Segmented Alignment Mark for Dual-Side Lithography
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Solution Overview
Problem
Conventional methods for fabricating compound optical devices for augmented and virtual reality face challenges in aligning multiple optical elements due to the size limitations of photomasks, requiring rotational and inversion movements of substrates, which complicates the precision and accuracy of alignment marks, especially when both sides of the substrate need to be patterned.
Innovation Solution
The use of segmented alignment marks on a single side of the substrate, which are more reflective and readable by scanners, allowing for precise alignment and patterning of optical devices on both sides without the need for complex inversion and rotation procedures, enabling accurate stitching of optical elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional alignment marks are used on both sides of the substrate, then both sides can be patterned, but the alignment accuracy deteriorates due to rotational and inversion movements required
Solution Approach 1:
The alignment mark is segmented into multiple bars (e.g., three parallel bars) instead of using a single continuous mark. This segmentation makes the alignment mark more readable by the scanner and maintains alignment accuracy even when the substrate is rotated or inverted, as the relative positions of the segmented bars remain consistent and identifiable
Solution Approach 2:
The same alignment mark design (segmented parallel bars) is copied and placed on both the first and second sides of the substrate. This allows the scanner to read identical alignment features regardless of which side is facing up, eliminating the need for complex alignment procedures when flipping or rotating the substrate
2Area of stationary object
If the substrate is rotated and inverted to pattern optical devices on both sides, then larger compound optical devices can be fabricated, but the alignment precision deteriorates
Solution Approach 1:
The segmented alignment bars are oriented in specific directions (e.g., parallel to each other in a defined orientation) that create an asymmetric pattern which is easily identifiable by the scanner. This asymmetric design allows the system to determine substrate orientation and maintain precise alignment even when the substrate is rotated or inverted during the fabrication process
Solution Approach 2:
The alignment marks are pre-patterned on both sides of the substrate before the actual optical device fabrication begins. This preliminary placement of alignment features allows the scanner to establish accurate reference points in advance, ensuring that subsequent lithography steps maintain high precision regardless of substrate manipulation
3Manufacturing precision
If segmented alignment marks are used, then alignment accuracy improves, but the manufacturing process complexity increases
Solution Approach 1:
The alignment mark is divided into multiple separate bars that are spaced apart. This segmentation is implemented using standard lithography techniques, where the segmented pattern is created in a single lithography step by defining multiple rectangular features. The segmented design actually simplifies the lithography process compared to creating complex single-piece alignment marks, as it uses basic geometric shapes that are easily fabricated with conventional tools
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 and predictability of photolithography processes, allowing for the precise alignment and patterning of compound optical devices, improving the overall efficiency in fabricating larger optical structures from smaller elements.
Implementation Method 1
scanning the alignment mark on the first side with the scanner, through the second side
Implementation Method 2
The use of segmented alignment marks on a single side of the substrate, which are more reflective and readable by scanners
Data Source
AI summary
A method for aligning a substrate for fabrication of an optical device is disclosed that includes receiving a substrate having a first side and a second side opposite the first side, the first side of the substrate being oriented towards a scanner, the substrate having an alignment mark formed on the first side of the substrate, scanning the alignment mark with the scanner, and fabricating a first pattern for a first optical device on the first side of the substrate. The method includes positioning the substrate such that the second side is oriented toward the scanner, scanning the alignment mark on the first side with the scanner, through the second side, and fabricating a second pattern for a fourth optical device on the second side of the substrate.