Backside Structure for BSI Image Sensors with Uniform Dielectric Layer
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Solution Overview
Problem
Conventional BSI image sensor manufacturing processes result in non-uniform buffer oxide thickness over sensor array areas, negatively impacting quantum efficiency, signal-to-noise ratio, and light mean uniformity due to the etch process removing either a portion or all of the buffer oxide layer.
Innovation Solution
A method involving the formation of a bottom antireflective coating (BARC) and a metal shield over the semiconductor substrate, followed by a selective etch process to remove the metal shield and buffer oxide from the sensor array area, with a subsequent re-deposition of a uniform dielectric layer to maintain oxide thickness uniformity across the sensor array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional etch process is used to remove the metal shield from the sensor array area, then the metal shield is successfully removed, but the buffer oxide layer is also removed or becomes non-uniform in thickness
Solution Approach 1:
A bottom antireflective coating (BARC) layer is introduced as an intermediary between the buffer oxide layer and the metal shield. The BARC layer has different etch selectivity compared to the buffer oxide, allowing the metal shield to be removed while the BARC protects the buffer oxide from being etched away. This intermediary layer enables selective removal of the metal shield without damaging the underlying buffer oxide structure.
Solution Approach 2:
The patent modifies the etch process parameters by introducing a multi-step etch sequence with different etch chemistries and conditions. The first etch step removes the metal shield, while subsequent steps are optimized to stop at the BARC layer without penetrating into the buffer oxide. By changing etch selectivity parameters through process optimization, the harmful co-removal of buffer oxide is prevented.
2Ease of manufacture
If the buffer oxide layer is completely removed to expose the sensor array, then subsequent processing can be performed, but quantum efficiency, signal-to-noise ratio, and light mean uniformity are degraded
Solution Approach 1:
The BARC layer serves as a protective intermediary that remains after metal shield removal, preventing direct exposure and damage to the buffer oxide layer. This intermediary layer maintains the protective function of the buffer oxide while still allowing subsequent processing steps to access the sensor array area through controlled openings or thinning of the BARC layer where needed.
Solution Approach 2:
The BARC layer is applied in advance before metal shield removal to establish protective coverage. This preliminary action ensures that when the metal shield is removed, the buffer oxide is already protected, preventing the need for later protective measures and ensuring consistent sensor performance from the outset.
3Manufacturing precision
If a selective etch process is used to remove only the metal shield, then the buffer oxide can be preserved, but the process complexity increases
Solution Approach 1:
The BARC layer acts as a built-in etch stop and protective intermediary that simplifies the selective etch process. Instead of requiring complex process control to selectively etch only the metal shield, the BARC layer provides a clear etch selectivity boundary, making the process more robust and easier to control despite the additional material layer.
Solution Approach 2:
The patent uses a composite structure consisting of multiple layers with different etch selectivities (buffer oxide, BARC, metal shield). This composite material approach allows for selective removal of specific layers through tailored etch processes, achieving high precision buffer oxide preservation while managing process complexity through material property differentiation.
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 ensures uniform dielectric layer thickness over the sensor array, enhancing quantum efficiency, signal-to-noise ratio, and light mean uniformity, while allowing for tuning of the light path for improved image sensor performance.
Implementation Method 1
forming a bottom antireflective coating (BARC) and a metal shield over the semiconductor substrate
Implementation Method 2
followed by a selective etch process to remove the metal shield and buffer oxide from the sensor array area
Implementation Method 3
with a subsequent re-deposition of a uniform dielectric layer to maintain oxide thickness uniformity across the sensor array
Data Source
AI summary
BSI image sensors and methods. In an embodiment, a substrate is provided having a sensor array and a periphery region and having a front side and a back side surface; a bottom anti-reflective coating (BARC) is formed over the back side to a first thickness, over the sensor array region and the periphery region; forming a first dielectric layer over the BARC; a metal shield is formed; selectively removing the metal shield from over the sensor array region; selectively removing the first dielectric layer from over the sensor array region, wherein a portion of the first thickness of the BARC is also removed and a remainder of the first thickness of the BARC remains during the process of selectively removing the first dielectric layer; forming a second dielectric layer over the remainder of the BARC and over the metal shield; and forming a passivation layer over the second dielectric layer.