Backside Illumination Image Sensor Pad Structure
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Solution Overview
Problem
Conventional bond structures for backside illumination image sensor chips suffer from film peeling during ball shearing tests due to inferior adhesion between the metal pad and the underlying etch stop layer, typically silicon carbide, leading to delamination.
Innovation Solution
A pad structure is formed with a glue layer and a metal layer that includes a first portion electrically connected to the metal pad, a second portion for bonding, and a third portion interconnecting the first and second portions, where the bonding is performed to a non-low-k dielectric material, enhancing adhesion and reducing the likelihood of film delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a metal pad is bonded directly to an etch stop layer (silicon carbide), then the bonding process is simple, but the adhesion is inferior causing film peeling and delamination
Solution Approach 1:
A glue layer is introduced as an intermediary between the metal pad and the etch stop layer. This glue layer serves as a mediator that improves adhesion between the two layers, preventing film peeling and delamination while maintaining the simplicity of the bonding process. The glue layer is specifically designed to bond well with both the metal pad and the silicon carbide etch stop layer.
Solution Approach 2:
The bond structure is transformed from a simple two-layer configuration (metal pad on etch stop layer) to a composite multi-layer structure including the glue layer. This composite structure combines materials with complementary properties: the metal pad provides electrical conductivity, the glue layer provides adhesion, and the etch stop layer provides mechanical support and etch resistance, resulting in improved overall reliability.
2Device complexity
If the metal pad is directly bonded to the etch stop layer, then the structure is simple, but film peeling occurs during ball shearing tests
Solution Approach 1:
The glue layer acts as a mediator that enhances bond strength during ball shearing tests. It distributes mechanical stresses more effectively across the interface between the metal pad and etch stop layer, preventing film peeling while adding minimal complexity to the overall bond structure.
3Ease of manufacture
If bonding is performed to the etch stop layer, then the process is straightforward, but delamination occurs due to inferior adhesion
Solution Approach 1:
The glue layer serves as a stabilizing intermediary that maintains structural integrity and prevents delamination. It is specifically formulated to provide strong adhesion to both the metal pad and etch stop layer, ensuring long-term stability of the bond structure without complicating the manufacturing process.
Solution Approach 2:
The introduction of the glue layer changes the interfacial parameters between the metal pad and etch stop layer. The glue layer has optimized chemical and physical properties that enhance adhesion strength and structural stability, transforming the interface from a delamination-prone configuration to a stable, delamination-resistant structure.
Data Source
AI summary
An image sensor device includes a semiconductor substrate having a front side and a backside. A first dielectric layer is on the front side of the semiconductor substrate. A metal pad is in the first dielectric layer. A second dielectric layer is over the first dielectric layer and on the front side of the semiconductor substrate. An opening penetrates through the semiconductor substrate from the backside of the semiconductor substrate, wherein the opening includes a first portion extending to expose a portion of the metal pad and a second portion extending to expose a portion of the second dielectric layer. A metal layer is formed in the first portion and the second portion of the opening.