Resolution enhancement for advanced mask aligner lithography using phase-shifting photomasks

Abstract

The application of the phase-shift method allows a significant resolution enhancement for proximity lithography in mask aligners. Typically a resolution of 3 µm (half-pitch) at a proximity distance of 30 µm is achieved utilizing binary photomasks. By using an alternating aperture phase shift photomask (AAPSM), a resolution of 1.5 µm (half-pitch) for non-periodic lines and spaces pattern was demonstrated at 30 µm proximity gap. In a second attempt a diffractive photomask design for an elbow pattern having a half-pitch of 2 µm was developed with an iterative design algorithm. The photomask was fabricated by electron-beam lithography and consists of binary amplitude and phase levels.

Intensity and phase fields behind phase-shifting masks studied with high-resolution interference microscopy

“…18 Here, the test structure is a group of corners or elbow structures from a phase-shifting mask. 19 Tina Weichelt (Friedrich-Schiller-Universität Jena) has developed the mask. The structure and details reported in Ref.…”

High-resolution proximity lithography for nano-optical components

“…In contrast to projection lithography, for which the phase-shifting method was explored in-depth [85], it was not realized for generalized geometries in proximity lithography for over 30 years. Recent works [86,87] have picked up the PSM concept again to achieve better resolution, contrast and depth of focus and will be discussed in detail in Sections 3.3 and 4.3.…”

“…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]. This allows a significant simplification of mask fabrication and has been enabled by inclusion of phase shifts in the aerial image definition (Holographic PSM) according to Levenson's work from 1982 [83].…”

“…Advanced e-beam written photomasks with wavelength-scale features and multiple lithography layers: (a) Three-level phase mask for pulse compression grating fabrication[86], width of the smallest ridge: 100 nm, (b) Combined amplitude and phase mask to realize Levinson-type phase shifted aerial images with non-periodic geometries[87], minimum features size: 200 nm.…”

Intensity and phase fields behind Phase Shifting Masks studied with High Resolution Interference Microscopy

“…The local pitch of the structure is 4 µm. The height of the surface structuring is chosen to obtain a phase shift of half wavelength (π) at the design wavelength, which was set to 365 nm 13 . .…”