Sequential plasma activation methods for hydrophilic direct bonding at sub-200 °C

Abstract

We present our newly developed sequential plasma activation methods for hydrophilic direct bonding of silica glasses and thermally grown SiO2 films. N2 plasma was employed to introduce a metastable oxynitride layer on wafer surfaces for the improvement of bond energy. By using either O2-plasma/N2-plasma/N-radical or N2-plasma/N-radical sequential activation, the quartz–quartz bond energy was increased from 2.7 J/m2 to close to the quartz bulk fracture energy that was estimated to be around 9.0 J/m2 after post-bonding annealing at 200 °C. The silicon bulklike bond energy between thermal SiO2 films was also obtained. We suggest that the improvement is attributable to surface modification such as N-related defect formation and asperity softening by the N2 plasma surface treatment.

Demonstration of Low-Temperature Fine-Pitch Cu/SiO₂ Hybrid Bonding by Au Passivation

“…Because an O atom is coordinated by two Si atoms in the molecular structure of SiO2 and an N atom is coordinated by three Si atoms in the molecular structure of Si3N4, the O atom can be substituted by the N atom during the N2 plasma pretreatment. Thus, reconstruction and stabilization of the metastable oxynitride bonding layer can occur to form the surface with more dangling bonds and lower bonding energy [19]. However, for the hybrid bonding structure, the plasma pretreatment may damage the surface of metal region, and this method needs a high vacuum environment of 10 -5 torr.…”

Progress in wafer bonding technology towards MEMS, high-power electronics, optoelectronics, and optofluidics

“…Compared with the room-temperature bonding, more kinds of direct bonding methods have been investigated at low temperatures, such as multistep chemical treatment, [49][50][51] single plasma activation, sequential plasma activation, [52,53] ultraviolet or vacuum ultraviolet/ozone (UV or VUV/O 3 ) activation, [54][55][56][57][58] and anodic bonding. Most of them have the advantages of low cost and batch production.…”

Effect of Combined Hydrophilic Activation on Interface Characteristics of Si/Si Wafer Direct Bonding

“…Surface activation is considered to be an effective way for low temperature direct bonding [9]. Different surface treatment methods have been developed to realize high bonding strength and good interface characteristics, such as wet chemical activation [10,11], reactive ion etching (RIE) plasma activation [12,13], N 2 microwave (MW) radicals [14], Ar fast atom bombardment (FAB) [15], and so on. Furthermore, intermediate nano-layers (such as Al 2 O 3 , Si, Fe) are also used as an assisted layer in wafer direct bonding [16][17][18].…”