Encoder Array for Wafer Alignment Measurement
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Solution Overview
Problem
Current lithographic exposure tools face challenges in achieving precise alignment and overlay of patterns on semiconductor wafers due to limitations in measurement accuracy and throughput, particularly with the use of microscope systems and autofocus systems, which are costly and inefficient for simultaneous measurement of multiple exposure fields.
Innovation Solution
The implementation of an optical measurement system using an array of encoders and spatially-periodic alignment marks that measure in-plane distortions and phases of optical signals, allowing for simultaneous phase-based measurements across all exposure fields without relying on wavelength or angle changes, thereby improving alignment accuracy and throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If microscope systems and autofocus systems are used for alignment measurement, then measurement capability is provided, but measurement accuracy and throughput are limited and costs increase
Solution Approach 1:
The patent divides the measurement system into multiple encoder units, each responsible for measuring a specific exposure field. This segmentation allows simultaneous measurement of multiple fields, dramatically increasing throughput while maintaining high precision through phase-based optical measurement in each encoder unit
Solution Approach 2:
The patent combines multiple encoder units into a single integrated measurement system that can simultaneously measure all exposure fields. This merging of measurement functions into parallel-operating encoder units resolves the contradiction by enabling both high accuracy (through phase measurement) and high throughput (through simultaneous multi-field measurement)
2Adaptability or versatility
If wavelength or angle changes are used for phase measurement, then measurement flexibility is achieved, but measurement accuracy deteriorates due to reliance on these parameter changes
Solution Approach 1:
Instead of measuring phase by detecting changes in wavelength or angle, the patent inverts the approach by measuring the optical path length directly through interference of beams with different path lengths. This inversion eliminates the need for wavelength or angle changes, providing both high flexibility and high accuracy
3Productivity
If array of encoders with spatially-periodic alignment marks is implemented, then simultaneous measurement of multiple exposure fields is enabled, but device complexity increases
Solution Approach 1:
The patent employs spatially-periodic alignment marks that serve multiple functions: they enable phase measurement, provide positioning references, and facilitate simultaneous measurement across all exposure fields. This multi-functionality reduces the need for separate measurement mechanisms, thereby managing complexity while achieving high throughput
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 solution enhances the precision and efficiency of wafer alignment by enabling simultaneous measurement of multiple exposure fields with improved accuracy and reduced costs, maintaining high throughput in the lithographic exposure process.
Implementation Method 1
an objective optical system positioned to receive the measurement beam from the first optical system, to form a condensed measurement beam by condensing the measurement beam, and to direct the condensed measurement beam towards the mark region
Implementation Method 2
a positive-order diffraction beam of light and a negative-order diffraction beam of light through the objective optical system (where the positive-order and negative-order diffraction beams have both been generated at the mark region as a result of diffraction of the condensed measurement beam at the mark region)
Implementation Method 3
the second optical system is configured to interfere said positive-order and negative order diffraction beams of light to form an interference beam of light
Data Source
AI summary
System and method for accurately measuring alignment of every exposure field on a pre-patterned wafer without reducing wafer-exposure throughput. Diffraction grating disposed in scribe-lines of such wafer, used as alignment marks, and array of encoder-heads (each of which is configured to define positional phase(s) of at least one such alignment mark) are used. Determination of trajectory of a wafer-stage scanning during the wafer-exposure in the exposure tool employs determining in-plane coordinates of such spatially-periodic alignment marks by simultaneously measuring position-dependent phases of signals produced by these marks as a result of recombination of light corresponding to different diffraction orders produced by these marks. Measurements may be performed simultaneously at all areas corresponding to at least most of the exposure fields of the wafer, and/or with use of a homodyne light source, and/or in a wavelength-independent fashion, and/or with a pre-registration process allowing for accommodation of wafers with differently-dimensioned exposure fields.