Field Results From 45nm Die-to-Database Reticle InspectionWilliam Broadbent, Ichiro Yokoyama, Paul Yu, Heiko Schmalfuss, Jean-Paul Sier – KLA-Tencor Corporation
Ryohei Nomura, Kazunori Seki – Toppan Printing Co., Ltd
Jan Heumann – Advanced Mask Technology Center GmbH & Co Testing of the TeraScanHR system at Toppan and the AMTC demonstrated high sensitivity, low false detections, and high scan speed. The system’s higher NA optics, new autofocus, smaller pixel size, and improved rendering and modeling algorithms resulted in significant improvements in inspection capability of small linewidths, small defects, and aggressive OPC. Reflected light inspection integrated with transmitted light can be used with no additional scan time for some modes, providing the best defect detection capability and resulting in the highest quality reticles. A new reticle inspection platform, the TeraScanHR, improves upon the prior TeraScanTR platform with higher optical imaging resolution to better resolve small features; higher precision database modeling to better represent small OPC in die-todatabase inspection; and higher speed image processing for higher productivity, especially when using integrated modes (e.g., transmitted + reflected). Besides its 45nm capability, the TeraScanHR platform can also be configured for 65nm, 90nm, and 130nm nodes. This paper describes technical aspects of the TeraScanHR platform and presents selected results from the field testing of beta systems located at Toppan Printing in Japan and the Advanced Mask Technology Center in Germany. The testing used applicable programmed defect test reticles to measure defect detection sensitivity, along with a large set of product and product-like reticles from the 90nm to the 32nm logic nodes, and comparable memory nodes, to assess both sensitivity and inspectability when using the available pixel sizes (72/90/125/150nm). The beta systems are currently being used for advanced production. 
Reticle Inspection Development
To serve the 45nm node advanced production requirements and 32nm node development requirements, the TeraScanHR platform delivers higher performance and new capabilities. This platform can be configured as a variety of different models that are intended to cost-effectively inspect reticles from the 130nm node to the 32nm node. In this way, a reticle manufacturer or wafer fab can purchase just the capability needed at the time, and then upgrade as more capability is needed in the future. A typical TeraScanHR system is shown in Figure 1 (note that the three electronic racks may be remotely located). The new system’s imaging technology uses significantly higher resolution imaging of the reticle than the wafer lithography system, allowing direct inspection of both the primary structures and the sub-resolution structures; its single wavelength can provide good performance inspecting reticles from a variety of lithographic wavelengths. The TeraScanHR handles typical binary (COG), 6% EPSM (including simple tri-tone), and dark field alternating PSM reticles. The system supports both transmitted and reflected light inspection modes, which can be easily integrated into a single inspection. Using the new 72nm pixel, the system enables development of 32nm logic reticles and approximately 45nm half-pitch memory reticles. Additional capability extensions are in development for more aggressive RET, such as Mask Enhancer, complex tri-tone, and chromeless. Larger pixels are available with faster scan times for the 65nm logic node up to the 130nm node. Image Acquisition
The image acquisition subsystem is shown in Figure 2. A high-resolution microscope and linear sensor architecture are used with both transmitted and reflected illumination paths. The illumination source is a 257nm wavelength continuous wave (CW) laser (>5,500 hours lifetime). An active beam steering subsystem compensates for beam drift. The transmitted illuminator has several different configurations that can be selected by the user. Two illuminator configurations are currently implemented: standard contrast for COG and EPSM reticles, and phase contrast for quartz etch reticles such as alternating, Mask Enhancer, chromeless, etc. The phase contrast mode provides improved imaging contrast to quartz phase defects (bumps and divots), allowing for higher defect sensitivity. The custom-designed objective images the reticle surface through a zoom lens onto the imaging sensor. The zoom lens allows different pixel sizes to be selected by the user at runtime; this provides faster scan times when a less sensitive inspection is desired – four pixel sizes are available depending upon the model (72, 90, 125, and 150nm). Image pickup is done with a time-domain-integration (TDI) sensor, which offers high-speed continuous image pick-up at much lower light levels than a conventional CCD linear sensor. For reflected light inspection, the system uses a single imaging sensor with a switching device to select between transmitted and reflected illumination. This allows an integrated inspection using both transmitted and reflected illumination (integrated T+R mode). Since each illumination mode has the best performance for different classes of defects and different geometry types, the integrated T+R mode provides the highest quality inspection. 
To achieve the needed performance level, the new system provides a higher NA capability to resolve smaller lines, OPC, and defects (approximately 1.2 times higher NA than the previous 90nm pixel TeraScanTR platform). The higher NA supports the new 72nm pixel. A new autofocus subsystem provides the necessary precision for the higher NA optics, which have lower depth of focus; an advanced pre-mapping technique improves the ability to maintain proper focus, especially when inspecting reticles with significant topology such as the quartz etch types. Image Processing
The TeraScanHR image processing subsystem features a Tera Image Supercomputer, which utilizes a fully programmable and scalable multi-processor architecture using high-speed processors. The basic detection method is to overlay a test image with a matching reference image and identify differences above a pre-selected size; since the images should basically match, any differences are the result of a defect. For die-to-die inspection, the test and reference images compared are from adjacent die; for die-to-database inspection, the reference image is reconstructed from the design or write database. For a STARlight inspection, the transmitted light image is compared to the reflected light image – any differences are the result of a contamination- type defect. The new image computer uses higher speed processors and contains 2x the number of processors compared with the previous image computer. The additional processing power improves scan time for the more processing-intensive modes; this can also allow multiple modes to be processed together with minimal inspection slowdown. For example, a transmitted light inspection and a reflected light inspection can be processed together without slowing the inspection station; this allows a much more cost-effective T+R inspection than the prior TeraScanTR system. Additional processing blocks for die-to-database inspection reconstruct a database image in real time from the reticle design or write database. Sophisticated modeling algorithms ensure that the database image exactly matches the optical image since any error reduces defect detection sensitivity. A new die-to-database defect detection algorithm, UHR, provides much more precise modeling of small OPC structures in both transmitted and reflected light as compared to the previous algorithm. The test image is subtracted from the reference image to produce a difference image. Since the test and reference images should exactly match, the difference image should have a uniform gray background except where there is a defect. Click here to learn more about Field Results From 45nm Die-to-Database Reticle Inspection | 
