Multi-Head Alignment Calibration via Primary Reference
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Solution Overview
Problem
Calibration of secondary alignment heads in multi-head alignment systems is inaccurate due to defective marks and low signal-to-noise ratio, affecting overlay accuracy and product yield in lithographic processes.
Innovation Solution
A method and apparatus for calibrating secondary alignment heads using primary alignment heads, where the primary head measures an alignment mark, and at least one secondary head measures the same mark, with the offset of the secondary head derived from these measurements, ensuring accurate alignment and improved robustness through multiple measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple alignment heads are used to measure alignment marks in parallel, then measurement throughput is improved, but calibration accuracy deteriorates due to defective marks and low signal-to-noise ratio
Solution Approach 1:
The patent performs a preliminary calibration phase where the primary alignment head measures alignment marks to establish reference data before the secondary alignment heads perform their measurements. This preliminary action creates a reliable baseline that compensates for potential defects or low signal-to-noise ratios during the parallel measurement process, thereby maintaining both high throughput and calibration accuracy
Solution Approach 2:
The primary alignment head acts as an intermediary between the reference measurement system and the secondary alignment heads. It first measures alignment marks to create reference data, which then serves as a mediator to calibrate and correct the measurements from secondary alignment heads, ensuring accuracy even when secondary heads encounter defective marks or low signal conditions
2Device complexity
If secondary alignment heads are calibrated with respect to primary alignment head using single measurements, then calibration process is simplified, but calibration robustness deteriorates due to defective marks and low signal-to-noise ratio
Solution Approach 1:
The system performs preliminary measurements by the primary alignment head to establish reference alignment mark positions before secondary alignment heads conduct their measurements. This preliminary action creates a robust reference dataset that can be used to correct and validate secondary head measurements, significantly improving calibration robustness against defective marks and low signal-to-noise conditions
Solution Approach 2:
The patent implements a feedback mechanism where the primary alignment head's reference measurements are used to evaluate and correct the measurements from secondary alignment heads. The system compares secondary head measurements against the reference data, identifies deviations caused by defects or noise, and applies corrections accordingly, thereby enhancing calibration reliability without substantially increasing process complexity
Data Source
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AI summary
A calibration method is disclosed, for the position calibration of secondary alignment heads with a primary alignment head in a multi-head alignment system, such as that used for the measurement of markers on the surface of a wafer, as carried out during a lithographic process in the formation of circuits in or on the wafer. A plurality of offset measurements are made for at least one of the secondary alignment heads, so that the offset of the secondary alignment heads with respect to the primary alignment head can be measured, and used as correction data in subsequent wafer measurement calculations.