Optical Error Correction for Semiconductor Mask Writer Positioning
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Solution Overview
Problem
Existing position measurement methods in semiconductor manufacturing face challenges due to optical distortions and aberrations across the field of view, leading to errors in precision and throughput, particularly when measuring photolithography masks, as they assume high-frequency errors from the mask writer and discard low-frequency information.
Innovation Solution
A method involving shifting an array of targets within the field of view of an imaging system, determining an alignment function to correct for optical errors, and averaging measurements to minimize variations, allowing for precise and efficient correction of position measurements and identification of mask writer errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-region-of-interest registration measurement is used to measure multiple targets simultaneously, then productivity is improved, but measurement precision deteriorates due to optical distortion and aberrations across the field of view
Solution Approach 1:
The patent applies parameter changes by measuring targets at multiple different field of view positions and using an alignment function to correct the measured positions. The alignment function transforms positions measured at different field of view locations to a common reference frame, compensating for optical distortion and aberration effects that vary across the field of view.
Solution Approach 2:
The patent performs preliminary characterization of optical errors by measuring targets at multiple field of view positions before final position determination. The alignment function is determined in advance from these preliminary measurements, allowing subsequent position measurements to be corrected using pre-computed transformation parameters.
2Measurement precision
If high-pass filtering is applied to remove low frequency imaging errors, then measurement precision is improved for high frequency stitching errors, but loss of information occurs regarding low frequency mask writer errors
Solution Approach 1:
The patent inverts the conventional approach by not filtering out low frequency components, but instead preserving and analyzing them. The alignment function corrects positions for all frequency components, and the residual errors after correction are analyzed to identify both high frequency stitching errors and low frequency mask writer errors, rather than discarding the latter.
Solution Approach 2:
The patent introduces an intermediary alignment function that corrects position measurements for optical errors. This intermediary correction step allows the subsequent error analysis to access both high and low frequency components separately, enabling identification of mask writer errors without losing low frequency information through filtering.
3Measurement precision
If individual target measurements are performed by moving each target to the center of the field of view, then measurement precision is improved, but productivity deteriorates due to very low throughput
Solution Approach 1:
The patent merges multiple measurement operations into a single field of view measurement. By capturing an image containing multiple targets simultaneously and determining their positions from that single image using the alignment function, the method combines the precision benefits of centered measurements with the throughput benefits of parallel measurement.
Solution Approach 2:
The patent transitions from a sequential one-dimensional measurement approach (measuring one target at a time) to a parallel two-dimensional approach (measuring multiple targets simultaneously in a single field of view image). The alignment function enables this dimensional expansion by providing position corrections for all targets in the field of view.
4Measurement precision
If measurements are performed over a long period to measure all targets individually, then measurement precision is improved, but reliability deteriorates due to drift errors of the metrology tool
Solution Approach 1:
The patent maintains continuity of useful action by measuring all targets within a single field of view capture rather than sequentially over time. This continuous measurement approach eliminates time-dependent drift errors while maintaining precision through the alignment function correction, allowing all targets to be measured simultaneously in one continuous operation.
Data Source
AI summary
A method for correcting optical errors occurring in coordinates of positions of a plurality of targets measured via an imaging system comprising a field of view. The plurality of targets includes a first array of targets and a second array of targets overlapping the first array of targets, and a portion of the plurality of targets are outside of the field of view. The method broadly includes the following steps: a) placing the first array of targets in the field of view of the imaging system; b) measuring coordinates of each target within the first array of targets repeatedly via the imaging system; c) placing the second array of targets in the field of view of the imaging system; d) measuring coordinates of each target within the second array of targets repeatedly via the imaging system; e) determining an alignment function from the measurement results of step b, step d, or steps b and d, the alignment function being a function of coordinates of the field of view of the imaging system and giving an additive correction for optical errors of the coordinates of positions of the plurality of targets measured by the imaging system; f) correcting the coordinates of the positions of the plurality of targets measured by the imaging system by adding the respective value of the alignment function at the field-of-view coordinates at which the coordinates of the position of the respective target were measured; and, g) obtaining a final result for the position of each target of the plurality of targets by averaging over the corrected coordinates found in step f for the respective target at each relative position of the plurality of targets and field of view of the imaging system.