Submicron Wafer Alignment Using Beam Splitter and Moiré Patterns
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Solution Overview
Problem
Standard alignment techniques for wafer stacks in wafer-level cameras face challenges due to limited depth of field in microscopes, leading to inaccurate alignment and slow processing, as they struggle to focus on alignment marks on both wafers simultaneously, especially when the marks are more than a few microns apart, resulting in systematic errors.
Innovation Solution
The use of a beam splitter to reflect the top wafer mark and make it appear at a larger distance, combined with complementary patterns that produce a Moiré effect for precise alignment, allowing for simultaneous viewing and alignment of marks within a tolerance of 1 micron, and automated alignment through image data analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard alignment techniques using microscope observation are used, then alignment process is simple, but alignment precision deteriorates due to limited depth of field and systematic errors
Solution Approach 1:
The patent introduces a beam splitter as an intermediary optical component that reflects alignment marks from different wafer layers into a common observation path. This mediator enables simultaneous viewing of multiple marks that would otherwise be at different focal depths, resolving the depth of field limitation without requiring complex microscope systems.
Solution Approach 2:
The patent transforms the alignment observation from a single-dimensional focal plane to a multi-dimensional optical path by using beam splitting and mark reflection. This allows alignment marks from different vertical positions (z-dimension) to be projected onto the same observation plane, enabling simultaneous focus on multiple marks.
2Measurement precision
If microscope is moved to focus on different wafer marks, then both marks can be viewed, but alignment speed deteriorates and systematic errors are introduced
Solution Approach 1:
The patent merges multiple alignment mark observations into a single simultaneous view by combining light paths through beam splitting. Both the top wafer mark and bottom wafer mark are reflected into the same optical path, allowing the microscope to capture both marks at once without moving between focal planes, thus improving alignment speed while maintaining measurement accuracy.
3Measurement precision
If large depth of field microscope objectives are used, then both marks can be focused simultaneously, but magnification decreases and small marks become invisible
Solution Approach 1:
The beam splitter acts as an intermediary that creates virtual images of alignment marks at a common optical distance. This allows the use of high-magnification microscope objectives with limited depth of field, as the beam splitter compensates for the vertical separation between marks, making both visible simultaneously without sacrificing magnification or field of view.
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 method enables precise submicron alignment of wafer stacks with improved accuracy and efficiency, reducing systematic errors and increasing the magnification, allowing for alignment within 250 nm tolerance, suitable for high-resolution imaging devices.
Implementation Method 1
One disclosed method of alignment between wafers employs a beam splitter (that is, a 50% transparent mirror) that reflects the top wafer mark and makes it appear at a larger distance than it actually is.
Implementation Method 2
Another disclosed method of alignment between wafers implements complementary patterns to aid in visually determining proper alignment between the wafer and the mask.
Data Source
AI summary
Certain aspects relate to systems and techniques for submicron alignment in wafer optics. One disclosed method of alignment between wafers to produce an integrated lens stack employs a beam splitter (that is, a 50% transparent mirror) that reflects the alignment mark of the top wafer when the microscope objective is focused on the alignment mark of the bottom wafer. Another disclosed method of alignment between wafers to produce an integrated lens stack implements complementary patterns that can produce a Moiré effect when misaligned in order to aid in visually determining proper alignment between the wafers. In some embodiments, the methods can be combined to increase precision.