Backside Illumination Image Sensor Dark Level Uniformity
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Solution Overview
Problem
In backside illumination CMOS image sensors, the difference in dark levels between light-receiving and light-shielding regions is significant due to defects at the interface between the insulating layer and the semiconductor layer, which is not effectively addressed by existing hydrogen alloy or UV processes, leading to image quality degradation.
Innovation Solution
The introduction of a potential drain region in the light-shielding region to accumulate and drain electrons generated by defects, along with a barrier region to extinguish excess electrons, and electron adjustment paths to manage electron flow, reducing the dark level difference between regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a light-shielding pattern is used in BSI CMOS image sensors, then light-shielding regions are defined, but the efficiency of hydrogen alloy or UV processes is lowered due to the light-shielding pattern, increasing the difference between dark levels of light-receiving and light-shielding regions
Solution Approach 1:
The light-shielding region is segmented into multiple potential drain regions with different potentials, allowing selective electron drainage. This segmentation enables the light-shielding pattern to maintain its light-blocking function while creating localized zones that can effectively manage defect-generated electrons without requiring uniform process treatment across the entire light-shielding region.
Solution Approach 2:
Potential drain regions act as intermediary structures between the light-shielding pattern and the photoelectric conversion devices. These intermediary regions capture and drain electrons generated by interface defects, mediating the harmful effect of the light-shielding pattern on process efficiency while maintaining dark level uniformity across the image sensor.
2Reliability
If hydrogen alloy or UV processes are used to fix dangling bonds and interface defects, then image quality is improved, but the efficiency is lowered in light-shielding regions due to the light-shielding pattern
Solution Approach 1:
Potential drain regions are formed in advance during the manufacturing process to preemptively address the efficiency problem caused by light-shielding patterns. By pre-configuring these electron-draining structures, the patent ensures that even when hydrogen alloy or UV processes have reduced efficiency in light-shielding regions, defect-generated electrons are still effectively managed, maintaining image quality without requiring perfectly efficient process treatment.
3Reliability
If the difference between dark levels of light-receiving and light-shielding regions is reduced, then image quality is enhanced, but additional structures (potential drain regions, barrier regions) are required
Solution Approach 1:
The patent merges multiple functions into the potential drain regions: they serve as both electron accumulation zones and electron drainage pathways. By combining these functions in a single structure rather than using separate components, the patent reduces overall device complexity while still achieving the goal of reducing dark level differences and enhancing image quality.
Solution Approach 2:
Rather than uniformly treating the entire light-shielding region, the patent applies local quality by creating potential drain regions with specific potentials only where needed. This localized approach allows the patent to address dark level differences in critical areas without adding complexity to the entire device structure, maintaining simplicity while improving image quality.
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 configuration effectively reduces the dark level difference between light-receiving and light-shielding regions, enhancing image quality by addressing defect-related noise and improving sensitivity and color accuracy.
Implementation Method 1
a potential drain region formed in the semiconductor layer adjacent to an interface between the semiconductor layer and the insulating layer in the light-shielding region, wherein electrons generated due to defects occurring at the interface are accumulated in the potential drain region
Implementation Method 2
a barrier region formed in the semiconductor layer adjacent to the potential drain region in the light-shielding region, wherein the barrier region is configured to extinguish electrons in the potential drain region
Data Source
AI summary
An image sensor including a semiconductor layer including a plurality of unit pixels each including a photoelectric conversion device and read devices; and an insulating layer including a light-shielding pattern defining a light-receiving region and a light-shielding region of the semiconductor layer, the insulating layer covering one surface of the semiconductor layer. The semiconductor layer further includes a potential drain region formed adjacent to an interface between the semiconductor layer and an insulating layer in the light-shielding region, wherein electrons generated due to defects occurring at the interface are accumulated in the potential drain region. At least one of the unit pixels in the light-shielding region provides a drain path for draining the electrons accumulated in the potential drain region.