Precise release and insulation technology for vertical Hall sensors and trench-defined MEMS

Vertical Hall sensors have been fabricated using a new process combining deep-RIE silicon trench etching and anisotropic TMAH silicon wet etching to precisely define the sensor´s active area. The demonstrated release of the bottom of the devices with a wet etching step results in a well-defined and uniformly doped active area. The trench-defined vertical Hall sensors show a very high current related sensitivity of up to 1000 V/AT, a non-linearity of 0.06% FSO, and a residual offset (after spinning current offset reduction) of about 0.5 mT. A method for etching the polysilicon inside the trenches using XeF₂ without an additional mask is demonstrated on an SOI wafer. While the technology is demonstrated for vertical Hall sensors, it is also well suited for the fabrication and release of trench-defined MEMS, such as thin beams.