Effect of Formic Acid Vapor <italic>In Situ</italic> Treatment Process on Cu Low-Temperature Bonding

Abstract

Low-temperature Cu/Cu direct bonding technology using formic acid vapor in situ treatment was developed. Effect of formic acid vapor treatment conditions on Cu surface and bonding was studied. Cu surface oxide was reduced using formic acid vapor in situ treatment at 150 and 200°C, respectively. With higher temperature and longer treatment time, surface reduction is more effective. Grain boundary etching was found on chemical mechanical polished Cu film after initial treatment by formic acid. However, Cu surface roughness is minimally influenced by long-time formic acid vapor treatment. Cu film/Cu film direct bonding was realized in N 2 atmosphere with formic acid vapor in situ treatment under temperature below 200°C. For lower treatment temperature, longer treatment time is required to achieve good bonding. The bonding strength is about 9.0 MPa when Cu surface is treated at 200°C for 10 min.Index Terms-Cu/Cu direct bonding, formic acid vapor, low temperature.

Robust Ag-Cu Sintering Bonding at 160 °C via Combining Ag2O Microparticle Paste and Pt-Catalyzed Formic Acid Vapor

“…that sintered with formic acid. One reasonable reason is that the Pt-catalyzed formic acid vapor is helpful for the Ag sintering via reducing the oxygen concentration by its strong reductivity [29][30][31][32][33][34][35]. In accordance of the thermal characteristic of Ag2O paste, the bonding was determined to be carried out at 160 °C.…”

“…Since oxygen can also be generated by the decomposition of Ag 2 O, an effective reductive gas atmosphere is assumed to be necessary. Recently, we have demonstrated that a Pt-catalyzed formic acid vapor is more effective for the reduction of Cu oxides compared to the normal formic acid vapor, thanks to the generation of H radicals during catalyzation [29][30][31][32][33][34][35][36]. Its combination with Cu nanoparticles sintering can realize a low-temperature Cu bonding with a large surface-oxidation tolerance [16,36].…”

Thermogravimetric investigation on the interaction of formic acid with solder joint materials

“…21 The mechanisms of the decarboxylation (eqn (1)) and decarbonylation (eqn (2)) of formic acid in the presence of metal and metal oxides are shown in Scheme 1 on the basis of previous studies on the catalysis. [21][22][23] In a low temperature low-vacuum Cu bonding process with formic acid vapors Suga et al 6,29,30 have reported that formic acid dissociates into formate and H + adsorbing on the Cu surface, and H + bonds with O 2À to form OH À . 31,32 Above ca.…”

Room-temperature Hermetic Packaging Using Ultrasonic Cu?Cu Bonding with Compliant Rim

“…Recently, low-temperature Cu-Cu bonding has been achieved using a surface activation process based on the reduction effect with formic acid treatment. (23) Ultrasonic bonding is also an effective method because of its advantages of rapid bonding and low-temperature process. (24)(25)(26) The low-temperature Cu-Cu bonding of conventional bumps in ambient air has been investigated using ultrasonic assist with surface treatments.…”