We show, both theoretically and experimentally, that for a turbid tissue medium where Mie scattering is dominant, multiple scattering not only reduces the illumination power in the forward direction but also exhibits an anisotropic distribution of scattered photons. Thus, a signal level under two-photon excitation drops much faster than that under single-photon excitation although image resolution is much higher in the former case. As a result, the penetration depth under two-photon excitation is limited by the strength of two-photon fluorescence and is not necessarily larger than that under single-photon excitation.
This paper presents lithographic performance results obtained from the newest member of ASML's TWINSCAN TM platform-based step & scan systems, the TWINSCAN TM XT:1400. The system has been designed to meet the semiconductor industry's aggressive requirements on CD control, overlay and productivity at and below the 65 nm node. This dual stage 193 nm lithographic system combines the worlds highest NA, with excellent overlay and CD control at high throughput on both 200 and 300 mm wafers and is intended for use in volume production environments. Advances in stage technology have enabled further extension of stage scan speeds and an associated increase in tool productivity. However, maximizing the number of yielding die per day also requires stringent overlay and Critical Dimension (CD) control. Tight CD control at improved resolution is supported by the Starlith TM 1400 projection lens and the extended sigma capabilities of the new AERIAL TM -E illumination system. Focus control is improved in line with the stringent requirements posed by low-k 1 imaging applications, taking full advantage of the unique dual-stage TWINSCAN TM system architecture.
Advanced Process Control (APC) on overlay is in use for high-volume production fabs with enough data available to statistically filter out noise contributions. In a foundry that is characterized by multiple products, each with a low production volume, very limited data is available per product. With the proposed advanced process control system we want to solve the issues related to this low amount of data by using data from lots that have a different history, e.g. lots that are exposed on other machines or lots from other products. To be able to do this production data is first corrected for machine contributions by use of monitor data for each machine. The resulting estimated process induced errors are maintained for all products and all layers in a database with reference to used machines, layers, product type and process family. The process induced errors for each lot are selected from the database by sharing available data that is expected to behave most similar. The proposed advanced process control system is partially implemented in production for a couple of layers. Simulations are run on more layers to test the data sharing concept. The simulation results are in reasonable agreement with actual product measurements and predict that the advanced process control system performs similar for lots for which the proposed data sharing concept is used as for lots for which the identical context is available.
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