High Resolution Acoustic Metrology By Combining High Ghz Frequency Ultrasound And Scanning Probe Microscopy

In order to extract ever more performance from semiconductor devices on the same device area, the semiconductor industry is moving towards device structures with increasingly complex material combinations and 3D geometries. To ensure cost effective fabrication of next generation devices, metrology solutions are needed that tackle the specific challenges that come from these developments such as 3 dimensional imaging of structures and imaging of deeply buried structures under arbitrary, complex layers. Compared to existing metrology solutions for high end manufacturing, ultrasonic inspection techniques have advantages: they are unaffected by optically opaque layers, the acoustic wavelength (60nm @ 100GHz in SiO2) can be smaller than optical wavelengths and the measurement depth can be larger. However, traditional acoustic microscopy tops out at a few GHz due to manufacturing tolerances and the required liquid couplant. We propose to combine very high frequency ultrasound with scanning probe microscopy. By locating the transducer above the cantilever tip, it guides sound into the sample with a dry tip-sample contact. This allows for very high acoustic frequencies and a resolution of O(wavelength).