Laser backside contact annealing of SiC power devices: A prerequisite for SiC thin wafer technology

We developed a new backside contact formation process for SiC power devices based on pulsed laser annealing providing an ohmic contact with lower contact resistance and better adhesion properties than contacts formed by conventional rapid thermal annealing. This process does not add any significant thermal budget to the wafer front side and therefore allows a “short thin wafer” process, means completing the wafer front side including the imide process before thinning and backside metallization. By that means both the risk of wafer breakage and substrate contribution to the total device resistance are minimized at the same time. This is clearly shown by comparing 650V SiC Schottky diodes with identical device structure but different total chip thickness (360 vs 110 μm). Besides the advantage in differential resistance also other properties like heat flux through the device (Rth), non destructive surge current density (I²t) and reliability are improved by the SiC thin wafer technology enabled by the laser backside contact annealing.