Effects of wet treatment conditions and pattern densities on interfacial bonding characteristics of Cu–Cu direct bonds

Abstract

Effects of both wet chemical treatments and line pattern densities on the interfacial bonding characteristics of Cu–Cu pattern direct bonds were systematically investigated. The silicon oxide (SiO2) on a parallel Cu lines patterned wafer could be removed effectively by using a solution of buffered oxide etch and sulfuric acid (BOE/H2SO4) to improve the bonding quality of Cu–Cu pattern direct bonds. The Cu surface after BOE/H2SO4 wet pretreatment revealed the complete removal of both the residue particles and the surface oxide layer. After BOE/H2SO4 wet pretreatment, the interfacial adhesion energies of 0.06, 0.09, and 0.23 pattern densities were 7.9, 4.8, and 4.1 J/m2, respectively, where the dielectric erosion due to chemical–mechanical polishing (CMP) process with increasing pattern density significantly affected the Cu–Cu pattern direct bonding quality. Therefore, CMP planarization performance is critical for reliable Cu pattern direct bonding.

Effects of post-annealing and temperature/humidity treatments on the interfacial adhesion energy of the Cu/SiNx interface for Cu interconnects

“…The Cu 2 O peak includes the Cu peak because the binding energy of the Cu peak (932.5 eV) is close to that of the Cu 2 O peak. 27,28) The peak area fractions of Cu+Cu 2 O and CuO were quantitatively calculated, as shown in Table I. In both the without and with treatments, the peak area fraction of CuO in the Cu 2p peak increased with the annealing and T=H treatment for 500 h. It is notable that the with chemical treatment showed less formation of CuO oxide than the without treatment for all conditions, which could be understood by the effective removal of the Cu oxide by the wet chemical treatment.…”

Effects of forming gas plasma treatment on low-temperature Cu–Cu direct bonding

“…The latter was successfully applied to removing the surface Cu oxide layer prior to bonding in previous studies. 13,32) It is generally accepted that in 3D IC applications, the Cu-Cu bonding strength must be higher than 1.2 J=m 2 in order for the Cu-Cu bonding interface to survive in the subsequent fabrication process such as chemical mechanical polishing (CMP) after the Cu-Cu bonding step. 29) As shown in Fig.…”

“…There have been many attempts to lower the bonding temperature, even down to room temperature. [6][7][8][9][10] Most of them have focused on controlling Cu surface properties to obtain an oxide-free and flat surface by applying a self-assembled monolayer, 11) wet treatment, 12,13) surface activation, 14,15) or depositing Sn on top of Cu. 16,17) Hydrogen is the most representative reducing agent, and in the wafer bonding process, 18) it has been used to prevent further oxidation by producing a reducing atmosphere.…”

“…Moreover, some pretreatments could increase the bonding strength, which should be generally higher than 1.2 J=m 2 for process reliability. 13,29) To examine this assumption, atmospheric-pressure plasma of forming gas was applied to the Cu surface prior to the thermocompression bonding and the effects of pretreatment conditions on Cu oxide reduction and bonding strength were investigated.…”

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

“…Therefore, pre-cleaning and native oxide removal are possible with a solution such as HF, H 2 SO 4 , and BOE. [52,53] This chemicalbased cleaning process is more compatible with polymers because polymer's chemical resistance to acid is quite strong; so, it can maintain a stable form without surface damage even after chemical treatment.…”