novel wafer bonding technology survey
DESCRIPTION
NOVEL WAFER BONDING TECHNOLOGY SURVEY. Po-Wen Chen Department of Electrical Engineering and Graduate Institute of Electronics Engineering National Taiwan University, Taipei, Taiwan, R.O.C. Outline. Introduction Wafer bonding Wafer bonding application TEM inspection of our - PowerPoint PPT PresentationTRANSCRIPT
Department of Electrical Engineering, National Taiwan University
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NOVEL WAFER BONDING NOVEL WAFER BONDING TECHNOLOGY SURVEYTECHNOLOGY SURVEY
Po-Wen Chen
Department of Electrical Engineering and Graduate Institute of Electronics Engineering
National Taiwan University, Taipei, Taiwan, R.O.C.
Department of Electrical Engineering, National Taiwan University
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Outline
•Introduction•Wafer bonding•Wafer bonding application•TEM inspection of our bonding achievement
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Introduction
• Clean(hydrophilic)
• Alignment• Pre-bonding• Anneal
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Wafer Bonding
• Anodic Bonding
•Silicon Direct Bonding/Fusion Bonding
• Intermediate-Layer Bonding
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Anodic Bonding
•Rely on charge migration
•Silicon and glass with alkali metal
–Glass with 3.5% Na2O
•Negative voltage to glass to attract and neutralize Na+
•Due to electric field , O2- transported to glass-silicon interface form SiO2
•Electrostatic attraction between glass-silicon interface
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•Enhance positive ion mobility at 500℃•Produce uniform bonds,but charged carriers make it incompatible with active device•Useful for pressure sensors, solar cells and piezoresistive and package applications
Anodic Bonding
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Silicon Direct Bonding/Fusion Bonding
• Join silicon wafer by – Create and contact hydrophobic or
hydrophilic surfaces– Anneal at high temperature
• Hydrophobic case – HF dip before contact– More challenging than hydrophilic
wafer ,but ultimately better?• Hydrophilic case
– SC1(standard cleaning) before bonding
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Silicon Direct Bonding/Fusion Bonding
• AfterSC1 ,the mirror polished silicon wafer filled with hydroxyl radicals(OH- )
• OH- on polished silicon face permit a good initial contact bond
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Silicon Direct Bonding/Fusion Bonding
• Subsequent heating dehydrates• OH- cause oxidation of the bondi
ng surface resulting in a Si-O-Si bond• As annealing temperature are inc
reased beyond 1000℃ ,the strength of the bond approaches that of silicon itself
• Viscosity and pressure of ambient gas ,wafer contact energy influence speed
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• Press in the middle of wafer to create a preliminary point of contact
• While mechanical spacer maintain wafer physically separated
• Retract spacer to form a single bonding wave from center to wafer
• Spacer integrity is important– Multiple bonding waves promote warpage
and voids– Gas trapped in pocket form by multiple wa
ves
Silicon Direct Bonding/Fusion Bonding
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Silicon Direct Bonding/Fusion Bonding
• From room temperature 110C– Slow fracture effect and interface
water rearrangement• From 110 C to 150 C
– Polymerization of silanol groups across the interface
• From 150 C to 800 C– Bonding energy limited by conta
cted area• From 800 C and above
– Complete bonding via oxide flow
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Influence of particle
Schematic of particle leading to an unbonded areaEx :a particle of about 1um diameter leads to an unbonded area with a diameter of about 0.5cm of typical 4-in diamet
er silicon wafers with a thickness of 525um
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Influence of surface
R＞ 2tw
R＜ 2tw
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Intermediate-Layer Bonding
Options for intermediate layer bonds
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Intermediate-Layer Bonding
Eutectic and glass-frit bonding techniques– Deposition of intermediate metallic and glass films
• Eutectic bond– Examine a two component phase diagram
• Little solubility between the component , reveal eutectic point located at the lowest melting temperature
• Alloy– Formed by solid-liquid inter-diffusion at contact interface – Followed by solidification upon cooling
• Gold and silicon– 363℃,2.85%Si,97.1%Au by weight
• Good eutectic bond– Remove silicon oxide films that hamper gold diffuse into
silicon
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Intermediate-Layer Bonding
• Before bonding– Exposure to ultraviolet light to remove organic contaminants
• Low temperature – Reach eutectic point make this technique attractive for
active device processes
• Glass frit bond– Create hermetic seals using relatively low temperature– Thin glass layer is deposited and pre-glazed– Wafer brought into contact at rated melting temperature of
glass ,less than 600℃– Pressure is applied to maintain contact– Lead borate with significant lead oxide content is often used
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Checking for wafer-to-wafer
bonding integrity• Three dominant methods for
imaging a bonded pair of silicon wafer– Infrared transmission– Ultrasonic– X-ray topography
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Visualization of the bonded wafer pair
X-ray topography Ultrasonic IR transmission
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Bonding Strength Measurement
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Wafer bonding application
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BESOI(ELTRAN)
Smart-cut
Wafer bonding application
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TEM inspection of our bonding achievements
Department of Electrical Engineering, National Taiwan University
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TEM inspection of our bonding achievements