High-Sensitivity Profilometry for Measurement of Multilayer Structure with Low-Coherence Composite Interferometer

High-sensitivity profilometry provides valuable tools for measurement of the surface structure of a device. On the other hand, tomographic techniques such as ultrasound imaging or optical coherence tomography can be used to measure the inner structure of a device with micrometer resolution. However, the multilayer structure of a device such as a display panel cannot be measured with nanometer sensitivity using conventional profilometry and tomographic techniques. For this purpose, a new type of profilometry based on the technique of low-coherence composite interferometer is proposed and demonstrated. With the phase compensation mechanism of the technique, phase fluctuation resulted from the instability of scanning component and environment can be significantly reduced and a high axial sensitivity can be achieved. The technique is demonstrated by measuring nine interfaces of a display panel with a displacement sensitivity of 11.73 nm without requiring any preknowledge on the structure and has the potential to become a new technique for inspecting the multilayer structure of a packaged device in industry.