Lithographic Reticle Thermal Distortion Correction
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Solution Overview
Problem
Current lithographic processes face challenges in accurately measuring and correcting in-plane distortions caused by reticle heating, which affect overlay accuracy, as existing methods require additional marks or sensors that impact throughput and cost.
Innovation Solution
A method involving the measurement of reference marks around the patterning device's peripheral portion, followed by calculation of local positional deviations using a back-projection algorithm, allows for the estimation and correction of thermal-induced distortions without additional marks or sensors within the patterned area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional marks or sensors are added to measure reticle distortions, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The reticle itself serves as the measurement tool by utilizing its existing periodic pattern structure. The pattern features act as self-contained reference markers that enable distortion measurement without requiring external sensors or additional marks, thus maintaining measurement precision while avoiding increased device complexity
Solution Approach 2:
The periodic pattern on the reticle serves dual functions: it acts as both the product pattern to be transferred to the substrate and simultaneously as the measurement reference for detecting reticle distortions. This multi-functionality eliminates the need for separate measurement marks or sensors, resolving the contradiction between measurement precision and device complexity
2Measurement precision
If additional marks are added to the reticle for distortion measurement, then measurement precision improves, but manufacturing precision of the product pattern deteriorates
Solution Approach 1:
The existing periodic pattern features on the reticle are utilized for both product pattern transfer and distortion measurement purposes. By making the pattern features serve dual functions, the invention avoids adding separate measurement marks that would compromise product pattern manufacturing precision while still achieving accurate distortion measurement
3Measurement precision
If measurement time is increased to capture thermal distortions, then measurement precision improves, but productivity decreases
Solution Approach 1:
The measurement process is integrated continuously with the lithographic exposure process. The periodic pattern is measured before, during, and after exposure without interrupting the workflow, allowing thermal distortion measurements to be captured continuously as they occur rather than requiring separate measurement steps, thus maintaining measurement precision while preserving productivity
Solution Approach 2:
The measurement system provides real-time feedback on reticle position and distortion during the exposure process. This continuous feedback enables dynamic correction of thermal distortions without stopping production, maintaining both measurement precision and high throughput by allowing adjustments to be made during ongoing lithographic operations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the monitoring and reduction of time-varying positional deviations, improving overlay accuracy by modifying exposure parameters and reducing the need for additional sensing equipment, thus maintaining apparatus performance and cost-effectiveness.
Implementation Method 1
the patterning device having a patterned portion which in operation is illuminated with a radiation beam so as to impart a pattern to the radiation beam in its cross-section
Implementation Method 2
calculating local positional deviations induced by thermal heating of the patterning device by said radiation beam
Data Source
AI summary
A lithographic reticle is illuminated to transfer a pattern to a substrate, inducing distortions due to heating. The distortions are calculated using reference marks in a peripheral portion of the reticle and measuring changes in their relative positions over time. A plurality of cells are defined for which a system of equations can be solved to calculate a dilation of each cell. In an embodiment, each equation relates positions of pairs of marks to dilations of the cells along a fine (s, s1, s2) connecting each pair. Local positional deviations can be calculated for a position by combining calculated dilations for cells between at least one measured peripheral mark and the position. Corrections can be applied in accordance with the result of the calculation. Energy may be applied to the patterning device (for example by thermal input or mechanical actuators) to modify a distribution of the local positional deviations.