Chip to Wafer Hybrid Bonding with Cu Interconnect: High Volume Manufacturing Process Compatibility Study

Abstract

Solder reflow technology is volume manufacturing ready to an interconnect pitch of about 60um for two main reasons. Solder has the ability to compensate for height differences among the interconnects on a die or package through the melting and re-solidification process. The second reason is that pick-and-place tools combined with mass reflow process offer an extremely high throughput and low cost process. Unfortunately, this technology appears to be limited to a minimum pitch of $40 \mu \mathrm{m}$ . Therefore, the industry is searching for a solid state bonding technology to enable further pitch scaling. The candidate technology should have the following key attributes: 1) a mechanism to precisely control the metal height variation to prevent open joints, 2) high assembly throughput; 3) low temperature for certain applications; and 4) a pathway to future generations of pitch scaling. DBI® Ultra is a die to wafer (D2W) Direct Bond Interconnect (DBI®) technology that utilizes D2W low temperature hybrid bonding to achieve all of the attributes listed above. It offers precise Cu height variation control through the chemical mechanical polishing (CMP) process. With an extremely efficient pick and place process for assembly, it has a throughput comparable to the solder flip chip reflow process. A spontaneous dielectric-to-dielectric bond at room temperature with a metal-to-metal connection (usually Cu-to-Cu bond) by a low temperature batch annealing process (150–300°C) is attractive for heterogeneous integration. Ultimately, it can scale to a sub-micron pitch. In the past two years, significant progress has been made in the DBI Ultra technology. A bonding process with high volume production throughput has been demonstrated with electrical test yield above 90% with a daisy chain structure that covers 50 mm2 of bonding area. The bonded parts also showed superior reliability performance in temperature cycling, high temperature storage and autoclave testing. This paper demonstrates the low temperature anneal capability of the technology and presents the detailed comparative analysis of the technology against the competing solid Cu-to-Cu thermal compression bonding (Cu-Cu TCB) process.