Patterning via optical-saturable transformations: A review and simple simulation model

Abstract

Most of the nanoscale fabrication in the semiconductor industry is based on patterning with scanning-electron beam lithography (SEBL). Although this approach is very versatile and has very high resolution, it is intrinsically a serial writing process, and therefore, relatively slow. Our group has been investigating alternative nano-fabrication techniques, adapted from ideas of saturating optical transitions such as those used in stimulated emission-depletion microscopy and related methods, and optical interference lithography. Linewidths and resolutions on the scale of a few tens of nanometers and below are highly desirable for various applications in nanotechnology. However, the spatial resolution of optical lithography is restricted by diffraction. In the past, we developed absorbance modulation to overcome this limit. This approach utilizes photochromic molecules that can be optically switched between two thermally stable states, one opaque and the other transparent. However, absorbance modulation is limited to surface (2-D) patterning. Here, we report on an alternative approach that exploits unique combinations of spectrally selective reversible and irreversible photochemical transitions to achieve deep subwavelength resolution with potential extension to 3-dimensions. This approach, which we refer to as patterning via optical-saturable transformations have the potential for massive parallelism, enabling the creation of nanostructures and devices at a speed far surpassing what is possible with SEBL. The aim of our research is to translate the success in circumventing Abbe's diffraction limit in optical microscopy to optical lithography.