Offset UBM Layer Structure to Prevent Solder-Induced Delamination
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Solution Overview
Problem
Existing semiconductor package structures and fabrication methods face challenges in achieving reliable adhesion between metal layers and underfill layers, leading to delamination issues due to the formation of intermetallic compounds and poor adhesion, which affects the overall reliability of the semiconductor structure.
Innovation Solution
The implementation of an under bump metallurgy (UBM) structure with a specific layer configuration, where the third metal layer has a sidewall laterally offset from the second metal layer, creating a buffer region to prevent solder from wetting the sidewalls of the second metal layer, and optionally incorporating a blocking structure to further enhance adhesion, thereby preventing delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional UBM structure with aligned metal layers is used, then the fabrication process is simpler, but adhesion between metal layers and underfill layers deteriorates due to intermetallic compound formation and delamination
Solution Approach 1:
The patent applies asymmetry by configuring the third metal layer with a sidewall that is laterally offset inwardly from the sidewalls of the first and second metal layers. This asymmetric configuration creates a buffer region that prevents solder from wetting the sidewalls of the second metal layer, thereby preventing intermetallic compound formation and improving adhesion between the UBM structure and the underfill layer.
Solution Approach 2:
The buffer region created by the laterally offset third metal layer acts as an intermediary between the second metal layer and the solder. This buffer region prevents direct contact between solder and the second metal layer sidewalls, eliminating the harmful intermetallic compound formation at the interface and improving overall structural adhesion.
2Reliability
If the third metal layer sidewall is laterally offset to create a buffer region, then adhesion and reliability improve, but the device complexity increases
Solution Approach 1:
The UBM structure is segmented into multiple metal layers (first, second, and third metal layers) with distinct functions. The third metal layer is specifically segmented with a laterally offset sidewall configuration to create the buffer region. This segmentation allows each layer to perform its specific function while maintaining overall structural integrity and adhesion.
3Ease of manufacture
If solder is allowed to wet the sidewalls of the second metal layer, then the filling process is simpler, but intermetallic compounds form causing delamination
Solution Approach 1:
The buffer region created by the laterally offset third metal layer sidewall performs preliminary anti-action by preventing solder from wetting the second metal layer sidewalls before the harmful intermetallic compound formation can occur. This preventive configuration eliminates the need for additional process steps to control solder wetting while avoiding delamination.
Data Source
AI summary
Provided are a semiconductor structure and a method of forming the same. The semiconductor structure includes: a substrate, an under bump metallurgy (UBM) structure, and a solder. The UBM structure is disposed over the substrate. The UBM structure includes a first metal layer; a second metal layer disposed on the first metal layer; and a third metal layer disposed on the second metal layer. A sidewall of the first metal layer is substantially aligned with a sidewall of the second metal layer, and a sidewall of the third metal layer is laterally offset inwardly from the sidewalls of the first and second metal layers. The solder is disposed on the third metal layer.