AlN-AlN Wafer Bonding and Its Thermal Characteristics (original) (raw)
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Low-Temperature Aluminum-Aluminum Wafer Bonding
ECS Transactions, 2016
Aluminum-aluminum thermo-compression wafer bonding is becoming increasingly important in the production of microelectromechanical systems (MEMS) devices. As the chemically highly stable aluminum oxide layer acts as a diffusion barrier between the two aluminum metallization layers, up to now the process has required bonding temperatures of 300°C or more. By using the EVG®580 ComBond® system, in which a surface treatment and subsequent wafer bonding are both performed in a high vacuum cluster, for the first time successful Al-Al wafer bonding was possible at a temperature of 100°C. The bonded interfaces of blank Al wafers and Al wafers with patterned frames were characterized using C-mode scanning acoustic microscopy (C-SAM) and transmission electron microscopy (TEM) as well as dicing yield and pull tests representative for the bonding strength. The investigations revealed areas of oxide-free, atomic contact at the Al-Al bonded interface.
Journal of Electronic Materials, 2018
In this study, a low-cost aluminum nitride (AlN) sintering process to produce thick AlN film substrate with a high thermal conductivity is developed. The thermal conductivity of the present produced thick AlN film substrate is about 163.8 W/mK, which is very close to the reported thermal conductivity of the AlN material. Also, a Sn-Bi die-bonding system is developed to die-bond light emitting diodes (LEDs) on the present sintered AlN substrate with a relatively low die-bonding temperature (below 160°C). In this work, to enhance a better wetting at the die-bonding interface, three external forces (10 N, 15 N, and 20 N) were applied on LED chips during the die-bonding process. We found that the 15-N applied force can achieve a better die-bonding interface among three external forces (10 N, 15 N, and 20 N). The LED die-attached on the AlN substrates by 15 N normal force has the best shear strength (41.5 MPa), compared to the shear strength of 36.9 MPa and 31.5 MPa of the LED dieattached on AlN substrates by 20 N and 10 N normal force, respectively. The LED chips die-attached on the AlN substrate by 15-N normal force shows the best thermal resistance (7.3°C/W). The agreement between the thermal resistance tests and the shear strength tests implies that the better diebonding interface produced a higher shear strength and a lower thermal resistance of the LED chips die-bonded on the AlN substrates.
Overview of recent direct wafer bonding advances and applications
Advances in Natural Sciences: Nanoscience and Nanotechnology, 2010
Direct wafer bonding processes are being increasingly used to achieve innovative stacking structures. Many of them have already been implemented in industrial applications. This article looks at direct bonding mechanisms, processes developed recently and trends. Homogeneous and heterogeneous bonded structures have been successfully achieved with various materials. Active, insulating or conductive materials have been widely investigated. This article gives an overview of Si and SiO 2 direct wafer bonding processes and mechanisms, silicon-on-insulator type bonding, diverse material stacking and the transfer of devices. Direct bonding clearly enables the emergence and development of new applications, such as for microelectronics, microtechnologies, sensors, MEMs, optical devices, biotechnologies and 3D integration.
Au-Sn SLID Bonding: A Reliable HT Interconnect and Die Attach Technology
Metallurgical and Materials Transactions B, 2013
Au-Sn solid-liquid interdiffusion (SLID) bonding is an established reliable high temperature (HT) die attach and interconnect technology. This article presents the life cycle of an optimized HT Au-Sn SLID bond, from fabrication, via thermal treatment, to mechanical rupture. The layered structure of a strong and uniform virgin bond was identified by X-ray diffraction to be Au/f (Au 0.85 Sn 0.15 )/Au. During HT exposure, it was transformed to Au/b (Au 1.8 Sn 0.2 )/Au. After HT exposure, the die shear strength was reduced by 50 pct, from 14 Pa to 70 MPa, which is still remarkably high. Fractographic studies revealed a change in fracture mode; it was changed from a combination of adhesive Au/Ni and cohesive SiC fracture to a cohesive b-phase fracture. Design rules for high quality Au-Sn SLID bonds are given.
Fluxless Bonding of Silicon to Alumina Substrate Using Electroplated Eutectic Au-Sn Solder
56th Electronic Components and Technology Conference 2006
Large 6mm x 9mm silicon dice have been successfully bonded on alumina substrate with electroplated Au80Sn20 eutectic alloy. Eutectic AuSn is one of the best known hard solders having excellent fatigue-resistance and mechanical properties. A fluxless bonding process in 50militorrs of vacuum environment is presented. Vacuum environment is employed to prevent tin oxidation during the process. The oxygen content is expected to be reduced by a factor of 15,200, comparing to bonding in air. One of the challenges in silicon-to-alumina bonding is the large mismatch in thermal expansion between silicon of 2.7x10-6 ppm/°C and alumina of 7x10-6 ppm/°C. Electroplating method is used to build multi-layer solder. It is an economical alternative to vacuum deposition method and can produce thick solders. Joints fabricated are examined using Scanning Electron Microscope (SEM), and Energy Dispersive X-ray Spectroscopy (EDX). It is found that proper bonding condition is needed to turn the stacked layers into a uniform AuSn eutectic alloy. Nearly void-free joints are achieved and confirmed by a Scanning Acoustic Microscope (SAM). To evaluate the reliability of the solder joint and the bonded structure, samples will go through thermal cycling test to determine failure modes. Microstructural changes of the solder joints during thermal cycling test will also be investigated.
Impact of SiO 2 on Al–Al thermocompression wafer bonding
Journal of Micromechanics and Microengineering, 2015
Al-Al thermocompression bonding suitable for wafer level sealing of MEMS devices has been investigated. This paper presents a comparison of thermocompression bonding of Al films deposited on Si with and without a thermal oxide (SiO 2 film). Laminates of diameter 150 mm containing device sealing frames of width 200 µm were realized. The wafers were bonded by applying a bond force of 36 or 60 kN at bonding temperatures ranging from 300-550 °C for bonding times of 15, 30 or 60 min. The effects of these process variations on the quality of the bonded laminates have been studied. The bond quality was estimated by measurements of dicing yield, tensile strength, amount of cohesive fracture in Si and interfacial characterization. The mean bond strength of the tested structures ranged from 18-61 MPa. The laminates with an SiO 2 film had higher dicing yield and bond strength than the laminates without SiO 2 for a 400 °C bonding temperature. The bond strength increased with increasing bonding temperature and bond force. The laminates bonded for 30 and 60 min at 400 °C and 60 kN had similar bond strength and amount of cohesive fracture in the bulk silicon, while the laminates bonded for 15 min had significantly lower bond strength and amount of cohesive fracture in the bulk silicon.
Eutectic and solid-state wafer bonding of silicon with gold
2012
The simple Au Si eutectic, which melts at 363 • C, can be used to bond Si wafers. However, faceted craters can form at the Au/Si interface as a result of anisotropic and non-uniform reaction between Au and crystalline silicon (c-Si). These craters may adversely affect active devices on the wafers. Two possible solutions to this problem were investigated in this study. One solution was to use an amorphous silicon layer (a-Si) that was deposited on the c-Si substrate to bond with the Au. The other solution was to use solid-state bonding instead of eutectic bonding, and the wafers were bonded at a temperature (350 • C) below the Au Si eutectic temperature. The results showed that the a-Si layer prevented the formation of craters and solid-state bonding not only required a lower bonding temperature than eutectic bonding, but also prevented spill out of the solder resulting in strong bonds with high shear strength in comparison with eutectic bonding. Using amorphous silicon, the maximum shear strength for the solid-state Au Si bond reached 15.2 MPa, whereas for the eutectic Au Si bond it was 13.2 MPa.
Au-Sn Eutectic Chip-Bonding for High Heat-Flux Vapor-Chamber Applications
2018
Chip-level bonding between components has been a widely studied subject for decades in the electronics industry, where several bonding methods like high temperature hydrophilic/hydrophobic, fusion, anodic and intermediate metal layer bonding have been investigated. Eutectic bonding, which leverages the diffusion between metal layers at relatively low temperature has gained popularity because of its superior strength, hermeticity and significantly relaxed restrictions on substrate type, roughness and flatness.