Next-generation lithography technology is required to meet the needs of advanced design nodes. Directed Self Assembly (DSA) is gaining momentum as an alternative or complementary technology to EUV lithography. We investigate defectivity on a 2xnm patterning of contacts for 25nm or less contact hole assembly by grapho epitaxy DSA technology with guide patterns printed using immersion ArF negative tone development. This paper discusses the development of an analysis methodology for DSA with optical wafer inspection, based on defect source identification, sampling and filtering methods supporting process development efficiency of DSA processes and tools.
This paper discusses the defect density detection and analysis methodology using advanced optical wafer inspection capability to enable accelerated development of a DSA process/process tools and the required inspection capability to monitor such a process. The defectivity inspection methodologies are optimized for grapho epitaxy directed self-assembly (DSA) contact holes with 25 nm sizes. A defect test reticle with programmed defects on guide patterns is designed for improved optimization of defectivity monitoring. Using this reticle, resist guide holes with a variety of sizes and shapes are patterned using an ArF immersion scanner. The negative tone development (NTD) type thermally stable resist guide is used for DSA of a polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer (BCP). Using a variety of defects intentionally made by changing guide pattern sizes, the detection rates of each specific defectivity type has been analyzed. It is found in this work that to maximize sensitivity, a two pass scan with bright field (BF) and dark field (DF) modes provides the best overall defect type coverage and sensitivity. The performance of the two pass scan with BF and DF modes is also revealed by defect analysis for baseline defectivity on a wafer processed with nominal process conditions.
Defect inspection is a challenge in the edge of wafer region and several new inspection tools and techniques have come
to the market to fulfill this inspection need. Current inspection methodology excludes inspection of partial die located at
the wafer edge, which has lead to the development of a technique available for patterned wafer inspection tools to inspect
these partially printed die. In this paper we identify and develop a robust methodology for the characterization and
monitoring of defectivity on the partially printed edge die. The methodology includes the development of methods for
inspection optimisation requirements, characterization and isolation of defect sources, optimisation of clustering and
binning and control of partial die defectivity.
Increasing inspection sensitivity may be necessary for capturing the smaller defects of interest (DOI)
dictated by reduced minimum design features. Unfortunately, higher inspection sensitivity can result in a
greater percentage of non-DOI or nuisance defect types during inline monitoring in a mass production
environment. Due to the time and effort required, review sampling is usually limited to 50 to 100 defects
per wafer. Determining how to select and identify critical defect types under very low sampling rate
conditions, so that more yield-relevant defect Paretos can be created after SEM review, has become very
important. By associating GDS clip (design layout) information with every defect, and including defect
attributes such as size and brightness, a new methodology called Defect Criticality Index (DCI) has
demonstrated improved DOI sampling rates.
Lithographic characteristics of dual-trench type alternating phase-shifting mask (PSM), whose shifters are made of perpendicular trenches with different depth alternately, are evaluated numerically and experimentally. The structure of dual-trench type PSM could reduce the difference of adjacent peak intensities created by topography on the mask. Exposure characteristics of the mask varied with depth of deep and shallow trenches, and depth of both trenches should be controlled so as to have the optimum value. Mainly, the difference in depth of deep and shallow trenches caused varying "effective phase" and depth of shallow trench caused varying "effective transmission". The depth of focus using the mask was sensitive to the effective phase difference controlled by adjusting etched depth difference between both trenches, and insensitive to depth of shallow portion. From analysis of mask process margin, respecting acceptable error of depth of both trenches, it was found that the effective transmission error caused reduction of acceptable depth error.
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