Backside Illumination Trench Isolation for Noise Reduction
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Solution Overview
Problem
Backside illuminated image sensors face challenges with increased capacitive coupling between deep well isolation structures and bond pads, leading to reduced noise isolation and high-frequency performance.
Innovation Solution
The implementation of trench isolation regions in the image sensor substrate, which electrically isolates digital control circuitry from analog circuitry and bond pads, using a common silicon etch step to form islands of silicon and reduce coupling capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If backside illuminated image sensors are used, then light reception efficiency is improved, but capacitive coupling between deep well isolation structures and bond pads increases
Solution Approach 1:
The substrate is segmented into isolated regions using deep well isolation structures that create electrically separate zones. This segmentation prevents capacitive coupling between adjacent circuit elements while maintaining the backside illuminated architecture for improved light reception.
Solution Approach 2:
Deep well isolation structures serve as intermediary elements between bond pads and active substrate regions. These isolation structures act as electrical mediators that reduce unwanted capacitive coupling while allowing the backside illuminated design to function effectively.
2Reliability
If deep well isolation structures are used in backside illuminated sensors, then circuit isolation is attempted, but effectiveness is reduced due to increased capacitive coupling
Solution Approach 1:
The substrate is divided into electrically isolated segments using deep well isolation structures. This segmentation creates distinct electrical zones that prevent signal interference and maintain circuit isolation effectiveness despite the thin substrate in backside illuminated sensors.
Solution Approach 2:
The electrical parameters of the substrate are modified by introducing deep well isolation structures that change the capacitive coupling characteristics. This parameter change enables effective circuit isolation in the backside illuminated configuration where the thin substrate would otherwise create excessive coupling.
3Ease of manufacture
If bond pads are placed on thin substrate, then connection is simplified, but capacitive coupling to active substrate increases
Solution Approach 1:
Deep well isolation structures are positioned between bond pads and the active substrate to serve as intermediary elements. These structures reduce the direct capacitive coupling pathway while maintaining the simplified connection architecture of backside illuminated sensors.
Solution Approach 2:
The substrate is segmented to create isolated regions around bond pads using deep well isolation structures. This segmentation reduces the effective capacitive coupling area between bond pads and active substrate while maintaining ease of manufacture.
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 improves noise isolation and high-frequency performance by reducing capacitive coupling, maintaining process complexity and cost without additional masking steps.
Implementation Method 1
an etch step to form trenches and conductive via openings in the substrate and intermetal dielectric
Implementation Method 2
the relatively thin semiconductor substrate can increase the capacitive coupling between deep well isolation structures as well as increasing the capacitive coupling between bond pads on the chip and the active substrate
Data Source
AI summary
An image sensor such as a backside illumination image sensor may be provided with analog circuitry, digital circuitry, and an image pixel array on a semiconductor substrate. Trench isolation structures may separate the analog circuitry from the digital circuitry on the substrate. The trench isolation structures may be formed from dielectric-filled trenches in the substrate that isolate the portion of the substrate having the analog circuitry from the portion of the substrate having the digital circuitry. The trench isolation structures may prevent digital circuit operations such as switching operations from negatively affecting the performance of the analog circuitry. Additional trench isolation structures may be interposed between portions of the substrate on which bond pads are formed and other portions of the substrate to prevent capacitive coupling between the bond pad structures and the substrate, thereby enhancing the high frequency operations of the image sensor.