Two recipes to stabilize the surface melting in FLASiC structures


Two recipes to stabilize the surface melting in FLASiC structures

Voelskow, M.; Mücklich, A.; Stoemenos, J.; Skorupa, W.

Due to the lattice misfit between the silicon and the silicon carbide lattices the epitaxial deposition of SiC layers normally results in a highly defected carbide layer. Short time annealing seems to be an effective method to improve the crystal structure of the epitaxial layer using intense light pulses from flash lamps.
From the present point of view the annealing mechanism is based on the rapid melting of a thin silicon interface layer due to the intense light pulse, giving the non molten SiC layer the possibility for relaxation and annealing. Consequently, after the pulse is over and the liquid silicon intermediate layer solidifies epitaxially on the monocrystalline substrate one receives a high temperature annealed epitaxial SiC on silicon structure.
Although the annealing of the SiC layer due to the flash irradiation could be verified by TEM investigations a serious problem remains, connected with the facetted melting of the monocrystalline silicon surface after rapid heating above the melting temperature. Due to the layer by layer crystallisation within the molten pyramides, including a lateral growth component and due to the 5 % higher density of liquid silicon in comparison to solid silicon a surface relief will be formed after the solidification process is completed.
Two techniques were tested to circumvent the deep facetted melting.
The first procedure to homogenize the melting depth is based on the introduction of a so called melt stop layer in a certain depth below the SiC / Si interface. For this purpose carbon admixture which increases the melting temperature of silicon was implanted at a dose of 2*1017cm-2 and a energy of 140 keV through a 30 nm thick SiC layer into silicon, forming a approximately 200 nm thick melt barrier in a depth of 400 nm.
As a further possibility to prevent the facetted melting ion implantation of germanium admixture as a element reducing the melting temperature of silicon was tested.
It could be experimentally shown that both, the introduction of a melt stop layer at any depth behind the Si / SiC interface as well as the modification of the silicon surface, leading to a decrease of the silicon melting temperature, are usefull methods for the homogenization of the melting depth at the bulk silicon surface.

Keywords: flash lamp; annealing; pulse; melting; SiC

  • Lecture (Conference)
    HeT-SiC-05, 26.04.-01.05.2005, Krippen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7371
Publ.-Id: 7371