MEMS Ultrasonic Sensor Cavity Etching via TEG Observation
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Solution Overview
Problem
The manufacturing of capacitive-type ultrasonic sensors using MEMS technology faces challenges in ensuring the complete removal of sacrificial layers during etching, which affects the shape of the cavity and the performance of the sensor, and the placement of the upper electrode blocks optical observation, making it difficult to confirm the presence of residual sacrificial layers.
Innovation Solution
A semiconductor device design where a sacrificial pattern is formed on both the sensor region and a separate Test Element Group (TEG) region, with specific openings allowing observation of the etched state, and a method to form cavities between insulating films, ensuring accurate etching and preventing residual sacrificial layers, while maintaining the distance between electrodes to optimize sensor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the upper electrode is formed above the sacrificial layer to create the cavity, then the cavity can be formed, but the upper electrode blocks optical observation making it difficult to confirm the presence of residual sacrificial layers
Solution Approach 1:
The device is divided into a sensor region and a TEG region. The TEG region contains dummy cavities that serve as observation windows, allowing optical detection of sacrificial layer removal without interfering with the sensor region's upper electrode structure. This segmentation enables separate functions: sensing in one area and observation in another.
Solution Approach 2:
Dummy cavities in the TEG region act as intermediaries for observation. These dummy cavities provide optical access to verify sacrificial layer removal through the insulating films, serving as a mediator between the manufacturing process and quality verification without affecting the actual sensor performance.
2Manufacturing precision
If the sacrificial layer is completely removed by etching, then the cavity shape is accurate, but residual sacrificial layers cause performance degradation
Solution Approach 1:
The TEG region with dummy cavities provides feedback on the etching process completion. By observing the dummy cavities optically, manufacturers can determine whether sacrificial layers have been fully removed, allowing process adjustment to ensure complete removal and prevent performance degradation.
Solution Approach 2:
The dummy cavities in the TEG region serve the dual purpose of being structural elements like the sensor cavities while simultaneously providing self-verification of the manufacturing process. The TEG region essentially monitors and validates its own manufacturing quality.
3Difficulty of detecting and measuring
If the cavity is formed before the upper electrode, then observation is possible, but an additional insulating film increases the distance between electrodes reducing sensitivity
Solution Approach 1:
The device structure is segmented into sensor region and TEG region. The TEG region contains the additional insulating film and dummy cavities for observation, while the sensor region maintains the optimized electrode spacing for sensitivity. This segmentation allows observation functionality without compromising sensor performance.
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 improves the productivity and performance of the semiconductor device by ensuring accurate cavity formation and preventing residual sacrificial layers, enhancing the sensitivity and reliability of the ultrasonic sensor.
Implementation Method 1
a cavity is formed by etching the sacrificial layer away by way of a hole formed in the insulating film
Implementation Method 2
Applying overlapping (multiplexing) direct current and alternating current voltages to each electrode causes a membrane to oscillate in the vicinity of the resonant frequency to generate ultrasonic waves
Implementation Method 3
causes a membrane to oscillate in the vicinity of the resonant frequency to generate ultrasonic waves
Data Source
AI summary
A method for improving productivity when manufacturing a semiconductor device. A lower electrode, insulating films, an upper electrode and insulating films are formed on a semiconductor substrate in a sensor region. A cavity is formed between the insulator films above the lower electrode. The lower electrode, insulating film, the cavity and insulating film, and an upper electrode form a variable capacity sensor. The cavity is formed by etching a sacrificial pattern between the insulation films by way of a hole formed in a pair of insulation films. Other than in the above sensor region, a dummy lower electrode and four insulating films are formed on the TEG region on the semiconductor substrate; and a dummy cavity is formed between a pair of insulation films above the lower electrode however no conductive layer on the same layer as the upper electrode is formed on the dummy cavity.