Metal Redistribution Layer Alignment via Recessed Marks
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Solution Overview
Problem
The increasing complexity of integrated circuits requires closer spacing of input and output connections, making it costly to redesign circuits with conductive pads at the interior of silicon substrates, and existing methods struggle with unclear alignment marks during metal redistribution layer fabrication.
Innovation Solution
A method for fabricating a metal redistribution layer involves forming dielectric layers with specific openings and depositing metal material to fill these openings, using recesses as alignment marks to pattern the metal layer effectively, ensuring clear alignment for interconnecting conductive pads at the periphery with those at the interior of the silicon substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conductive pads are located at the periphery of the silicon substrate, then wire bonds can be attached for electrical connections, but the pitch between conductive pads decreases with increased circuit complexity requiring closer spacing
Solution Approach 1:
The patent introduces a metal redistribution layer that extends from the interior region to the periphery region of the substrate, creating a three-dimensional interconnection structure. This allows conductive pads to remain at the periphery for wire bonding while interior conductive elements are connected through the redistribution layer, effectively adding a vertical dimension to the interconnection architecture and resolving the pitch constraint.
Solution Approach 2:
The metal redistribution layer acts as an intermediary structure between interior conductive elements and peripheral conductive pads. It provides a bridging connection that allows signals to be routed from interior regions to peripheral regions without requiring direct peripheral pad placement, thus maintaining both high circuit complexity and adequate pad spacing.
2Manufacturing precision
If conductive pads are relocated to the interior of the silicon substrate surface, then pad pitch can be increased, but redesign cost becomes prohibitively expensive
Solution Approach 1:
The patent forms the metal redistribution layer structure during the existing fabrication process before final pad formation. By preparing the redistribution layer infrastructure in advance, the design can accommodate both interior and peripheral pad configurations without requiring costly post-design modifications or complete redesign of the circuit layout.
Solution Approach 2:
The metal redistribution layer serves multiple functions: it provides electrical connection between interior and peripheral regions, acts as an alignment reference structure, and enables both interior and peripheral pad configurations. This multi-functionality allows the same fabrication approach to work for different design configurations without requiring expensive redesign.
3Reliability
If metal material is deposited to fill openings for redistribution layer formation, then electrical connections are established, but alignment marks may become unclear during photolithography patterning
Solution Approach 1:
The patent creates recesses in specific local regions of the metal redistribution layer to serve as alignment marks, while other regions maintain continuous metal coverage for electrical connections. This local differentiation allows the alignment function to be separated from the conduction function, with recesses providing optical contrast for photolithography alignment while the surrounding metal ensures electrical connectivity.
Solution Approach 2:
The recesses formed in the metal redistribution layer create optical contrast differences that serve as visible alignment marks during photolithography. The variation in light reflection or absorption between recessed and non-recessed areas provides clear visual references for alignment without compromising the underlying electrical connection functionality.
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 accurate patterning and connection of conductive pads, reducing the need for costly redesigns by providing a clear alignment mark for photolithography processes, ensuring reliable electrical connections without voids or seams.
Implementation Method 1
A metal material is formed over the dielectric layer and in the first, second, third and fourth openings
Data Source
AI summary
A method for fabricating a metal redistribution layer is described. A first opening and a second opening are formed in a dielectric layer over a first region and a second region thereof, respectively. A plurality of third openings are formed in the dielectric layer exposed by the first opening in the first region and a plurality of fourth openings are formed in the dielectric layer exposed by the second opening in the second region. A metal material is formed over the dielectric layer and in the first, second, third and fourth openings. A plurality of recesses is formed in the metal materials overlying the third and fourth openings. The metal material in the first region is patterned by using the recesses formed in portions of the metal material overlying the fourth openings in the second region as an alignment mark to form a metal redistribution layer.