Wafer-level metal thin film thickness scanning based on multiple probe wavelengths nanosecond transient thermoreflectance

The present metal film thickness (d_Metal) measurement methods (e.g., profiler and electron microscope) are not able to simultaneously achieve non-invasion, wide measurement range, high-resolution, and wafer-level scanning. In this work, a d_Metal measurement method based on multiple probe wavelengths transient thermoreflectance (MW-TTR) is developed. Through a systematic sensitivity discussion, the guidance for reliable d_Metal measurement is illustrated theoretically. The realization of measuring different types of metals (Au, Al, Ni, Ti) is achieved with different wavelengths of probe lights. After the rigorous comparison with profiler and picosecond acoustic measurement, the accuracy of measuring nanosized film is verified (∼1% difference). The fitting uncertainties of d_Metal are < 5 % for Au and Al metals. The high-throughput wafer-level scanning measurement, with a spatial resolution of ∼ 50 μm, is also realized by integrating automatic displacement control and deep learning fast predicting model into MW-TTR. Spatial mapping of d_Metal is consistent with profiler measurement (∼5% deviation in 2000 μm length).