Phase Shift Mask Angle Verification via Lithography Calibration
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Solution Overview
Problem
The precise control of phase shift angles in phase shift masks (PSM) is challenging due to difficulties in accurately adjusting substrate or film thickness, leading to deviations in resolution and errors in lithography performance, such as pattern positions, depth of focus, and critical dimensions, which current methods like proximity-type probes can take time and potentially damage the PSM.
Innovation Solution
A method involving the creation of a calibration curve using standard PSMs with known phase shift angles to measure characteristic values like depth of focus, position of focus, or critical dimensions of photoresist patterns, allowing for the derivation of the real phase shift angle without damaging the PSM, and the inclusion of phase-shift-angle test patterns on the PSM for easy checking and adjustment of exposure conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a proximity-type probe is used to measure substrate or film thicknesses to check the phase shift angle, then the phase shift angle can be measured, but the measurement process consumes much time and possibly damages the surface of the PSM
Solution Approach 1:
The patent creates test patterns (such as line-space patterns or hole arrays) on the PSM that copy the phase shift characteristics. By measuring the lithography performance of these test patterns instead of directly measuring the PSM thickness, the phase shift angle can be derived indirectly. This copying approach avoids direct contact with the PSM surface, preventing damage while enabling measurement.
Solution Approach 2:
The patent introduces test patterns as an intermediary between the PSM and the measurement process. These test patterns serve as a mediator that translates the phase shift angle into measurable lithography characteristics (such as line width, spacing, or focus depth). By measuring the test pattern outcomes rather than the PSM directly, the system achieves measurement without damage.
2Measurement precision
If a proximity-type probe is used to measure substrate or film thicknesses to check the phase shift angle, then the phase shift angle can be measured, but the measurement process possibly damages the surface of the PSM to degrade the quality of pattern transfer
Solution Approach 1:
The patent creates test patterns (such as line-space patterns or hole arrays) on the PSM that copy the phase shift characteristics. By measuring the lithography performance of these test patterns instead of directly measuring the PSM thickness, the phase shift angle can be derived indirectly. This copying approach avoids direct contact with the PSM surface, preventing damage while enabling measurement.
Solution Approach 2:
The patent introduces test patterns as an intermediary between the PSM and the measurement process. These test patterns serve as a mediator that translates the phase shift angle into measurable lithography characteristics (such as line width, spacing, or focus depth). By measuring the test pattern outcomes rather than the PSM directly, the system achieves measurement without damage.
3Manufacturing precision
If the phase shift angle deviates from the required value due to difficult thickness control, then the PSM can be returned to the manufacturer for calibration, but this process is time-consuming and costly
Solution Approach 1:
The patent performs preliminary measurement and evaluation of the phase shift angle using test patterns before the PSM is used for actual IC pattern transfer. This preliminary action allows early detection of phase shift angle deviations, enabling timely compensation or rejection decisions without delaying the overall manufacturing process.
Solution Approach 2:
The patent establishes a feedback mechanism where test pattern measurements provide information about the phase shift angle accuracy. This feedback allows for real-time assessment and compensation, enabling the system to adjust exposure conditions or reject problematic PSMs without requiring time-consuming return trips to the manufacturer for calibration.
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 saves time, prevents damage to the PSM, and allows for quick adjustment of exposure conditions to achieve predetermined values, ensuring accurate phase shift angle checking and maintaining IC pattern transfer quality.
Implementation Method 1
a phase shift mask is required to improve the resolution of the pattern transfer. Generally, a PSM utilizes a phase angle difference between adjacent light-transmittable regions
Implementation Method 2
The patterns of a PSM of the type to be checked are transferred to a photoresist layer through exposure to form photoresist patterns
Data Source
AI summary
A method for checking a phase shift angle of a PSM is described. A calibration curve of a characteristic value of lithography performance with respect to the phase shift angle of a type of PSM is acquired. The patterns of a PSM of the type to be checked are transferred to a photoresist layer to form photoresist patterns, and the characteristic value is measured. The real phase shift angle of the PSM is derived based on the characteristic value according to the calibration curve.