3D Integration via D2D Bump-Less Cu Bonding with Protruded and Recessed Topographies

Abstract

Bump-less copper (Cu) bonding is currently the most attractive approach for fine-pitch (< 20 µm) 3D integration due to its compatibility with the wafer back-end-of-the-line fabrication process. In this study, themocompression bonding of bump-less Cu pads with a diameter of 4 µm and a pitch size of 10 µm was pursued, while chemical mechanical polishing (CMP)-processed Cu pads enclosed in SiO2 were employed with both protruded and recessed topographies. The effects of Cu topography (protruded or recessed) and bonding temperature on the electrical and microstructural properties of the die bonds as well as mechanical bonding strength were investigated. It was found that thermocompression bonding of CMP-processed Cu can be realized at shorter processing times, lower bonding temperatures, and pressures than standard electroplated Cu bonding. The bonding yield of the three configurations, i.e. protruded-protruded, protruded-recessed, and recessed-recessed Cu pads was also compared.

Effect of Cu Film Thickness on Cu Bonding Quality and Bonding Mechanism

“…The success of the hybrid bonding process relies on the final chemical mechanical polishing (CMP) stage of the copper [18,19]. During this stage, it is essential to achieve a flat oxide surface while ensuring that the copper is slightly recessed from the oxide Materials 2024, 17, 2150 2 of 10 surface [12][13][14].…”

Measurement of Thermal Stress by X-ray Nano-Diffraction in (111)-Oriented Nanotwinned Cu Bumps for Cu/SiO2 Hybrid Joints

“…Moreover, the solder joint has destructive reliability issues with decreasing pitch, such as sidewall wetting, brittle intermetallic compound (IMC) formation, and bridge failure [1][2][3]. Thus, Cu/SiO 2 or Cu/SiCN hybrid bonds have replaced the solder joints in HPC devices [4][5][6][7][8][9][10][11][12][13][14]. However, the current temperature to achieve Cu hybrid bonding is about 300 • C. Several studies propose different approaches to achieve low-temperature bonding, including (111)-oriented nano-twinned Cu, adoption of the passivation layer, and plasma treatment [10,[15][16][17][18][19][20][21][22][23][24].…”