Microsphere probe for in-situ high-resolution thickness measurement

Precise thickness measurement of nanometer-scale dielectrics is crucial for the manufacturing and packaging of high-performance integrated optoelectronic devices. Traditional methods, such as atomic force microscopy, ellipsometry, and evanescent wave sensing techniques, are renowned for their precision but face challenges, such as the need for reference surfaces, precise knowledge of the material's optical properties, and difficulties with large-area, non-uniform measurements. Here, we propose a high-resolution, full-field thickness measurement technique utilizing the evanescent fields of high-order cavity modes in microsphere resonators. By exploiting the discrepancy in sensitivity among different modes, this method directly achieves consistent thickness measurements across extensive lateral dimensions without requiring reference surfaces. Compared to other optical methods, it offers a simple design and efficient readout, while maintaining a precision of about 0.10 nm per nanometer of spectral shift. When combined with optical manipulation and machine learning algorithms, this technique could provide an alternative solution for real-time monitoring of dielectric layers in semiconductor manufacturing.