LETI INNOVATION DAYS NANOSECOND LASER ANNEALING FOR 3D MONOLITHIC INTEGRATION LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th
3D SEQUENTIAL INTEGRATION : THERMAL BUDGET LIMITATION • ‘Cold’ processing required for the top level, to avoid any degradation of the bottom one. BEOL Challenging for : Top device • Epitaxy tier • Spacers deposition • Dopant activation • Gate stack formation i-BEOL Using ‘ classical ’ thermal treatment, i.e. heating the whole wafer, maximum thermal budget is limited to ~ 500°C during ~2 hours Bottom device tier LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th | 2
ALTERNATIVE : UV NANOSECOND LASER ANNEALING (UV-NLA) • Principle : surface exposed to a sub-µs pulsed laser beam UV pulse • High-T° anneal : extremely fast heating of the surface region during Absorption the laser pulse. Sub-melt or melt regimes possible in Si • Selective anneal : only the surface is heated, not the volume Limited heat UV radiation (308nm) energy deposited in first 10-20 nm Si diffusion Ultra-short pulse ( ~ 160ns) very limited heat diffusion • UV-Nanosecond laser annealing enables selective surface annealing : UV-NLA only heats the top transistor ! LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th | 3
UV NANOSECOND LASER ANNEALING PLATFORM : SCREEN LT-3100 • XeCl excimer laser : • = 308nm 160ns • Pulse duration : 160ns (FWHM) SCREEN LT-3100 platform • Repetition rate : 4Hz for UV-NLA • Laser energy density range : 0.08 4.2 J/cm² ( bulk Si melts @ 1.75 J/cm²) • Large uniform laser beam : 26x36mm² or smaller (full die) • Scan mode : step & repeat • Other process conditions : 15x15mm² beam profile : • Wafers : 300mm, 200mm, pieces Uniformity : • +/-1.5% (+/-3 ) Heating chuck : 25-450°C • Atmosphere : N2 or Ar • In-situ metrology : surface melt detection LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th | 4
APPLICATION : CRYSTAL CURING & DOPANT ACTIVATION Sheet resistance (ohm/sq.) • Melt regime : single laser pulse • Perfect crystal recovery • Dopant activation at least equivalent to high-T° RTP SOI perfectly SOI amorphized by recrystallized As implantation Liquid phase epitaxy Start • Sub-melt regime : multi-pulse Solid phase epitaxial regrowth • In-situ monitoring of the regrowth Final [Kerdilès et al, IWJT 2016] [Fenouillet-Béranger et al, S3S 2016] [Acosta et al, SSDM 2019] LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th | 5
APPLICATION : GATE STACK ANNEALING • Low temperature gate stack integration • No anneal : Rs ~ 540 ohm/sq. Challenges : low resistance & good reliability • Laser annealing used to crystallize a-Si:P & activate the dopants = 308 nm AFM 1x1µm² Poly-Si:P UV-NLA UV-NLA TiN a-Si:P poly-Si:P 50 or a-Si:P poly-Si:P 70 nm SOI Minimal resistivity reached at the ‘ near-total HfO2 50 nm melt ’ of the a-Si:P layer HfO 2 +TiN SOI SiO 2 (145 nm) Poly-Si grains ~ 100-300nm & SOI channel still Bulk Si 10 nm BOX monocrystalline LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th | 6
SIMULATION CAPABILITY • 1D, 2D & 3D numerical simulations • LIAB software, developped by SCREEN • Temperature, phase, dopant concentration as a function of time and depth Ex : Gate stack annealing Liquid phase Solid phase a-Si:P SOI SiO 2 0.50 J/cm² 0.75 J/cm² 0.95 J/cm² 1.05 J/cm² Guidelines on the process conditions LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th | 7
TAKE AWAY MESSAGES • UV-Nanosecond laser annealing enables selective surface annealing : it only heats the top layer, not the embedded structures • Particularly relevant for 3D sequential integration but not only • UV Nanosecond Laser Annealing : available @ LETI, open for any collaboration LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th | 8
Leti, technology research institute Commissariat à l’énergie atomique et aux énergies alternatives Minatec Campus | 17 rue des Martyrs | 38054 Grenoble Cedex | France www.leti-cea.com
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