Non-Planar Alignment Structures for Lithographic Mask Registration
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Solution Overview
Problem
The alignment of lithographic photomasks to optically opaque layers on semiconductor wafers is challenging due to the inability of exposure tools to visually locate alignment structures covered by these opaque layers, leading to potential alignment errors during the lithographic patterning process.
Innovation Solution
The use of optically opaque non-planar alignment structures in non-die areas of the wafer, such as mesa or trench structures, which are formed using conformal layers of optically opaque materials to serve as alignment marks for aligning lithographic photomasks to die areas, even when the die areas are covered by optically opaque layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If alignment marks are formed on optically opaque layers, then alignment information is provided, but the exposure tool cannot visually locate these marks due to optical opacity
Solution Approach 1:
The patent introduces an intermediary alignment structure consisting of optically transparent features formed in the etch stop layer, which mediates between the optically opaque patterned layers and the exposure tool's visualization system. These transparent intermediaries allow the exposure tool to detect alignment information without being blocked by the opaque layers above, while still maintaining the necessary alignment relationship with the underlying structure.
Solution Approach 2:
The patent applies local quality by creating alignment structures with different optical properties in different locations. The etch stop layer contains both optically opaque patterned regions (for device formation) and optically transparent alignment regions (for visualization). This spatial differentiation of optical properties allows simultaneous achievement of device functionality and alignment detectability.
2Manufacturing precision
If conformal layers of optically opaque material are deposited to form alignment structures, then alignment marks are created, but the underlying alignment features become invisible
Solution Approach 1:
The patent segments the alignment structure into multiple functional components: the etch stop layer provides the structural foundation with embedded alignment features, while conformal optically opaque layers are deposited selectively to create visible alignment marks without completely obscuring the underlying features. The segmentation allows each layer to fulfill its specific function while maintaining overall alignment capability.
Solution Approach 2:
The patent transitions from two-dimensional planar alignment marks to three-dimensional non-planar alignment structures by forming conformal layers that wrap around underlying features. This dimensional transformation creates alignment marks with enhanced visibility and detectability while maintaining the spatial relationship to the underlying structure, allowing detection from multiple angles and improving alignment precision.
Data Source
AI summary
Techniques are provided for fabricating and utilizing optically opaque non-planar alignment structures in non-die areas (e.g., kerf areas) of a wafer to align photomasks to die areas on the wafer. For example, an insulating layer is formed over non-die and die areas of the wafer. A non-planar alignment feature is formed in the insulating layer in the non-die area. An optically opaque layer stack is formed in the die and non-die areas of the wafer, which conformally covers the non-planar alignment feature to form an optically opaque non-planar alignment structure in the non-die area. A lithographic patterning process is performed to pattern the optically opaque layer stack in the die area, wherein the optically opaque non-planar alignment structure in the non-die area is utilized to align a photomask to the die area. The optically opaque non-planar alignment structure can include any type of non-planar structure having a stepped sidewall surface.