Multi-Layer UBM Structure for Semiconductor Bump Interface Sealing
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Solution Overview
Problem
The contact interface between bumps and redistribution layers in semiconductor devices is prone to failure due to delamination of the passivation layer, leading to moisture penetration and oxidation, which weakens the interface and can result in device rejection or failure during manufacturing or in the field.
Innovation Solution
A method involving the formation of a multi-layer Under Bump Metallization (UBM) structure around the bump formation area to seal the contact interface between the bumps and the conductive layers, preventing delamination and moisture penetration, thereby enhancing the reliability of the semiconductor device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-layer passivation structure is used, then the manufacturing process is simple, but the contact interface is prone to delamination and moisture penetration
Solution Approach 1:
The UBM structure is divided into multiple functional layers (first UBM layer, second UBM layer, third UBM layer) with each layer serving specific purposes: adhesion, barrier, and sealing functions. This segmentation allows each layer to optimize its specific function rather than requiring a single complex layer to handle all requirements.
Solution Approach 2:
The patent employs composite material structure where different UBM layers with distinct material properties are stacked together. The first UBM layer provides adhesion to the substrate, the second layer provides barrier properties, and the third layer provides sealing around the bump formation area, creating a composite structure that leverages the strengths of each material.
2Reliability
If the passivation layer is removed to expose metal pads for bump formation, then bump connection is enabled, but the contact interface becomes vulnerable to oxidation
Solution Approach 1:
The UBM layers are formed in advance before bump deposition, with the first UBM layer providing initial adhesion, the second layer providing oxidation barrier, and the third layer providing sealing. This preliminary formation of protective layers ensures that when metal pads are exposed for bump formation, the underlying structure is already protected against oxidation and delamination.
Solution Approach 2:
The multi-layer UBM structure acts as an intermediary between the exposed metal pads and the external environment. It provides a transition zone that maintains electrical connection while protecting the sensitive metal-pad-bump interface from oxidation and moisture, without requiring the entire passivation layer to remain intact.
3Reliability
If a multi-layer UBM structure is formed around the bump formation area, then delamination and moisture penetration are prevented, but the manufacturing process becomes more complex
Solution Approach 1:
The manufacturing process is segmented into distinct stages corresponding to each UBM layer formation, allowing for optimized process parameters at each stage. The first UBM layer is formed with adhesion-focused parameters, the second with barrier-focused parameters, and the third with sealing-focused parameters, improving overall process efficiency despite multiple steps.
Solution Approach 2:
The multi-layer UBM structure serves multiple functions simultaneously: electrical conduction, mechanical adhesion, oxidation barrier, and moisture sealing. This multi-functionality consolidates what would otherwise require separate structures or processes, actually improving manufacturing efficiency by combining multiple protective functions into a single integrated UBM system.
Data Source
AI summary
A semiconductor wafer has a first conductive layer formed over its active surface. A first insulating layer is formed over the substrate and first conductive layer. A second conductive layer is formed over the first conductive layer and first insulating layer. A UBM layer is formed around a bump formation area over the second conductive layer. The UBM layer can be two stacked metal layers or three stacked metal layers. The second conductive layer is exposed in the bump formation area. A second insulating layer is formed over the UBM layer and second conductive layer. A portion of the second insulating layer is removed over the bump formation area and a portion of the UBM layer. A bump is formed over the second conductive layer in the bump formation area. The bump contacts the UBM layer to seal a contact interface between the bump and second conductive layer.