SEM Pattern Contour Restoration via Shrinkage Correction
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Solution Overview
Problem
The reliability of dimension and shape measurements in scanning electron microscopes (SEM) is compromised by physical dimensional changes due to shrinkage and electrostatic charging, leading to inaccuracies in measuring semiconductor patterns, especially for complex two-dimensional patterns with varying taper angles.
Innovation Solution
A scanning electron microscope system that includes an electron source, convergent lens, deflection coil, detector, and calculating means to correct the pattern contour based on shape change amounts and taper angles, using databases to store and restore the original shape contour before electron beam irradiation, accounting for stress and positional shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an electron beam is used to measure pattern dimensions, then measurement capability is provided, but the resist material shrinks due to electron beam irradiation causing dimensional errors
Solution Approach 1:
The patent applies preliminary action by measuring the relationship between electron beam irradiation conditions and resist shrinkage before actual measurement. A shrinkage amount database is created in advance by irradiating reference patterns with various electron beam conditions and recording the resulting shrinkage amounts. During actual measurement, this pre-acquired data is used to correct the measured dimensions, compensating for the shrinkage effect without needing to re-measure under multiple conditions.
2Difficulty of detecting and measuring
If electron beam irradiation is increased to improve signal detection, then detection sensitivity improves, but electrostatic charging increases causing image darkening and measurement errors
Solution Approach 1:
The patent implements feedback by measuring the secondary electron emission coefficient δ as an indicator of electrostatic charging state. The system continuously monitors δ values during electron beam irradiation and uses this feedback information to adjust measurement parameters or apply corrections. When δ deviates from expected values indicating charging problems, the system can compensate for the resulting measurement errors using the stored relationship between δ values and measurement errors.
3Ease of operation
If conventional measurement methods are used, then measurement process is simple, but reliability of measurement results decreases due to uncorrected shrinkage and charging effects
Solution Approach 1:
The patent introduces an intermediary approach by using a shrinkage amount database and secondary electron emission coefficient measurements as intermediate data. Instead of directly correcting raw measurements, the system first measures δ values and references them against the pre-built database to determine appropriate correction amounts. This intermediary step allows the system to maintain operational simplicity while incorporating sophisticated correction mechanisms, as users only need to perform standard measurements while the system automatically applies corrections based on the intermediary δ measurements and database lookups.
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
Enables high-accuracy reconstruction of the original shape contour of two-dimensional patterns before electron beam irradiation, reducing errors and improving the reliability of measurements.
Implementation Method 1
A secondary electron which is generated from a surface of the sample by irradiating the surface with the electron beam is caught by a secondary electron detector
Implementation Method 2
an electron beam which is emitted from an electron gun that is installed upward from a wafer is focused to slenderize by a convergent lens
Implementation Method 3
is two-dimensionally scanned on a sample to be evaluated by a deflector
Data Source
AI summary
Disclosed is a scanning electron microscope provided with a calculation device (403) for measuring the dimension of a pattern on a sample (413), characterized in that the amount of change of a pattern shape, caused by electron beam irradiation, is calculated and stored, and a pattern shape contour (614; 815; 1512) before the sample is irradiated with an electron beam is restored from a pattern shape contour (613; 814; 1511) in a scanning electron microscope image (612; 813; 1510) after the sample is irradiated with an electron beam using the calculated amount and, then, the pattern shape contour (614; 815; 1512) is displayed. Thus, the shrinking of a resist and/or the effect of electrostatic charge caused when a sample is irradiated with an electron beam are eliminated, so that the shape contour of a two-dimensional pattern before irradiating an electron beam can be restored with a high degree of accuracy, and the dimension of a pattern can be measured with a high degree of accuracy, using the restored image.