Overlay Error Measurement in Area-Imaging E-Beam Lithography
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Solution Overview
Problem
Programmable-pattern area-imaging electron beam lithography systems face challenges in measuring and correcting overlay errors caused by space-charge effects and aberrations, leading to undesirable pattern distortions.
Innovation Solution
A method involving the printing of patterned cells in swaths with controlled-exposure areas, where overlay errors are measured by imaging distortions between a base array and an overlay array, and corrections are applied by pre-distorting patterns based on exposure conditions to minimize errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If area-imaging electron beam lithography uses collection of electron beams to print patterns, then productivity is improved, but overlay errors occur due to space-charge effects and aberrations
Solution Approach 1:
The patent applies pre-distortion to pattern data before writing, where the pattern coordinates are mathematically transformed to compensate for expected space-charge effects and aberrations. This preliminary correction ensures that after the beams traverse the exposure field and experience physical distortions, the final printed pattern achieves the desired overlay accuracy.
Solution Approach 2:
The system dynamically adjusts beam parameters including voltage, current, and focal length based on position within the exposure field. By changing these parameters adaptively, the system compensates for space-charge effects and optical aberrations that vary across different regions of the writing field, maintaining overlay precision while using area-imaging for high productivity.
2Manufacturing precision
If overlay errors are measured and corrected, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The system uses the lithography apparatus itself to write overlay measurement targets and perform the measurements, rather than requiring separate dedicated measurement equipment. The same electron beam system that prints patterns also creates and reads the overlay targets, reducing additional hardware complexity while maintaining measurement capability.
Solution Approach 2:
The patent introduces overlay measurement targets as intermediary structures that mediate between the complex physical effects and the measurement process. These specially designed target patterns serve as reference objects that encode overlay error information in a measurable form, simplifying the extraction of precision data from the complex beam-substrate interaction.
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 allows for quantitative measurement and reduction of overlay errors across the e-beam lithography writing field, improving pattern accuracy and reliability by controlling local exposure conditions and applying pre-compensation techniques.
Implementation Method 1
programmable-pattern area-imaging electron beam lithography apparatus
Implementation Method 2
overlay errors caused by space-charge effects and aberrations
Implementation Method 3
overlay errors caused by space-charge effects and aberrations
Data Source
AI summary
One embodiment relates to a method of measuring overlay errors for a programmable pattern, area-imaging electron beam lithography apparatus. Patterned cells of an overlay measurement target array may be printed in swaths such that they are superposed on patterned cells of a first (base) array. In addition, the overlay array may have controlled-exposure areas distributed within the swaths. The superposed cells of the overlay and base arrays are imaged. The overlay errors are then measured based on distortions between the two arrays in the image data. Alternatively, non-imaging methods, such as using scatterometry, may be used. Another embodiment relates to a method for correcting overlay errors for an electron beam lithography apparatus. Overlay errors for a pattern to be printed are determined based on within-swath exposure conditions. The pattern is then pre-distorted to compensate for the overlay errors. Other embodiments, aspects and features are also disclosed.