Concave-Convex Pad Structure for 3D Wafer Bonding
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Solution Overview
Problem
In 3D-IC technology, the bonding force between the solder ball and the pad is often insufficient, leading to the solder ball being peeled off, which can cause the chip to malfunction.
Innovation Solution
A wafer structure with a concave-convex pad is created by forming a concave-convex structure in the dielectric layer under an opening in the wafer, increasing the contact surface area with the solder ball without expanding the pad's footprint, thereby enhancing the bonding force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a traditional flat pad structure is used, then the manufacturing process is simple, but the bonding force between the pad and solder ball is insufficient
Solution Approach 1:
The invention transitions from a two-dimensional flat pad surface to a three-dimensional concave-convex structure. By forming concave portions that extend into the dielectric layer and convex portions on the surface, the pad structure gains vertical dimensionality, increasing the contact surface area with the solder ball from a flat plane to a multi-level surface, thereby enhancing bonding force.
Solution Approach 2:
The pad surface is segmented into multiple concave and convex portions rather than remaining as a single flat surface. This segmentation creates multiple contact zones between the pad and solder ball, distributing the bonding stress across several areas and increasing the overall bonding strength.
2Strength
If the pad surface area is increased to improve bonding force, then the bonding force increases, but the footprint of the pad expands
Solution Approach 1:
Instead of expanding the pad footprint in the horizontal plane, the invention utilizes the vertical dimension by forming concave portions extending into the dielectric layer. This allows the contact surface area to increase without increasing the horizontal footprint, as the additional bonding surface is achieved through vertical depth rather than horizontal expansion.
Solution Approach 2:
The concave portions are nested within the existing pad footprint area, extending downward into the dielectric layer rather than outward at the surface. This nesting approach allows the pad to contain a larger effective bonding surface area within the same horizontal footprint by utilizing the vertical space beneath the original pad boundaries.
Data Source
AI summary
A wafer structure, a method for manufacturing the wafer structure, and a chip structure are provided. In a case that two wafers are bonded together, an opening extending through a substrate of one of the wafers is formed at a back surface of the wafer, and a concave-convex structure is formed in the dielectric layer under the opening. At least one of concave portions of the concave-convex structure extends to expose the interconnection layer of the wafer structure. A pad is formed on the concave-convex structure by filling the concave-convex structure, and the pad has the same concave-convex arrangement as the concave-convex structure. In this way, the pad has a concave-convex surface, such that a contact surface area of the pad is effectively increased without increasing a floor space of the pad.