smaller than the previously reported one. Furthermore, other contaminations in the ultrapure water do not increase after this process.

Inductively coupled plasma generator for an environmentally benign perfluorocarbon abatement system

Although conventional plasma-resolution-type abatement systems for perfluorocarbons (PFCs) achieve PFC removal efficiencies of more than 98%, they consume a lot of electricity. To diminish global warming by reducing CO2 equivalent emissions, an effective low power-consumption plasma generator is essential. The authors found that the pressure at which the electrical discharge can be maintained at the same rf power supply output increased with the number of turns per unit length of coil. In addition, they revealed that the CF4 removal efficiency rose with increasing pressure. A plasma generator employing a modified cylindrical inductively coupled plasma chamber with 1.1turns∕cm achieved a CF4 removal efficiency of 99.0% under conditions of a CF4 flow rate of 10cm3∕min, a pressure of 0.9kPa, and a rf power supply output of 1.5kW. The CO2 equivalent removal efficiency was calculated to be 93.5%, an improvement of 6.7% over that of the previous system.

High-Efficiency PFC Abatement System Utilizing Plasma Decomposition and Ca(OH)

In order to minimize contributions to global warming, it is important to develop a perfluorocompound (PFC) abatement system that can remove PFCs effectively with low electric power. We have developed a new PFC abatement system consisting mainly of a 2-MHz ICP plasma source and two Ca(OH)2/CaO columns operated under a decompression pressure. Reactive fluorinated compounds including SiF4 are immobilized in the Ca(OH)2/CaO columns without a water scrubber. Stable compounds such as CF4 are excited by the 2-MHz ICP plasma. When the emissions from an Si oxidation film etching process chamber were treated by this abatement system, F2 equivalent removal efficiency was 99.6%, which was about one order of magnitude larger than that of a conventional abatement system. But the CO2 equivalent removal efficiency was calculated to be 91.4% because over 95% of CO2 equivalent emissions were caused by the plasma source power consumption of 2.4 kWh. It means that minimization of the plasma source power consumption, depending on PFC emissions, is a very effective method of minimizing contributions to global warming in a manner similar to improving the PFC removal efficiency.

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We have carried out ab initio quantum chemical calculations for the decomposition reactions and propagation reactions of germane (GeH4). All self-decomposition reaction series are endothermic, and in contrast, Ge-chain propagation reactions are exothermic at the B3LYP/6-31G** and B3LYP/6-311G** levels. The exothermicity of Ge-chain propagation is a characteristic property of GeH4 in contrast to methane and silane, though the activation energy is estimated to be as large as about 80 kcal/mol. We have confirmed that the activation energy of the decomposition reaction is reduced due to catalytic water in the form of (H2O)2 dimer. We have also presented the mechanism of Ge-chain propagation with a low activation energy due to catalytic water leading to the explosive decomposition of GeH4 gas.

/CaO Immobilization

震災発生時は,揺れが収まるまで居室・実験室等で待機状 態であったが,その後決められた手順により,敷地内の指定 避難場所に総員避難した.当研究所では年に 2 回防災訓練 を実施し,その中で毎回避難訓練を実施している.当日も訓 練と同様に,各自ヘルメットを着用し,避難場所に集合し た.但し,停電のため避難指示放送ができない状態で,他の 所員が避難開始をしている状況を見て,避難行動に移った所 員もいた.また,避難に際しては,所定の位置にある非常時 情報書類袋を携帯することが決められており,その袋には点 呼表や建屋情報,扱いガス種等が記されている.この点呼表 を用いて,避難場所では直ちに人員点呼を行い,当日の在席 者全員の無事を確認した.震災直後から電気・水道の所謂ラ イフラインが停止状態となり,当日は16時に全所員帰宅措 置を採った. 当研究所では種々のガスを扱っており,数多くのガス検知 器が各実験室に設置されている.停電時のガス検知器の動作 を保証するため,ガス検知器は非常用発電機に接続されてい る.この発電機は200 kVA 容量であり,ガス検知器の他消 火設備にも接続されている.震災発生直後から停電となり, 当該非常用発電機が作動し,ガス検知器電源は瞬時に非常用 発電機へと切り替わった.幸いなことに大地震にも拘わらず ガス漏れは検知されず,大きな揺れが収束後,各自帰宅準備 に取り掛かった.但し,非常用電源は燃料在庫の関係で数時 間のみの稼働であった. また,当研究所は高圧ガス設備を幾つか保有するが,これ らの設備には全く被害無く,幸いであった.震災発生が金曜 日のことであり,月曜日に改めて高圧ガス設備・ガス配管の 気密テストを行い,合わせてガス検知器復帰作業も実施し, 所内の安全を確認した.

Reaction processes of germane molecules with catalytic water

Xenon (Xe) has been used in damage-free plasma processes for realizing future semiconductor device manufacturing, even though being very rare and expensive. Therefore, we developed a system that can recycle with a high recovery ratio and supply low-cost Xe. This system can separate Xe from gas mixtures, including Nitrogen (N2), Argon (Ar), Oxygen (O2), Hydrogen (H2), and Helium (He), with a 99.999 % recovery ratio. Usage of this system lowered Xe costs to less than 1/100th the cost of a Xe cylinder.

Damages from Great East Japan Earthquake

We have developed a PFC abatement system utilizing a 2 MHz ICP plasma source and two columns filled with Ca(OH)2/CaO under a decompression atmosphere without fluorine acid drainage treatment. The 2 MHz ICP plasma decomposes the PFCs. The Ca(OH)2/CaO columns immobilize the reactive fluorinated compounds. When we treated the emissions from a Si oxidation film etching process chamber by using this abatement system, F2 equivalent removal efficiency and CO2 equivalent removal efficiency were 99.64% and 90.59%, respectively. The discrepancy between the two efficiencies can be attributed to the fact that 98% of CO2 equivalent emissions were caused by power consumption.