Front-End-of-Line Cavity for Ion-Sensitive Transistor Sensors
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Solution Overview
Problem
The existing methods for integrating ion-sensitive field effect transistors as sensors in semiconductor devices are costly due to the need for large modifications in the back-end-of-line structure to accommodate solution-receiving cavities, and require complex packaging for analyte solution introduction and removal.
Innovation Solution
A structure and method for forming a sensor with a cavity integrated in the front-end-of-line processing, using a semiconductor layer, transistor with a gate electrode, and interconnect structure, where openings through the metallization levels and semiconductor layer define a fluid inlet and outlet, allowing for fluid circulation without the need for extensive back-end-of-line modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the solution-receiving cavity is incorporated into a modified back-end-of-line structure, then the sensor can detect ion concentration, but the manufacturing cost increases due to large area reservation and complex packaging requirements
Solution Approach 1:
Instead of forming the cavity in the conventional back-end-of-line structure, the patent inverts the approach by forming the cavity in the front-end-of-line substrate. This reversal allows standard back-end metallization processes to be used without modification, eliminating the need for large area reservation and complex packaging while maintaining sensor detection capability
Solution Approach 2:
The cavity is formed preliminarily in the substrate before the standard front-end-of-line transistor fabrication processes. This preliminary action allows the cavity to be integrated into the substrate structure itself, enabling subsequent metallization layers to be formed over the cavity without requiring special back-end modifications
2Reliability
If the cavity is formed in the back-end-of-line structure, then the sensor structure is complete, but the device complexity increases due to extensive modifications and packaging requirements
Solution Approach 1:
The patent applies inversion by moving the cavity formation from the back-end-of-line structure to the front-end-of-line substrate. This eliminates the need for extensive back-end modifications and complex packaging, as the cavity is integrated into the substrate before standard fabrication processes begin
Solution Approach 2:
The cavity formation process is merged with the front-end-of-line substrate preparation steps. The same substrate that undergoes standard transistor fabrication also contains the pre-formed cavity, eliminating the need for separate back-end cavity formation and reducing overall device complexity
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 the footprint and cost of sensor integration by relocating the cavity to the front-end-of-line, simplifying packaging and enabling efficient fluid circulation for chemical or biochemical analysis without the need for MEMS elements.
Implementation Method 1
removing the sacrificial layer with an etching process to define a cavity
Data Source
AI summary
Structures for transistor-based sensors and related fabrication methods. A layer stack is formed that includes a semiconductor layer and a cavity. A transistor is formed that has a gate electrode over the layer stack, and an interconnect structure is formed over the layer stack and the transistor. First and second openings are formed that extend through the metallization levels of the interconnect structure and the semiconductor layer to the cavity. The first opening defines a fluid inlet coupled to the cavity, and the second opening defines a fluid outlet coupled to the cavity.