Blog Post posted on Oct 10, 2023
In recent years, power semiconductor applications have expanded from industrial and consumer electronics to renewable energy and electric vehicles. Looking to the future, the most promising power semiconductor devices will be insulated gate bipolar transistor (IGBT) and power metal oxide semiconductor field effect transistor (power MOSFET) modules.
During the manufacturing of these devices, metal films are deposited on the die of MOSFET and IGBT power devices. These layers of film have two main functions: they connect the elementary cells constituting the power dies to the source (power MOSFET) or emitter (IGBT) and allow for the welding of bond wires on the chip or for the solder bonding, facilitating thermal conduction. Because power devices run high currents at high-operating temperatures, the metal layers need to be properly controlled for electrical properties and thickness to enhance thermal conductivity.
Furthermore, power devices are transitioning from 6-inch to 8-inch wafers; this is happening at the same time as process windows are shrinking. As a result, measuring multi-layer metal thickness accurately and characterizing the uniformity of metal film deposition at the wafer edge has become increasingly important. For example, the front side of wafers requires deposition of a thick metal layer, typically 5µm or more of aluminum alloy. The uniform coverage of aluminum to conduct high currents across the entire wafer is key to device yield and reliability.