Annealing and thermal Recrystallization of amorphous SiC


  • Room temperatur implantation with high doses (> 1014 cm-2) in SiC results in amorphous surface layers and is accompanied by strong volume swelling.
  • The limited success in thermal annealing of amorphous (a) SiC led to contradictory de scriptions of the recrystallization of a-SiC in the literatur
  • Recently low temperature densification of a-SiC after thermal annealing at 500°C was reported.

 Aim of the investigations

  • Revealing the reason of the low temperature densification of a-SiC.
  • Throw light on the thermal recrystallization behaviour of amorphous SiC.


  • Substrate (bulk)material :

  • 6H-SiC wafers (n type, (0001) orientation, Si surface )
  • Amorphization :by 2 MeV, 2x1016 Si+/cm-2 implantation at room temperature 1.8 µm thick amorphous surface layer
  • Recrystallization :

  • - by stepwise thermal annealing in the temperaturerange between 250 and 1100°C over a wide spread time scale (5s ... 10h)
    - by use of  a resistance heated furnace and  a rapid thermal processor (ADDAX) under identical annealing conditions (Ar gas flow, ...)


  • Density determination : Volume swelling during amorphization enables step height measurements at unimplanted regions on the sample surface.


  • Structure analysis : X-ray diffraction (XRD) measurements under grazing incidence were performed to obtain signal only from the amorphous surface layer.
  • Surface morphology: Optical microscopy under dark field and transmitted-light illumination at a conventional optical microscope.


I. Step height measurements



Two stages of annealing were found :


  • Annealing at temperatures between 250 and 700?C leads to a specific densification of the amorphous layer after the first annealing period of 5 min.
  • The density increase can be described by an Arrhenius law with an activation energy of 184 meV.
  • Further thermal annealing up to 10 h leads only to minor density changes.
  • The structure is metastable.
  • Annealing at temperatures above 700°C leads to a second drop of the step height which ends up in a final step height of 40 nm.

 II. XRD, Nature of the two annealing stages




  • Low intensity, broad and featureless peaks occur which are almost identical with the spectrum of the as-amorphized layer.
  • The structure is still amorphous.
  • XRD pattern typical for polycrystalline SiC are observed from samples where the step height was decreased to the final value of 40 nm.
  • The second stage densification is an indication for recrystallization.
  • The complete disappearance of the residual step height can not be expected since grain boundaries occupy additional volume in the polycrystalline material.

III. Mechanism, process kinetics

  • Both the rapidity (5s at 850°C) and the low activation energy of the densification suggest that annealing of vacancy clusters is responsible for low temperature densification of a-SiC.



  • Johnson-Mehl-Avrami theory was used to describe the recrystallization kinetics:
                 The densification is determined by the crystalline fraction X(t) in the amorphous layer :
                                X(t) = SH(t) - SHra / SHpc - SHra
                                       = 1 - exp{-(Kt) n }, (K = K0 exp[-EA / kT])

The decreasing slope of the transformation curve indicates the change of the crystallization mode from nucleated growth (n>2) at 800°C to epitaxial growth (n>1) at 1000°C.

IV. Surface morphology