Reticle Thermal Calibration via Alignment Deformation
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Solution Overview
Problem
Current reticle heating models in lithographic processes are inaccurate and inefficient, leading to delays, rework of production substrates, and reduced throughput due to reliance on sensor-based approaches that exhibit errors and require calibration lots of production wafers.
Innovation Solution
A method that conditions the reticle to a predetermined temperature using modal deformation approaches, eliminates the need for reticle temperature sensors by measuring alignment and shape deformation, and employs decision-based and machine learning to calibrate the reticle heating model, reducing parasitic thermal effects and increasing calibration speed and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sensor-based approach is used to calibrate the reticle heating model, then temperature measurement can be obtained, but calibration accuracy is reduced and calibration time increases
Solution Approach 1:
The patent removes the reticle temperature sensor (RTS) from the calibration system entirely. Instead of using sensor-based temperature measurement, the invention extracts thermal effect information from alignment mark measurements, eliminating the need for direct temperature sensing and the associated calibration delays.
Solution Approach 2:
The patent introduces alignment marks as an intermediary element. Rather than measuring temperature directly with sensors, the system measures the thermal expansion of alignment marks, which serves as a proxy for reticle temperature and enables indirect calibration without additional time penalties.
2Reliability
If a reticle temperature sensor is used for calibration, then temperature data can be obtained, but calibration accuracy is reduced due to sensor errors
Solution Approach 1:
The patent eliminates the reticle temperature sensor from the system, removing the source of sensor errors entirely. Calibration is performed using alignment mark measurements instead, which do not suffer from the same error characteristics as temperature sensors.
Solution Approach 2:
The patent uses alignment marks as a copy or proxy for direct temperature measurement. The thermal expansion of the alignment marks provides an alternative measurement that correlates with reticle temperature but avoids the errors inherent in direct temperature sensing.
3Reliability
If calibration lots of production wafers are used, then the reticle heating model can be calibrated, but productivity is reduced and rework is required
Solution Approach 1:
The patent performs calibration using non-production substrates before actual production begins. This preliminary calibration action ensures the reticle heating model is ready for production without requiring production wafers to be used for calibration purposes, thus avoiding rework and maintaining productivity.
Solution Approach 2:
The patent uses non-production substrates for calibration instead of valuable production wafers. These calibration substrates are discarded after calibration, while production substrates are preserved for actual manufacturing, eliminating the need to rework production wafers and maintaining high throughput.
4Manufacturing precision
If the reticle is conditioned to a predetermined temperature, then thermal effects can be reduced, but conditioning time increases
Solution Approach 1:
The patent implements a feedback mechanism where alignment mark measurements are continuously monitored during reticle conditioning. When the measurements indicate that thermal stability has been achieved, the conditioning process stops, eliminating the need for fixed-time conditioning and reducing overall conditioning time while maintaining pattern accuracy.
Solution Approach 2:
The patent transitions from static, fixed-time conditioning to dynamic, adaptive conditioning. The conditioning duration is adjusted based on real-time measurements of reticle thermal state, allowing the process to terminate as soon as thermal stability is achieved rather than waiting for a predetermined time period.
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 method enhances calibration accuracy and speed, reduces rework of production substrates, and increases fabrication throughput and yield by accurately adjusting reticle temperature and reducing thermal stress, thereby improving the overall lithographic process.
Implementation Method 1
conditioning the reticle to adjust an initial temperature of the reticle to a predetermined temperature
Implementation Method 2
conditioning the reticle to adjust an initial temperature of the reticle to a predetermined temperature
Implementation Method 3
calibrating a reticle heating model by exposing the reticle and a non-production substrate to a dose of radiation
Data Source
AI summary
A method of reducing effects of heating and/or cooling a reticle in a lithographic process includes conditioning the reticle to adjust an initial temperature of the reticle to a predetermined temperature, reducing stress in the reticle to reduce parasitic thermal effects, calibrating a reticle heating model by exposing the reticle and a non-production substrate to a dose of radiation, and processing a production substrate by exposing the reticle and a production substrate to a dose of radiation based on the reticle heating model. The method can increase calibration accuracy and speed of the reticle heating model, reduce conditioning times of the reticle, reduce stress in the reticle, avoid rework of production substrates, and increase throughput, yield, and accuracy.