Multiple Metal Film Stack for BSI Image Sensor Shielding
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Solution Overview
Problem
The formation of metal shields and backside metal pads in Backside Illumination (BSI) image sensor chips can damage or degrade the image sensors due to the deposition and etching processes, particularly when using plasma, which affects the accuracy of electrical signal calibration by introducing non-optically generated signals.
Innovation Solution
A multiple metal film scheme is employed to form a metal shield and backside metal pad, where a first conductive layer is used to form a metal pad and a second conductive layer is used to form a metal shield, with a patterning process that protects the image sensors from damage by plasma, allowing for precise calibration and reduction in step heights for subsequent processes like micro-lenses and color filters formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If plasma deposition and etching steps are used to form metal shield and backside metal pads, then the metal structures can be formed with good conductivity and adhesion, but the image sensors are damaged or degraded
Solution Approach 1:
The patent segments the metal formation process into separate steps for different regions. A first metal layer is deposited and patterned to form the metal shield in the black reference pixel region, then a second metal layer is deposited and patterned to form backside metal pads in non-pixel regions. This segmentation allows selective plasma exposure, protecting image sensors during critical deposition and etching operations while still achieving the necessary metal structures for shielding and bonding.
2Measurement precision
If black reference image sensors are covered by metal shield to block light, then non-optically generated signals can be measured accurately, but the image sensors are exposed to plasma damage during metal shield formation
Solution Approach 1:
The patent performs preliminary actions to protect image sensors before plasma deposition and etching steps. A protective layer is formed over the image sensors prior to metal shield formation, and the metal shield is formed in the black reference pixel region with controlled plasma exposure. This preliminary protection allows accurate measurement of non-optically generated signals while preventing plasma damage to the image sensors.
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 effectively prevents damage to image sensors during metal shield and backside metal pad formation, enhances signal calibration by reducing non-optically generated signals, and simplifies the formation of micro-lenses and color filters by minimizing step heights, leading to improved image sensor performance.
Implementation Method 1
The deposition steps and the etch steps may be performed using plasma.
Implementation Method 2
The deposition steps and the etch steps may be performed using plasma.
Data Source
AI summary
A device includes a semiconductor substrate, a black reference circuit in the semiconductor substrate, a metal pad on a front side of, and underlying, the semiconductor substrate, and a first and a second conductive layer. The first conductive layer includes a first portion penetrating through the semiconductor substrate to connect to the metal pad, and a second portion forming a metal shield on a backside of the semiconductor substrate. The metal shield is aligned to the black reference circuit, and the first portion and the second portion are interconnected to form a continuous region. The second conductive layer includes a portion over and contacting the first portion of the first conductive layer, wherein the first portion of the first conductive layer and the portion of the second conductive layer form a first metal pad. A dielectric layer is overlying and contacting the second portion of the first conductive layer.