Solder and Organic Adhesive Hybrid Bonding Technology with Non-strip Type Photosensitive Resin and Injection Molded Solder (IMS)
For maximization of the benefit of semiconductor device scaling, at the same time, for system performance improvement by heterogeneous integration (HI), demand for fine pitch interconnects continue to rise. Solder and organic adhesive hybrid bonding is a candidate to realize fine pitch interconnects. One of technical challenges of solder and organic adhesive hybrid bonding in fine pitches, is that compressed (deformed) solder may result in short circuit (bridge) between adjacent interconnects. This is because solder becomes liquid-phase and organic adhesive's modulus becomes low at bonding temperature such as 250°C. To solve this challenge, we propose novel solder and organic adhesive hybrid bonding technology, based on Injection Molded Solder (IMS) with non-strip type photosensitive resin (resist) and unique thin adhesive. Conventional strip-type resist is stripped away after IMS, but the non-strip type resist is not stripped away and used as permanent resist. In IMS, molten solder is injected into fine pitch cavities which are made in resist on a wafer. By using non-strip type resist (permanent resist), the resist can be used for IMS bumping mask and also for encapsulation after chip joining. As the early phase of the process development, we perform a series of process steps required for 10 - 20 μm pitch interconnects using 80 μm pitch and 40 μm pitch test vehicles (TVs). We also conduct reliability evaluations under thermal cycling (from -55°C to 125°C), temperature humidity bias (85°C, RH 85%, 3.7V), and high temperature storage (150°C). There are no critical issues in these early demonstration and it supports that by further process optimization, this solder and organic adhesive hybrid bonding can be extendable to 20 μm pitch or 10 μm pitch.