Phase-shift mask

About: Phase-shift mask is a research topic. Over the lifetime, 2088 publications have been published within this topic receiving 18058 citations.

Focus latitude enhancement of symmetrical phase mask design for deep submicron contact hole patterning

Abstract: The mechanism of focus latitude enhancement for contact/via hole printing is explained by approximating the axis intensity distribution of an image as a series of cosine functions to characterize the interference between each pair of diffraction beams. It is found that a phase-shifting mask (PSM) with symmetrical assist features improves the depth of focus (DOF) by introducing destructive interference to counterbalance the intensity fluctuation from constructive interference as defocus. A simple formula was derived to represent the capability of focus latitude enlargement. It shows that the extent of enhancement depends on the exposure wavelength and numerical aperture of a projection lens only. Increasing the degree of partial coherence degrades the focal range enlargement because a larger illumination angle elongates the destructive interference pattern in the optical-axis direction to weaken its ability for intensity compensation. On the other hand, the lack of constructive interference in dense hole imaging fails the mask pattern transfer, which limits the application of the phase-shifting method to pattern pitch greater than 2λ/NA. A tiny amount of spherical aberration results in prominent asymmetrical defocus behavior because the wave deformation in the projection lens shifts the distribution of constructive and destructive interference patterns to opposite defocus directions. The printing characteristics of 0.17 μm contact using an 18% transmission, rim-type attenuated phase-shifting mask are investigated to corroborate our analysis of defocus behavior. The dependence of depth of focus on pattern duty is stressed to elucidate the difference in mechanisms of focus latitude improvements for a sparse hole and periodic dense hole.

Mask blank, phase shift mask, method for producing them, and method for producing semiconductor device

Abstract: PROBLEM TO BE SOLVED: To provide a mask blank capable of suppressing occurrence of a transfer failure even when a translucent substrate has minute concave defective parts.SOLUTION: Provided is a mask blank comprising a phase shift film disposed on a main surface of a translucent substrate. The translucent substrate has concave defective parts on the main surface on which the phase shift film is formed. The phase shift film includes a structure where, from a side of the translucent substrate, a high-transmission layer and a low-transmission layer having lower light transmittance than the former are laminated in this order. Inner regions of the high transmission layer formed on the concave defective parts have low-density regions, where density in the low-density region is relatively lower than that in an inner region of the high-transmission layer formed on the main surface which is free from the concave defective parts.

New Critical Dimension Uniformity measurement concept based Reticle Inspection Tool

Abstract: The Critical Dimension Uniformity (CDU) specification on photo-mask is getting increasingly tighter which each successive node. The ITRS roadmap for optical masks indicates that, the CDU (3 sigma) for dense lines for binary or attenuated phase shift mask is 3.4nm for 45nm half-pitch (45HP) node and will go down to 2.4nm for 32HP node. The current variability in mask shop processes results in CDU variation across the photo-mask of ~2-3nm. Hence, we are entering in a phase where the mask CDU specification is approaching the limit of the capability of the current POR (process on record). Hence, mask shops have started exploring more active mechanisms to improve or compensate for the CDU of the masks. A typical application is in feeding back the CDU data to adjust the mask writer dose and compensate for non-uniformity in the CDs, resulting in improved quality of subsequent masks. Another option is to feed the CD uniformity information forward into the wafer FAB and adjust the scanner dose to correct for reticle non-uniformity. For these purposes mask makers prefer a dense measurement of CDs across the reticle in a short time. Mask makers are currently using the CD-SEM tool for data collection. While the resolution of SEM data ensures its position as the industry standard, an output map of CDU from a reticle inspection tool has the advantage of denser sampling over larger areas on the mask. High NA reticle inspection systems scan the entire reticle at high throughput, and are ideally suited for collecting CDU data on a dense grid. In this paper, we describe the basic theory of a new, reticle inspection-based CDU tool, and results on advanced memory masks. We discuss possible applications of CDU maps for optimizing the mask manufacturing and wafer production processes.

Photomask process development for next generation lithography

Abstract: For the coming technology nodes, lithography options that use 1X masks are becoming practical candidates. Especially the nano-imprint lithography (NIL) is expected as one of the candidates for 32nm node and below, because of its potential low lithography cost. Naturally, 1X masks require features finer than those on today's 4X masks, and for mask making this means a big and hard technology jump. From the mask making point of view, even the 1X mask is still a candidate, it would be a technology driver in terms of patterning process development for the coming nodes. In this paper, we focused on the NIL mold (or mask) making evaluation. Among the important factors dominating the resolution of the mask making process, we studied particularly on the resist and the dry etch. We found that with tools currently used in the commercial mask shops today, and by modification of resists, we could achieve 30nm isolated spaces and 50nm dense lines and holes. We also discuss about our initial results of mask EB writing method evaluation. We found that, to improve the resolution further, the implementation of high resolution EB tools into the mask manufacturing line is inevitable to made molds for 32nm or 22nm technology nodes.

The role of strong phase shift masks in Intel's DFM infrastructure development

Abstract: Intel has reported on three separate styles and applications of strong phase shift masks (PSMs) over the last decade including alt-PSM for gate patterning, alt-PSM with assist features for contact patterning and Pixelated Phase Masks (PPMs) for metal layer patterning. Each had a prominent role in Intel's Design For Manufacturing (DFM) infrastructure development in terms of design rules and DFM tooling. By gradually inserting design rule changes for alt-PSM for gate patterning starting from the 130nm technology node, density and design impact were minimally effected. Alt-PSM for contact layer required development of complex methods of SRAF placement and coloring while also forcing advances in phase shift mask manufacturing infrastructure. Pixelated phase masks for metal patterning when combined with Inverse Lithography Techniques (ILTs) were successful in supporting a high level of flexibility for metal design rules including multiple feature sizes, pitches and two-dimension content.