Copper Interconnection Oxidation Prevention in CMOS Image Sensors
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Solution Overview
Problem
The increasing number of pixels in CMOS image sensors reduces pixel size, limiting the size of micro-lenses and metal interconnection layers, which can lead to oxidation and reliability issues with copper interconnections, affecting image sensor sensitivity and quality.
Innovation Solution
A semiconductor device with a metal interconnection structure that includes a copper seed layer, copper layer, spacers formed from Ta or TaN to prevent oxidation, and a diffusion barrier of CoWx to inhibit copper diffusion, enhancing the reliability and image quality by improving refractive index and transmittance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of pixels is increased, then the pixel density and image quality are improved, but the pixel size is reduced which limits the micro-lens size and metal interconnection size
Solution Approach 1:
The patent segments the metal interconnection structure into multiple functional layers: a copper seed layer, a copper layer for low resistance, a diffusion barrier layer to prevent oxidation and diffusion, and spacers for structural support. This segmentation allows each layer to perform its specific function optimally within the reduced pixel size constraints.
Solution Approach 2:
The patent employs composite material structure by combining multiple materials in the interconnection system: copper (for conductivity), Ta or TaN (for diffusion barrier and spacer), and CoWx (for oxidation prevention). This composite approach enables the small-sized interconnection to maintain both electrical performance and structural reliability.
2Area of stationary object
If the metal interconnection size is reduced to match smaller pixels, then the pixel area is enlarged, but the copper interconnection is more prone to oxidation and reliability issues
Solution Approach 1:
The patent applies preliminary protective actions by forming the diffusion barrier layer and spacers before the copper interconnection is exposed to oxidizing environments. The diffusion barrier layer is deposited on the copper layer to prevent oxidation, and spacers are formed to protect sidewalls, ensuring the copper remains protected throughout subsequent processing steps.
Solution Approach 2:
The diffusion barrier layer acts as an intermediary between the copper interconnection and the oxidizing environment. Materials like Ta or TaN serve as mediators that prevent direct contact between copper and oxygen, while CoWx provides an additional intermediary layer specifically for oxidation prevention, thereby protecting the copper without requiring direct exposure control.
3Reliability
If a diffusion barrier is formed on the metal interconnection, then copper oxidation is prevented, but the manufacturing process complexity increases
Solution Approach 1:
The patent merges multiple protective functions into a unified interconnection structure. The diffusion barrier layer simultaneously serves as an oxidation barrier, a diffusion barrier, and part of the adhesion system. The spacers are formed to provide both structural support and protection during subsequent etching processes, reducing the need for separate protective measures.
Solution Approach 2:
The patent utilizes parameter changes in the form of material selection and layer thickness optimization to achieve protection with minimal process complexity. By selecting materials with appropriate properties (Ta/TaN for diffusion barrier, CoWx for oxidation prevention) and optimizing layer thicknesses, the patent achieves reliable protection without requiring excessive process steps.
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
The solution improves the reliability and sensitivity of CMOS image sensors by reducing focal length and preventing copper oxidation, thereby enhancing image quality and reducing defects caused by misalignment.
Implementation Method 1
preventing copper oxidation
Implementation Method 2
inhibit copper diffusion
Data Source
AI summary
A metal interconnection of semiconductor device and method for fabricating the same is provided. The semiconductor device can include a semiconductor substrate formed with device structures such as transistors. An interlayer dielectric layer can be formed on the semiconductor substrate with a metal interconnection formed therethrough. A spacer can be formed on at least a portion of a sidewall of the metal interconnection. A diffusion barrier can be formed on an upper surface of the metal interconnection.