Diffractive phase-shift lithography photomask operating in proximity printing mode

Abstract

A phase shift proximity printing lithographic mask is designed, manufactured and tested. Its design is based on a Fresnel computergenerated hologram, employing the scalar diffraction theory. The obtained amplitude and phase distributions were mapped into discrete levels. In addition, a coding scheme using sub-cells structure was employed in order to increase the number of discrete levels, thus increasing the degree of freedom in the resulting mask. The mask is fabricated on a fused silica substrate and an amorphous hydrogenated carbon (a:C-H) thin film which act as amplitude modulation agent. The lithographic image is projected onto a resist coated silicon wafer, placed at a distance of 50 µm behind the mask. The results show a improvement of the achieved resolution -linewidth as good as 1.5 µm -what is impossible to obtain with traditional binary masks in proximity printing mode. Such achieved dimensions can be used in the fabrication of MEMS and MOEMS devices. These results are obtained with a UV laser but also with a small arc lamp light source exploring the partial coherence of this source.

High-resolution proximity lithography for nano-optical components

“…Two years later, Neto et al [182] and in 2009 Cirino et al [183,184] both demonstrated 1.5 lm resolution with a very similar configuration. Recently, Weichelt et al have demonstrated that a phase mask with only two phase levels and an additional chromium layer is sufficient to realize a resolution of 2 lm for a non-periodic pattern in 30 lm separation [87].…”

Numerical optimization of illumination and mask layout for the enlargement of process windows and for the control of photoresist profiles in proximity printing

“…The Talbot effect allows to directly image the shape of the angular spectrum onto the wafer, 6 while phase shift masks can be used in conjunction with a coherent illumination to print extremely small structures using the principles of holograpy. 7 Although these techniques have a great potential for special applications, we will focus on a more general approach in the following.…”

Digital Holography: Computer-Generated Holograms and Diffractive Optics in Scalar Diffraction Domain

“…Schematic diagram of the phenomenon of free space propagation, and its relation with frequency and image spaces, as well as mask and wafer planes. Reprinted with permission of OSA (Cirino, G. A., 2010).…”

“…A(x',y') and (c) phase φ(x',y') distributions of the resulting phase shift photomask. Reprinted with permission of OSA (Cirino, G. A., 2010). Figure 11 shows schematically the entire process to fabricate the proposed diffractive phase shift proximity photomask.…”