The photo-elastic stress metrology is well known measurement technique widely used in mechanical engineering applications since at least 1940 . Its use in semiconductor manufacturing has been limited since the direct measurements of the stress in silicon are complicated by relatively low values of stress-optic coefficient and need of use on NIR array detectors. The advent of flexible electronics and wide spread of use of PI films as passivation layer give opportunity to take advantage of very strong stress induced birefringence effect in PI for practical application. Here we present practical tool enabling measurement of stress in PI films with resolution down to 1 MPa.
The optical system comprises of (light emitting device) LED panel (light source), polarization components, color filters and camera. Due to the birefringence caused by the stress, the sample changes the light into the elliptically polarized light. To analyze the elliptically polarized light and to eliminate the ambiguity when unwrapping the phase, we employed three (550 nm, 589 nm, and 632 nm) placed directly in front of the camera.
We demonstrate performance of this system for flat panel displays having dimensions up 185 cm x 150 cm (G6). Discuss throughput and repeatability of this metrology. We also discuss scalability of this metrology.
 K. Ramesh, “Digital Photoelasticity Advanced Techniques and Applications,” Springer, 2000.
We discuss the application of new synchronized, and virtually synchronized multiprobe real space and frequency domain low coherence interferometers for measurement of wafer thickness and topography. The recently developed low coherence frequency domain interferometers have been proved to be fast and effective tool for measurement of wafer topography, thickness and individual layers within multilayer structures. In our paper we present simple models describing performance of multiprobe metrology and compare it with other solutions.
We report exceptionally good repeatability in non-contact Frequency Space Moire (FSM) Fiber Optic Wafer Thickness Metrology. The FSM method, which is a frequency domain interferometry technique, takes advantage of the low frequency beat-like pattern observed by grating spectrograph in the recorded spectra of the light reflected from the thick samples, and subsequently filtered through the well characterized etalon. In this paper we focus on semiconductor application of the FSM method. The FSM experimentally achieved static repeatability of 0.35 nm for the measurement of thickness of the nominally 508 um thick blanket silicon wafer, which is about 1 part per million, for the acquisition time of 10 ms.