Backside Illuminated Image Sensor Light-Blocking Pattern
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Solution Overview
Problem
Backside illuminated image sensors face challenges with light loss and crosstalk due to the difficulty in etching tungsten light-blocking patterns, which limits their thickness and increases reflection on side surfaces.
Innovation Solution
A backside illuminated image sensor design featuring a light-blocking pattern with a width decreasing toward the substrate surface, formed using a damascene process with a metal material, and including diffusion barrier layers to reduce light reflection and enhance crosstalk reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a tungsten light-blocking pattern is formed by etching, then the light-blocking pattern can be created, but the thickness is limited and light reflection on side surfaces increases
Solution Approach 1:
Instead of forming the light-blocking pattern by etching away material to create cavities, the patent inverts the approach by depositing tungsten material to build up the light-blocking pattern. This damascene process fills recesses with tungsten, creating a positive relief structure rather than a negative cavity structure, thereby eliminating etching limitations on thickness.
Solution Approach 2:
The patent changes the formation parameter from etching (removal process) to deposition (addition process). By using tungsten deposition instead of etching, the thickness parameter of the light-blocking pattern can be increased without being constrained by etching depth limitations, and the side surface angle can be optimized to reduce light reflection.
2Object-generated harmful factors
If the thickness of the light-blocking pattern is increased, then crosstalk reduction is improved, but light reflection on side surfaces increases
Solution Approach 1:
The patent applies different properties to different parts of the light-blocking pattern. The top surface is optimized for light blocking, while the side surfaces are engineered with specific angles and covered with diffusion barrier layers to minimize light reflection. This local optimization allows thick patterns that effectively block crosstalk while maintaining low reflection losses.
Solution Approach 2:
The patent introduces diffusion barrier layers as intermediary materials between the tungsten light-blocking pattern and the surrounding environment. These barrier layers serve as mediators that prevent light reflection from the tungsten side surfaces, allowing the pattern to be made thicker for better crosstalk reduction without suffering from increased reflection losses.
3Ease of manufacture
If the light-blocking pattern has a positive slope on side surfaces, then etching is easier, but light reflection increases and crosstalk reduction is limited
Solution Approach 1:
The patent inverts the conventional etching approach by using a deposition-based damascene process. Instead of creating a positive slope through etching limitations, the tungsten is deposited to fill recesses, allowing the side surfaces to be formed with optimal angles for minimizing light reflection while achieving the necessary thickness for effective crosstalk reduction.
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
Significantly reduces light loss and crosstalk by minimizing light reflection on the side surfaces of the light-blocking pattern, while allowing for increased thickness and improved crosstalk reduction.
Implementation Method 1
an anti-reflective layer disposed on a backside surface of the substrate
Implementation Method 2
a light-blocking pattern disposed on the anti-reflective layer and having openings corresponding to the pixel regions
Implementation Method 3
a color filter layer disposed on the light-blocking pattern
Implementation Method 4
a micro lens array disposed on the color filter layer
Data Source
AI summary
A backside illuminated image sensor includes pixel regions disposed in a substrate, an anti-reflective layer disposed on a backside surface of the substrate, a light-blocking pattern disposed on the anti-reflective layer and having openings corresponding to the pixel regions, a color filter layer disposed on the light-blocking pattern, and a micro lens array disposed on the color filter layer, wherein the light-blocking pattern has a width decreasing toward the backside surface of the substrate.