PECVD below 200°C - Emerging Applications in MEMS
Many micro electromechanical systems (MEMS) contain materials such as polymers, magnetic layers or bonding adhesives, whose properties are degraded by high temperatures. In such cases the manufacturing process must be tailored to maintain a thermal threshold typically below 200°C to avoid affecting device performance and yield.
Plasma enhanced chemical vapour deposition (PECVD) is a commonly used process for depositing thin dielectric films. In traditional MEMS manufacturing, PECVD dielectric films are used for hard masks, sacrificial layers, mechanical or etch stop layers and passivation, using deposition temperatures typically 350°C – 450°C.
Emerging MEMS applications demanding low temperature (<200°C) PECVD processes include; magnetic sensor passivation for magnetometers, anti-reflective coatings on polymer based micro-optics , via-last TSV dielectric isolation layers for MEMS wafer level packaging, and bow compensation layers for thinned silicon.
By re-engineering system hardware and processes, SPTS Delta® PECVD systems produce uniform and stable SiN and SiO film properties at deposition temperatures as low as 100°C.
Mobile phone compass application uses internal magnetometer to sense direction.
Active platen cooling in the PECVD chamber allows low temperature control whilst enabling high deposition and chamber clean rates – critical for high system productivity. Provision of a wafer degas option allows outgassing substrates to be heated prior to the PECVD step, thereby preventing plasma instability and yield loss.
SPTS’ optimised low temperature PECVD processes produce SiO and SiN films with unrivalled stability and electrical isolation performance whilst both tensile and compressive films stresses can be provided. Film stresses can be controlled to +-5MPa wafer to wafer, a significant benefit when working with the fragile structures used in modern MEMS devices. With a range of films already proven in high volume manufacturing, SPTS leads the way in low temperature PECVD technology.
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