Image Pickup Unit Protective Stack for Bonding Interface Reliability
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Solution Overview
Problem
Existing image pickup units with direct-bonded semiconductor devices face reliability issues due to exposed bonding interfaces, which can lead to moisture penetration and reduced performance.
Innovation Solution
The implementation of a multi-layer protective structure covering the bonding interface, comprising an inorganic insulating layer, a metal conductor layer, and an organic solder resist film, which are applied during the manufacturing process of the image pickup unit to prevent exposure and enhance reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the bonding interface is exposed to the cut surface, then the manufacturing process is simpler, but the reliability decreases due to moisture penetration
Solution Approach 1:
The patent applies preliminary action by forming the protective layer covering the bonding interface before the cutting process. The protective layer is deposited on the bonded wafer prior to dicing, so that when the wafer is cut, the bonding interface is already protected and the cut surface automatically exposes the protective layer rather than the vulnerable bonding interface. This resolves the contradiction by preparing the protection in advance, maintaining both manufacturing simplicity and reliability.
Solution Approach 2:
The protective layer serves as an intermediary element between the bonding interface and the external environment. This intermediate layer prevents direct contact between moisture and the bonding interface, thereby maintaining reliability without complicating the manufacturing process. The protective layer mediates the interaction between the sensitive bonding interface and the harsh external environment.
2Reliability
If the bonding interface is covered with protective layers, then the reliability increases, but the device complexity increases
Solution Approach 1:
The patent applies local quality by providing protection only where it is most needed - at the bonding interface between the image pickup device and peripheral circuit device. Rather than protecting the entire device uniformly, the protective layer is specifically positioned to cover the vulnerable bonding interface area. This localized approach increases reliability without unnecessarily complicating the overall device structure.
Solution Approach 2:
The patent utilizes parameter changes by controlling the thickness and material properties of the protective layer. The protective layer is formed with a specific thickness range (50-500 nm) and specific material composition (silicon oxide, silicon nitride, or silicon oxynitride) to provide adequate protection while minimizing added complexity. By optimizing these parameters, the patent achieves reliable protection without excessive structural complexity.
3Ease of manufacture
If a single protective layer is used, then the manufacturing process is simpler, but the protection against multiple harmful factors is insufficient
Solution Approach 1:
The patent applies composite materials by using multiple layers of different protective materials (silicon oxide, silicon nitride, and silicon oxynitride) with distinct properties. Each material provides different protective characteristics - silicon oxide offers good adhesion and basic protection, silicon nitride provides excellent moisture barrier properties, and silicon oxynitride offers complementary protection. This composite structure enhances protection against multiple harmful factors including moisture, corrosion, and mechanical stress, while the layered deposition process using standard semiconductor techniques keeps manufacturing complexity manageable.
Data Source
AI summary
An image pickup unit includes: a bonded device provided with a light receiving surface, an undersurface, and four side faces, the bonded device including a light receiving element provided with a light receiving circuit, and a circuit element provided with a peripheral circuit and direct-bonded to the light receiving element; a first protective layer covering the four side faces, the first protective layer being made of an inorganic material; a second protective layer covering the first protective layer, the second protective layer being made of metal; and a third protective layer covering the second protective layer, the third protective layer being made of an organic material.