Lithography Stitching for Large Chips With Seamless Metal Rings
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Solution Overview
Problem
Current methods for forming large chips through stitching face challenges in aligning and stitching metal features across reticle fields, leading to incomplete or misaligned patterns, which restrict the size of the resulting chip.
Innovation Solution
A dual exposure process using two lithography masks to expose and develop photoresist patterns, allowing for the formation of wider conductive features and seal rings that extend across stitching zones, enabling larger chip sizes by aligning and stitching metal features beyond the reticle field limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If traditional single exposure lithography is used, then the manufacturing process is simple, but the chip size is limited by reticle field boundaries and metal features cannot be seamlessly stitched across fields
Solution Approach 1:
The lithography process is divided into multiple sequential exposures, with each exposure covering a specific reticle field. Multiple reticle fields are stitched together through overlapping exposures to form a complete large-chip pattern that exceeds the area of a single reticle field.
Solution Approach 2:
The patent extends the lithography process from a single 2D reticle field exposure to a multi-field 2D array with overlapping regions. The stitching zones create a dimensional extension where patterns from adjacent reticle fields are merged and aligned to form continuous metal features across the entire large chip area.
2Manufacturing precision
If multiple lithography masks are used for dual exposure, then metal features can be stitched across reticle fields, but the alignment precision becomes more difficult to maintain
Solution Approach 1:
Alignment marks are pre-formed on the substrate before the actual pattern exposure. These alignment marks serve as reference features that guide the positioning of subsequent lithography masks, ensuring precise alignment of metal features across multiple reticle fields during the stitching process.
Solution Approach 2:
The patent introduces alignment marks as intermediary reference features between the lithography masks and the metal features. These alignment marks act as mediators that facilitate the precise positioning and stitching of metal patterns across multiple reticle fields by providing a common reference framework.
3Shape
If reticle field boundaries are respected, then manufacturing is straightforward, but seamless metal rings and large chip sizes cannot be achieved
Solution Approach 1:
Adjacent reticle fields are merged through overlapping exposures in stitching zones. The metal features from multiple reticle fields are combined and stitched together to form continuous, seamless patterns such as large metal rings that would otherwise be broken by reticle field boundaries.
Solution Approach 2:
The lithography process creates overlapping copies of the same pattern from adjacent reticle fields. By exposing the same geometric features from multiple reticle fields with proper alignment, seamless metal rings and continuous patterns are formed through the superposition and merging of these copied patterns.
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 the creation of larger chips with seamless metal rings and improved connectivity, enhancing the interconnectivity and preventing moisture penetration into low-k dielectric layers, thus overcoming the limitations of traditional stitching methods.
Implementation Method 1
A dual exposure process using two lithography masks to expose and develop photoresist patterns
Data Source
AI summary
A method includes performing a first light-exposure and a second a second light-exposure on a photo resist. The first light-exposure is performed using a first lithograph mask, which covers a first portion of the photo resist. The first portion of the photo resist has a first strip portion exposed in the first light-exposure. The second light-exposure is performed using a second lithograph mask, which covers a second portion of the photo resist. The second portion of the photo resist has a second strip portion exposed in the second light-exposure. The first strip portion and the second strip portion have an overlapping portion that is double exposed. The method further includes developing the photo resist to remove the first strip portion and the second strip portion, etching a dielectric layer underlying the photo resist to form a trench, and filling the trench with a conductive feature.