Test Key Transistor Detection of Deep Trench Isolation Depth
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Solution Overview
Problem
Current semiconductor devices lack a reliable and efficient method to determine the depth of deep trench isolations (DTIs) during manufacturing or operation, which is crucial for ensuring effective electrical and optical isolation between pixels in CMOS image sensors.
Innovation Solution
The implementation of JFET-like test key transistors with specific preset source-drain voltage differences, gate voltages, and predetermined currents allows for the detection of DTI depths by measuring current flow through the transistors, determining if the DTIs encroach at the intended depth, and identifying defects if the depth is insufficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep trench isolation is used to suppress electrical and optical crosswalks, then isolation effectiveness is improved, but manufacturing complexity increases due to the need for precise depth control
Solution Approach 1:
The patent applies preliminary action by incorporating a test key transistor into the device structure during manufacturing, which is pre-configured with specific dimensions and electrical characteristics. This test structure enables subsequent depth verification without requiring additional manufacturing steps, thus resolving the contradiction between achieving reliable isolation and managing manufacturing complexity
Solution Approach 2:
The patent implements feedback by measuring the electrical characteristics (threshold voltage, drain current) of the test key transistor and comparing them against predetermined values that correspond to the required DTI depth. This feedback mechanism provides quantitative verification of isolation effectiveness while maintaining straightforward manufacturing procedures
2Reliability
If DTI depth is increased to improve isolation between pixels, then crosswalk suppression is enhanced, but measurement difficulty increases due to lack of efficient detection methods
Solution Approach 1:
The patent introduces an intermediary element - the test key transistor - whose electrical characteristics serve as a mediator between the physical DTI depth and measurable electrical parameters. By measuring threshold voltage and drain current of this intermediary structure, the actual DTI depth can be indirectly determined, resolving the measurement difficulty while ensuring adequate crosswalk suppression
Solution Approach 2:
The patent replaces mechanical or physical measurement methods with electrical measurement techniques. Instead of using physical probes or optical methods to measure DTI depth, the invention uses electrical characteristics (current-voltage relationships) of the test key transistor to infer depth, thereby simplifying the measurement process and enabling efficient detection
3Measurement precision
If test key transistor is designed with precise specifications, then measurement precision is improved, but device complexity increases due to additional structures
Solution Approach 1:
The patent applies local quality by designing the test key transistor with specific, localized characteristics (certain width, length, and doping profiles) that are optimized for depth measurement functionality. This localized specialization enables precise depth detection without requiring the entire device structure to be complex, as only the test key region has enhanced features
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 method enables accurate detection of DTI depths, ensuring effective isolation between pixels and preventing electrical and optical crosstalk, thereby enhancing the performance and reliability of CMOS image sensors.
Implementation Method 1
the test key transistor is configured to generate a current within a threshold difference from the predetermined current in the channel in response to receiving the preset gate voltage at the gate and the preset source-drain voltage difference at the source and the drain
Data Source
AI summary
This application describes systems and methods for detecting depth in deep trench isolation with semiconductor devices using test key transistors. An example semiconductor device comprises a test key transistor comprising a source, a drain, a channel connected to the source and the drain, and a gate; and a deep trench isolation encroaching into the channel of the test key transistor, wherein: the test key transistor is associated with a specification including a preset gate voltage, a preset source-drain voltage difference, and a predetermined current, and the test key transistor is configured to generate a current within a threshold difference from the predetermined current in the channel in response to receiving the preset gate voltage at the gate and the preset source-drain voltage difference at the source and the drain, and the deep trench isolation encroaches into the channel at a preset depth.