Image Sensor Bond Pad Structure for Wire Bonding Strength
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Solution Overview
Problem
The thin metal layer in CMOS image sensors results in weak bonding strength and open circuits during wire bonding, affecting the reliability and yield of the packaging process.
Innovation Solution
A novel bonding pad structure is created by forming a substrate with a first metal layer, a passivation layer, and a second metal layer that fills the opening in the passivation layer, increasing the thickness of the bonding pad to enhance compressive strength and reliability without compromising light absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the metal layer is made thin to increase light absorption, then light absorption is improved, but bonding strength deteriorates
Solution Approach 1:
The patent transitions from a single-layer thin metal structure to a multi-layer vertical structure. The bonding pad evolves from a simple thin metal layer to a composite structure with first metal layer, passivation layer with opening, and second metal layer filling the opening, creating a three-dimensional configuration that simultaneously achieves light absorption and bonding strength
Solution Approach 2:
The bonding pad structure combines multiple materials with different properties: the first metal layer (aluminum) for electrical connection and light absorption, the passivation layer (silicon oxide and silicon nitride) for protection and structural support, and the second metal layer for enhanced bonding surface. This composite structure resolves the contradiction between thinness for light absorption and thickness for bonding strength
2Illumination intensity
If the metal layer is made thin to increase light absorption, then light absorption is improved, but reliability deteriorates
Solution Approach 1:
The patent creates a vertical multi-layer structure that adds depth dimension to the bonding pad. The opening in the passivation layer extending to the first metal layer, filled with second metal layer, creates a recessed bonding surface that improves reliability without compromising the thin profile needed for light absorption
Solution Approach 2:
The passivation layer acts as an intermediary between the first metal layer and the external environment. It provides protection while its opening filled with second metal layer creates an optimized bonding interface, mediating between the need for thin structure and the need for reliable bonding
Data Source
AI summary
A method for manufacturing a bond pad structure includes providing a substrate structure including a substrate, a first metal layer on the substrate, and a passivation layer on the first metal layer, the passivation layer having an opening extending to the first metal layer; and filling the opening of the passivation layer with a second metal layer. The bond pad structure has a significantly increased thickness compared with the thickness of the exposed portion of the first metal layer in the opening, thereby ensuring wire bonding reliability and yield.