Intel and French research lab CEA-Leti have optimized a hybrid direct-bonding, self-assembly manufacturing process that could facilitate "die-to-wafer" (D2W) bonding applications .

According to eeNews, the D2W hybrid bonding process is considered a necessary process for bonding memory, high-performance computing chips and photonic chips on wafer substrates, but it is much more complex than wafer-to-wafer bonding and has lower Alignment accuracy and lower die assembly throughput.

For several years, CEA-Leti has been developing a self-assembly method with the goal of dramatically increasing throughput and placement accuracy. The newly developed technology can improve alignment accuracy, increasing manufacturing throughput by thousands of dies per hour by using droplets to align dies on target wafers.

Emilie Bourjot, CEA-Leti 3D Integration Program Manager, said that the increase in D2W self-assembly throughput to commercial scale overcomes two major challenges associated with die processing. “If the self-assembly process is combined with a pick-and-place tool, by reducing the alignment time, yields can be improved because the precise alignment is performed by droplets. When self-assembly is combined with a collective die handling solution, due to all the The dies are glued together at the same time without any high-precision placement at any point in the process flow, increasing yield.”

A paper presented this week at the 2022 Electronic Components and Technology Conference (ECTC) describes a technique that exploits capillary forces, which arise from the principle of surface minimization, and pass through surfaces in the case of liquids Tension applied.

Macroscopically, liquids tend to minimize their liquid/air interface to reach an energy-minimizing equilibrium state. This mechanism allows self-alignment of the die at the bond site. The liquid chosen as the rearrangement vector must have high surface tension and must be compatible with direct bonding. Most liquids have surface tensions between 20 and 50 mN/m, with the exception of water, which has a surface tension of 72.1 mN/m, making it an excellent candidate for self-assembly processes using hydrophilic bonding, which is already a key mechanism parameters.

CEA-Leti developed an in-house D2W system that showed average deviations at 150 nm at various die sizes (8 × 8 mm, 2.7 × 2.7 mm, 1.3 × 11.8 mm, and 2.2 × 11.8 mm). In contrast, pick-and-place tool post-bond 1m alignment, and 700nm best-case, and self-alignment processes can provide sub-500nm and even sub-200nm post-bond alignment.

The paper aims to encourage assembly equipment manufacturers to adopt the technology. "Many aspects of self-assembly still need to be explored, and huge improvements can only be achieved when device vendors develop an adapted device to automate the process," the researchers said.