Hisao Osawa

Polarization Effect on Signal from Optical ROM Using Solid Immersion Lens

In a high-numerical-aperture optical head using a solid immersion lens (SIL), it is anticipated that the polarization of the diffracted beam is disturbed, this affects the signals. To study this problem, a rigorous simulator based on the three-dimensional vector diffraction theory has been developed. Polarization disturbance for various NAs has been estimated and it has been clarified that the polarization is disturbed not only in the SIL head but also in the conventional high-NA head whose disk substrate is not covered with protective glass. The influence of polarization disturbance on the readout signals has been determined and discussed for the various polarizations.

Theoretical consideration on quantum lithography with conventional projection

At the end of last century, the name of “quantum lithography” has been emerged. This exciting approach was proposed for making a resolution two times higher than that of the conventional optics without changing a wavelength and a numerical aperture. For those who want optical lithography to last long, this has been thought to be a great technology. However, an applicability of the proposed method to the current exposure system i.e., reduced projection exposure system has not yet been examined clearly. We have investigated the proposed quantum lithography to apply into the current exposure system using reticle. For simplicity, coherent illumination i.e. sigma is zero condition is used for calculation. Our quantum lithography compatible to mask exposure system explains probability of one and two photon absorption on the image plane i.e. on wafer. We have shown that the half-wavelength quantum lithography using conventional mask exposure system is impossible because diffraction at the mask makes biphoton into two photon. We have found that there is still super-resolution quantum lithography using mask exposure, however, there is little possibility of quantum lithography practically today because biphoton light source is as dark as stars. To realize quantum lithography practically, further development of not only biphoton light source but also two-photon absorption resist is indispensable.

Instrumentation of a deep-UV microscope resolving less than 0.15 μm

Remarkable improvement in resolution when observing critical dimensions in semiconductor inspection by using a newly- developed deep-UV optical microscope is presented. At present, while scanning electron microscope (SEM) is the only imaging tool for less than 0.20-micron geometry, improvement in resolution of optical microscope has strongly been desired because of its easier operations and less damage including feature. Simulation of resolution to be achieve indicated that deep-UV wavelength only clearly resolve less than 0.15-micron geometry and images acquired at 266nm in the following experiment well agreed with the simulation. An objective lens especially for deep-UV, laser light source, illumination and imaging optics, and image detection device were built on a conventional microscope stand. This high-resolution microscope may extend the field of optical inspection and even open up new inspection applications.