William R. Heffner

Chalcogenide glass e-beam and photoresists for ultrathin grayscale patterning

The advantages and applications of chalcogenide glass ChG thin film photoresists for grayscale lithography are demonstrated. It is shown that the ChG films can be used to make ultrathin 600 nm, high-resolution grayscale patterns, which can find their ap- plication, for example, in IR optics. Unlike polymer photoresists, the IR transparent ChG patterns can be useful as such on the surface or can be used to transfer the etched pattern into silicon or other substrates. Even if the ChG is used as an etch mask for the silicon substrate, its greater hardness can achieve a greater etch selectivity than that obtained with organic photoresists. The suitability of ChG photoresists is demonstrated with inexpensive and reliable fabrication of ultrathin Fresnel lenses that are transparent in the visible as well as in the IR region. The optical functionality of the Fresnel lenses is confirmed. Application of silver pho- todissolution in grayscale lithography for microelectromechanical sys- tems MEMS applications is also shown. A substrate to ChG/silver thick- ness etching ratio of 10 is obtained for the transfer of patterns into silicon using reactive ion etching RIE, more than a fivefold increase compared to traditional polymer photoresist.

Influence of Bi on topological self-organization in arsenic and germanium selenide networks

The influence of Bi on the network structure of Ge20Se80−yBiy and As40−ySe60Biy glasses is investigated by high-resolution X-ray photoelectron spectroscopy (XPS). The results show that Bi enters the glass network of both Ge–Se and As–Se glass systems in the form of BiSe3/2 pyramids, with a significant increase in the concentration of homopolar Ge–Ge and As–As bonds, respectively, compared to Bi-free samples. In these compositions, topological self-organization is found to play a minor role in comparison to phase separation tendencies at the nanoscale caused by Bi addition. It is suggested that BiSe3/2 rich regions occur as partially ordered nano-thin sheets, which may account for the percolative-type response of electrical conductivity observed in similar Bi containing systems.

Chalcogenide glass thin film resists for grayscale lithography

The advantages and applications of chalcogenide glass (ChG) thin film photoresists for grayscale lithography are demonstrated. It is shown that the ChG films can be used to make ultrathin (~600 nm), high-resolution grayscale patterns, which can find their application, for example, in IR optics. Unlike polymer photoresists, the IR transparent ChG patterns can be useful as such on the surface, or be used to transfer the etched pattern into silicon or other substrates. Even if the ChG is used as an etch mask for the silicon substrate, its greater hardness can achieve a greater transfer ratio than that obtained with organic photoresists. The suitability of ChG photoresists is demonstrated with inexpensive and reliable fabrication of ultrathin Fresnel lenses that are transparent in the visible as well as in the IR region. The optical functionality of the Fresnel lenses is confirmed. Application of silver photodissolution in grayscale lithography for MEMS applications is also shown. The process consists of the following steps: ChG film deposition, Ag film deposition, irradiation through a grayscale mask, removal of the excess Ag and the transfer of the pattern to Si by dry etching. A substrate to ChG thickness etching ratio of ~ 10 is obtained for the transfer of patterns into silicon, more than a five fold increase compared to traditional polymer photoresist.

Building a Low Cost, Hands-on Learning Curriculum on Glass Science and Engineering using Candy Glass

We have developed a program to connect students, as well as the general public, with glass science in the modern world through a series of hands-on activities and learning experiences using sucrose based glass (a.k.a. hard candy). The scientific content of these experiments progresses systematically, providing an environment to develop an understanding of glassy materials within a framework of “active prolonged engagement” with the material. Most of the experiments can be assembled in a high school lab, or even in a home setting with minimal cost, and yet are appropriate for inclusion in an undergraduate materials lab. The cost is minimized by utilizing common, everyday materials and devices. Some of the activities included in our experiments include: synthesis, density, refractive index determination, glass transition, crystallization, kinetics of devitrification, thermal properties, etc. Temperature measurement, temperature control, and even automated data collection are part of the experience, providing an open path for the students to continue their own interesting and creative ideas.