Surface melting by flash lamps

Controlled surface melting by means of flash lamp irradiation


High intensity flash lamp irradiation is capable to melt semiconductor surfaces up to micrometer depths. Hereby results the possibility of a controlled manipulation of dopant profiles. In dependence on the value of the segregation coefficient of previously introduced dopant atoms into the substrate material, complete different profiles can be produced. For boron in silicon, for example, with a segregation coefficient near one, the epitaxial crystallisation results in a rectangular profile. However, for doping elements with a low segregation coefficient (e.g. antimony) the crystallisation process leads to an enrichment near the surface.

A serious problem results from the high overheating of the surface inducing spontaneous faceted melting with laterally varying melting depth. Besides inhomogeneous doping a strong surface relief is formed during the solidification process.

Molten Si

Optical micrograph of a  ( 100 )  Si wafer after 20 ms flash lamp irradiation ( magnification: 200 ).


Previous experimental work within the framework of the European FLASiC project was performed with the aim to homogenize laterally the melting depth by introducing a buried layer into silicon having a increased melting temperature. High dose carbon implantation was used successfully to install a so called melt stop layer in a depth about 100 nm beneath the surface. Taking up some experience from FLASiC it shall be tried in a starting DFG project to realize a limited buried melting by lowering of the melting temperature using high dose Germanium implantation. An additional deposited mechanically stabilizing capping layer system should guarantee a maximum of surface smoothness after the solidification. In parallel with the experiments computer simulation will be performed to predominate temperature profiles and melt depths in the system and to confine the range of experimental parameters. These simulations will be performed in cooperation with the University Cambridge using the existing computer program, which was used successfully during the FLASiC work.

Melt depth

The figure shows the calculated melting depths for a typical FLASiC – layer system, consisting of: 60 nm SiC / 200 nm Si (SOL) / 65 nm SiC / bulk Si in  dependence on the irradiated energy density

Recent publication:

  • M. Voelskow, M. Smith, W. Skorupa, R. McMahon
    Appl. Phys. Lett. 87, 241901 (2005)
  • M. Smith, R. McMahon, M. Voelskow, W. Skorupa, J. Stoemenos, G. Ferro,
    J. Appl. Phys. 100, 094909 (2006)