Lithographic Apparatus Scan Path Distortion Correction
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Solution Overview
Problem
Lithographic processes suffer from mask pattern distortions and defects, which lead to overlay errors during the transfer of patterns onto substrates, particularly in integrated circuit manufacturing, where these distortions contribute to intra-field overlay errors.
Innovation Solution
A lithographic apparatus and method that includes a control system capable of correcting local and overall pattern distortions by making temporal adjustments to the pattern image along a scan path, using a combination of dynamic adjustments of lens parameters and scan parameters to minimize overlay errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mask pattern is transferred onto substrate using conventional lithography, then pattern transfer is achieved, but mask pattern distortions cause overlay errors in the target portion
Solution Approach 1:
The patent applies preliminary action by measuring and characterizing mask pattern distortions before the actual pattern transfer process. A distortion map is created that captures the spatial distribution of distortions across the mask field, which is then used to pre-calculate correction parameters for the projection optics or scanning motion, allowing distortions to be compensated before they affect overlay accuracy
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting projection optics parameters (such as focus, magnification, or astigmatism) or scanning parameters (scan speed, acceleration) as a function of position within the exposure field. These parameter variations are specifically designed to counteract the measured mask distortions, transforming the projection or scanning behavior to compensate for mask pattern defects and improve overlay accuracy
2Ease of manufacture
If entire pattern is exposed onto target portion at one time (stepper), then pattern transfer is achieved, but local distortions cannot be corrected spatially
Solution Approach 1:
The patent applies segmentation by dividing the exposure field into multiple zones or regions, each with its own distortion characteristics. Correction parameters are calculated and applied independently for each zone, allowing local distortion correction while maintaining the overall exposure process. This can be implemented through zoned optics correction or by dividing the scan path into segments with different correction profiles
3Area of stationary object
If pattern is transferred by scanning (scanner), then large area coverage is achieved, but scan-induced distortions add to overlay errors
Solution Approach 1:
The patent employs dynamics by making the scanning system dynamically adjustable. The scan speed, acceleration, or synchronization between mask and substrate scanning is varied as a function of position to compensate for distortions. This dynamic control allows the scanner to maintain high productivity while correcting scan-induced overlay errors through real-time parameter modulation during the scanning process
Solution Approach 2:
The patent applies feedback by using measured overlay errors or distortion maps to iteratively refine scanning parameters or projection settings. Metrology measurements taken on previously exposed wafers provide feedback that is used to update correction models, which then adjust subsequent scanning operations to minimize overlay errors while maintaining productivity
Data Source
AI summary
A lithographic apparatus includes an illumination system configured to condition a radiation beam, a support for a patterning device, a substrate table for a substrate, a projection system, and a control system. The patterning device is capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam. The projection system is configured to project the patterned radiation beam as an image onto a target portion of the substrate along a scan path. The scan path is defined by a trajectory in a scanning direction of an exposure field of the lithographic apparatus. The control system is coupled to the support, the substrate table and the projection system for controlling an action of the support, the substrate table and the projection system, respectively. The control system is configured to correct a local distortion of the image in a region along the scan path by a temporal adjustment of the image in that region.