Design and implementation of plenoptic imaging system with reduced aberrations

Abstract

Industrial inspection is critical for 3D semiconductor manufacturing process and automated optical inspection for 3D ICs has attracted a lot of attentions in these years. Plenoptic imaging systems, based on a micro-lens array, acquire light field from parallax and computes 3D information with lower costs. To reduce aberrations from the optical design with microlens array, especially for off-axial micro lenses, the design flow for plenoptic imaging systems is proposed. Based on the parameters designed from paraxial approximation, lateral image quality is optimized by a commercial optical design software, and then depth-related performances are estimated from the simulated images of the optical system. The experimental system for validation is tested quantitatively with modulation transfer function (MTF), by the slanted-edge method of ISO 12233. The difference of MTF between the paraxial and off-axial regions is approximately 0.02, which is within the repeatability error 0.03. Moreover, the synthesized images of a PCIe card refocused on the chip and the board clearly show the elements at the refocusing depth only. The depth map and the all-in-focus image are estimated to build a 3D model. However, significant artifacts appear on depth maps when lighting is not uniform. With combination of the ring light and coaxial light, the depth maps of objects with different surface properties can be estimated with less artifacts. Furthermore, accuracy and resolution can be enhanced by deep-learning technologies, which will be implemented in the future.