Monitoring critical process steps in 3D nand and advanced RF using picosecond ultrasonic metrology

Picosecond Ultrasonics (PULSE™) is a rapid, non-contact, non-destructive first principles acoustic metrology technique for in-line metal film thickness measurements. We demonstrate measurement capability for transparent and semi-transparent films, by analyzing the oscillatory component of the signal described as Brillouin oscillations. Longitudinal sound velocity, thus calculated, is used in determining film thickness. In this paper, we discuss the application of the technology in 3D NAND and advanced RF filters. The additional parameter not only helps characterize the material and improve the accuracy of the reported thickness but is also correlated to critical process parameters; etch rate in 3D NAND and resonant frequencies in RF filter.