Revolutionising power: the impact of laser-based ohmic contact formation in SiC semiconductors

The realm of power electronics is witnessing a paradigm shift with the advent of silicon carbide (SiC).

BY 3D-MICROMAC

The realm of power electronics is witnessing a paradigm shift with the advent of silicon carbide (SiC). SiC is especially advantageous for applications in electric vehicles, renewable energy systems, and high-voltage power transmission.

A pivital factor in harnessing these advantages is the Ohmic Contact Formation (OCF) process, especially for 4H-SiC power semiconductor devices with their complex vertical structures. Efficient backside processing, which is integral to OCF, is a critical aspect in ensuring the operational efficacy and reliability of these devices.

The basics of ohmic contact formation OCF is a fundamental yet complex process in the manufacture of semiconductor devices. It involves the creation of metal contacts on the semiconductor material, facilitating efficient current flow. For SiC devices, OCF is a challenging endeavor due to the material’s inherent properties. The conventional approach typically involves the application of nickel or titanium layers. This process facilitates the transition from Schottky to Ohmic contacts, which is essential for efficient device operation. However, the traditional OCF methods, including high-temperature annealing, pose significant challenges. They often lead to contact degradation, increased stress on the device and limited electrical properties, particularly in thinner SiC wafers, thereby necessitating more innovative and delicate approaches.

Figure 1: The Ni-layer is annealed by exposure to laser radiation forming an ohmic contact formation based on Ni_xSi_y.

Advancements in laser-based OCF
The evolution of OCF in SiC semiconductors has taken a significant leap forward with the introduction of laser-based techniques. This innovative approach stands in stark contrast to the traditional high-temperature annealing methods. Laser-based OCF utilizes specialized laser systems, such as those employing nanosecond pulses, to form Ohmic contacts with a high degree of precision and control. The key advantage of using laser systems lies in their ability to deliver targeted energy to specific areas of the semiconductor. This localized approach minimizes thermal stress and potential damage, a crucial factor for maintaining the integrity of thinner SiC wafers – especially when their front side has been already processed with heat sensitive electrical applications.