As increasing complexity of1 devices and scaling have continued to push the lithography to low k1 limit, lithographic scientists have been developing various resolution enhancement techniques (RET) to extend 193nm immersion lithography. Chrome-less phase shift mask (PSM) is one of the RET techniques which can produce frequency doubling to half the pitch. The shifter is changed from MoSi to quartz for chrome-less PSM. And the shifter in quartz that is challenging to control at mask etch process. This will cause phase error, lead to image shift and CD asymmetry impacts wafer CD uniformity (CDU) due to intensity imbalance. In this paper, based on aerial image simulations, the conditions to generate frequency doubling have been studied, the resolution limit of the frequency doubling has been investigated. The phase error tolerance of frequency doubling for accepted wafer CDU referring ITRS road map plus budget breakdown to reticle CDU contribution has been studied. The phase error tolerance for smaller pitch is predicted with polynomial fitting extend too.
As lithography patterning focus tolerance shrinkage in advanced production fab, defocus due to scanner wafer table or pre-layer contamination has been considered as a yield-loss killer and wafer scrap contributor. Traditionally, we can only apply a fixed by-wafer/by-zone spec to monitor leveling performance, lacking flexibility for further defense system design or root-cause analysis. In this paper we develop a comprehensive solution to capture focus/chuck spot in a high-volume manufacturing environment. This algorithm can automatically detect and categorize defocus spot into focus and chuck spots. Meanwhile, this algorithm produces an overlapped map for back-tracing pre-stage contamination and regularly send an alarm in customized schedule to prevent serious yield loss.
In a leading-edge high-volume manufacturing fab, lithographers focus on searching for a suitable alignment layout strategy to cover process-induced overlay variation. However, how to minimize scanner cross-chuck overlay impact also draws attention due to WPH loss from chuck dedication. In this paper we evaluate a novel algorithm to analyze lithography scanner process/metrology data and introduce a new KPI called “model accuracy” for alignment sampling layout strategy creation, which takes into account robustness index as wafer-to-wafer/chuck-to-chuck variation. Combined with simulated overlay performance, an optimal alignment layout strategy is recommended for a maximum coverage of cross-chuck overlay, which leads to maximum productivity.
In recent years, advances in semiconductor technologies have resulted in the continuous shrinkage of the process window required to fabricate a device, and specifically, the shrinkage of the overall overlay budget of the critical layers. Among other variables, a key contributor of wafer-to-wafer overlay variations is scanner alignment strategy. In high-volume manufacturing (HVM), the reduction in alignment mark count can lead to productivity improvement, however, that tradeoff impacts the scanner alignment layout and overlay model performance. In this paper, we present a comprehensive investigation of an in-line production experiment and simulation results to evaluate overlay performance by cooptimization of scanner alignment mark count, layout for High Order Wafer Alignment (HOWA) model.
As semiconductor industry moves to advanced node, capability to well-control On Product Overlay (OPO) becomes a major task force in HVM environment in recent years. In order to continuously sustain OPO at better production level for critical layers, processing on one dedicated immersion (IMM) scanner is a traditional method to meet the quality purpose. However, the tool dedication method impacts IMM scanner throughput and therefore increases cost of ownership for the manufacturing. The ability of smoothly de-stacking the process layers to other IMM scanner without heavily losing OPO performance levels up the full-route productivity, hence enables the cost down opportunity. In this paper, we present a run-to-run APC control methodology and demonstrate the capability to well predict the model terms for inline production scenarios.
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