Lithographic Apparatus Self-Calibration Using Production Markers
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Solution Overview
Problem
Lithographic apparatuses face challenges in maintaining optimal performance due to drift in overlay and focus stability, requiring frequent recalibration, which disrupts production and reduces accuracy as chip features shrink, necessitating more frequent use of reference wafers that deteriorate over time.
Innovation Solution
A method of calibrating lithographic apparatuses by performing multiple exposures with overlapping regions to form markers, measuring marker positions, and deriving calibration correction factors from the differences, allowing for continuous system parameter correction without relying on aged reference wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If frequent recalibration is performed to maintain overlay and focus stability, then manufacturing precision is improved, but productivity deteriorates due to increased production downtime
Solution Approach 1:
The lithographic apparatus performs self-calibration by automatically measuring overlay and focus parameters using marks on the substrate and computing correction factors without requiring external reference wafers or manual intervention. The system uses its own measurement device and processing unit to detect errors and generate corrections, eliminating the need for separate calibration operations that would interrupt production.
Solution Approach 2:
The system continuously monitors overlay and focus parameters during normal operation by measuring marks on substrates and comparing them against expected values. The measurement device provides feedback signals to the processing unit, which computes correction factors and adjusts system parameters in real-time, enabling dynamic calibration without stopping production.
2Manufacturing precision
If reference wafers are used for calibration, then manufacturing precision is improved, but reliability deteriorates as reference wafers deteriorate over time
Solution Approach 1:
The invention extracts the calibration function from external reference wafers and embeds it directly into the lithographic apparatus itself. The system uses marks that can be exposed and measured during normal production operations, eliminating dependence on separate reference wafer materials that degrade over time. The calibration capability is integrated into the apparatus hardware and software.
Solution Approach 2:
Instead of using physical reference wafers that deteriorate, the system creates virtual references through computational methods. The processing unit calculates correction factors by comparing measured mark positions against expected values and generates calibration data that can be stored and applied without physical degradation. This digital copying approach eliminates the aging problem inherent in physical reference materials.
3Manufacturing precision
If additional calibration measurements are performed using monitor wafers, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The lithographic apparatus uses the same exposure and measurement capabilities required for normal production to perform calibration functions. The marks exposed during production are the same type of marks measured for calibration, and the measurement device used for quality inspection also serves calibration purposes. This multi-functionality eliminates the need for separate calibration hardware and simplifies the overall process.
Data Source
AI summary
System parameters are checked through self-assessment of a production wafer without a reference or a monitor wafer. In particular, exposure errors and substrate table positioning errors can be corrected for.