Low-Cost 1-[Formula Omitted]m Photolithography Technologies for Large-Body-Size, Low-Resistance Panel-Based RDL

• Published in: IEEE transactions on components, packaging, and manufacturing technology (2011) packaging, and manufacturing technology (2011), 2019-01, Vol.9 (7), p.1426
• Main Authors: Liu, Fuhan, Nair, Chandrasekharan, Ito, Hirokazu, DeProspo, Bartlet H, Ravichandran, Siddharth, Akimaru, Hisanori, Hasegawa, Koichi, Tummala, Rao R
• Format: Article
• Language: English
• Subjects: Bandwidths; Body size; Cost analysis; Density; Depth of field; Glass substrates; High aspect ratio; Low cost; Multilayers; Numerical aperture; Organic chemistry; Photolithography; Photoresists
• ISSN: 2156-3950; 2156-3985
• DOI: 10.1109/TCPMT.2019.2896173

This paper presents the latest advances in photolithography technologies to enable scaling of package redistribution layer (RDL) toward critical dimensions (CD) of [Formula Omitted] and below. High-bandwidth memory channels require not only fine pitch but also low-trace-delay RDL. High-aspect-ratio (AR) traces enable lower delays, and the photolithographic advances to achieve such traces are demonstrated on panel-based glass substrates for packages with low cost, high input/output (I/O) density, high bandwidth, and large body size. CD of 0.9-[Formula Omitted] line and space with an AR of 5.5 was successfully demonstrated using a low-numerical aperture (NA = 0.16) [Formula Omitted] i-line projection stepper tool with a novel chemically amplified plating photoresist. The 1-[Formula Omitted] lithography technology is a must for high-density RDL to enable 2.5-D interposer and embedded fan-out package substrates. These architectures can achieve I/O densities of 500 IOs/mm/layer. The resistance of the trace with an AR of 5 is five times lower than a trace with an AR of 1. This technological advance will greatly reduce the signal propagation loss and increase the data rate of the RDL traces. The combination of high density and high data rate will greatly increase the system interconnect bandwidth. Furthermore, low-NA stepper with a large exposure area will enable the fabrication of large-body-size interposers at low cost. This paper analyzes the relationship between trace width resolution ([Formula Omitted]), depth of focus, and materials to conclude that it is feasible to fill the gap between semiconductor back-end-of-line and package substrate RDL technologies. The final section discusses the issues in process development of lithography for multilayer fine-line RDLs.