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One of the most critical challenges in the lithography process is to effectively control all critical patterns over the full exposure field, across wafer, and from lot to lot consistently. ASML’s advanced dose-control solutions have been widely adopted to control CDU of critical patterns. A new high-order dose-control capability is introduced with extended controllability over a larger number of patterns to mitigate the stochastic effect and optimize dies-in-spec performance. Traditionally, designed marks or patterns are placed in the die for dense metrology sampling required for the advanced high-order dose-control applications. However, this method has a few disadvantages especially for logic foundry use cases. For example, the designed marks are often not identical to random logic critical patterns, thus leading to a situation in which marks are controlled well while device patterns are not. In-die placement of the designed marks normally imposes constrains in device layout, which is not acceptable in some cases such as large-die layouts. A preferred approach would be to measure directly on device-critical and/or weak-point (WP) patterns. But this brings up another challenge in metrology of device WP patterns. With conventional CDSEM the amount of data points is limited by the tool throughput. WP patterns are typically 2D patterns, with normally a high noise contribution from local variations (due to resist stochastics) and metrology. Thus to suppress the local variations, averaging of many local measurements of 2D WP patterns is preferred. This requires a high throughput e-beam metrology tool capable of making massive amount of inline measurements within a given cycle time. To address these challenges, we have developed a method of using yield-limiting device patterns to directly control dose and thus improve CDU. Close to 100 WPs per in-die location have been selected with a dense die coverage to minimize the contribution to global CDU from the local variations and metrology noise. A high-speed e-beam metrology tool is used to measure all the selected WP patterns. A CDU budget breakdown (BB) has been analyzed to identify and quantify CDU contributors, such as reticle fingerprint, OPC error, local CDU, metrology noise, etc. Different in-die WP sampling and dose-control methods are studied in this work to achieve optimal CDU correction while keeping the metrology cycle time under control for HVM implementation.
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