Flash lamp & Pulsed laser annealing

The department has a long time experience in sub-second thermal annealing. It allows a fast heating up of solid surfaces on a time scale of nanoseconds (pulsed laser annealing) or within hundreds of microseconds to tens of milliseconds. Thereby, the achievable final temperature of the layer could be more than 2000 °C depending on the operation conditions and the optical and thermodynamic properties of the sample.

FLA Schema

Fig. 1: Basic Scheme of a FLA tool.

A typical tool for flash lamp annealing (FLA) is made by a chamber as shown in the Fig. 1 which can be flooded by an inert gas if needed. A bank of halogen lamps can preheat the wafer or another type of sample from the backside, whereas the flash itself is provided by a bank of Xe flash lamps from the front side. The reflector above the flash lamps directs the light toward the wafer and ensures a better homogeneity of irradiation. In order to protect the preheating and flash lamps they are separated from the wafer by suitable quartz windows.

PLA Schema

Fig. 2: Basic Scheme of a PLA tool.

In pulsed laser annealing (PLA) a XeCl excimer laser with a wavelength of 308 nm and a repetition rate of 10 Hz is guided onto the sample which can be moved underneath. Because of the short pulse time of 30 ns only a narrow region close to the surface is heated, whereas the backside stays at room temperature.

Main technical parameters

  FLA PLA
pulse length

130 µs - 80 ms

30 ns
sample size up to 300 x 200 mm2

5 x 5 mm2 (spot size)
annealing gas

N2, Ar, O2, atmosphere

atmosphere
energy density / energy per pulse

up to 135 Jcm-2

up to 500 W per pulse
preheating

up to 900°C

 no
handling mode

one flash one wafer

 raster scan of the wafer

Benefits:

  • maximum temperature only at surface
  • allows temperature-sensitive substrates
  • defect annealing after implantation
  • allows dynamic physical processes like explosive crystallization
  • suppresses unwanted phenomena like diffusion or segregation
  • is energy saving and suitable for roll-to-roll applications

Applications:

  • activation of dopants and defect annealing in semiconductors and semiconductor nanostructures
  • hyperdoping, i.e. doping above the solubility limit
  • Bandgap engineering of Si or Ge, e.g. by Sn alloying
  • thermal treatment of wide bandgap materials
  • thin films on glass substrates
  • flexible and printed electronics

Projects

  • Helmholtz Innovation Lab blitzlab for ultra-short time annealing, start 02/20,
  • DFG project Dotierung mittels FLA and ALD, start 2018
  • SAB project SiNERGY, 09/17 – 09/19
  • Humboldt Research Fellowship for Postdoctoral Researchers, Y. Berencén, 06/16 – 05/19

Publications

  1. Flash Lamp Annealing: From Basics to Applications
    L. Rebohle, S. Prucnal, D. Reichel
    Springer Series in Materials Science 288, Springer International Publishing, 2019
  2. Determination of the thermal cycle during flash lamp annealing without a direct temperature measurement
    L. Rebohle, M. Neubert, T. Schumann, W. Skorupa
    International Journal of Heat and Mass Transfer 126 (2018) 1–8
    https://doi.org/10.1016/j.ijheatmasstransfer.2018.05.119
  3. Doping by flash lamp annealing
    Prucnal, L. Rebohle, W. Skorupa
    Materials Science in Semiconductor Processing 62 (2017), 115-127
    https://doi.org/10.1016/j.mssp.2016.10.040
  4. Millisecond thermal processing using flash lamps for the advancement of thin layers and functional coatings
    Skorupa, T. Schumann, L. Rebohle
    Surface & Coatings Technology 314 (2017) 169–176
    https://doi.org/10.1016/j.surfcoat.2016.08.010
  5. A review of thermal processing in the subsecond range: semiconductors and beyond
    Rebohle, S. Prucnal, W. Skorupa
    Semiconductor Science and Technology 31(10), 103001 (2016)
    doi:10.1088/0268-1242/31/10/103001
  6. Subsecond annealing of advanced materials
    Skorupa and H. Schmidt (Ed.)
    Cham : Springer International Publishing, 2014