Intermetallic Bonding for High-Temperature Microelectronics and Microsystems: Solid-Liquid Interdiffusion Bonding

Abstract

Solid-liquid interdiffusion (SLID) bonding for microelectronics and microsystems is a bonding technique relying on intermetallics. The high-melting temperature of intermetallics allows for system operation at far higher temperatures than what solder-bonded systems can do, while still using similar process temperatures as in common solder processes. Additional benefits of SLID bonding are possibilities of fine-pitch bonding, as well as thin-layer metallurgical bonding. Our group has worked on a number of SLID metal systems. We have optimized wafer-level Cu-Sn SLID bonding to become an industrially feasible process, and we have verified the reliability of Au-Sn SLID bonding in a thermally mismatched system, as well as determined the actual phases present in an Au-Sn SLID bond. We have demonstrated SLID bonding for very high temperatures (Ni-Sn, having intermetallics with melting points up to 1280°C), as well as SLID with low process temperatures (Au-In, processed at 180°C, and Au-In-Bi, processed at 90-115°C). We have verified experimentally the high-temperature stability for our systems, with quantified strength at temperatures up to 300°C for three of the systems: Cu-Sn, Au-Sn and Au-In.Keywords: microelectronics/microsystem assembly, bonding technology, harsh environments, wafer processing, reliability, transient liquid phase © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Motivation for SLID The challenge of die attach and interconnectionFor all electronic systems, the attachment of components to substrates and their electrical connection is a crucial part of the system. Traditionally, the processes for attachment and interconnection have been considered more a craft than a science. The historical focus of electronics and microtechnology has been on the design, manufacturing and testing of components, circuits and devices, rather than on the system integration and the processes needed for actually building the system. The 'electronic revolution' has given ever-increasing performance of devices at ever-decreasing prices for more than half a century. Initial milestones were the invention of the transistor (1947) and the integrated circuit (IC) (1958). The driving factor has been a continuous decrease in size (of components and on features of components) and cost, made possible through batch processing of silicon wafers. Single-crystal silicon is a very well-defined material with extremely well-characterized properties, allowing process technology that yields extremely small features (10 nm by 2017, with a further decrease expected). Miniaturization of components and the use of large Si wafers give a huge number of components manufactured in every batch, lowering the cost. Furthermore, miniaturization allows an increase in operating frequency (or a decrease...

Recent Developments in Low Temperature Wafer Level Metal Bonding for Heterogenous Integration

“…As shown in Figure 2, the bond is indeed solid at temperatures well above the melting temperature of In, and even shows increased strength at 300 °C. This increase in strength was explained to be related to the actual composition and geometry of our investigated bond (1,2). A solid-state phase transition occurring in the Au-In system above 224 °C leads to interdiffusion of Au and In across the original bond interface, giving an annealing effect at this interface.…”

Solid-Liquid InterDiffusion (SLID) Bonding, for Thermally Challenging Applications

“…This paper presents the extensive work on various SLID systems in our group [13]. We have optimized flux-free Cu-Sn SLID bonding for wafer-level hermetic encapsulation of MEMS devices, being ready for industrial implementation [14][15][16][17].…”