Backside Illuminated Image Sensor Bonding via Buffer Layer
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Solution Overview
Problem
The challenge in fabricating backside illuminated image sensors is the generation of voids during the bonding of oxide and silicon wafers due to the rough and hydrophobic nature of the oxide surface, leading to poor bonding stability and transmission inefficiencies.
Innovation Solution
A method involving the formation of a semiconductor device with specific insulating layers, including a filling insulating layer, a buffer insulating layer, and a capping insulating layer, where the capping insulating layer is denser than the buffer insulating layer, and the use of HDP oxide and PE-TEOS oxide materials, along with nitrogen plasma treatment, to enhance bonding stability and reduce voids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If oxide and silicon wafers are bonded together directly, then the bonding process is simple, but voids are generated in the surface of the oxide due to the rough and hydrophobic nature of the oxide surface, resulting in poor bonding stability
Solution Approach 1:
The patent introduces an intermediary layer (buffer insulating layer comprising PE-TEOS oxide) between the oxide wafer and silicon wafer to mediate the bonding process. This intermediary layer has intermediate surface properties that facilitate better adhesion between the hydrophobic oxide surface and the silicon wafer, preventing void formation while maintaining process simplicity
Solution Approach 2:
The patent changes the surface parameters of the oxide wafer by forming a buffer insulating layer with different material composition (PE-TEOS oxide) and surface characteristics. This parameter change transforms the rough, hydrophobic oxide surface into a surface with improved wettability and adhesion properties, enabling stable bonding without compromising ease of manufacture
2Reliability
If a buffer insulating layer softer than the filling insulating layer is formed on the filling insulating layer, then bonding stability is improved, but the device structure becomes more complex
Solution Approach 1:
The patent applies local quality by creating a buffer insulating layer with specific local properties (softer material composition of PE-TEOS oxide) only at the bonding interface where improved adhesion is needed. The filling insulating layer (HDP oxide) maintains its original harder properties in non-bonding regions, thus improving bonding stability without unnecessarily complicating the entire device structure
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the physical stability and bonding strength of the substrates, reduces voids at the interface, and enhances the light receiving efficiency of the image sensor by ensuring a more stable and efficient bonding process.
Implementation Method 1
forming a buffer insulating layer softer than the filling insulating layer on the filling insulating layer
Implementation Method 2
forming a capping insulating layer denser than the buffer insulating layer on the buffer insulating layer
Implementation Method 3
applying a nitrogen plasma treatment to the surface of the second substrate before bonding the first substrate to the second substrate
Data Source
AI summary
Provided is a semiconductor device having a backside illuminated image sensor and a method of forming same. The method includes providing a first substrate and a second substrate, forming metal interconnections on a first surface of the first substrate, forming a filling insulating layer filling spaces between sides of the metal interconnections and covering upper surfaces of the metal interconnections, forming a buffer insulating layer softer than the filling insulating layer on the filling insulating layer, forming a capping insulating layer denser than the buffer insulating layer on the buffer insulating layer, and bonding a surface of the capping insulating layer to a surface of the second substrate.