Backside Trench Isolation Structure for CMOS Image Sensor Defects
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Solution Overview
Problem
The formation of sharp angles and protrusions during semiconductor substrate etching can lead to issues such as dark current and white pixel defects in CMOS image sensors, and the trapezoidal trench cross-section makes it challenging to insert passivation and isolation structures effectively.
Innovation Solution
An additional etching process is employed to enlarge the trench near the backside of the semiconductor substrate, removing sharp angles and facilitating the insertion of passivation and isolation structures, while using a hard mask to protect the substrate during etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If standard etching process is used to form trench, then trench is formed with sufficient depth, but sharp angles and protrusions are created causing dark current and white pixel defects
Solution Approach 1:
A hard mask layer is deposited on the front surface of the substrate before the etching process. This preliminary action protects the front surface and prevents the formation of sharp angles and protrusions that would otherwise cause dark current and white pixel defects during etching.
Solution Approach 2:
The hard mask layer acts as an intermediary between the etching process and the substrate. It mediates the etching process by controlling the etching front and preventing direct contact between the etchant and the front surface, thereby eliminating the harmful sharp angles and protrusions.
2Productivity
If standard etching process is used, then etching is completed efficiently, but trapezoidal trench cross-section is formed making insertion of passivation and isolation structures difficult
Solution Approach 1:
The hard mask layer is deposited in advance to control the etching process. This preliminary action ensures that the trench maintains a substantially rectangular cross-section throughout etching, making it easy to insert passivation and isolation structures without requiring complex additional processing.
3Length of stationary object
If etching continues to sufficient depth, then trench depth requirement is met, but sharp corners are formed around the trench
Solution Approach 1:
The hard mask layer is applied before etching to protect the substrate and control the etching front. This preliminary action prevents the formation of sharp corners around the trench by maintaining a uniform etching process that progresses evenly through the substrate depth.
Solution Approach 2:
The hard mask layer serves as an intermediary that controls the interaction between the etchant and the substrate. It prevents the etchant from creating sharp corners by providing a controlled interface that maintains a substantially rectangular trench cross-section throughout the etching process.
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 reduces dark current and white pixel defects by ensuring smooth insertion of passivation and isolation structures, enhancing electrical isolation and device performance.
Implementation Method 1
a trench is formed from a first side of a substrate; The substrate is thinned from a second side of the substrate opposite the first side; An etching process is then performed on the substrate to expose the sacrificial layer from the second side of the substrate
Implementation Method 2
using a hard mask to protect the substrate during etching
Implementation Method 3
A passivation structure is then formed to cover the second side of the substrate and extend from the second side of the substrate to the etching stop structure within the trench along a sidewall of the trench
Data Source
AI summary
A semiconductor device and a manufacturing method thereof are provided. The semiconductor device includes a substrate, an etching stop structure, a passivation structure and an isolation structure. The etching stop structure is embedded in a front side of the substrate. The passivation structure is covering a backside of the substrate, and extending from the backside of the substrate to the etching stop structure within a trench of the substrate. The isolation structure is embedded in the trench of the substrate from the backside of the substrate. The passivation structure is located between the etching stop structure and of the isolation structure. The isolation structure has a first sidewall and a second sidewall unparallel to the first sidewall. The first sidewall is located between the second sidewall and a bottom surface of the isolation structure.