Lithographic Scanner Stability Control via Multiple Exposure Passes
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Solution Overview
Problem
The existing lithographic scanner stability module faces challenges in maintaining accuracy due to significant noise sources from limited overlay data from monitor wafers, typically 4 to 12 wafers per week, which affects the control of scanner stability and alignment.
Innovation Solution
A system and method that includes a scanning control module which periodically retrieves measurements from reference substrates to determine baseline control parameters, allowing for drift correction by performing multiple exposure passes on these substrates, thereby improving scanner stability module control accuracy without increasing the number of monitor wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple exposure passes are performed on reference substrates, then measurement precision and control accuracy are improved, but productivity and processing time are reduced
Solution Approach 1:
Multiple exposure passes are performed on reference substrates before production to establish accurate baseline control parameters. This preliminary characterization of the scanner's random overlay error allows the system to compensate for drift during actual production runs, improving measurement precision without impacting production throughput.
Solution Approach 2:
The system uses reference substrates as copies or test versions to characterize scanner performance. By performing multiple exposures on these reference substrates, the system builds a statistical model of overlay error that can then be applied to correct production substrates, achieving high precision without repeatedly testing production parts.
2Measurement precision
If multiple exposure passes are performed on reference substrates, then noise from alignment processes is reduced, but device complexity and process complexity increase
Solution Approach 1:
The system performs periodic multiple exposure passes on reference substrates at scheduled intervals (e.g., at the beginning of each day or production run). This periodic characterization builds up statistical data about scanner overlay error, allowing noise reduction through averaging while maintaining a manageable process complexity by not requiring continuous monitoring.
Solution Approach 2:
The system uses the measured baseline control parameters from reference substrate exposures to provide feedback for correcting production substrate alignment. The measured random overlay error characteristics are fed back into the alignment model to compensate for scanner drift, reducing noise without requiring complex real-time adjustments during production.
Data Source
AI summary
A method produces at least one monitor wafer for a lithographic apparatus. The monitor wafer is for use in combination with a scanning control module to periodically retrieve measurements defining a baseline from the monitor wafer, thereby determining parameter drift from the baseline. In doing this, allowance and/or correction can be to be made for the drift. The baseline is determined by initially exposing the monitor wafer(s) using the lithographic apparatus to perform multiple exposure passes on each of the monitor wafer(s). An associated lithographic apparatus is also disclosed.