Wafer capping of MEMS with fab-friendly metals

Martin, Jack

doi:10.1117/12.701573

Cited by 11 publications

(13 citation statements)

References 12 publications

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“…12 A shear strength of 740 g was reported for 30 μm wide rings, which was equal to the shear strength of a 150 μm wide glass frit bond. Bond force was said be to the key metric in this report.…”

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confidence: 93%

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Interfacial characterization of Al-Al thermocompression bonds

Malik

Carvalho

Poppe

et al. 2016

Journal of Applied Physics

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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

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confidence: 93%

“…The metals mainly used for bonding include Al, [12][13][14] Au 15 and Cu. 16 Au and Cu can be bonded at relatively low temperatures compared to Al as Al forms a native oxide on its surface on exposure to the air, this oxide is mechanically very strong.…”

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confidence: 99%

Interfacial characterization of Al-Al thermocompression bonds

Malik

Carvalho

Poppe

et al. 2016

Journal of Applied Physics

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“…Thermocompression bonding using deposited metal films as bonding material is promising for wafer-level encapsulation. Metals such as Au [3,4], Cu [4,5] and Al [4,[6][7][8][9] have been demonstrated as bonding layer between two silicon wafers. Bonding with an intermediate metallic layer is an attractive choice for MEMS devices.…”

Section: Introductionmentioning

confidence: 99%

“…Successful Al thermocompression bonding has been reported, but only limited details of bonding parameters for wafers having patterned bonding area have been presented [4,[6][7][8][9]. Yun et al bonded wafers by applying a range of bond forces for Al films with a range of Cu impurity levels (0% to 4%).…”

Section: Introductionmentioning

confidence: 99%

“…Fraux [10] reports that the company STMicroelectronics shrunk the size of their accelerometers by 57% when using Au-Au thermocompression bonding instead of glass-frit bonding. At the company Analog Devices, bond frames as narrow as 10 µm have been investigated for Al-Al thermocompression bonding [9]. Farrens [11] shows that a seal of a certain width can sustain a hermetic seal for a longer time when it is sealed by a metal than by glass.…”

Section: Introductionmentioning

confidence: 99%

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AlAl thermocompression bonding for wafer-level MEMS sealing

Malik

Schjølberg-Henriksen

Poppe

et al. 2014

Sensors and Actuators A: Physical

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Al-Al thermocompression bonding has been studied using test structures relevant for wafer level sealing of MEMS devices. Si wafers with protruding frame structures were bonded to planar Si wafers, both covered with a sputtered Al film of 1 µm thickness. The varied bonding process variables were the bonding temperature (400 °C, 450 °C and 550 °C) and the bonding force (18, 36 and 60 kN). Frame widths 100 µm, 200 µm, with rounded or sharp frame corners were used. After bonding, laminates were diced into single chips and pull tested. The effect of process and design parameters was studied systematically with respect to dicing yield, bond strength and resulting fractured surfaces. The test structures showed an average strength of 20-50 MPa for bonding at or above 450 °C for all three bonding forces or bonding at 400 °C with 60 kN bond force. The current study indicates that strong Al-Al thermocompression bonds can be achieved either at or above 450 °C bonding temperature for low (18 kN) and medium (36 kN) bond force or by high bond force (60 kN) at 400 °C. The results show that an increased bond force is required to compensate for a reduced bonding temperature for Al-Al thermocompression bonding in the studied temperature regime. HIGHLIGHTS Al-Al thermocompression bonding was demonstrated at a temperature as low as 400 °C. High dicing yield was achieved by applying a high bond force of 60 kN.  The possibility of reducing the bond force to 18 kN was demonstrated. The reduction in bond force required an increase in the bonding temperature to 450 °C.  Cohesive fracture in the bulk silicon below the Al layers was observed to a large extent, indicating good adhesion between Si and Al, and strong Al-Al bonded interfaces.

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Non-destructive wafer-level bond defect identification by scanning acoustic microscopy

et al. 2014

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Metal-based thermocompression bonding enables the creation of hermetic seals formed at relatively low processing temperatures and occupying a small portion of the device area. In the current study we have investigated the application of scanning acoustic microscopy (SAM) for assessing the quality of metal thermocompression bonds, both by evaluating its capabilities of localizing areas of poor bonding, and by finding defects in the integrity of the bond seal. Wafer laminates containing a test vehicle with pre-defined defects in the bond metal layer were sealed by Au-Au and Al-Al thermocompression bonding. Employing SAM, an area of 5 chips of poor bonding was identified non-destructively on the Al-Al laminate.Line defects of width 3.6 µm and point defects of diameter 22.4 µm have also been identified by SAM. The dicing yield for sealing frames was above 96% for all frame structures and both bond metal systems. The average bond strength was 31.5 ± 11.9 MPa for Al-Al thermocompression bonds and 37.3 ± 9.7 MPa for Au-Au thermocompression bonds.Scanning acoustic microscopy operates non-destructively and proved to be an extremely useful tool complementing current state-of-the-art methods for bond quality assessment.

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Wafer capping of MEMS with fab-friendly metals

Cited by 11 publications

References 12 publications

Interfacial characterization of Al-Al thermocompression bonds

Interfacial characterization of Al-Al thermocompression bonds

AlAl thermocompression bonding for wafer-level MEMS sealing

Non-destructive wafer-level bond defect identification by scanning acoustic microscopy

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