Abstract

As extreme ultraviolet lithography tools with higher image numerical apertures are introduced, the range of angles at the mask multilayer are increased. This represents a challenge for maintaining through-angle mask reflection using the current periodic mask multilayer structures. In addition to reflectance amplitude, the phase of reflected light, which plays an important role in imaging, is also strongly influenced by increasing angles. The propagation of light through each bilayer in the stack imparts a phase shift based on incidence angle. This accumulates over many layers, inducing phase effects which are unique to each illumination point. While adjustments to multilayer period are sufficient to achieve acceptable reflectance, periodic multilayers may suffer in normalized image log slope (NILS) and image placement error (IPE) metrics as a result of strong oblique multilayer phase effects. In this work we present a methodology for systematic reduction of oblique multilayer effects through use of aperiodic multilayer design. For the same reasons, introduction of high and hyper-NA tooling for extreme ultraviolet lithography (EUVL) will again raise the importance of polarization. As the angle in resist approaches 90 degrees, the modulation of TM polarized light will reduce to zero. However, TE polarized light loses no modulation at these angles. During the deep ultraviolet (DUV) era, photoresist materials with refractive indices over 1.7 reduced the angle between diffracted rays, but for EUV systems, resist materials will not significantly alter the incidence angle. Introduction of a TE polarizer could solve the contrast issue, but would be difficult due to source power, throughput and implementation considerations. Instead, through careful tuning of the EUV mask, enhanced TE polarization can be achieved through the interaction of the absorber and the multilayer stack. TE Polarization induced by the mask greatly simplifies integration, while reducing adverse polarization effects from TM light at high incidence angles. Through optimization of EUV multilayers using aperiodic bilayers this work analyzes EUV films and their effect on polarization.

Publication Date

11-15-2024

Document Type

Dissertation

Student Type

Graduate

Degree Name

Microsystems Engineering (Ph.D.)

Department, Program, or Center

Microsystems Engineering

College

Kate Gleason College of Engineering

Advisor

Bruce W. Smith

Campus

RIT – Main Campus

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