BioFET Microwell Self-Alignment via Selective Etching
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Solution Overview
Problem
The fabrication of biological field-effect transistors (BioFETs) faces challenges due to compatibility issues between semiconductor fabrication processes and biological applications, sensitivity, and resolution limitations, particularly in maintaining signal intensity and preventing misalignment-induced corrosion and bridging signals as the number of microwells increases on biochips.
Innovation Solution
A method involving selective etching to form self-aligned microwells with larger bottoms than tops, allowing for increased bio-sensing layer area without misalignment issues, using a single additional photomask, and depositing a bio-sensing layer on the microwell sidewalls and field, with selective removal to isolate microwells and prevent signal bridging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of microwells on biochips is increased to enhance biochip capacity, then more biochemical reactions can be performed simultaneously, but misalignment-induced corrosion and bridging signals occur more frequently
Solution Approach 1:
The patent applies preliminary action by forming the microwell pattern before the metal interconnect layer, and using the metal layer as a self-aligned mask during etching. This preliminary positioning ensures that microwells are correctly aligned with underlying structures before subsequent fabrication steps, preventing misalignment-induced corrosion and bridging signals while enabling increased microwell density for enhanced biochip capacity
Solution Approach 2:
The metal interconnect layer serves a dual function: as both the electrical connection layer and as a self-aligned etch mask for defining the micrawell positions. This self-service approach eliminates the need for separate alignment processes, allowing higher micrawell density without increasing misalignment errors, thus resolving the contradiction between biochip capacity and signal accuracy
2Ease of manufacture
If conventional photomask alignment processes are used, then fabrication is straightforward, but misalignment causes corrosion and bridging signals that reduce sensing accuracy
Solution Approach 1:
The metal interconnect layer automatically serves as the etch mask for defining micrawell positions, eliminating the need for separate photomask alignment steps. This self-aligned approach maintains fabrication simplicity while dramatically improving manufacturing precision, as the mask position is determined by the metal layer deposition rather than by photolithographic alignment
Solution Approach 2:
The patent merges the function of the metal interconnect layer with the function of the etch mask. The same metal layer that provides electrical connections also defines the micrawell positions during etching, combining two fabrication functions into one step and eliminating alignment errors between separate masking and metal deposition processes
3Manufacturing precision
If micrawell bottom area is increased to prevent misalignment issues, then alignment tolerance is improved, but bio-sensing layer area is reduced
Solution Approach 1:
The patent replaces the mechanical photomask alignment system with a self-aligned chemical etching process. Instead of relying on mechanical precision of photomask positioning, the micrawell positions are defined by the chemical etching process using the metal layer as a mask, substituting mechanical alignment with a chemically-defined alignment system that has higher precision and allows optimized micrawell dimensions for maximum bio-sensing area
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 enhances biochip capacity, maintains signal intensity, reduces noise, and minimizes manufacturing costs by creating self-aligned microwells that are less sensitive to misalignment, thus improving the accuracy and reliability of bio-sensing operations.
Implementation Method 1
etching micrawells in the passivation layer to expose a subset of the plurality of top metal plates, removing the exposed top metal plates
Data Source
AI summary
The present disclosure provides a biological field effect transistor (BioFET) and a method of fabricating a BioFET device. The method includes forming a BioFET using one or more process steps compatible with or typical to a complementary metal-oxide-semiconductor (CMOS) process. The BioFET device includes a plurality of microwells having a bio-sensing layer and a number of stacked well portions over a multi-layer interconnect (MLI). A bottom surface area of a well portion is different from a top surface area of a well portion directly below. The microwells are formed by removing a top metal plate on a topmost level of the MLI.