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• Zoschke, Kai; Manier, Charles Alix; Oppermann, Hermann; Meier, Dirk; Malik, Nishant & Zakizade, Elahe [Show all 10 contributors for this article] (2023). Wafer Level Capping Technology for Vacuum Packaging of Microbolometers. In O’Conner, Lisa (Eds.), IEEE 73rd Electronic Components and Technology Conference (ECTC). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9798350334982. p. 1571–1578. doi: 10.1109/ECTC51909.2023.00267. Full text in Research Archive Show summary

  This paper presents novel technology developments for vacuum wafer level packaging of microbolometer arrays for thermal infrared sensors targeting applications in automotive, safety, and security/surveillance. The concept is based on fabrication of large cap structures on temporary carrier wafers and their subsequent transfer bonding to device wafers. The objective of the presented work was to develop and test wafer level vacuum packaging for MEMS microbolometer arrays (MBA) fabricated on read out integrated circuit (ROIC) wafers. For that, related MBA layouts integrating diverse Pirani vacuum test structures were fabricated on 200-mm silicon wafers. With intent of hermeticity, all wafer bonding steps were done by AuSn soldering using seal rings, which were deposited by electroplating. The relevant process flows with alternative process options as well as the obtained results of the capping approaches are presented and discussed extensively in this article. For characterization of the sealing results, Pirani test structures were utilized. First, their resistance vs. pressure behavior was determined under controlled reference vacuum. The measured resistance values of identical structures after capping were then compared with the reference data to estimate the residual vacuum inside the cavity of the bonded cap structures.

• Schjølberg-Henriksen, Kari; Malik, Nishant; Ambhore, Pranav & Goorsky, Mark S. (2018). The Synergistic Roles of Temperature and Pressure in Thermo-Compression Bonding of Au. ECS Transactions. ISSN 1938-5862. 86(5). doi: 10.1149/08605.0129ecst. Full text in Research Archive
• Ambhore, Pranav; Mani, Karthick; Beekley, Brett; Malik, Nishant; Schjølberg-Henriksen, Kari & Iyer, Subramanian S. [Show all 7 contributors for this article] (2018). The synergistic roles of temperature and pressure in thermo-compression bonding of Au. ECS Transactions. ISSN 1938-5862. 86(5), p. 129–135. doi: 10.1149/08605.0129ecst. Full text in Research Archive Show summary

  Abstract Au-Au thermocompression bonding is a widely used technique for a variety of applications including hermetic sealing and packaging at a fine pitch. We have investigated the roles of pressure and temperature individually at different pressures (15 -100 MPa) and temperatures (150 and 250° C) of sputter deposited 1.2 μm thick Au thin films using a flattening technique. The initial surface root mean square (RMS) roughness of deposited films was 3-5 nm. Void morphology and the evolution of the interface was studied using atomic force microscopy. Power spectral density function plots were used to study variation in asperities at the surface. The void morphology and evolution was different when flattening and bonding at different temperatures and pressures.

• Goorsky, Mark S.; Schjølberg-Henriksen, Kari; Beekley, Brett; Bai, Tingyu; Mani, Karthick & Ambhore, Pranav [Show all 9 contributors for this article] (2018). Characterization of interfacial morphology of low temperature, low pressure Au-Au thermocompression bonding. Japanese Journal of Applied Physics (JJAP). ISSN 0021-4922. 57(2). doi: 10.7567/JJAP.57.02BC03. Full text in Research Archive Show summary

  Au-Au thermocompression bonding is a versatile technique of high interest for a variety of applications. We have investigated Au-Au bonding using sputter deposited Au films under conditions of low temperature (150-250 °C) and low bonding pressure (∼3 MPa) for short times (15 min). The combination of low temperature and short times is important for applications involving both hermetic sealing and packaging scaling. The initial surface roughness of the Au film was in the 3-5 nm range with peak-to-valley heights of 20-30 nm and a lateral correlation length of ∼400 nm. For samples bonded at 150 °C, the void morphology at the bonded interface was related to the initial surface roughness. The void morphology was different when bonding at the higher temperatures: the void length (along the bonded interface) decreased significantly but the void height (perpendicular to the interface) increased. These results can be understood in terms of a combination of increased surface Au diffusivity and decreased yield stress and elastic modulus with increased bonding temperature. © 2018 The Japan Society of Applied Physics.

• Taklo, Maaike M. Visser; Schjølberg-Henriksen, Kari; Malik, Nishant; Poppe, Erik Utne; Moe, Sigurd T. & Finstad, Terje (2017). Al-Al Wafer-Level Thermocompression Bonding applied for MEMS, 2017 5th International Workshop on Low Temperature Bonding for 3D Integration (LTB-3D), Tokyo, 16-18 May 2017. IEEE (Institute of Electrical and Electronics Engineers). ISSN 9784904743034. p. 11–11. doi: 10.23919/LTB-3D.2017.7947407. Full text in Research Archive Show summary

  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.

• Malik, Nishant; Venkatachalapathy, Vishnukanthan; Dall, Wilhelm; Schjølberg-Henriksen, Kari; Poppe, Erik Utne & Taklo, Maaike M. Visser [Show all 7 contributors for this article] (2017). Texture of Al films for wafer-level thermocompression bonding. Superlattices and Microstructures. ISSN 0749-6036. 106, p. 216–233. doi: 10.1016/j.spmi.2017.03.053. Full text in Research Archive Show summary

  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 <111> 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.

• Malik, Nishant; Carvalho, Patricia; Poppe, Erik & Finstad, Terje (2016). Interfacial characterization of Al-Al thermocompression bonds. Journal of Applied Physics. ISSN 0021-8979. 119(20). doi: 10.1063/1.4952709. Full text in Research Archive Show summary

  Interfaces formed by Al-Al thermocompression bonding were studied by the transmission electron microscopy. Si wafer pairs having patterned bonding frames 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 the bonded interfaces of 200 μm wide sealing frames were investigated. It was observed that the interface had voids 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.

• Rebhan, Bernhard; Hinterreiter, Andreas; Malik, Nishant; Schjølberg-Henriksen, Kari; Dragoi, Viorel & Hingerl, Kurt (2016). Low-Temperature Aluminum-Aluminum Wafer Bonding. ECS Transactions. ISSN 1938-5862. 75(9), p. 15–24. doi: 10.1149/07509.0015ecst. Full text in Research Archive Show summary

  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.

• Schjølberg-Henriksen, Kari; Malik, Nishant; Gundersen, Elin Vold; Christiansen, Oscar Rincon; Imenes, Kristin & Fournel, Frank [Show all 7 contributors for this article] (2015). Electrical, Mechanical, and Hermetic Properties of Low-Temperature, Plasma Activated Direct Silicon Bonded Joints. ECS Journal of Solid State Science and Technology. ISSN 2162-8769. 4(7), p. P265–P271. doi: 10.1149/2.0271507jss. Full text in Research Archive Show summary

  The electrical, mechanical, and hermeticity properties of low-temperature, plasma activated direct silicon bonds were investigated. On individual dies with a bonding area ranging from 1–4 mm2, the bonded interface was found to have a capacitance ranging from 2.62 pF/mm2–2.89 pF/mm2 at 1 kHz. Linear I-V curves showed ohmic behavior without hysteresis. A resistance around 2.2 Ω and a current density of 1.1 × 104 A/m2 was measured at DC. We speculate that the capacitive and resistive responses are related to traps that are formed during the plasma activation process. The applied bonding process resulted in hermetic sealing with 100% yield on 2 × 481 dies. The maximum leak rate of the seals was 2.4 × 10−11 mbar⋅l⋅s−1, but could be significantly lower. No gross leaks were observed following a steady-state life test, a thermal shock test, and a moisture resistance test applied on 100 dies.

• Malik, Nishant; Poppe, Erik; Schjølberg-Henriksen, Kari; Taklo, Maaike Margrete Visser & Finstad, Terje (2015). Environmental Stress Testing of Wafer-Level Al-Al Thermocompression Bonds: Strength and Hermeticity. ECS Journal of Solid State Science and Technology. ISSN 2162-8769. 4(7), p. P251–P257. doi: 10.1149/2.0181507jss. Full text in Research Archive Show summary

  Hermeticity, reliability and strength of Al-Al thermocompression bonds realized by applying different bonding parameters have been investigated. Laminates of diameter 150 mm were realized by bonding wafers containing membrane structures to wafers with patterned bonding frames. The laminates were bonded applying a bond force of 36 or 60 kN at temperatures ranging from 300 to 400°C for 15, 30 or 60 minutes. The hermetic properties were estimated by membrane deflection measurements with white-light interferometry after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. Bond strength was measured by shear test and pull tests. Laminates bonded applying a bond force of 60 kN at temperatures of 350 or 400°C resulted in hermetic bonds. No significant change in membrane deflection was observed after the steady-state life test or the thermal shock test. However, a gross leakage was observed in 1–11% of the dies after exposure to the moisture resistance test. The maximum leakage rate (MLR) estimated from membrane deflection measurements was below 10−11 mbar·l·s−1 for all laminates. The measured average bond strength of dies from selected laminates ranged from 28 to 190 MPa.

• Malik, Nishant; Tofteberg, Hannah Rosquist; Poppe, Erik; Finstad, Terje & Schjølberg-Henriksen, Kari (2015). Environmental Stress Testing of Wafer-Level Au-Au Thermocompression Bonds Realized at Low Temperature: Strength and Hermeticity. ECS Journal of Solid State Science and Technology. ISSN 2162-8769. 4(7), p. P236–P241. doi: 10.1149/2.0201507jss. Full text in Research Archive Show summary

  Hermeticity, reliability and strength of four laminates bonded at different temperatures by Au-Au thermocompression bonding have been investigated. Laminates with a diameter of 150 mm were realized by bonding a wafer containing membrane structures to a Si wafer with patterned bond frames. A bond tool pressure of 2266 mbar was applied for 15 minutes at temperatures ranging from 150–300°C. The hermetic properties were estimated by membrane deflection measurements applying white-light interferometry after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. Bond strength was estimated by pull test measurements. A dicing yield above 90% was obtained for all laminates. Laminates bonded at 200°C and above had significantly higher hermetic yield than the laminate bonded at 150°C. No degradation in hermeticity was observed after the reliability tests. The maximum leakage rate (MLR) was estimated from two measurements of membrane deflection executed at two different times and was below 10−11 mbar ⋅ l ⋅ s−1. The average bond strength ranged from 44 to 175 MPa.

• Malik, Nishant; Schjølberg-Henriksen, Kari; Poppe, Erik; Taklo, Maaike Margrete Visser & Finstad, Terje (2015). Impact of SiO2 on Al–Al thermocompression wafer bonding. Journal of Micromechanics and Microengineering (JMM). ISSN 0960-1317. 25:035025(3). doi: 10.1088/0960-1317/25/3/035025. Full text in Research Archive Show summary

  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 (SiO2 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 SiO2 film had higher dicing yield and bond strength than the laminates without SiO2 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.

• Malik, Nishant; Schjølberg-Henriksen, Kari; Poppe, Erik; Taklo, Maaike Margrete Visser & Finstad, Terje (2014). Al-Al thermocompression bonding for wafer-level MEMS sealing. Sensors and Actuators A-Physical. ISSN 0924-4247. 211, p. 115–120. doi: 10.1016/j.sna.2014.02.030. Full text in Research Archive Show summary

  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, 450 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 AlAl 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 AlAl thermocompression bonding in the studied temperature regime

• Taklo, Maaike Margrete Visser; Schjølberg-Henriksen, Kari; Malik, Nishant; Tofteberg, Hannah Rosquist; Poppe, Erik & Vella, David Oscar [Show all 11 contributors for this article] (2014). Low-temperature bonding technologies for MEMS and 3D-IC. In Suga, Tadatomo (Eds.), 2014 4th IEEE International Workshop on Low Temperature Bonding for 3D Integration (LTB-3D), Tokyo, Japan, 15-16 July 2014. IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781479952601. p. 129–133. doi: 10.1109/LTB-3D.2014.6886173. Full text in Research Archive Show summary

  Recent developments within MEMS and IC call for a reduction in bonding temperature down to 350 °C and below. For MEMS, sensitive mechanical structures, thinned wafers, and heterogeneous integration of temperature-sensitive materials or materials with dissimilar temperature responses are main driving forces. For 3D-ICs, transistors' sensitivity to stress, and stress-induced failures in fragile dielectric layers are important motivations. The ongoing research on low-temperature bonding in the fields of MEMS and 3D-IC integration are partly overlapping. Therefore, extended knowledge exchange can be of mutual benefit, and will be attempted in this invited talk.

• Malik, Nishant; Tofteberg, Hannah Rosquist; Poppe, Erik; Finstad, Terje & Schjølberg-Henriksen, Kari (2014). Hermeticity and Reliability of Au-Au Thermocompression Bonds, Realized at Low Temperature. In Moriceau, Hubert; Baumgart, H; Goorsky, M.S.; Hobart, K.D.; Knechtel, R.; Suga, T. & Tan, C.S. (Ed.), 2014 ECS and SMEQ Joint International Meeting, October 5, 2014 - October 9, 2014 Semiconductor Wafer Bonding 13: Science, Technology, and Applications. The Electrochemical Society. ISSN 9781623321857. p. 167–176. doi: 10.1149/06405.0167ecst. Full text in Research Archive Show summary

  Hermeticity and reliability of four laminates bonded at different temperatures by Au-Au thermocompression bonding have been investigated. Laminates of diameter 150 mm were realized by bonding a wafer containing membrane structures to Si wafers with patterned bond frames. The laminates were bonded applying a bonding pressure of 8.5 MPa at temperatures of 150–300 °C for 15 minutes. The hermetic properties were estimated by measurement of membrane deflection at two different times after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. A dicing yield above 90 % was obtained for laminates bonded at or above 150 °C. Laminates bonded at 200 °C and above had significantly higher hermetic yield than the laminate bonded at 150 °C. No degradation in hermeticity was observed after the reliability tests. A maximum leak rate in the range of 10-11 mbar×l×s-1 was estimated.

• Schjølberg-Henriksen, Kari; Malik, Nishant; Gundersen, Elin Vold; Christiansen, Oscar Rincon; Imenes, Kristin & Moe, Sigurd T. (2014). Electrical, Mechanical, and Hermeticity Properties of Low-Temperature, Plasma Activated Direct Silicon Bonded Joints. In Moriceau, Hubert; Baumgart, H; Goorsky, M.S.; Hobart, K.D.; Knechtel, R.; Suga, T. & Tan, C.S. (Ed.), 2014 ECS and SMEQ Joint International Meeting, October 5, 2014 - October 9, 2014 Semiconductor Wafer Bonding 13: Science, Technology, and Applications. The Electrochemical Society. ISSN 9781623321857. p. 275–284. doi: 10.1149/06405.0275ecst. Full text in Research Archive Show summary

  The electrical, mechanical, and hermeticity properties of low-temperature, plasma activated direct silicon bonds were investigated. On individual dies with a bonding area ranging from 1 – 4 mm2, the bonded interface was found to have a capacitance ranging from 2.62 pF/mm2 – 2.89 pF/mm2 at 1 kHz. Linear I-V curves showing ohmic behavior without hysteresis and a resistance around 2.2 W were measured at DC voltage. We speculate that the capacitive and resistive responses are related to traps that are formed during the plasma activation process. The applied bonding process resulted in hermetic sealing with 100% yield on 2 × 481 dies. The maximum leak rate of the seals was 3.5 × 10-11 mbar×l×s-1, but could be significantly lower. No gross leaks were observed following a steady-state life test, a thermal shock test, and a moisture resistance test applied on 100 dies.

• Schjølberg-Henriksen, Kari; Malik, Nishant; Sandvand, Åsmund; Kittilsland, Gjermund & Moe, Sigurd T. (2014). Leak Rates and Residual Gas Pressure in Cavities Sealed by Metal Thermo-Compression Bonding and Silicon Direct Bonding. In Moriceau, Hubert; Baumgart, H; Goorsky, M.S.; Hobart, K.D.; Knechtel, R.; Suga, T. & Tan, C.S. (Ed.), 2014 ECS and SMEQ Joint International Meeting, October 5, 2014 - October 9, 2014 Semiconductor Wafer Bonding 13: Science, Technology, and Applications. The Electrochemical Society. ISSN 9781623321857. p. 305–314. doi: 10.1149/06405.0305ecst. Full text in Research Archive Show summary

  The residual gas pressure (RGP) in sealed cavities was measured by residual gas analysis (RGA). The cavity sealed by fusion bonding had the lowest RGP of 16 µbar. Cavities sealed by Au-Au thermocompression bonding and plasma bonding had RGPs of 0.18 and 0.22 mbar, respectively. The cavity sealed by Al-Al thermocompression bonding had RGP of 1.3 mbar. Cavities sealed by thermocompression bonding contained 0.16 – 0.21 mbar Ar. The leak rates of the four seal types were estimated by three methods. RGA measurements revealed that the maximum leakage rates were between 10-13 and 10-15 mbar·l·s-1.

• Malik, Nishant; Poppe, Erik; Schjølberg-Henriksen, Kari; Taklo, Maaike Margrete Visser & Finstad, Terje (2014). Hermeticity and Reliability of Al-Al Thermocompression Wafer Bonding. In Moriceau, Hubert; Baumgart, H; Goorsky, M.S.; Hobart, K.D.; Knechtel, R.; Suga, T. & Tan, C.S. (Ed.), 2014 ECS and SMEQ Joint International Meeting, October 5, 2014 - October 9, 2014 Semiconductor Wafer Bonding 13: Science, Technology, and Applications. The Electrochemical Society. ISSN 9781623321857. p. 149–160. doi: 10.1149/06405.0149ecst. Full text in Research Archive Show summary

  Hermeticity and reliability of laminates bonded by Al-Al thermocompression bonding applying different bonding parameters have been investigated. Laminates of diameter 150 mm were realized by bonding a wafer containing membrane structures to wafers with patterned bonding frames. The laminates were bonded applying a bond force of 36 or 60 kN at temperatures ranging from 300 to 400 °C for 15, 30 or 60 minutes. The hermetic properties were estimated by optical measurement of membrane deflection after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. Laminates bonded applying a bond force of 60 kN at temperatures of 350 °C or higher resulted in hermetic and reliable bonds. All the dies on the laminates survived steady-state life test and thermal shock test. Leakage was observed in some dies after exposure to moisture resistance test. Measurements of membrane deflection estimated a maximum leak rate below 10-11 mbar×l×s-1 for all tested bonding parameters.

• Malik, Nishant; Schjølberg-Henriksen, Kari; Poppe, Erik & Finstad, Terje (2013). Al-Al thermocompression bonding for wafer-level MEMS packaging, The 17th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS & EUROSENSORS XXVII), 2013 Transducers & Eurosensors XXVII, Barcelona, Spain June 16-20. IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781467359825. p. 1067–1070. Full text in Research Archive Show summary

  The Al-Al thermocompression bonding is studied on test structures suitable for wafer level packaging of MEMS devices. Si wafers with protruding frame structures have been bonded to planar Si wafers all covered with a 1 μm sputtered Al film. The varied bonding process variables were temperature (400 °C-550 °C), bonding force (18-36 kN) and frame widths (100 μm, 200 μm, rounded or sharp corners). The delamination caused by dicing and pull tests is systematically studied. It is concluded that bonding is incomplete at 400 °C, with a low dicing yield. The quality of the bonding is increased by increasing bonding temperature and force as expected. The fractured surfaces and the bonding strength have been studied in detail. The test structures showed an average strength of 20-50 MPa for bonding at or above 450 °C. The current study indicates that strong Al-Al thermocompression bonds can be achieved at or above 450 °C for a typical MEMS bond frame.

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• Zoschke, Kai; Manier, Charles Alix; Oppermann, Hermann; Meier, Dirk; Malik, Nishant & Zakizade, Elahe [Show all 10 contributors for this article] (2023). Wafer Level Capping Technology for Vacuum Packaging of Microbolometers. Full text in Research Archive Show summary

  This paper presents novel technology developments for vacuum wafer level packaging of microbolometer arrays for thermal infrared sensors targeting applications in automotive, safety, and security/surveillance. The concept is based on fabrication of large cap structures on temporary carrier wafers and their subsequent transfer bonding to device wafers. The objective of the presented work was to develop and test wafer level vacuum packaging for MEMS microbolometer arrays (MBA) fabricated on read out integrated circuit (ROIC) wafers. For that, related MBA layouts integrating diverse Pirani vacuum test structures were fabricated on 200-mm silicon wafers. With intent of hermeticity, all wafer bonding steps were done by AuSn soldering using seal rings, which were deposited by electroplating. The relevant process flows with alternative process options as well as the obtained results of the capping approaches are presented and discussed extensively in this article. For characterization of the sealing results, Pirani test structures were utilized. First, their resistance vs. pressure behavior was determined under controlled reference vacuum. The measured resistance values of identical structures after capping were then compared with the reference data to estimate the residual vacuum inside the cavity of the bonded cap structures.

• Ambhore, Pranav; Mani, Karthick; Beekley, Brett; Malik, Nishant; Schjølberg-Henriksen, Kari & Iyer, Subramanian S. [Show all 7 contributors for this article] (2018). The Synergistic Roles of Temperature and Pressure in Thermo-Compression Bonding of Au. Full text in Research Archive
• Taklo, Maaike M. Visser; Schjølberg-Henriksen, Kari; Malik, Nishant; Poppe, Erik Utne; Moe, Sigurd T. & Finstad, Terje (2017). Al-Al Wafer-Level Thermocompression Bonding applied for MEMS. Full text in Research Archive
• Rebhan, Bernhard; Hinterreiter, Andreas; Malik, Nishant; Schjølberg-Henriksen, Kari; Dragoi, Viorel & Hingerl, Kurt (2016). Low-Temperature Aluminum-Aluminum Wafer Bonding. Full text in Research Archive
• Beekley, Brett; Bai, Tingyu; Marathe, N.; Tofteberg, Hannah Rosquist; Malik, Nishant & Schjølberg-Henriksen, Kari [Show all 7 contributors for this article] (2015). Au-Au bonded interface microstructure and nanostructure formation during low temperature annealing. Full text in Research Archive
• Malik, Nishant; Venkatachalapathy, Vishnukanthan; Poppe, Erik; Schjølberg-Henriksen, Kari; Taklo, Maaike Margrete Visser & Finstad, Terje (2015). Grain structure of Aluminium films for wafer-level thermocompression bonding. Full text in Research Archive
• Taklo, Maaike Margrete Visser; Schjølberg-Henriksen, Kari; Malik, Nishant; Tofteberg, Hannah Rosquist; Poppe, Erik & Vella, David Oscar [Show all 10 contributors for this article] (2014). Low-temperature bonding technologies for MEMS and 3D-IC. Full text in Research Archive
• Schjølberg-Henriksen, Kari; Malik, Nishant; Sandvand, Åsmund; Kittilsland, Gjermund & Moe, Sigurd T. (2014). Leak Rates and Residual Gas Pressure in Cavities Sealed by Metal Thermo-Compression Bonding and Silicon Direct Bonding. Full text in Research Archive
• Malik, Nishant; Tofteberg, Hannah Rosquist; Poppe, Erik; Finstad, Terje & Schjølberg-Henriksen, Kari (2014). Hermeticity and Reliability of Au-Au Thermocompression Bonds, Realized at Low Temperature. Full text in Research Archive
• Malik, Nishant; Poppe, Erik; Schjølberg-Henriksen, Kari; Taklo, Maaike Margrete Visser & Finstad, Terje (2014). Hermeticity and Reliability of Al-Al Thermocompression Wafer Bonding. Full text in Research Archive
• Schjølberg-Henriksen, Kari; Malik, Nishant; Gundersen, Elin Vold; Christiansen, Oscar Rincon; Imenes, Kristin & Moe, Sigurd T. (2014). Electrical, Mechanical, and Hermeticity Properties of Low-Temperature, Plasma Activated Direct Silicon Bonded Joints. Full text in Research Archive
• Malik, Nishant; Poppe, Erik; Schjølberg-Henriksen, Kari; Taklo, Maaike Margrete Visser & Finstad, Terje (2014). Hermeticity and reliability characterization of Al-Al thermocompression bonding. Full text in Research Archive
• Malik, Nishant; Schjølberg-Henriksen, Kari; Poppe, Erik & Finstad, Terje (2013). Al-Al thermocompression bonding for wafer-level MEMS packaging. Full text in Research Archive
• Malik, Nishant; Schjølberg-Henriksen, Kari; Poppe, Erik; Taklo, Maaike Margrete Visser & Finstad, Terje (2013). Optimization of Al-Al thermocompression bonding. Full text in Research Archive
• Malik, Nishant (2017). Metal thermocompression bonding for MEMS. Universitetet i Oslo. Full text in Research Archive

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