Wafer bonding process for zero level vacuum packaging of MEMS

It is well known that the packaging of electronic devices is of paramount importance, none more so than in MEMS were fragile mechanical elements are realized. Among the different approaches, wafer to wafer bonding guarantees the advantages of the wafer scaling and provides protection of the devices during the final phase of fabrication. Direct bonding, also known as fusion bonding, is seldom implemented in MEMS fabrication due to the high surface quality required, the high temperature involved and the compulsory wet activation process. In this paper a direct bonding process for MEMS inertial sensor without the need of any wet activation step is presented.acceptedVersio

Wafer bonding process for zero level vacuum packaging of MEMS

It is well known that the packaging of electronic devices is of paramount importance, none more so than in MEMS were fragile mechanical elements are realized. Among the different approaches, wafer to wafer bonding guarantees the advantages of the wafer scaling and provides protection of the devices during the final phase of fabrication. Direct bonding, also known as fusion bonding, is seldom implemented in MEMS fabrication due to the high surface quality required, the high temperature involved and the compulsory wet activation process. In this paper a direct bonding process for MEMS inertial sensor without the need of any wet activation step is presented.acceptedVersio

Plastic Deformation of Thin Si Membranes in Si-Si Direct Bonding

The effect of bond anneal in Si-Si direct bonding of laminates With thin membranes suspending closed cavities is studied. For membranes of a certain size and thickness, it is found that the under-pressure in the cavity during bond anneal leads to plastic deformation of the membrane. By controlling the cavity pressure it is found that the Si crystal of the membrane can be kept intact during bond anneal.acceptedVersio

Metal Films for MEMS Pressure Sensors: Comparison of Al, Ti, Al-Ti Alloy and Al/Ti Film Stacks

Thermo-mechanical stability of metal structures is one of the key factors affecting accuracy of micro-electromechanical (MEMS) piezoresistive pressure sensors. In this work, we present the measurement results of stress and hysteresis for the following metals deposited in the same sputtering equipment -Al, Ti, Al-Ti alloy and stacks of Al/Ti films-enabling, for the first time, a direct comparison between their thermo-mechanical properties supported with analysis of surface morphology (grain size, hillocks and voids).acceptedVersio

Al-Al Wafer-Level Thermocompression Bonding applied for MEMS

Wafer-level thermocompression bonding (TCB) using aluminum (Al) is presented as a hermetic sealing method for MEMS. The process is a CMOS compatible alternative to TCB using metals like gold (Au) and copper (Cu), which are problematic with respect to cross contamination in labs. Au and Cu are commonly used for TCB and the oxidation of these metals is limited (Au) or easily controlled (Cu). However, despite Al oxidation, our experimental results and theoretical considerations show that TCB using Al is feasible even at temperatures down to 300−350 °C using a commercial bonder without in-situ surface treatment capability.acceptedVersio

Texture of Al films for wafer-level thermocompression bonding

Properties of aluminum thin films for thermocompression bonding have been studied in terms of surface roughness, grain size, and grain orientation by AFM, SEM, XRD and EBSD for thermocompression bonding. Al films were sputter deposited directly on Si and thermally oxidized Si wafers, respectively. The resulting Si/Al and Si/SiO2/Al sample types were compared after annealing (300–550 °C) in vacuum. The Si/SiO2/Al film samples showed higher surface roughness than the Si/Al samples. The as-deposited films had (111) preferred orientation, while (100) and (110) oriented Al grains were also present in Si/SiO2/Al samples. The Si/SiO2/Al samples and Si/Al sample annealed at 550 °C had a conical texture. The observed evolution of the grain structure with annealing temperature is discussed in terms of native oxide, surface roughness, diffusivity and grain orientation dependent mechanical properties in order to shine light on previously observed differences in Alsingle bondAl thermocompression wafer-level bonding with Si/SiO2/Al and Si/Al wafers.acceptedVersio

Metal Films for MEMS Pressure Sensors: Comparison of Al, Ti, Al-Ti Alloy and Al/Ti Film Stacks

Thermo-mechanical stability of metal structures is one of the key factors affecting accuracy of micro-electromechanical (MEMS) piezoresistive pressure sensors. In this work, we present the measurement results of stress and hysteresis for the following metals deposited in the same sputtering equipment -Al, Ti, Al-Ti alloy and stacks of Al/Ti films-enabling, for the first time, a direct comparison between their thermo-mechanical properties supported with analysis of surface morphology (grain size, hillocks and voids).acceptedVersio

Metal Films for MEMS Pressure Sensors: Comparison of Al, Ti, Al-Ti Alloy and Al/Ti Film Stacks

Thermo-mechanical stability of metal structures is one of the key factors affecting accuracy of micro-electromechanical (MEMS) piezoresistive pressure sensors. In this work, we present the measurement results of stress and hysteresis for the following metals deposited in the same sputtering equipment -Al, Ti, Al-Ti alloy and stacks of Al/Ti films-enabling, for the first time, a direct comparison between their thermo-mechanical properties supported with analysis of surface morphology (grain size, hillocks and voids)

Al-Al wafer-level thermocompression bonding applied for MEMS

Wafer-level thermocompression bonding (TCB) using aluminum (Al) is presented as a hermetic sealing method for MEMS. The process is a CMOS compatible alternative to TCB using metals like gold (Au) and copper (Cu), which are problematic with respect to cross contamination in labs. Au and Cu are commonly used for TCB and the oxidation of these metals is limited (Au) or easily controlled (Cu). However, despite Al oxidation, our experimental results and theoretical considerations show that TCB using Al is feasible even at temperatures down to 300−350 °C using a commercial bonder without in-situ surface treatment capability