Maskless Lithography Based on Heat-Mode Resists and Flat Optics

Date of Award

5-9-2026

Degree Name

Ph.D. in Electro-Optics

Department

Department of Electro-Optics and Photonics

Advisor/Chair

Jason Deibel

Abstract

Photolithography remains a cornerstone of modern micro- and nanofabrication; however, conventional mask-based approaches face increasing challenges in cost, flexibility, and scalability, particularly for low-volume production and rapid prototyping. This dissertation presents a comprehensive investigation of maskless lithography based on heat-mode resist mechanisms and flat optics, with the goal of enabling high-resolution, cost-effective, and scalable patterning platforms. First, a low-cost heat-mode lithography technique based on phase-change germanium-antimony-telluride (Ge₂Sb₂Te₅, GST) thin films is developed and experimentally demonstrated. In this approach, direct laser writing (DLW) induces localized amorphous-to-crystalline phase transitions in a photo-insensitive GST layer, which subsequently serves as a robust hard mask for pattern transfer. The process achieves near 100% pattern transfer yield and exhibits exceptional long-term stability, with no measurable degradation after extended exposure to ambient conditions. By eliminating the need for conventional photoresists and stringent processing environments, this method significantly reduces fabrication complexity and cost while maintaining high pattern fidelity. Building upon this lithographic platform, the dissertation further explores the integration of computational design and flat diffractive optics. An extended-depth-of-focus Fresnel zone plate (EFZP) is designed using a hybrid strategy that combines normalized angular spectrum compression and a linear focal-length increment. A genetic algorithm is employed to optimize the strongly coupled design parameters, resulting in a device with a simulated depth of focus of 67.62 µm at a wavelength of 532 nm, representing nearly a 60-fold improvement over conventional designs. The EFZP is fabricated using the GST-based heat-mode lithography process with dimensional deviations below 5%, and experimental characterization confirms close agreement with theoretical predictions, demonstrating both the effectiveness of the design methodology and the precision of the fabrication technique. To further enhance throughput, this work introduces a parallel maskless lithography system based on a dielectric metalens array integrated with a digital micromirror device (DMD). The metalens array, composed of subwavelength silicon nitride nanopillars, is designed using a propagation phase approach to achieve high numerical aperture focusing at 532 nm with a FWHM of 385 nm. A 20 × 20 metalens array is fabricated and incorporated into a custom optical system capable of generating hundreds of independently addressable focal spots. Combined with DMD-based spatial modulation, the platform enables parallel direct laser writing with significantly improved throughput while preserving the resolution of single-beam systems. Together, these contributions establish a unified framework that combines heat-mode resist materials, computationally optimized flat optics, and parallel optical architectures for next-generation maskless lithography. The results demonstrate a viable pathway toward scalable, flexible, and cost-effective nanofabrication, with potential applications in electronics, photonics, sensing, and advanced manufacturing technologies.

Keywords

Optics

Comments

OCLC No. 1591829940

Rights Statement

Copyright 2026, author.

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