Toshiyuki Yoshimura

MAGNETIC NANOPARTICLE ARRAY WITH PERPENDICULAR CRYSTAL MAGNETIC ANISOTROPY

By using electron beam lithography, a continuous CoCrPt film with a perpendicular crystal magnetic anisotropy has been patterned into a magnetic nanoparticle array of 29 Gdot/in.2 with a 150 nm period, an 80 nm diameter, and a 44 nm height. Studies of magnetic properties using a magnetic force microscope and a vibrating sample magnetometer show that this patterning increases the remanent-to-saturation magnetization ratio from 0.2 of the continuous film to 1 of the particles, and that each particle has a single magnetic domain with perpendicular anisotropy. The application of this array to future high density magnetic recording media is discussed.

Nano edge roughness in polymer resist patterns

Ultrasmall edge roughness in delineated patterns (nano edge roughness) is investigated in nanostructures made of negative‐type electron beam polymer resists by atomic force microscope measurements. Very narrow isolated lines 10–20 nm wide are fabricated with a finely focused electron beam provided by a scanning electron microscope. A chemical amplification novolak resin‐based resist shows nano edge roughness which cannot be neglected in nanofabrication. To investigate the origin of the roughness, conventional two‐component resist systems are microscopically compared. An azide polyvinylphenol‐based resist and an azide novolak resin‐based resist are used. The novolak resin‐based resist exhibits a rougher surface than the polyvinylphenol‐based one. This result suggests that the polymer structures of the base resins cause nano edge roughness of a chemical amplification resist in connection with the acid diffusion during the post‐exposure bake process.

Correlation of Nano Edge Roughness in Resist Patterns with Base Polymers

The origin of ultra small edge roughness in delineated resist patterns (nano edge roughness) is investigated from the viewpoint of molecular structures of the base polymers of the resists. In this article, conventional two-component negative-type electron beam resists are studied to clarify the correlation of the nano edge roughness with base polymers. The base polymers are cresol novolak and polyvinylphenol mixed with the same concentrations of photoactive azide compound. The weight-average molecular weight (Mw) and polydispersity (Mw/Mn) of the base resins are controlled. Nanometer feature microscopic surface characteristics obtained with an atomic force microscope (AFM) show that the cresol novolak-based resist exhibits a rougher surface than the polyvinylphenol-based one. Nano edge roughness can be suppressed by using base resins with lower Mw and Mw/Mn, suggesting that nano edge roughness reflects the molecular characteristics of the base polymers. There is nanometer level swelling in resist patterns (nano swelling) in polyvinylphenol-based resist. These results suggest that the structures of the base polymers and the interaction with developers affect the nano edge roughness.

0.1 mu m CMOS devices using low-impurity-channel transistors (LICT)

Summary form only given. It was found that LICTs are very effective for providing low threshold voltages with good turn-offs in 0.1 mu m CMOS devices. Attention is given to device fabrication criteria, key process technologies used, and the features achieved using LICTs.<<ETX>>

Design and performance of 0.1- mu m CMOS devices using low-impurity-channel transistors (LICT's)

0.1- mu m CMOS devices using low-impurity-channel transistors (LICTs) with dual-polysilicon gates have been fabricated by nondoped epitaxial growth technology, high-pressure oxidation of field oxide, and electron-beam lithography. These devices, with gate lengths of 0.135 mu m, achieved normal transistor operation at both 300 and 77 K using 1.5-V supply voltage. Maximum transconductances are 203 mS/mm for nMOS transistors and 124 mS/mm for pMOS transistors at 300 K. Low-impurity channels grown on highly doped wells provide low threshold voltages of about 0.35 V for nMOS transistors and about -0.15 V for pMOS transistors at 77 K, and preserve good turn-offs with subthreshold swings of 25 mV/decade at 77 K. LICTs suppress short-channel effects more effectively, compared with conventional devices with nearly uniform dopings.<<ETX>>

Coulomb blockade in the inversion layer of a Si metal‐oxide‐semiconductor field‐effect transistor with a dual‐gate structure

We have studied the transport properties of artificially squeezable inversion layers in a Si metal‐oxide‐semiconductor field‐effect‐transistor with a dual‐gate structure. Increasing the potential barrier height with constant intervals along the one‐dimensional channel gradually transforms a simple quantum wire into coupled quantum dots. The clear change in transport properties has been observed by changing the tunnel barrier height at low temperatures. The experimental results are discussed in terms of one‐dimensional subbands and the Coulomb blockade of single‐electron tunneling.

Acid‐diffusion effect on nanofabrication in chemical amplification resist

Acid‐diffusion effect on nanometer pattern fabrication in a chemical amplification resist, SAL601 (Shipley Co.), is investigated with a finely focused electron beam. During postexposure bake (PEB), acid generated by the electron beam exposure diffuses and is assumed to cause pattern size changes. A scanning electron microscope, S‐900 (Hitachi), which has a beam diameter of approximately 2 nm at 5 kV, is used to make latent images of nanometer isolated lines in a resist film. After electron beam exposure, the resist films with a thickness of 20 nm are baked in different conditions before development. The measured linewidths are found to be proportional to the square root of the PEB time. According to a simple acid diffusion model, this can be explained by the diffusion of generated acid during PEB. A minimum feature size of a 20 nm isolated line is obtained by adjusting the PEB conditions. It is therefore important to control the PEB conditions to suppress the acid diffusion for the critical dimension cont...

Nanometer‐scale imaging characteristics of novolak resin‐based chemical amplification negative resist systems and molecular weight distribution effects of the resin matrix

Molecular weight distribution effects of novolak resin‐based chemical amplification negative resist systems are investigated for electron‐beam lithography. The resist systems investigated consist of onium salts as an acid generator, a methoxymethyl melamine crosslinker, and a conventional/fractionated novolak resin matrix. Delineated patterns of both types of resist systems are compared to evaluate submicron‐scale resolution. The conventional novolak resin‐based system shows higher contrast than the fractionated one. High aspect ratio patterns are resolved for the conventional novolak‐based resist, whereas poor results are obtained for the fractionated resin‐based one on the submicron scale. Very thin films (30 nm) of both resist systems are delineated with a finely focused electron beam (diameter: approximately 2 nm at 5 kV) from a scanning electron microscope. Nanometer‐scale edge roughness (nanoedge roughness) is observed for the conventional novolak resin‐based resist. On the contrary, the degree of n...

Polycrystalline silicon ‘‘slit nanowire’’ for possible quantum devices

Polycrystalline silicon (poly‐Si) ‘‘slit nanowire’’ was fabricated in a slit formed with 100 nm lithography, microwave dry etching of silicon substrate, conformable filling of the trench by chemical vapor deposition (CVD) SiO2, slit etching of the CVD SiO2, conformable deposition of doped amorphous silicon, followed by etchback and annealing. Observation with transmission electron microscope confirmed that a poly‐Si slit nanowire, with a cross section of ∼5–8 nm×20 nm is fabricated. Appropriate annealing of the a‐Si layer makes the poly‐Si grains grow to more than 2 μm in length. This technique would make it possible to realize silicon quantum devices, and to fabricate conventional integrated circuit devices and light emitting slit nanowire devices on a same silicon chip, which would allow the fabrication of integrated optoelectronic circuits.

Suppression of acid diffusion in chemical amplification resists by molecular control of base matrix polymers

Suppression of acid diffusion during post-exposure baking (PEB) of chemical amplification resists is investigated from the standpoint of molecular control of base matrix polymers. Negative-type chemical amplification resists composed of cresol novolak-based matrix polymers, acid-catalyzed crosslinkers of melamine resins, and acid generators of onium salts are prepared. The molecular weight distributions of the base matrix polymers are controlled by means of a precipitation method. The resists are exposed with electron beams in isolated lines to evaluate the acid diffusion characteristics. Dependence of pattern sizes on the PEB time clearly shows that acid diffusion determines the resist pattern sizes based on Ficks law. The diffusion coefficients of resists with base matrix polymers with small polydispersities are smaller than those of resists with base matrix polymers with large polydispersities. Acid diffusion can still be suppressed by applying base matrix polymers with small weight-average molecular weights and small polydispersities. Diffusion coefficients can be further decreased by using base matrix polymers with more p-cresol components. A diffusion mechanism is proposed based on acid diffusion channels composed of active OH-groups and vacancies in the base matrix polymers.