IWLPC (Wafer-Level Packaging) Conference Proceedings

Optical Run-Out Correction for Improved Lithography Overlay Accuracy for FOWLP Applications

Authors: Markus Arendt, Matthew Gingerella, Habib Hichri
Company: SUSS MicroTec Photonic Systems Inc.
Date Published: 10/23/2018   Conference: IWLPC (Wafer-Level Packaging)

Abstract: In Fan-Out wafer level packaging (FOWLP), errors from the die placement robot, and from expanding and shrinking mold compound in which the dies are embedded (magnification error), lead to undesirable errors in layer to layer overlay, creating increasing demands to improve lithography equipment overlay control beyond the inherent equipment capability ("tool-to-itself"). Mask-less laser direct imaging (LDI) technologies, or die-by-die alignment strategies on steppers can deal with these error contributions, but they cannot provide adequate throughput and have a high cost-of-ownership, and therefore offer a limited solution for the industry.

An active Optical Run-Out Correction and Beam-Steering technology for a full-field UV projection scanner has been developed, that directly translates into a better overlay for errors caused by the embedding of dies in mold compound for Chip-First FOWLP applications, without loss in resolution, printing performance, and resolution. This feature allows compensation of any type of symmetrical run-out or run-in up to +/- 200 ppm, as well as asymmetrical run-out in Y up to 50 ppm. With additional alignment information, the system’s flexibility also allows for other compensation schemes, like trapezoidal or other form of compensation.

In this paper, we will detail the principle and realization of this optical run-out correction technology. Performance data results for magnification error mitigation will be presented, and its effects on overlay, patterning performance, resolution, and throughput will be studied. Other properties of full-field exposure such as non-repeated dies, stitching-free exposure of any die size especially for very large packages for data center applications, and large depth-of-focus are explored. This feature is available on wafer and panel format full-field exposure systems.

Key Words: 

FOWLP, Projection Lithography, Run-Out Correction, Overlay Improvement

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