Metallization Scheme for 800 °C Silicon Carbide Microsystems

We have developed and validated a high temperature metallization scheme that can sustain silicon carbide (SiC) microsystem operation at 800 °C in the absence of protective packaging. The metallization system consisted of the ohmic contact, diffusion barrier, and interconnect layers made up of three primary and conventional metallizations of Ti, TaSi₂, and Pt. The ohmic contact to the SiC layer is comprised of sequentially deposited Ti (100 nm)/TaSi₂ (300 nm) that provides low contact resistance, followed by the diffusion barrier layer of Ti (100 nm/Pt (300 nm) to prevent the native oxygen and excessive upper layer platinum migrations to the underlying SiC layer. The interconnecting layer is comprised of Ti (20 nm)/TaSi₂ (20 nm/Pt (300 nm)/Ti (20 nm)/TaSi₂ (20 nm), which also functions as a diffusion barrier against oxygen from the atmosphere. The bond pad contact layer is Ti (100 nm)/Pt (300 nm)/Au (500 nm). The metallization was implemented on the n-type epilayer of batch fabricated 4H-SiC pressure sensors to demonstrate functionality in a real device. The metallization system on the sensor was analyzed with Auger Electron Spectroscopy (AES), Focus Ion Beam (FIB) Field Emission Scanning Electron Microscopy (FE-SEM), and X-ray Photoelectron Spectroscopy (XPS) at various sections and stages during different steps of the fabrication. Further analyses were performed after fabrication at high temperature up to 800 °C in air. Electrical measurement was also performed on the bare die under a worst-case condition of no package protection of the sensor at high temperature in air.<br/>The FIB-FESEM cross section after soaking the bare die at 800 °C in air revealed non-smooth interfaces between the layers of the oxide and metallization. The metallization on the oxide layers followed the undulating surfaces of the oxide layers, resulting in likely local discontinuities. However, these presumed discontinuities did not affect the electrical conduction path from the ohmic contact, through the interconnect, and to the bond pad. The observed rough surfaces of the oxide were believed to have occurred during the series of reactive ion etching steps of the oxide via for the ohmic contact, the interconnect, and the bond pad. Overall, the elemental analyses showed a well-preserved metallization, with only native oxygen observed in expected places. Electrically, the SiC sensors that were packaged and tested confirmed the effectiveness of the metallization scheme to support reliable operation at 800 °C. Further improvement to realize a smooth surface morphology was subsequently implemented. The complete details of this work will be presented at the meeting.