The Effect of an Ag Nanofilm on Low-Temperature Cu/Ag-Ag/Cu Chip Bonding in Air

Abstract

Low-temperature Cu-Cu bonding technology plays a key role in high-density and high-performance 3D interconnects. Despite the advantages of good electrical and thermal conductivity and the potential for fine pitch patterns, Cu bonding is vulnerable to oxidation and the high temperature of the bonding process. In this study, chip-level Cu bonding using an Ag nanofilm at 150 °C and 180 °C was studied in air, and the effect of the Ag nanofilm was investigated. A 15-nm Ag nanofilm prevented Cu oxidation prior to the Cu bonding process in air. In the bonding process, Cu diffused rapidly to the bonding interface and pure Cu-Cu bonding occurred. However, some Ag was observed at the bonding interface due to the short bonding time of 30 min in the absence of annealing. The shear strength of the Cu/Ag-Ag/Cu bonding interface was measured to be about 23.27 MPa, with some Ag remaining at the interface. This study demonstrated the good bonding quality of Cu bonding using an Ag nanofilm at 150 °C.

Unraveling diffusion behavior in Cu-to-Cu direct bonding with metal passivation layers

“…S3 and XRD part). In addition, the activation energy was compared after the annealing process at different temperatures, with various passivation applied samples 21 , 22 (Fig. S2 ).…”

“…In addition, various research is being conducted, such as using plasma to inhibit native oxide 6 , 7 and altering material properties by controlling the crystal orientation of copper 8 . Among these efforts, research utilizing a metal passivation layer on top of a copper layer is actively being conducted 9 – 11 . The metal passivation layer is a method similar to using SAM, inhibiting native oxide and enabling copper bonding.…”

“…Previously, a variety of passivation materials, including Au, Cr/Au, Pd, Ag, Pt, and Ti 9 – 11 , 14 – 17 , have been utilized. However, these materials have been primarily investigated solely for their role in enhancing bonding quality and electrical properties within homogeneous materials.…”

Advanced Cu/Polymer Hybrid Bonding System for Fine‐Pitch 3D Stacking Devices

“…Metal passivation technology can prevent oxygen from diffusing into Cu, and there should be no problem with electrical conductivity by low resistance or decomposition during TCB. [56][57][58][59][60][61][62][63][64][65] Figure 4 shows representative technologies of metal passivation through Ti and Au. After the bonding is finished, there is no capping layer left at the bonding interface, where Cu should be diffused to.…”

“…When passivating with Pd, [59,60] it shows a low contact resistance of less than 10 −8 Ω • cm 2 , and similar resistance values are shown in novel metals such as Au, Ag, and Pt. [61][62][63][64][65] Although this metal passivation technology provides high bonding reliability at low bonding temperatures, the metal residues on the dielectric layer may cause electrical shorts; so, precise patterning of the metal passivation layer is required. When polymers are used as dielectrics, its patterning is hardly possible, making the metal passivation process incompatible with the polymer.…”