Second Deep Reactive Ion (DRIE) Etcher at Semefab

Semefab has made a $750k investment in advanced MEMS sensor technology with a second dual chamber STS VPX DRIE etcher which complements its existing STS Pegasus DRIE capability. This second tool will cater for higher volume and additional specialised etching processes. The new tool is configured as follows: Chamber 1: Si, SiO2, Si3N4, Chamber 2: Si, SiO2. Both chambers are fitted with Electrostatic chucks with the second APS chamber also suitable for etching Platinum and PZT.

The new tool is being installed in Semefab's Fab 2 MEMS facility and will add significant additional capabilities to our already extensive MEMS process platforms. In particular, the ability to etch cavities and relieve surface membranes for pressure, gas, thermopile and micro-hotplate structures will be possible on wafers which have heavy metals such as Gold and Platinum already deposited.

Semefab's first DRIE etcher, the STS Pegasus tool and has been maintained as a metal ion free 'clean' DRIE machine associated solely with Semefab's Fabs 1 and 3 which are both MOS/Bipolar facilities. MEMS devices at Semefab benefit from starting their processing in Fabs 1 or 3 where long carrier lifetimes and low junction leakages are guaranteed by the complete absence of alkali metal (Na, K, Li) mobile ionic contamination and heavy metals (Au and Pt), allowing high performance, low leakage electrically active structures to be ion implanted and diffused. Those wafers requiring heavy metal processing are transferred to Fab 2 for the subsequent low temperature processing including sputtering and definition of Gold, Platinum or other metals. Here, these processes can be safely carried out to completion of the MEMS process without risk to the integrity of either of the MOS/Bipolar fabs, essential for producing reproducible, ultra low leakage junction performance in MEMS. Semefab’s Fab 2 is completely isolated from Fabs 1 and 3 and has separate services and facilities. A strict ‘one way traffic’ rule is observed for product passing from Fabs 1 and 3 to Fab 2, ensuring no risk of cross contamination.

The addition of the second DRIE tool to Fab 2 not only adds the ability to etch a variety of new materials and layers in addition to silicon but also removes a restriction requiring KOH etching for certain processes which leads to large die size due to the etch slope. Now we can offer Semefab's customers the cost benefit of smaller die size resulting from DRIE near vertical anisotropic etching across all MEMS processes.

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