Stress metrology for flexible and flat-panel display manufacturing (Conference Presentation)

Abstract

The photo-elastic stress metrology is well known measurement technique widely used in mechanical engineering applications since at least 1940 [1]. 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. [1] K. Ramesh, “Digital Photoelasticity Advanced Techniques and Applications,” Springer, 2000.