Lithography Process Window Signature Patterns for Focus and Exposure Control
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Solution Overview
Problem
Current lithography processes face challenges in accurately monitoring and controlling focus and exposure conditions within the device area, leading to variations in critical dimension (CD) and sidewall profiles, which can result in device failure and reduced yield due to the inability to effectively separate the influences of focus and exposure errors and account for other optical parameters.
Innovation Solution
The method involves identifying process window signature patterns within a device area that collectively respond to changes in process condition parameters, allowing for direct monitoring and feedback to the lithography control system to ensure all structures are printed within specifications, and optimizing the selection of measured patterns to provide precise corrections for maintaining optimal operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional lithography monitoring methods are used, then process control is simplified, but measurement precision of focus and exposure conditions deteriorates
Solution Approach 1:
The patent segments the monitoring function by introducing separate test patterns (isolated lines and dense lines) that respond differently to focus and exposure variations. This allows independent measurement of each parameter through differential analysis of pattern responses, improving measurement precision without requiring a single complex monitoring system.
Solution Approach 2:
The patent uses test patterns as intermediary objects that mediate between the lithography process parameters and the measurement system. These test patterns translate focus and exposure conditions into measurable CD variations, enabling precise indirect measurement of process conditions through their differential impact on isolated versus dense line patterns.
2Manufacturing precision
If multiple process parameters are monitored simultaneously, then manufacturing precision improves, but difficulty of detecting and measuring increases
Solution Approach 1:
The patent applies local quality by designing test patterns with different local characteristics (isolated lines versus dense lines) that are selectively sensitive to different process parameters. Isolated lines primarily respond to exposure conditions while dense lines primarily respond to focus conditions, enabling local differentiation of parameter influences through spatially distinct pattern responses.
Solution Approach 2:
The monitoring approach is segmented into separate measurement channels: one channel uses isolated line patterns to monitor exposure conditions, while another channel uses dense line patterns to monitor focus conditions. This segmentation allows independent analysis and separation of the two parameter influences, reducing the difficulty of detecting and measuring each parameter separately.
3Productivity
If signature patterns are identified and used for monitoring, then productivity improves, but device complexity increases
Solution Approach 1:
The patent performs preliminary action by pre-identifying and storing signature patterns (isolated lines and dense lines) that are known to be sensitive to specific process parameters. These pre-selected patterns are incorporated into the test mask design beforehand, enabling rapid productivity improvement through direct monitoring of known sensitive features without requiring complex real-time pattern analysis.
Solution Approach 2:
The patent uses simplified copies (test patterns) that replicate the essential sensitivity characteristics of full device structures to specific process parameters. By monitoring CD variations in these copied test patterns rather than analyzing complete device geometries, the system achieves productivity improvement through faster, simpler measurements while maintaining the ability to detect critical process variations.
Data Source
AI summary
A method for identifying process window signature patterns in a device area of a mask is disclosed. The signature patterns collectively provide a unique response to changes in a set of process condition parameters to the lithography process. The signature patterns enable monitoring of associated process condition parameters for signs of process drift, analyzing of the process condition parameters to determine which are limiting and affecting the chip yields, analyzing the changes in the process condition parameters to determine the corrections that should be fed back into the lithography process or forwarded to an etch process, identifying specific masks that do not transfer the intended pattern to wafers as intended, and identifying groups of masks that share common characteristics and behave in a similar manner with respect to changes in process condition parameters when transferring the pattern to the wafer.