Lithographic aspects for the fabrication of BiCMOS embedded bio-MEMS and RF-MEMS

P. Kulse; M. Birkholz; K.-E. Ehwald; M. Kaynak; M. Wietstruck; J. Bauer; J. Drews; K. Schulz

doi:10.1117/12.918021

16 April 2012 Lithographic aspects for the fabrication of BiCMOS embedded bio-MEMS and RF-MEMS

P. Kulse, M. Birkholz, K.-E. Ehwald, M. Kaynak, M. Wietstruck, J. Bauer, J. Drews, K. Schulz

Proceedings Volume 8352, 28th European Mask and Lithography Conference; 83520E (2012) https://doi.org/10.1117/12.918021
Event: 28th European Mask and Lithography Conference (EMLC 2012), 2012, Dresden, Germany

Abstract

Latest developments in micro-electro-mechanical systems (MEMS) have paved the way to follow the more than Moore approach. Several key components, such as silicon pressure sensors have been developed using MEMS processing techniques. Recently, MEMS technologies have been combined with standard CMOS processes and MEMS devices such as microviscosimeters and RF-MEMS switches were successfully demonstrated. The most challenging part of this MEMS process is the last long wet etch step, which remove the sacrificial layer to make the actuator moveable. Such long etch step is strongly influenced by the previous lithography steps. Especially the type of the photoresist has a strong influence on the performance of the final MEMS device. Here, we report a novel MEMS fabrication process, applied to the back-end-off-line (BEOL) of a 0.25μm SiGe BiCMOS technology. The full MEMS process flow is explained and the last lithography step is detailed. First, we show the influence of different substrate surface preconditions which defines the adhesion between the photoresist and the substrate. The final 6μm thick photoresist layer is required for the critical MEMS actuator release procedure due to the long wet etch process. In this wet etch process, a buffered hydrofluoric acid etchant penetrates the resist layer due to the long etch time (>80 min). Such penetration becomes more critical in the case of low adhesion between the photoresist and the wafer surface. Improving the latter can be achieved by using different primers or dehydration bakes. Furthermore, a new approach of an alternative standard lithography process is investigated. For both studies, additional SEM cross sections and contact angle measurements is presented.

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P. Kulse, M. Birkholz, K.-E. Ehwald, M. Kaynak, M. Wietstruck, J. Bauer, J. Drews, and K. Schulz "Lithographic aspects for the fabrication of BiCMOS embedded bio-MEMS and RF-MEMS", Proc. SPIE 8352, 28th European Mask and Lithography Conference, 83520E (16 April 2012); https://doi.org/10.1117/12.918021

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KEYWORDS

Etching

Microelectromechanical systems

Semiconducting wafers

Wet etching

Lithography

Head-mounted displays

Photoresist processing

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