BSI Image Sensor Stress-Adjusting Layers to Prevent Cracks
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Solution Overview
Problem
Backside illuminated (BSI) image sensors face reliability issues due to residual stress buildup in the stack of layers, leading to cracks and peeling, which compromises device performance.
Innovation Solution
Incorporating stress adjusting layers within the pixel region and other areas of BSI image sensors to counteract residual stress, using materials like silicon-rich oxide layers with specific silicon-to-oxygen ratios and graded profiles to induce compressive or tensile stress, thereby relaxing residual stress and preventing cracks and peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple layers are stacked in BSI image sensors to enhance functionality, then device performance is improved, but residual stress buildup increases causing cracks and peeling
Solution Approach 1:
A stress adjusting layer is introduced as an intermediary between the substrate and the stack of layers. This layer acts as a mediator to counteract residual stress buildup, preventing cracks and peeling while allowing the multi-layer structure to maintain its enhanced functionality. The stress adjusting layer includes a first portion and a second portion with different stress characteristics to manage stress in different regions of the device.
Solution Approach 2:
The stress adjusting layer utilizes changes in material composition and structure to alter stress parameters. By controlling the silicon-to-oxygen ratio and creating graded profiles in the stress adjusting layer, the device can adjust stress characteristics to counteract residual stress from the stacked layers, maintaining reliability while preserving functionality.
2Reliability
If stress adjusting layers are added to counteract residual stress, then device reliability is improved, but device complexity increases
Solution Approach 1:
The stress adjusting layer is segmented into a first portion and a second portion, each positioned at different locations relative to the pixel region. This segmentation allows stress management to be targeted specifically where needed, rather than requiring a uniform complex structure across the entire device. The first portion is positioned closer to the pixel region while the second portion is positioned farther away, enabling localized stress control.
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 use of stress adjusting layers increases device reliability by 40% to 50% by effectively managing stress within the sensor stack, enhancing the structural integrity and performance of BSI image sensors.
Implementation Method 1
The stress adjusting layer is configured to induce stress to counteract the residual stress within the stack of layers
Data Source
AI summary
An image sensor with stress adjusting layers and a method of fabrication the image sensor are disclosed. The image sensor includes a substrate with a front side surface and a back side surface opposite to the front side surface, an anti-reflective coating (ARC) layer disposed on the back side surface of the substrate, a dielectric layer disposed on the ARC layer, a metal layer disposed on the dielectric layer, and a stress adjusting layer disposed on the metal layer. The stress adjusting layer includes a silicon-rich oxide layer. The concentration profiles of silicon and oxygen atoms in the stress adjusting layer are non-overlapping and different from each other. The image sensor further includes oxide grid structure disposed on the stress adjusting layer.