Photomask / Direct Write Lithography Documents

New electron beam (EB) resists made of calixarene resists are introduced. Typical sensitivities of calixarene resists range from 700 µC/cm2 to 7 mC/cm2. High-density dot arrays with 15 µm diameter constructed using calixarene resist were easily delineated using a point EB lithography system. Our results suggest that the resolution limit of calixarene resists is dominated by a development process such as adhesion to a substrate rather than by the EB profile. Calixarene resists are resistant to etching by halide plasma. We also demonstrated nanoscale devices processed by using calixarene resists. Calixarene resists are promising materials for nanofabrication.

Along with the development of optical communication, optical integrated devices are now making rapid progress, and especially the grating, which is of a periodic structure, is now playing an important role in a wide variety of fields. In recent years, there is an increasing need for smaller grating pitches, and not only semiconductors bit also a variety of materials are used for substrates. Recently, we have established a technique to finely control the grating pitch to 1nm, less than the pattern data unit (5 nm), by E-beam (E-B) lithography. Also, the fabrication of gratings with phase shift has been simplified by changing the stage shift distance.

Electrons confined in ultrathin film of semiconductor heterostructure provided quantization of energy states by wave property of electrons. By using this one-dimensional quantization, quantum well lasers and high electron mobility transistors were realized. Progress of lithography will provide electron or optical devices based on new principles by two or three-dimensional quantized structures.

Sensors have to meet stringent requirements for space applications such as high quantum efficiency, extremely low noise, high temperature (or uncooled) operation, radiation hardness, narrow line widths, high output power, etc. Semiconductor quantum dots are very promising for optoelectronic device applications because of their capabilities for carrier confinement in all 3-dimensions, creating discrete energy levels with a sharp delta-function-like density of states, large optical nonlinearity, normal incidence radiation absorption, lower dark current (which results from weak electron-phonon coupling), and high radiation tolerance. Although fabrication methods using self-organization, such as Stranski-Krastanov growth, are being widely studied, site and size control multi layer quantum dots material has not been achieved to date. On the other hand, Stranski-Krastanov self-assembled quantum dots could not produce focal plane array worthy materials yet. This motivated us to continue the materials and device structure improvement of self-assembled QDIPs, and development of site and size controlled semiconductor quantum dots by using molecular beam epitaxial (MBE) growth on GaAs substrates.

Several recent experimental studies on microstructured samples of ferromagnetic materials are described. Magnetization reversal phenomena were investigated on submicron wire samples consisting of two magnetic layers with different coercivities utilizing the giant magnetorersistance (GMR) effect. From resistivity measurements, the domain wall movements are sensitively monitored and the velocity of propagation is determined. Experiments to estimate the contribution of domain wall to the resistivity are also introduced.

Spin structures of nanoscale magnetic dots are the subject of increasing scientific effort, as the confinement of spins imposed by the geometrical restrictions makes these structures comparable to some internal characteristic length scales of the magnet. For a vortex (a ferromagnetic dot with a curling magnetic structure), a spot of perpendicular magnetization has been theoretically predicted to exist at the center of the vortex. Experimental evidence for this magnetization spot is provided by magnetic force microscopy imaging of circular dots of permalloy (Ni80Fe20) 0.3 to 1 micrometer in diameter and 50 nanometers thick.

Patterning of glass or plastic substrates in the form of shallow square patches is a promising method of increasing the storage density for magneto-optical disks. The sidewalls of the patches pin the reverse-magnetized domains that develop in these samples. Confinement of domains within the patch boundaries during thermomagnetic recording has also been demonstrated. We have measured polarization conversion of the incident light on the sidewalls of the patches; a method to reduce the amount of such polarization conversion is proposed in this article.

The technics of higher integration of circuits is supported by instruments of applied electron beam. The electron beam lithograph is indispensable in the mass and test production of masks and devices. The electron microscope is widely used for evaluation of wafer process as well as defects and also for measuring length.

Demodulation of the servo tracking signals magnetically printed on hard disks by using a lithographically patterned master disk has been studied. Position signal decoded from the printed servo pattern was successfully demonstrated on a spin stand. Position error evaluated in a prototype drive was 30% track pitch. Pulse timing shift control by compensating the pattern dimension, and introduction of more sophisticated servo control system for actively controlling the printed pattern eccentricity would be key issues for further improvements.

As an alternative method for the servo track writing of hard disk drives (HDDs), a magnetic contact duplication method by using a lithographically patterned master disk has been proposed and investigated. On the master disk, magnetic film pattern according to the information signal to be printed on slave disks is provided by a lithography technique. In this method, unlike the anhysteretic process of tile conventional contact duplication method for magnetic tapes, the master information never disappears when a large external field is applied to the master while printing. This duplication method, as we call the Printed Media technology, can provide a very effective and inexpensive lump-sum servo track writing method for HDDs.