Flat plate radiography systems demonstrate the highest potential for high image quality when reducing the exposure dose. Depending on the system generation, the storage phosphor systems also show an improved image quality, but the possibility of a dose reduction is limited in comparison with the flat plate detector system.
In modern mask manufacturing, a successful defect mitigation strategy has been become crucial to achieve defect free masks for high-end lithography. The basic steps of such a strategy include inspection, repair, and subsequent post-repair qualification of repair sites. For the latter task, actinic aerial image measurements have been proven to be the technique of choice to assess the printability of a repaired site. In the last three years, International SEMATECH in cooperation with Infineon/AMTC-Dresden and SELETE, funded a joint development project at Carl Zeiss to develop an AIMS tool operating at the 157nm wavelength. The three beta tools were shipped in 2003 to the three beta customer sites. In this paper are presented the first results obtained with these beta tools, including measurements on binary as well as alternating phase shift masks. The technical properties of the tool were discussed with regards to the capability of the tool for defect qualification on photomasks. Additionally, preliminary results of the evaluation of alternating phase shift masks will be discussed, including measurements performed on dense lines-and-spaces structures with various pitch sizes.
%675$&7The worldwide first Aerial Image Measurement System (AIMS TM ) for 157 nm lithography has been used to measure binary chrome and attenuated phase shift masks at 157 nm wavelength. The AIMS TM measurements were done for line structures from 200 nm up to 400 nm and for 500 nm contacts. Through focus series have been conducted to calculate the process windows for various structures and feature sizes..H\ZRUGV: AIMS, 157 nm lithography, photo masks, process window ,1752'8&7,21The Aerial image measurement System (AIMS TM ) is an optical system for evaluating reticles under specific exposure tool conditions of numerical aperture (NA), sigma, wavelength and illumination type. The image taken with the system is optically equivalent to the latent image incident on the photo resist of the wafer, but magnified and recorded with a CCD camera. Thus, the AIMS TM tool provides early information about the printing characteristics of a reticle without carrying out full resist exposure depth of focus matrix and following SEM measurement of the printed features [1, 2].For DUV (deep ultraviolet: 248, 193 nm) these kinds of tools are commercially available as AIMS TM fab and AIMS TM fab 193. They are state-of-the-art in the photo mask industry for development, quality control, repair verification and defect classification. Infineon, International SEMATECH and Selete are currently engaged in a project with Carl Zeiss Microelectronic Systems GmbH to develop an AIMS TM tool for direct optical simulation of 157 nm lithography.Similar to the AIMS TM fab tools mentioned above, the new system for 157 nm will have adjustable illumination type, numerical aperture and partial coherence to match the conditions in various exposure tools. Due to the wavelength in the vacuum ultraviolet (VUV) spectrum, major efforts had been required for the illumination and imaging part of the optical system as well as for the purging of the beam path.The project consists of two phases: an alpha tool and a beta tool phase. The alpha tool is a fully functional 157 nm AIMS TM tool with minor limitations in terms of mask handling and throughput comparing with the future beta and production tools. The value of the tool for mask evaluations and lithographic assessments is not affected by these limitations. The purpose of the alpha tool is to test and prove out technical concepts for an 157 nm AIMS TM tool. TM AIMS is trademark of IBM
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