Optimized phase-shifting masks for high-resolution resist patterning by interference lithography

Abstract

The EUV laboratory exposure tool (EUV-LET) is a versatile stand-alone resist patterning tool. Main applications are resist characterization for industrial lithography as well as the patterning of high-resolution arrays over large areas as required in research and small-volume production. High-resolution patterns are achieved by interference lithography based on the achromatic Talbot effect. The theoretical resolution limit for achromatic Talbot lithography (ATL) of 10 nm half-pitch (HP) is mainly resist-limited, as long as necessary high-resolution transmission masks can be fabricated. In this paper we focus on the transmission mask fabrication technology with a low number of process steps that allows to maximize yield and offers high flexibility. Diffraction order efficiencies (DOEs) of the masks are optimized to achieve maximal aerial image contrast (MTF) in the achromatic Talbot distance. The developed four-step mask fabrication process of contact-hole masks with HPs of 50 nm, 40 nm and 30 nm over areas of 1 × 1 mm2 is presented. The transmission masks are characterized within the EUV-LET to determine the achievable MTF that can be used for resist patterning and characterization. Based on the carried out in-tool measurements the achievable MTF is 63.7 % and the total diffraction efficiency into the 1st diffraction orders (DOs) is 41.7 % (both for 50-nm-HP masks) which makes the masks perfectly suited for the achromatic Talbot approach. Furthermore, we demonstrate high-resolution patterning down to 28 nm HP describing an effective in-lab tool that can be used at facilities for the characterization of photoresists for the upcoming lithography generations

Development of an ultra-compact inline transmission grating spectrograph for extreme ultraviolet wavelengths

“…A maximized 1 st order diffraction efficiency of 39% into all four diffraction orders (in sum) is achieved for an opening ratio of 0.38 and a polymer thickness of 320 nm (Fig. 4b) 16,17 . Figure 4.…”

“…The lithographic process of the Talbot lithography requires transmission gratings with a low intensity into the 0 th diffraction order and a high diffraction efficiency into the 1 st diffraction orders, which is also beneficial for the use in EUV-TGS. This is achieved by introducing a -phase-shift to the radiation passing the grating material with respect to the radiation passing between the grating structures by optimizing the grating material thickness and the opening ratio (gap/period) 16 . Top-down and cross-sectional SEM images (Fig.…”

Investigation of the resolution limit of Talbot lithography with compact EUV exposure tools

“…In this configuration, the interference pattern can be understood as a two-beam interference, where the ±1st diffraction orders dominate. To achieve a complete suppression of the 0th diffraction order, the beam passing through the grating material must experience a precise π-phase-shift, and the intensities of the beams passing through the material and gaps need to be equal, accounting for the unavoidable absorption of EUV radiation in the grating material 25 . Meeting these requirements requires high precision and quality in both mask design and fabrication processes.…”

“…In the currently used mask design, an electron beam resist is used as the phase-shifting material. This allows a simple and robust fabrication process 25 without the need for an additional etching transfer process. With this approach, the fabrication of 28 nm half-pitch contact hole patterns in a standard EUV photoresist could be demonstrated 16 .…”

Towards the resolution limit of Talbot lithography with compact EUV exposure tools

“…In the currently used mask design, an electron beam resist is used as the phase-shifting material. This allows a comparatively simple and robust fabrication process 25 without the need for an additional etching transfer process. With this approach, the fabrication of 28 nm half-pitch contact hole patterns in a standard EUV photoresist could be demonstrated 17 .…”