Atomic diffusion bonding of wafers with thin nanocrystalline metal films

Abstract

Effect of 3 d , 4 d , and 5 d transition metal doping on damping in permalloy thin filmsBonding between two flat wafers with thin metal films was studied for 14 thin metal films with various crystal structures and self-diffusion coefficients. Thin nanocrystalline metal films were fabricated on two flat wafers' surfaces using sputter deposition. Bonding of the two metal films on the wafers was accomplished immediately after film deposition in vacuum. For the films, Al, Au, Ag, Cu, Si, Co, Ni, Pt, Ti, Ru, Fe, Cr, Mo, and Ta were used. The wafers were bonded at room temperature over the entire bonded area ͑1 or 2 in. wafers of either Si or SiO 2 ͒ using these metal films. Transmission electron microscopic cross-section images revealed that complete crystalline grains were formed across the original surfaces of the films, probably because of recrystallization occurring at the bonded interface when Al-Al, Ag-Ag, Au-Au, Cu-Cu, and Ti-Ti nanocrystalline films were bonded. A clear interface corresponding closely to the original film surface was visible in the bonded Pt-Pt films. However, fcc-͑111͒ lattices were formed continuously across the films' original surfaces. A thin amorphous layer was formed at the interfaces of Cr-Cr, Fe-Fe, and Ta-Ta bonded films. Experimental results revealed that the two films' bonded structure was related closely to the self-diffusion coefficients of the metals used for bonding. A high atomic diffusion coefficient at the grain boundaries and film surfaces is likely to have enabled bonding at room temperature. Moreover, results obtained using Cu-Cu, Al-Al, Ti-Ti, Cr-Cr, and Ta-Ta films demonstrated that the wafers were bonded even with only 0.2-nm-thick films on both sides. Bonding films of different materials was also achieved, e.g., Ta-Cu films. The bonding technique described herein is promising for use with bonding wafers to fabricate new thin film devices and microelectromechanical systems.

Comparison of Argon and Oxygen Plasma Treatments for Ambient Room-Temperature Wafer-Scale Au–Au Bonding Using Ultrathin Au Films

“…Low-temperature wafer bonding is increasingly required due to the increasing use of heterogeneous integrations [1,2,3]. An effective approach to such bonding is to use intermediate layers [4,5]. Gold (Au) is a good candidate material for these bonding layers because of its high electrical and thermal conductivity, good deformability, and high oxidation resistance.…”

Advances in High-Power, Ultrashort Pulse DPSSL Technologies at HiLASE

“…It was proven that the peak surface temperature of ADB disk pumped at 280 W (4.5 kW cm −2 for the incident pump beam) is 57 • C lower than the temperature of the soldered disk under identical operating conditions. By a thin-disk surface deformation measurement setup developed at HiLASE [37], we also demonstrated the different mechanical behaviors of the disk when pump radiation is applied. The CW output power reached in the proof of principle experiment was 100 W and 177 W from the soldered and the ADB disk, respectively.…”

“…Therefore, the usual approach is to use a special epoxy bonding to a diamond heatsink. We employed another technique for the first time, so-called Atomic Difusion Bonding (ADB) [36], which is an epoxy-free process based on the recrystallization of the contacting layers, which thus allows the formation of a perfect thermal bridge [37].…”

Review of Low‐Temperature Bonding Technologies and Their Application in Optoelectronic Devices

“…Research and development on low‐temperature processes using metallic submicron particles or nano‐particles and development of nano‐porous sponge Au bumps has recently been active. An atomic diffusion bonding method in which a microcrystalline metal thin film is formed by sputtering on the surfaces of two adjacent wafers, which are then bonded at room temperature by fusing the thin layers in a vacuum has also been developed . In addition, high‐precision low‐temperature bonding technology (bonding temperature from room temperature to about 150 °C) for optical elements based on Au–Au surface activated bonding has been developed .…”