NANOSECOND LASER ANNEALING FOR 3D MONOLITHIC INTEGRATION LETI - - PowerPoint PPT Presentation

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Nov 30, 2022 600 likes •710 views

LETI INNOVATION DAYS NANOSECOND LASER ANNEALING FOR 3D MONOLITHIC INTEGRATION LETI INNOVATION DAYS 2019 | Sbastien KERDILES | 2019, June 28th 3D SEQUENTIAL INTEGRATION : THERMAL BUDGET LIMITATION Cold processing required for the

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LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th

NANOSECOND LASER ANNEALING FOR 3D MONOLITHIC INTEGRATION

LETI INNOVATION DAYS

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| 2 LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th

‘Cold’ processing required for the top level, to

avoid any degradation of the bottom one.

Challenging for :

Epitaxy
Spacers deposition
Dopant activation
Gate stack formation

 Using ‘classical’ thermal treatment, i.e. heating

the whole wafer, maximum thermal budget is limited to ~ 500°C during ~2 hours 3D SEQUENTIAL INTEGRATION : THERMAL BUDGET LIMITATION

BEOL Top device tier i-BEOL Bottom device tier

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| 3 LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th

Principle : surface exposed to a sub-µs pulsed laser beam
High-T° anneal : extremely fast heating of the surface region during

the laser pulse. Sub-melt or melt regimes possible

Selective anneal : only the surface is heated, not the volume

UV radiation (308nm)  energy deposited in first 10-20 nm Si Ultra-short pulse ( ~ 160ns)  very limited heat diffusion

UV-Nanosecond laser annealing enables selective surface

annealing : UV-NLA only heats the top transistor ! ALTERNATIVE : UV NANOSECOND LASER ANNEALING (UV-NLA)

UV pulse Absorption in Si Limited heat diffusion

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| 4 LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th

SCREEN LT-3100

XeCl excimer laser :
 = 308nm
Pulse duration : 160ns (FWHM)
Repetition rate : 4Hz
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 :
Wafers : 300mm, 200mm, pieces
Heating chuck : 25-450°C
Atmosphere : N2 or Ar
In-situ metrology : surface melt detection

UV NANOSECOND LASER ANNEALING PLATFORM :

SCREEN LT-3100 platform for UV-NLA

 Uniformity : +/-1.5% (+/-3) 160ns 15x15mm² beam profile :

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| 5 LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th

Melt regime : single laser pulse
Perfect crystal recovery
Dopant activation at least

equivalent to high-T° RTP

 Liquid phase epitaxy

Sub-melt regime : multi-pulse

 Solid phase epitaxial regrowth

In-situ monitoring of the regrowth

APPLICATION : CRYSTAL CURING & DOPANT ACTIVATION

[Fenouillet-Béranger et al, S3S 2016]

SOI amorphized by As implantation SOI perfectly recrystallized

[Kerdilès et al, IWJT 2016] [Acosta et al, SSDM 2019]

Sheet resistance (ohm/sq.)

Start Final

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| 6 LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th

Low temperature gate stack integration
Challenges : low resistance & good reliability
Laser annealing used to crystallize a-Si:P & activate the dopants

APPLICATION : GATE STACK ANNEALING

UV-NLA 50 or 70 nm a-Si:P poly-Si:P UV-NLA a-Si:P poly-Si:P SiO2 (145 nm) HfO2+TiN SOI Bulk Si 50 nm  = 308 nm

No anneal : Rs ~ 540 ohm/sq.

AFM 1x1µm² Poly-Si:P TiN 10 nm HfO2 BOX SOI

 Minimal resistivity reached at the ‘near-total

melt’ of the a-Si:P layer

 Poly-Si grains ~ 100-300nm & SOI channel still

monocrystalline

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| 7 LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th

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  Guidelines on the process conditions

SIMULATION CAPABILITY

0.50 J/cm² 0.75 J/cm² 0.95 J/cm² 1.05 J/cm² Solid phase Liquid phase SiO2 SOI a-Si:P

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| 8 LETI INNOVATION DAYS 2019 | Sébastien KERDILES | 2019, June 28th

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

TAKE AWAY MESSAGES

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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