Scanning acoustic GHz-microscopy versus conventional SAM for advanced assessment of ball bond and metal interfaces in microelectronic devices

The current paper describes the application of acoustic GHz-microscopy in comparison to conventional scanning acoustic microscopy for the investigation of ball bond and metal interfaces of microelectronic devices. The non-destructive ultrasonic inspection method is based on a back-side approach with the ultrasonic pulses applied through the back side of the exposed and thinned Si chip. A direct comparison between the innovative ultra-high frequency setup using special highly focusing acoustic lenses enabling the application of up to 1 GHz acoustic frequency and a standard SAM setup based on a conventional 300 MHz transducer is presented for several samples. It is demonstrated that the lateral resolution can be drastically increased from 10-15 μm for the conventional setup to about 1 μm for the ultra-high frequency setup which thereby allows for new applications such as a reliable 2-dimensional quality assessment even of small ball bond interfaces with dimensions of a few 10 μm.