Wafer Alignment Calibration Using Multi-Wavelength APD Matching
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Solution Overview
Problem
As semiconductor technology advances to smaller feature sizes, the stringent alignment requirements in integrated circuit fabrication pose challenges due to misalignment issues caused by optical aberrations, fabrication processes like etching and chemical mechanical polishing, which existing alignment methods struggle to accurately address.
Innovation Solution
A lithography system equipped with a tunable light source and optical device for multi-wavelength alignment measurements, combined with an APD database for simulating and calibrating alignment errors, enables precise alignment by comparing measured alignment position deviations with simulated results to adjust the alignment marks and calibrate the exposure process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional alignment methods are used, then the alignment process is simple, but the alignment precision deteriorates due to optical aberrations and fabrication process variations
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing alignment position deviation (APD) simulation results for various mark profiles in a database before actual alignment measurements. During alignment, the measured APD is compared against these pre-computed simulation results to determine the actual mark profile and compensation parameters, eliminating the need for complex real-time calculations and enabling faster, more accurate alignment compensation.
Solution Approach 2:
The patent introduces an intermediary approach by using alignment marks with different known asymmetric profiles as reference standards. These reference marks serve as intermediaries between the measurement system and the actual wafer features, allowing the system to infer unknown mark profile characteristics and compensation parameters by comparing measured APD values against the known reference profiles stored in the database.
2Measurement precision
If alignment marks are assumed to be symmetric, then the alignment process is simplified, but measurement precision deteriorates due to asymmetric mark profiles caused by fabrication processes
Solution Approach 1:
The patent explicitly embraces asymmetry by designing alignment marks with known asymmetric profiles and storing their characteristic APD simulation results in a database. Instead of assuming symmetry, the system uses the asymmetric characteristics as identifiable features to determine the actual mark profile on the wafer, thereby improving measurement accuracy while managing complexity through pre-computed reference data.
Solution Approach 2:
The patent applies parameter changes by varying the asymmetric profile parameters of alignment marks (such as etch depth, side wall angle, and mark geometry) to create a diverse set of reference profiles in the database. This allows the system to handle different fabrication process conditions and mark variations by selecting the appropriate reference profile that matches the measured APD characteristics.
3Measurement precision
If multiple alignment measurements are performed at different wavelengths, then alignment precision improves, but the time required for alignment increases
Solution Approach 1:
The patent applies preliminary action by pre-computing and storing APD simulation results for multiple wavelengths and mark profiles in a database before production alignment measurements. During actual alignment, the system performs rapid comparison of measured multi-wavelength APD data against these pre-computed references to determine mark profile and compensation parameters, significantly reducing the time required for alignment calibration while maintaining high precision.
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 significantly improves overlay accuracy by reducing alignment errors, ensuring proper layer alignment in IC fabrication, even with asymmetric marks caused by processing variations, thereby enhancing the reliability of smaller feature size semiconductor manufacturing.
Implementation Method 1
a light source configured to provide a tunable light beam to an optical device
Implementation Method 2
the optical device is configured to direct a light beam to a mark region of the semiconductor structure and receive diffracted light from the mark region
Data Source
AI summary
A method for calibrating the alignment of a wafer is provided. A plurality of alignment position deviation (APD) simulation results are obtained form a plurality of mark profiles. An alignment analysis is performed on a mark region of the wafer with a light beam. A measured APD of the mark region of the wafer is obtained in response to the light beam. The measured APD is compared with the APD simulation results to obtain alignment calibration data. An exposure process is performed on the wafer with a mask according to the alignment calibration data.