SEM Linearity Calibration Using Interleaved Offset Patterns
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Solution Overview
Problem
Conventional scanning electron microscope (SEM) calibration methods using single pitch-based standards are limited and fail to accurately account for asymmetries in edge measurements, leading to errors in critical dimension measurements due to asymmetric waveforms caused by charge build-up and other non-ideal conditions, especially when measuring nanometer-scale features.
Innovation Solution
A method and system for calibrating an SEM using a reference sample with interleaved periodic structures having induced offsets, where the SEM measures and compares offsets between these structures, utilizing a laser interferometer to trace and compensate for overlay errors, enabling more accurate linearity calibration by considering both left and right edges of the structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single pitch-based standard is used for calibration, then the calibration process is simple, but measurement precision deteriorates due to asymmetries in edge measurements
Solution Approach 1:
The reference sample is divided into multiple periodic structures with different pitch values (e.g., 19.0 nm, 19.5 nm, 20.0 nm, 20.5 nm, 21.0 nm) arranged in series. Each structure provides independent measurement data points, allowing the calibration to account for asymmetries by comparing measurements across multiple known pitch values rather than relying on a single standard.
Solution Approach 2:
The calibration approach transitions from measuring only pitch dimensions to also measuring offset dimensions between periodic structures. By introducing offset measurements as an additional dimensional parameter, the method captures asymmetry information that single pitch measurements cannot provide, thereby improving measurement precision.
2Device complexity
If conventional single pitch calibration is used, then device complexity is low, but measurement precision deteriorates due to charge build-up asymmetries
Solution Approach 1:
The calibration process uses measured offsets between periodic structures as feedback to correct for asymmetries. The system measures the actual offset between structures with known pitch relationships, compares it to the expected offset, and uses this feedback information to adjust calibration parameters, thereby compensating for charge build-up effects and improving measurement accuracy.
Solution Approach 2:
The reference sample functions as a composite calibration standard combining multiple periodic structures with different pitches and deliberate offsets. This composite structure provides richer calibration information than a single pitch standard, enabling the system to separately characterize pitch accuracy and offset accuracy, thereby improving overall measurement precision.
3Measurement precision
If multiple periodic structures with induced offsets are used, then measurement precision improves, but device complexity increases
Solution Approach 1:
The reference sample incorporates multiple periodic structures with systematically varied pitch parameters (19.0 nm, 19.5 nm, 20.0 nm, 20.5 nm, 21.0 nm) and controlled offset parameters. By changing these parameters in a structured manner across multiple structures, the calibration process can extract accuracy information for both pitch and offset measurements, improving overall measurement precision while maintaining a systematic approach to complexity.
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 enhances the accuracy of SEM calibration by accounting for natural overlay errors and asymmetries, leading to improved measurement precision and reduced errors in critical dimension measurements, particularly for nanometer-scale features.
Implementation Method 1
The induced offset may be traceable to a laser interferometer
Implementation Method 2
measuring, by the SEM, an offset between the first periodic structure and the second periodic structure
Data Source
AI summary
A method for calibrating a scanning charged particle microscope, such as a scanning electron microscope (SEM), is provided. The method includes dividing a wafer into a plurality of regions; preparing, on each of the plurality of regions, a pattern including a first periodic structure interleaved with a second periodic structure, the first and second periodic structures having an induced offset; determining an actual pitch the first and second periodic structures and thereby determining actual induced offset on each of the plurality of regions; selecting a plurality of regions from among the plurality of regions; measuring, by the SEM, a pitch of first and second periodic structures on each of the plurality of regions; and performing linearity calibration on the SEM based on the determining and the measuring.