SiTime, Silicon MEMS Oscillators and Clock Generators

Manufacturing SiTime's MEMS Resonators

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manufacturing

SiTime manufactures MEMS resonators using a process called MEMS First™ that was developed at Bosch (from where our founders came) and significantly enhanced at SiTime. This process produces very small silicon resonator die that are fully vacuum-sealed in silicon, extremely stable and highly durable. Because this process uses state-of-the-art CMOS foundry tools and materials, MEMS are highly manufacturable with excellent yields, quality and reliability.

 

Features Benefits
  • MEMS resonators use single-crystal silicon
  • 100% predictable from lot to lot
  • Simpler temperature compensation scheme, better stability, lower cost
  • High temperature in-process encapsulation to protect MEMS structure
  • Annealing results in higher long term reliability and zero drift
  • Standard materials and processes
  • Leverage existing supply chain for lower cost
  • Industry standard process-control and six sigma philosophy
  • 90%+ yields, < 2 DPPM quality, zero MEMS failures to date


The MEMS First Process

Prior to the development of the MEMS First process, packaging was the key barrier to commercializing MEMS resonators. This barrier was overcome through this process by successfully encapsulating resonators within individual micro-vacuum chambers on silicon wafers.

The resonator structure is first etched in a silicon on insulator (SOI) layer using a deep reactive ion etching (DRIE) process. After the resonators are etched, the wafer surfaces are planarized by filling the trenches with oxide. The oxide is patterned to form contact holes that allow electrical connection to the resonator. Thin silicon layers are grown on top of the oxide and vents are patterned to allow removal of the oxide that surrounds the resonator beams. Oxide is removed with hydrofluoric acid vapor to create freestanding resonator beams, allowing the resonators to vibrate.

Final encapsulation using SiTime’s Epi-Seal™ process, an exceptionally clean epitaxial sealing method, is essential to forming stable resonators. This process is the only demonstrated fabrication process that produces MEMS resonators with stability that meets or exceeds that of quartz crystals. Within high-temperature epitaxial reactors, the resonators and vacuum cavities are cleaned with hydrogen and chlorine gas. They are sealed with a durable poly silicon cap that protects the resonator die and can withstand very high pressure.

Electrical vias are formed to the resonators and electrodes by etching and filling trenches. Electrical interconnects are made with aluminum traces and bond pads. The process is completed with final deposition of silicon oxide and nitride scratch masks steps. The resulting wafers can be back-grounded to less than 100 um thick and packaged with industry standard IC packaging processes such as plastic molding, flip chip and chip stack.

For a more detailed description of the MEMS First process, see MEMS First Process (Flash) or MEMS First Process (pdf).