Paul Francis Michaloski

Depth of focus and resolution enhancement of i-line and deep-UV lithography using annular illumination

Annular illumination has been studied as a method for improving depth of focus (DOF) in microlithographic systems. A 2X increase in DOF for 0.25 micrometers dense line/space features has been demonstrated using a deep-UV exposure tool with annular illumination. The same increase in DOF for 0.35 micrometers dense line/space patterns has been demonstrated using an i- line exposure tool employing annular illumination. No improvement in isolated features has been found. Annular illumination exhibits no degradation in isolated feature DOF, but the critical dimension (CD) split between dense and isolated features is affected when using annular illumination. Prototype i-line and deep-UV annular illumination systems have been built and tested which minimize the reduction in intensity and loss of uniformity control when using annular illumination. We have employed the use of conical optics as a high efficiency method of producing ring-shaped illumination in an i-line illumination system. The deep-UV prototype system uses a pre-uniformizer device to convert the collimated excimer laser light into a flat-top pupil fill which is then centrally obscured to produce annular illumination.

Optical design forms for DUV and VUV microlithographic processes

Microlithographic objectives have been developed for deep ultraviolet and vacuum ultraviolet wavelengths used for printing and inspection applications related to microlithographic processes. Refractive and catadioptric design solutions using fused silica, calcium fluoride and other crystals are discussed. Several reflective and catadioptric design forms having central obscurations will be compared to refractive forms. Design complexity, performance and limitations are compared.

A laser speckle reduction system

Speckle degrades the contrast of the fringe patterns in laser interferometers that measure rough objects. In this paper, we describe a speckle reduction system that can be used with high speed cameras to increase the frame rates of the interferometer and creates less vibration in the system.

A Deep UV Imaging System For Lithography And Process Development

A simple optical imaging system has been designed and built for printing sub-half-micron lithographic images at 248 nm. The following discusses the design considerations of producing a system that can achieve the optical and mechanical criteria of microlithography while still maintaining the simplicity and versatility for a research and development instrument. Also, discussed are designs of lenses that perform at other UV wavelengths and mount in the same mechanical system as the 248 nm lens.