Development of Evaluation system for EUV photoresist performance and Unique X-ray lithography process via Synchrotron radiation

Abstract

Lithography technology has been developed to improve resolution. In order to achieve high resolution, the wavelength of light used in lithography was reduced and techniques such as multi patterning have been applied. Extreme ultraviolet (EUV), X-ray, and charged particle lithography have been studied as next-generation lithography to replace deep ultraviolet (DUV) lithography. EUV lithography, which is appropriate for mass production, has been adopted and researched, and X-ray lithography is applied to the fabrication of various devices such as sensor, optics, and unique surface. High-performance photoresists must be developed to introduce EUV lithography, however the evaluation infrastructure is insufficient. To address this problem, the undulator of the 4A beamline in the Pohang accelerator laboratory (PAL) was employed to build an evaluation system. EUV beam was highly monochromatic and had high intensity. Developed system aimed to measure absorbance and photoresist performance, i.e. sensitivity, resolution and line edge roughness (LER). The absorbance was calculated from the transmittance because the reflection was negligible in the measurement setup. Sensitivity and contrast were acquired from the contrast curve, which was the remained thickness according to the exposure dose. In order to find out Resolution and LER, the line patterning was essential. The interference lithography, which was possible to fabricate high-resolution lines without flare and aberration, was introduced. The exposure dose was determined by dose-on-mask and diffraction efficiency calculated through rigorous coupled wave analysis (RCWA). 125 nm half pitch (HP) patterning was performed through the interference lithography. Exposure latitude could be extracted from the relationship between dose and line width, and a lumped parameter model (LPM) was introduced to examine the optimal exposure dose. X-ray lithography processes are required to fabricate various structures. The bending magnet of the 9D beamline in the PAL was chosen. Developed three X-ray exposure methods employed the characteristics of the X-ray, e.g. low diffraction and large depth of focus. First, microstructures of various shapes and slopes on one substrate were fabricated. This structure was utilized to improve the quality of an X-ray image acquired with an X-ray tube source by applying it to the focused anti-scatter grid. Second, sub-micron line patterns of hemispherical cross-section were fabricated by X-ray gray scale lithography. Molded Polydimethylsiloxane (PDMS) was applied to a cell culture platform, and sub-micron channel. Lastly, AAO was utilized as the X-ray mask. Sub-micron hole patterns were successfully fabricated, and were transferred to a Silicon (Si) wafer through deep reactive-ion etching (DRIE).