Interfacial characterization of Al-Al thermocompression bonds

Abstract

Interfaces formed by Al-Al thermocompression bonding were studied by transmission electron microscopy. Si wafer pairs were bonded using Al films deposited on Si or SiO2 as intermediate bonding media. A bond force of 36 or 60 kN at bonding temperatures ranging from 400-550 °C was applied for a duration of 60 min. Differences in bonded interfaces of 200 µm wide sealing frames were investigated. Interface having voids was observed for bonding with 36 kN at 400 °C for Al deposited both on Si and on SiO2. However, the dicing yield was 33 % for Al on Si and 98 % for Al on SiO2, attesting for the higher quality of the latter bonds. Both a bond force of 60 kN applied at 400 °C and a bond force of 36 kN applied at 550 °C resulted in completely bonded frames with dicing yields of, respectively, 100 and 96 %. A high density of long dislocations in the Al grains was observed for the 60 kN case, while the higher temperature resulted in grain boundary rotation away from the original Al-Al interface towards more stable configurations.Possible bonding mechanisms and reasons for the large difference in bonding quality of the Al films deposited on Si or SiO2 are discussed.3

Texture of Al films for wafer-level thermocompression bonding

“…Additional TEM results on the same films as reported here showed a grain size comparable to the Al film thickness, i.e. around 1 µm [42].…”

“…Hence, more metal should flow plastically due to lower resolved shear stress in case of Si/SiO 2 /Al samples bonded at lower temperatures contributing to higher bondability compared to Si/Al samples. The dislocation densities in bonded Si/SiO 2 /Al samples at 400 °C were found to be higher compared to that in Si/Al as observed in the TEM study, which may have been due to aided plastic deformation due to lower value of resolved shear stress [42].…”

Localized Induction Heating of Cu-Sn Layers for Rapid Solid-Liquid Interdiffusion Bonding Based on Miniaturized Coils

“…This corresponds to an average deposition rate of approximately a = 1.34 µm/min. The theoretical mass of the Cu layer m Cu can be determined using electrogravimetry with Faraday's law of electrolysis (10), where M Cu is the molar mass of copper, Q is the electrical charge, z is the ionic charge, and F is the Faraday constant.…”

“…The hermetic encapsulation of MEMS can be realized by zero-level or wafer-level packaging techniques to combine two or more substrates with various functional components [4]. Conventional wafer bonding methods such as silicon direct bonding, anodic bonding, glass frit bonding, thermo-compression bonding, or hybrid bonding are carried out at elevated temperatures and, in some cases, with subsequent annealing of the substrates [4][5][6][7][8][9][10][11]. This can cause damage to fragile and temperature-sensitive elements.…”

Electromagnetic-Shocking-Induced Interface Healing and Mechanical Properties Improvement in Pre-Bonded Stainless Steel

“…Generally, large-size austenitic stainless steel will inevitably produce metallurgical defects during casting, which will be detrimental to the mechanical properties after forging and forming [2,3]. Recently, a front-end study has been carried out on the solid-state hot-deformation bonding of small blanks to manufacture large forgings [4][5][6][7][8]. The newly developed method of hotdeformation pre-bonding can significantly avoid metallurgical defects, while the residual defects on the pre-bonded interface may deteriorate the uniformity of the interface structure.…”