Hiroshi Nozawa

Nanocomposite resist system

We propose a nanocomposite resist system that incorporates sub-nm carbon particles into a resist film to enable an ultrathin film resist process for nanometer pattern fabrication. Fullerene (C60) is found to be an excellent material for incorporation in view of its etching resistance, dissolution inhibiting effect, molecular size, and composite preparation. A nanocomposite system of C60 and an electron-beam positive resist, ZEP520, show enhancements in both pattern contrast and etching resistance and provide 50 nm patterns in a 50-nm-thick film with a sensitivity of ∼50 μC/cm2. Furthermore, a C60-incorporated chemically amplified resist, SAL601, shows strong environmental stabilization in postexposure delay (<10% after five days) presumably due to the reduction of free volume in the closely packed nanocomposite film.

High-Aspect-Ratio Nanometer-Pattern Fabrication Using Fullerene-Incorporated Nanocomposite Resists for Dry-Etching Application

This paper presents the improved performance of a nanocomposite resist system that incorporates an unseparated mixture of fullerenes C60 and C70 into ZEP520, a positive electron-beam resist, particularly focusing on the enhancement of mechanical strength and dry-etching resistance. This system exhibits similar improvements to that of a pure C60-incorporated system; 90-nm-pitch high-aspect-ratio (>5) resist patterns without pattern collapse and a 10-% enhancement of dry-etching resistance are obtained in a 10-wt% fullerene mixture-incorporated system due to the reinforcement effect induced by the fullerene incorporation. In addition, 80-nm-pitch resist patterns are successfully transferred to SiN film by C2F6-reactive ion etching without any harmful effects. The use of an unseparated mixture of C60 and C70, which is commercially available at a much lower price than pure C60, will greatly facilitate the practical application of the nanocomposite resist system from the economic point of view.

Imprint Model Based on Thermionic Electron Emission Under Local Fields in Ferroelectric Thin Films

We investigated the origin of the imprint mechanism of ferroelectric thin films such as PbZrxTi1-xO3 (PZT) or SrBi2Ta2O9 (SBT) by considering thermionic field emission under local fields. The electric fields inside the ferroelectric films are represented. Since the poled ferroelectric capacitors have strong local field inside, the thermionic field emission rate is enhanced by tunneling effect. The emission rate is estimated by taking the thermionic field emission into account. The dependence of imprint phenomenon on the emitted electrons from traps is explained in detail. We calculate the voltage shift that results from the imprint phenomenon. Comparing the results with the experiments, we successfully explain the imprint phenomenon based on pinning.

C60-incorporated nanocomposite resist system for practical nanometer pattern fabrication

We propose a nanocomposite resist system that incorporates sub-nm size fullerene C60 molecules into a highly sensitive and moderately dry-etching resistant electron-beam positive resist, ZEP520. C60 incorporation leads to carbon reinforcement in the original resist material and enhances resist performance for nanometer pattern fabrication. 10 wt % C60 incorporated ZEP520 shows enhancements of etching resistance (∼15%), thermal resistance (∼30 °C), and mechanical resistance (3.5–5.5 in the aspect ratio). By applying this new resist system to x-ray mask fabrication, an ultrafine mask with the minimum dimension of 45 nm has been successfully fabricated.

New Fatigue Model Based on Thermionic Field Emission Mechanism

We investigated the mechanism of the fatigue phenomenon in ferroelectric thin films such as Pb(Zr, Ti)O3 (PZT) and SrBi2Ta2O9 (SBT). The fatigue phenomenon in PZT was successfully explained by a new concept model introducing the effect of impact-ionization and energy distribution of trap levels to thermionic field emissions. This model can also explain the effect of applied voltage and temperature on the fatigue phenomenon. Moreover, we can simulate the fatigue characteristics in SBT by including the energy dissipation effect on the model for PZT. By introducing this result into an extrapolation method, the rewriting limit of ferroelectric thin films can be successfully predicted.

Low Activation Energy by Polarization in a Floating Gate Structure

This paper describes a new and essential mechanism for the low activation energy of charge retention, based on the electrostatic energy change of the floating gate due to a decrease in the stored electrons. The electrostatic potential in the floating gate when a positive space charge is generated at the interface is given by Debye-H?ckel. The electron cloud shifts and polarization arises. At this time, a pair consisting of a positive space charge and polarized electron cloud forms an exciton. An electron which forms an exciton recombines with a positive charge by tunneling through SiO2. As a result, the mechanism that an electron is emitted above the work function of 3.2 eV at the Si-SiO2 interface by supplying a thermionic activation energy of 1.2 eV has been revealed.

Fullerene incorporated nanocomposite resist systems for practical nano-fabrication

We propose a nanocomposite resist system that incorporates sub-nm fullerene C60 or C70 into a conventional resist material as a practical nanometer range resist system. Fullerene molecules show chemical and physical resistant characteristics, and their incorporation reinforces the original resist film, leading to substantial improvements in resist performance: etching resistance, pattern contrast, mechanical strength, and thermal resistance. A nanocomposite resist system based on an positive-type electron beam resist, ZEP520, and its application to the fabrication of X-ray masks, diffractive grating elements, nano-printing molds, and quantum dots are presented.

Dry etching of InP using a CH3Cl/Ar/H2 gas mixture with electron-cyclotron-resonance excitation

We have investigated the etching characteristics of InP etched with a CH3Cl/Ar/H2 gas mixture with electron-cyclotron-resonance excitation and compared them with those for a CH4/Ar/H2 gas mixture. Some advantages of CH3Cl/Ar/H2 over the CH4/Ar/H2 are found. A smooth etched surface without etch residue is obtained at 120 °C and above. Etch residue, which is drop shaped and originates from the preferential desorption of phosphorus, is inevitably generated when the CH4/Ar/H2 is used. The etch rate (15–25 nm/min at the temperatures of 120–175 °C) is larger than in CH4/Ar/H2 etching. This etch rate is controllable for fine structure fabrication, such as the grating in a semiconductor laser diode, and successful fabrication of a grating with 150 nm pitch and 30 nm depth is demonstrated.