In this paper we perform a foundational study on the impact of quartz etched depth, and optical density (OD) of mask opaque area, the 3D effect in ArF immersion lithography at advanced process node. The after development inspection (ADI) critical dimension (CD) variation may be caused by these 2 mentioned factors on the photomask, even the mask CD value of the measurement point is the same. Different cleaners and etchers which fix the same cleaning and etching time, induce different OD of reticle opaque patterns and several quartz etched depths. The relations between OD of reticle opaque patterns / quartz etched depth and ADI CD are the significant subject for successful pilot run which may moderate pilot run time and reduce rework costs in the lithography process. The focus of this study is the characterization of the correlation between OD of reticle opaque patterns / etched quartz depths and ADI CD. We experimentally study the structures from the theoretical introduction on the mask 3D phenomena, all of results are obtained using a MoSi binary ArF blank. A comprehensive wafer CD measurement result will be demonstrated in different OD of reticle opaque patterns and etched quartz depth, both simulation and experimentally based. The effect of fabricating the photomask quartz trenches will also be studied as well as the impact on through pitch CD and exposure latitude. The goal of this study is the demonstration of the practical influence on mask OD and the etched quartz depth of leading edge photomasks.
Design weak points that have narrow process window and limits wafer yield, or hotspots, continue to be a major issue in semiconductor photolithography. Resolution enhancement techniques (RET) such as advanced optical proximity correction (OPC) techniques and source mask optimization (SMO) are employed to mitigate these issues. During yield ramp for a given technology node, full-chip lithography simulation, pattern-matching and machine learning are adopted to detect and remedy the weak points from the original design [1], [2]. This is typically an iterative process by which these points are identified in short-loop lithography testing. Design retarget and/or OPC modifications are made to enhance process window until the yield goal is met. This is a high cost and time consuming process that results in a slow yield ramp for existing production nodes and increased time to market (TTM) for new node introduction. Local hotspot correction through mask and wafer harmonization is a method to enhance wafer yield with low cost and short cycle time compared to the iterative method. In this paper, a fast and low cost approach to hotspot correction is introduced. Hotspots were detected on wafer after OPC and characterized by using advanced mask characterization and optimization (AMCO) techniques. Lithographic simulations and AIMS measurement were used to verify the hotspot correction method. Finally, the validity of this new approach was evaluated by process window analysis and circuit probe yield test at wafer.
A new technology transforms mask inspection images through focus into 3D lithography images in resist. This enables early detection and ranking of hotspots, and distinguishes mask-induced and process-induced hotspots. The results can be used in several ways including: 1) feed back to OPC teams to improve process window; 2) feed forward to the litho team for scanner adjustment; and, 3) feed forward to wafer inspection in the form of care areas to reduce time to result for wafer-based process window discovery.
This paper discusses the most efficient mask re-qualification inspection mode for production memory reticles in
an advanced memory fab. Progressive and haze defects continue to be the primary cause of mask degradation and mask
re-clean mainly due to intensified density of photon energy involved with ArF exposure. Direct reticle inspection has
been widely implemented in wafer fabs to provide early warning of haze defects before they reach critical levels.
However, reticle inspection systems are increasingly challenged by aggressive optical proximity correction (OPC), subresolution
assist feature (SRAF) and high requirement to detect printable defects. As we know Die-to-Die (D2D) mode
has good sensitivity on main pattern but can't cover scribe line area. In this paper, we studied the integration inspection
mode which combines Die-to-Die (D2D) on main pattern area and Stralight2+ on scribes and frames area. The detection
capability of StarLight2+ and D2D on DRAM masks was evaluated and results shows that aggressive patterns (OPC,
SRAF) are resolved well and provide early warning for crystal growth type defect on mask. The objective of this paper is
to demonstrate both StarLight2+ and D2D capability to support memory wafer mask qualification requirements.
Chrome-less Phase Lithography (CPL) was introduced as a potential strong Resolution Enhancement Technology (RET) for 90nm to 65nm node critical layers. One of the important issue with trench type chrome-less mask manufacturing for post structure is quartz defect detection capability. This study will focus on half pitch 80nm (1X) design node and apply different trench sizes and programmed defect sizes. All test patterns will be inspected on KLA-Tencor TeraScan576 inspection tool with both standard Die-to-Die (DD) and TeraPhase DD inspection modes to determine defect detection capability. All programmed defects will also be simulated on the Zeiss AIMS Fab-193 to determine wafer CD error. Finally, we will establish the relationship between trench size, defect detection capability and printability, and summarize the chrome-less mask quartz defect detection capability for 80nm post structure application.
Progressive mask defect problem is an industry wide mask reliability issue. During the start of this problem when the defects on masks are just forming and are still non-critical, it is possible to continue to run such a problem mask in production with relatively low risk of yield impact. But when the defects approach more critical state, a decision needs to be made whether to pull the mask out of production to send for clean (repair). As this problem increases on the high-end masks running DUV lithography where masks are expensive, it is in the interest of the fab to sustain these problem masks in production as long as possible and take these out of production only when absolutely necessary; i.e., when the defects have reached such a critical condition on these masks that it will impact the process window. During the course of this technical work, investigation has been done towards understanding the impact of such small progressive defects on process window. It was seen that a small growing defect may not print at the best focus exposure condition, but it can still influence the process window and can shrink it significantly. With the help of a high-resolution direct reticle inspection, early detection of these defects is possible, but fabs are still searching for a way to disposition (make a go / no-go decision) on these defective masks. But it is not an easy task as the impact of these defects will depend on not only their size, but also on their transmission and MEEF. A lithographic detector has been evaluated to see if this can predict the criticality of such progressive mask defects.
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