Advantages of Picosecond Laser Acoustics to Process Control of Semiconductor Power Devices

Picosecond laser acoustic (PULSE™) technology is an industry benchmark for metal film metrology. The non-contact, non-destructive technique is well-suited for providing in-line simultaneous multilayer measurements on product wafers. The technology has found widespread adoption across multiple device segments, supporting both leading edge and specialty process monitoring and control.

 This paper highlights the advantages of PULSE technology in power semiconductor process monitoring; specifically insulated gate bipolar transistors (IGBTs) and metal oxide semiconductor field effect transistors (MOSFETs), covering both frontside (gate metallization) and backside (backside metallization). The reliability and performance of these devices significantly depend on various processing steps. Power devices run high currents at high-operating temperatures, and the metal layers need to be properly controlled for electrical properties and thickness to enhance thermal conductivity.

 By presenting specific examples, we showcase PULSE technology's capability to measure multiple-layer stacks, with excellent repeatability, and long-term stability. The technique is versatile and is well suited for applications in both Si as well as SiC-based devices. Recent modifications to the system include extending the measurement range to cover very thick, rough films and improvements to signal to noise ratios making it more convenient for power device manufacturers to use a single metrology tool to cover a wide range of applications. Additionally, we present PULSE technology’s non-destructive Young’s modulus measurement capability, which provides critical information about the mechanical strength of the material.