Fine Pitch Die-to-Wafer Hybrid Bonding

Hybrid bonding is being evaluated for advanced packaging of 2.5 and 3D modules due to the enhanced scalability and performance (thermal, electrical and reliability) of the interconnect. The direct bond interconnect (DBI®) Ultra technology is a die to wafer hybrid bonding assembly process that uses all die handling on dicing tape frames. We explore the assembly of various die sizes, pad and pitch dimensions to identify fundamental challenges and solutions to accelerate adoption of this technology in manufacturing. In this paper, we discuss the assembly process results of a test vehicle with an interconnect design of 3.5 μm pad on 7 μm pitch. The 8 mm by 12 mm chip contains daisy chain test structures ranging from 1,400 to 520,000 links. The component wafers were diced and transferred to tape frame for subsequent die preparation for bonding. The 3.5 μm bond pad requires sub-micron alignment accuracy within the bonder for 100% alignment yield. However, with careful process control, alignment yield greater than 98% and void free yield of 96-99% was achieved using a bonder with 3 μm alignment accuracy. The die stacks were characterized with electrical resistance measurement, C-mode scanning acoustic microscopy (CSAM), and cross-section microscopy analysis. A process to evaluate the defectivity in daisy chain test vehicles is described that includes correlation of alignment accuracy, CSAM and daisy chain electrical resistance. These test vehicles are compared to previous studies with pad sizes of 2 –10 μm.