CEA-Leti & Intel Optimize Self-Assembly Process
The approach uses the capillary forces of a water droplet to align dies on a target wafer.
CEA-Leti has worked together with Intel and have jointly optimized a hybrid direct-bonding, self-assembly process that has the potential to increase the alignment accuracy as well as fabrication throughput by several thousand dies per hour.
The approach uses the capillary forces of a water droplet to align dies on a target wafer.
“Commercial scale throughput with D2W self-assembly presents two main challenges related to die handling,” said Emilie Bourjot, CEA-Leti’s 3D integration project manager. “If the self-assembly process is combined with a pick-and-place tool, the throughput can be increased by reducing the time of alignment, since the fine alignment is performed by the droplet. When self-assembly is combined with a collective die-handing solution, the throughput is increased by the fact that all dies are bonded together at the same time without any high precision placement at any time along with the process flow.”
“Process optimization is also an important part of this work for increasing process maturity and targeting industrial requirements. “With such alignment and throughput performances, it is a promising step allying the magic of physics and a simple drop of water,” Bourjot said.
Explaining the “homemade collective self-assembly bonding bench”, CEA-Leti said: “As no industrial tools for the self-assembly approach exist, the team fabricated its lab bench enabling collective self-assembly. The low-reproducibility, manual process control nonetheless achieved alignment of 500nm and below, which strongly suggests that an industrial tool dedicated to this process would deliver higher reproducibility, robustness and precision.”
The paper’s conclusion emphasized this point: Despite these breakthroughs, “many aspects of the self-assembly still need to be explored and great improvements will only be possible when tool suppliers will develop (an) adapted tool to automate this process.”
The results were presented in a paper, “Collective Die-to-Wafer Self-Assembly for High Alignment Accuracy and High Throughput 3D Integration”, at the 2022 Electronic Components and Technology Conference (ECTC).
CEA-Leti has been developing a self-assembly method for several years, to substantially increase throughput and placement accuracy.
By comparison, state-of-the-art alignment is 1µm with a pick-and-place tool post bonding, and the best case is 700nm, while a self-alignment process offers an alignment below 500nm and even less than 200nm, post bonding.
For this collaboration, CEA-Leti designed the process flow and performed wafer processing and self-assembly bondings with its expertise in bonding physics, processes and process integration.
