The NXP-TSMC Research Center introduced a groundbreaking method for packaging MEMS components at the "MEMS 2008" conference held in the United States on January 17th. This innovative approach, detailed in paper number 156-Th, leverages materials commonly used in advanced CMOS LSI wiring layers to encapsulate MEMS devices. The technology bridges the gap between traditional MEMS packaging and existing CMOS manufacturing processes, making it compatible with TSMC's production lines.
This technique employs low-k materials—typically used in high-speed wiring of advanced LSIs—for MEMS packaging. While low-k materials are known for their low dielectric constant, which reduces signal interference and improves performance in ICs, they also possess unique porous characteristics that prove beneficial in MEMS applications.
In this process, the porous structure is utilized in the sacrificial layer etching stage. Normally, MEMS packaging involves creating cavities around the movable parts and covering them with a lid. A gap is then created to allow removal of the sacrificial layer through etching. By using a porous material as the lid, the sacrificial layer can be removed via vapor-phase etching, ensuring a more controlled and precise process.
A non-porous film is then deposited on top to create a hermetically sealed package. During the etching process, hydrofluoric acid (HF) is used, and the etching rate of the porous material is extremely slow—only 0.14 nm per minute. This allows for excellent selectivity between the sacrificial layer (typically silicon dioxide) and the porous material. For instance, if the porosity is just 7%, the sealing material cannot penetrate the cavity, preserving the integrity of the MEMS structure.
The low-k material used in this development is "Black Diamond" from Applied Materials, a well-known and widely used material in the semiconductor industry. The company aims to first apply this packaging technology to silicon oscillators, which have already been developed for RF circuits and were presented at the IEDM 2007 conference in December 2007.
This advancement not only enhances the compatibility of MEMS with mainstream semiconductor manufacturing but also opens up new possibilities for integrating MEMS into complex systems with higher reliability and performance.
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