CMUT Bottom Electrode Encapsulation to Prevent Breakdown
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Solution Overview
Problem
The 'patterning last' process in CMUT production exposes the bottom electrode, leading to sidewall or corner metal exposure during chemical-mechanical polishing, resulting in high charging and premature breakdown, especially during high voltage and/or high frequency operation.
Innovation Solution
A 'patterning first' process is employed where the bottom electrode is patterned before dielectric films, fully encapsulating it with multiple dielectric layers to protect the sidewalls and corners, reducing the risk of charging and breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the 'patterning last' process is used to produce CMUT devices, then the manufacturing process is simpler and more straightforward, but the bottom electrode becomes exposed during chemical-mechanical polishing, leading to sidewall or corner metal exposure, high charging, and premature breakdown
Solution Approach 1:
The bottom electrode is patterned in advance (patterning first) before the dielectric layers are deposited and removed. This preliminary patterning allows the electrode to be fully encapsulated by dielectric layers during subsequent processing, protecting it from exposure during chemical-mechanical polishing and eliminating the reliability issues associated with metal exposure, while still maintaining manufacturing feasibility
Solution Approach 2:
Dielectric layers are deposited over the patterned bottom electrode before the final cavity formation step. These dielectric layers act as a protective cushion that prevents direct exposure of the metal electrode during chemical-mechanical polishing, thereby preventing metal exposure, reducing charging effects, and avoiding premature breakdown
2Productivity
If the bottom electrode is exposed during chemical-mechanical polishing, then the manufacturing process can be completed with standard steps, but metal exposure occurs on sidewalls or corners, causing high charging and premature breakdown during high voltage and frequency operation
Solution Approach 1:
The bottom electrode is patterned before dielectric layer deposition, allowing it to be fully encapsulated. This preliminary action ensures that no metal exposure occurs during subsequent chemical-mechanical polishing, eliminating the harmful charging effects while maintaining manufacturing efficiency
Solution Approach 2:
Dielectric layers serve as an intermediary protective layer between the bottom electrode and the chemical-mechanical polishing process. This intermediary prevents direct contact between the polishing slurry and the metal electrode, thereby preventing metal exposure and the associated harmful charging effects during high voltage and frequency operation
Data Source
AI summary
A semiconductor device and method of manufacturing the device that includes a capacitive micromachined ultrasonic transducer (CMUT). The CMUT includes an integrated circuit substrate, and a sensing electrode positioned on the integrated substrate. The sensing electrode includes a sidewall that forms a wall of an isolation trench adjacent to the sensing electrode, and is patterned before covering dielectric layers are deposited. After patterning of the sensing electrode, one or more dielectric layers are patterned, with one dielectric layer patterned on the sensing electrode and sidewall, and which has a thickness corresponding to the surface roughness of the sensing electrode. The CMUT further includes a membrane positioned above the sensing electrode forming a cavity therein.