Use of layout automation and design-based metrology for defect test mask design and verification
This paper studies the impact of shape and local environment (pattern layout) on the ability to detect defects on the reticle and the extent to which they affect the dimension of the printed image on the wafer. The authors have made extensive use of design information to perform a thorough evaluation. OPC software was used to generate mask data that was comparable to product mask data. Defects were placed on the post-OPC layout and OPC software was also used to simulate the dimension of the defective features as printed on the wafer. "Design Based Metrology" was used to create accurate metrology recipes to support wafer and mask metrology. Ultimately the procedures described in this paper allow a direct correlation to be made between reticle inspectability and the impact of the same defects on wafer CD. Data is presented for the case of the Contact Hole layer of a "65nm" Logic technology, though the methods described in the paper are applicable to all layers.
Production evaluation of automated reticle defect printability prediction application
The growing complexity of reticles and continual tightening of defect specifications causes the reticle defect disposition function to become increasingly difficult. No longer can defect specifications be distilled to a single number, nor can past simple classification rules be employed due to the effects of MEEF on actual printing behavior. The mask maker now requires lithography-based rules and capabilities for making these go/no-go decisions at the reticle inspection step. We have evaluated an automated system that predicts the lithographic significance of reticle defects using PROLITHTM technology. This printability prediction tool was evaluated and tested in a production environment using both standard test reticles and production samples in an advanced reticle manufacturing environment. Reference measurements on Zeiss AIMSTM systems were used to assess the accuracy of predicted results. The application, called the Automated Mask Defect Disposition System, or AMDD, models defective and non-defective test and reference images generated by a high-resolution inspection system. The results were calculated according to the wafer exposure conditions given at setup such that the reticle could be judged for its 'fitness-for-use' from a lithographic standpoint rather than from a simple physical measurement of the film materials. We present the methods and empirical results comparing 1D and 2D Intensity Difference Metrics (IDMs) with respect to AIMS and discuss the results of usability and productivity studies as they apply to manufacturing environments.
Accurate aerial image simulation using high-resolution reticle inspection images
The use of hardware-based and software-based reticle defect printability simulation systems is expanding as the cost and complexity of reticles increases. Without such systems it has become increasingly difficult to predict the lithographic significance of a defect found on a reticle. The viability of such systems can be judged using several criteria including accuracy, ease of use, level of automation, and the degree to which they can be applied to a wide range of reticle types. Simulation systems have improved in each of these areas. Automated and semi-automated systems have now been developed and integrated into reticle manufacturing. We report on advances made in a software-based simulation system which uses high-resolution reticle inspection images as the basis for the description of the reticle. We show that the simulated aerial images can be compared quantitatively to results from a hardware-based simulation system (the Zeiss AIMSTM tool) for both 193 and 248 nm EPSM reticles. The development of a new set of metrics to judge lithographic significance will be explained. Common procedural mistakes in evaluating the impact of a defect will be discussed.