Fumiaki Kumasaka

Dielectric and Insulating Properties of Embedded Capacitor for Flexible Electronics Prepared by Aerosol-Type Nanoparticle Deposition

The rapid evolution in electronic equipment has created a demand for advanced devices that are flexible, thin, and light in weight. This demand is driving the development of a core technology for flexible and stretchable electronic devices. To produce wearable computers, we need to fabricate functional membranes that contain passive devices, such as capacitors and resistors, on resin sheets at low temperatures. These sheets can then serve as mounting boards for various electronic devices. By improving the technique for room-temperature aerosol-type nanoparticle deposition of a ceramic material, we have established a technology for forming a dielectric inorganic BaTiO3 film with an excellent degree of crystallinity and favorable electric properties for use in the production of flexible and stretchable electronic devices on a polyimide sheet. By this method of forming a homogeneous nanoparticle structure inside a film, we produced a capacitor film with a dielectric constant of 200 on a polyimide sheet at room temperature.

Precise stress control of Ta absorber using low stress alumina etching mask for X-ray mask fabrication

In the stress control of an X-ray mask absorber, the repeatability of control and stability are important. We found that the change in the stress in a Ta film resulting from annealing depends on the oxygen concentration in the film; the magnitude of the stress change is determined by the annealing temperature and time. Using this characteristic of Ta film, we have successfully controlled the stress in the Ta absorber to less than 5 MPa with good repeatability. In our mask fabrication process, Al 2 O 3 film was used as an etching mask. We found that the Al 2 O 3 film prevented the Ta absorber stress from changing in high-temperature atmospheres because the Al 2 O 3 film prevented oxygen diffusion into the Ta film. Utilizing Al 2 O 3 films, we succeeded in preventing changes in Ta absorber stress in the thermal processes after Ta stress control, such as frame bonding and resist baking. Consequently, we were able to precisely control the Ta absorber stress in X-ray masks with good repeatability and stability in a realistic X-ray mask fabrication process.

PATTERN ETCHING OF TA X-RAY MASK ABSORBER ON SIC MEMBRANE BY INDUCTIVELY COUPLED PLASMA

Patterning of an X-ray mask absorber after Si back-etching is desirable from the viewpoint of the pattern placement accuracy. We investigated Ta X-ray absorber etching on an SiC membrane equipped on a mask frame using a low-stress CrN hard mask and an ICP etcher with a He cooling system. In this system, the membrane temperature and the self-bias voltage could be controlled. A 40-nm-thick CrN film was etched using a 200-nm-thick resist and Cl2 and O2 gases with a selectivity of 0.72 and a vertical sidewall. A 400-nm-thick Ta film was etched using Cl2 gas at an electrode temperature of -10°C and a low gas pressure of 0.1 Pa. A high selectivity of Ta to CrN, 42, was obtained, and lines and spaces patterns below 0.1 µm with vertical sidewalls could be fabricated.

Sub-100 nm device fabrication using proximity X-ray lithography at five levels

Proximity X-ray lithography (PXL) is a promising technology for fabricating ultra-large-scale integrated (ULSI) devices smaller than 100 nm because it offers high-resolution capabilities and dimensional control with high throughput. We used PXL at five levels (mark, isolation, gate, contact, wiring) and fabricated 100-nm complicated dense patterns and sub-100-nm channel length MOSFETs. In this paper, we discuss lithographic performance and the performance of the MOSFET device.

Overlay evaluation of proximity x-ray lithography in 100 nm device fabrication

In the semiconductor manufacturing of below 100 nm devices, overlay accuracy is a critical issue for high resolution on proximity x-ray lithography (PXL). We applied PXL for five layers (mark, isolation, gate, contact, and wiring) to fabricate a 100 nm n-type metal–oxide–semiconductor field effect transistor and evaluated the accuracy. Alignment exposure was done with optical heterodyne alignment and magnification correction. The overall overlay accuracy (mean±3σ) was 25–45 nm, and the best was about 25 nm for the contact layer. The overlay error was classified into several components to estimate the error budget. The analysis revealed that the alignment error of the x-ray stepper is less than 20 nm under various conditions in device fabrication. Individual x and y scaling errors caused by mask image placement and the difference of wafer-to-mask gap was from 18–35 nm: the error of common in-plane deformation was about 20 nm. The present accuracy may make it possible to fabricate devices with a 100 nm grou...

Amorphous Refractory Compound Film Material for X-Ray Mask Absorbers

We proposed that the stress of the side walls of an absorber pattern causes the pattern distortion of an X-ray mask. The surfaces of the pattern side walls have a high compressive stress layer because they are easily oxidized in air after absorber pattern etching. This stress becomes a serious problem in proportion to the high degree of pattern integration. To lower the surface oxide layer stress of the film, we developed a TaGe nitride (TaGeN) absorber. The oxide layer stress of TaGeN films becomes lower with increasing the N2 content in the sputtering gas, and the stress value of Ta0.35Ge0.20N0.45 can be decreased to 1/17 that of TaGe. We fabricated a TaGeN X-ray mask and practically demonstrated that the TaGeN absorber was effective for high image placement accuracy to an X-ray mask having high dense patterns with a 0.1 µm pattern size.

An artificial photosynthesis anode electrode composed of a nanoparticulate photocatalyst film in a visible light responsive GaN-ZnO solid solution system.

The artificial photosynthesis technology known as the Honda-Fujishima effect, which produces oxygen and hydrogen or organic energy from sunlight, water, and carbon dioxide, is an effective energy and environmental technology. The key component for the higher efficiency of this reaction system is the anode electrode, generally composed of a photocatalyst formed on a glass substrate from electrically conductive fluorine-doped tin oxide (FTO). To obtain a highly efficient electrode, a dense film composed of a nanoparticulate visible light responsive photocatalyst that usually has a complicated multi-element composition needs to be deposited and adhered onto the FTO. In this study, we discovered a method for controlling the electronic structure of a film by controlling the aerosol-type nanoparticle deposition (NPD) condition and thereby forming films of materials with a band gap smaller than that of the prepared raw material powder, and we succeeded in extracting a higher current from the anode electrode. As a result, we confirmed that a current approximately 100 times larger than those produced by conventional processes could be obtained using the same material. This effect can be expected not only from the materials discussed (GaN-ZnO) in this paper but also from any photocatalyst, particularly materials of solid solution compositions.

Pattern Fabrication Technique for Ta-Ge Amorphous X-Ray Absorber on a SiC Membrane by Inductively Coupled Plasma.

We developed a pattern etching method for Ta–Ge (Ta3Ge) amorphous X-ray absorbers on a SiC membrane using a mixture of Cl2 and BCl3 gases with a single-layer e-beam resist. For this work, an inductively coupled plasma (ICP) etcher with a helium back surface cooling system was used. High etching selectivity and anistropic etching were achieved by regulating electrode temperature and BCl3 concentration ratio. The etching selectivity of Ta3Ge to the resist is 6.5. Ta3Ge patterns of 0.1 µm dimensions with vertical sidewalls were fabricated. Good etching rate uniformity was also obtained over a 61-mm-diameter membrane field. We found that Ru film was a suitable etching stopper material because it has high dry-etching durability and can be easily removed by oxygen plasma etching.

Characteristics of Ta-based amorphous alloy film for x-ray mask absorbers

We examined Ta-based amorphous alloy films and studied their characteristics for application in an x-ray mask with dimensions of the 0.1 μm design rule. From the viewpoint of x-ray absorption, Ge is a suitable element for a compound with Ta. We found that a Ge inclusion atomic ratio of 20%–30% in a Ta–Ge compound film was suitable with respect to stress control and stress stability. It was possible to adjust the stress of the Ta–Ge film after deposition by annealing it at high temperature while maintaining control as good as 0.56 MPa/ °C. During pattern fabrication by dry etching, it was possible to successfully etch the Ta–Ge film with a single-layer resist using a chroline based plasma, and scale patterns of 0.1 μm were obtained.

Origin of stress distribution in sputtered x-ray absorber film

To eliminate distortion in x-ray masks, not only lower average stress but also uniformity of the stress distribution in the x-ray absorber film are very important. We investigated the cause of stress distribution in sputtered x-ray absorber films both theoretically and experimentally. Our investigation clarified that stress distribution is determined by the distribution of the average velocity of sputtered and working gas atoms and/or the arrival frequency of incident working gas atoms when arriving at the wafer in sputtering systems. These determinants are strongly influenced by the geometry of the sputtering apparatus, i.e., the shape of the erosion area of the target and the substrate-to-target distance. We obtained a good uniformity of stress by optimizing the sputtering equipment configuration taking the erosion area of the target into consideration. Two ways to accomplish this are by adjusting the gap between the target and the substrate and by achieving uniformity of the erosion area.