Photolithography Simulation Calibration Using Traceable Reticle Dimensions
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Solution Overview
Problem
Existing photolithography simulation tools often fail to accurately predict the printed patterns due to inaccuracies in stepper parameters, resist parameters, and reticle dimensions, leading to calibration challenges in the chip design process.
Innovation Solution
A method involving a calibrated photomask reticle with traceably measured dimensions is used to simulate and compare the physical process, assigning a figure of merit based on the agreement between simulated and measured dimensions, ensuring high precision in photolithography processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional simulation tools are used without traceable calibration, then the simulation process is simple and quick, but the accuracy of predicted printed patterns deteriorates
Solution Approach 1:
The patent applies preliminary action by performing traceable measurements of reticle dimensions before the simulation process. A calibrated reticle with pre-measured and documented dimensions is used as input to the simulation, ensuring accuracy is established beforehand rather than attempting to achieve it through iterative post-simulation adjustments. This preliminary calibration data preparation resolves the contradiction by setting a solid measurement foundation that improves prediction accuracy without adding complex iterative calibration steps during the simulation itself.
Solution Approach 2:
The patent implements feedback by comparing simulated printed pattern dimensions against actual measured dimensions from test structures. This comparison provides feedback on simulation accuracy, allowing for verification and validation of the simulation model. The feedback loop ensures that the simulation predictions are grounded in real-world measurements, resolving the accuracy issue while maintaining a systematic rather than overly complex approach to calibration.
2Manufacturing precision
If iterative reticle simulation and manufacturing are performed to match intended design, then printed pattern accuracy improves, but time consumption and productivity deteriorate
Solution Approach 1:
The patent applies preliminary action by using traceably measured reticle dimensions as known accurate inputs to the simulation from the outset. This eliminates the need for iterative reticle manufacturing and re-simulation cycles, as the simulation starts with verified, accurate reticle data. The preliminary measurement and calibration work is done once, enabling direct comparison between simulated and actual results, thereby improving productivity by reducing repeated manufacturing iterations.
Solution Approach 2:
The patent uses physical test structures as reference copies to validate the simulation model. By creating actual test structures with known dimensions and comparing them against simulated results, the patent establishes a verified copy relationship between physical reality and simulation. This approach allows the simulation to be calibrated once against these reference copies, eliminating the need for continuous iterative manufacturing to verify accuracy.
3Reliability
If traceable measurements with known uncertainty are used for calibration, then measurement reliability improves, but measurement and calibration complexity increases
Solution Approach 1:
The patent extracts and separates the measurement uncertainty characterization from the main simulation process. By explicitly measuring and documenting reticle dimensions with known uncertainties using traceable measurement methods, the uncertainty information is extracted as a separate, well-defined parameter. This extracted uncertainty data is then used as input to the simulation, improving reliability without requiring the measurement system complexity to propagate through the entire simulation workflow. The uncertainty is taken out as a known quantity rather than being recalculated repeatedly.
Data Source
AI summary
A method for calibrating a computer program that simulates a physical process and a photomask are disclosed. A first physical artifact may be exposed to the physical process to produce a second physical artifact. The first physical artifact may include one or more features characterized by traceably measured known dimensions. One or more features of the second physical artifact may be measured to produce one or more measured dimensions. The physical process may be simulated with a computer simulation using the known dimensions of the first physical artifact as inputs to produce an output. The output may be compared to the measured dimensions of the second physical artifact to produce a result. A figure of merit may be assigned to the computer simulation based on the result. The photomask may have one or more features with one or more traceably measured dimensions.