Nanogap Formation via Knockoff Feature Removal
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Solution Overview
Problem
Existing methods for forming nanogaps between electrodes in nanochannel devices face challenges such as low throughput, irreversible modification of noble metal electrodes, and poor process control, leading to variations in nanogap dimensions and yield, which impede fluid flow and biomolecule detection.
Innovation Solution
A method involving the formation of a knockoff feature on a dielectric layer, trench etching, noble metal deposition, and subsequent polishing to create embedded electrodes with a nanogap, using hydrogen silsesquioxane as a sacrificial layer and water-based mechanical polishing to achieve precise and reproducible nanogaps down to 7 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If He ion beams are used to cut noble metal nanowires to form nanogaps, then nanogap electrodes can be formed, but the process requires labor intensive manual operation with low throughput and causes noble metal splatter that redistributes metal around the incision
Solution Approach 1:
The patent replaces the mechanical He ion beam cutting process with a chemical etching process using buffered oxide etch (BOE) to remove sacrificial silicon nitride bridges. This substitution eliminates manual operation requirements and enables batch processing, thereby increasing throughput while maintaining nanogap precision through controlled etching parameters.
Solution Approach 2:
The patent introduces sacrificial silicon nitride bridges as intermediary structures that are easily removable by chemical etching. These bridges serve as placeholders during electrode fabrication and are subsequently removed to create clean nanogaps without causing metal splatter or redistribution, thus improving both productivity and manufacturing precision.
2Ease of manufacture
If He beam cutting is used on SiO2 over silicon to form nanogaps, then gaps can be created, but swelling of the silicon occurs which complicates analysis
Solution Approach 1:
The patent uses sacrificial silicon nitride bridges as intermediary structures instead of directly cutting the silicon substrate. The silicon nitride layer is removed by selective chemical etching with BOE, which does not cause silicon swelling. This intermediary approach enables easy gap formation while maintaining silicon structural integrity and avoiding swelling complications.
3Ease of manufacture
If self-aligned sacrificial metal, electromigration, or dry/wet etching approaches are employed to form nanogaps, then gaps can be created, but these methods result in low process control, large nanogap variation, and low yield
Solution Approach 1:
The patent employs sacrificial silicon nitride bridges as intermediary structures that enable precise nanogap formation. The bridges are defined with controlled dimensions using standard semiconductor fabrication techniques, and their removal by selective BOE etching produces consistent nanogap dimensions with minimal variation, thereby improving process control and yield.
Solution Approach 2:
The patent controls nanogap dimensions by precisely controlling the thickness and dimensions of the sacrificial silicon nitride bridges through deposition parameters. By changing the deposition conditions and bridge geometry, the final nanogap dimensions can be accurately controlled with minimal variation across batches, improving manufacturing precision and yield.
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 enables high-yield, reproducible nanogap formation with narrow width variation, facilitating efficient detection of biomolecules and nanoparticles, and improving the reliability of lab-on-a-chip applications by ensuring precise electrical detection and sensing.
Implementation Method 1
A top surface is polished to remove the noble metal from regions outside the trenches including the knockoff feature
Implementation Method 2
The knockoff feature is removed during the polish with the subsequent nanochannel etch to form a nanogap between the electrodes
Data Source
AI summary
A method for forming a nanogap includes forming a knockoff feature on a dielectric layer and forming a trench in the dielectric layer on opposite sides of the knockoff feature. A noble metal is deposited in the trenches and over the knockoff feature. A top surface is polished to level the noble metal in the trenches with a top of the dielectric layer to form electrodes in the trenches and to remove the noble metal from the knockoff feature. A nanochannel is etched into the dielectric layer such that the knockoff feature is positioned within the nanochannel. The knockoff feature is removed to form a nanogap between the electrodes.