FET Sensor Cavity Fabrication Using an Oxidizable Sacrificial Plug
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Solution Overview
Problem
Current methods for fabricating field-effect transistor (FET) sensors face challenges in protecting the delicate gate dielectric and nanocavity during processing, particularly in achieving precise overlay accuracy and selective etching without damaging sensitive materials like Al, Al2O3, and Ti, which are common in FET sensors.
Innovation Solution
A method involving a sacrificial element that fills the sensor cavity to protect the substrate region during fabrication, allowing for oxidative removal using a peroxide-based wet etch, enabling precise and selective exposure of the gate dielectric while maintaining compatibility with existing CMOS technology and allowing for the formation of long fluidic channels without damaging the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a sacrificial plug is removed using non-plasma etch (e.g., TMAH, KOH, HNA), then the sacrificial plug can be removed, but other materials such as Al, Al2O3, Ti, and TixOy are also etched, requiring additional protective steps
Solution Approach 1:
The patent introduces a protective layer as an intermediary between the sacrificial plug and the etchant. This protective layer is selectively removed to expose only the sacrificial plug, allowing the etchant to affect only the intended target while leaving other materials like Al, Al2O3, Ti, and TixOy untouched. This mediator approach eliminates the need for multiple protective steps required by non-selective etchants.
Solution Approach 2:
The patent applies different protective measures to different regions: the sensitive materials (Al, Al2O3, Ti, TixOy) are covered with protective layers, while the sacrificial plug region is left exposed or differently protected. This localized differentiation allows selective etching without affecting other materials, resolving the contradiction between etching effectiveness and material protection.
2Productivity
If the gate dielectric is exposed early in the fabrication process, then processing can proceed, but the gate dielectric is prone to damage during subsequent process steps
Solution Approach 1:
The patent performs preliminary protective action by forming protective layers over sensitive materials before subsequent processing steps. The sacrificial plug is designed to be removed selectively after these protective layers are in place, ensuring the gate dielectric and other sensitive materials are protected throughout the fabrication process while still allowing processing to proceed.
Solution Approach 2:
The protective layers act as a cushioning barrier formed beforehand to protect the gate dielectric and other sensitive materials from damage during subsequent etching and processing steps. This prior cushioning ensures that even if etchants are used aggressively, the sensitive materials remain intact.
3Manufacturing precision
If deep etching is performed to create the sensor cavity, then the gate dielectric can be exposed, but achieving desired overlay accuracy with respect to the gate dielectric is extremely difficult
Solution Approach 1:
The sacrificial plug serves as an intermediary structure that simplifies the etching process. Instead of performing complex deep etching with stringent overlay requirements, the cavity is etched to expose the sacrificial plug, which then protects the gate dielectric during subsequent steps. The plug is removed selectively later, achieving the desired cavity formation with much relaxed overlay tolerances.
Solution Approach 2:
The sacrificial plug is formed preliminarily before the cavity etching step. This preliminary structure acts as a template and protective element, allowing the cavity to be etched with standard overlay accuracy rather than requiring extremely precise alignment with the gate dielectric. The plug's position and dimensions are controlled in earlier, more tolerant process steps.
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 protects the substrate region throughout the fabrication process, enables precise and selective exposure of the gate dielectric, and allows for the formation of long fluidic channels without damaging the substrate, improving the reliability and efficiency of FET sensor production.
Implementation Method 1
removing the sacrificial element, thereby exposing the substrate region... the sacrificial element being removable by oxidation... a peroxide-based wet etch
Data Source
Figure 1a~2b
Figure 3a~4b
Figure 5a~6c
AI summary
A method for forming an intermediate (100) in the fabrication of a field-effect transistor sensor, the method comprising: a. providing a substrate having a substrate region (210) comprising a gate dielectric (211) thereon and optionally a nanocavity therein (212), b. providing a sacrificial element (310) over the substrate region (210), c. providing one or more layers (400) having a combined thickness of at least 100 nm over the sacrificial element (310), d. opening an access (500) to the sacrificial element (310) through the one or more layers (400), and e. optionally selectively removing the sacrificial element (310), thereby opening a sensor cavity (300) over the substrate region (210); wherein the sacrificial element (310) is removable by oxidation and wherein, if step e is performed, selectively removing the sacrificial element (310) comprises an oxidative removal.