epdf.pub_nanotechnology-and-nanoelectronics-materials-devic

3.2 Characterization of Nanodefects in Crystals 19
planes end in the cut plane. n + 1 crystal planes may end on the other side of the
cut. Then an internal level remains without continuation. Roughly speaking, the
end line of this plane forms the dislocation, which can take the form of a loop.
We will now consider a case where silicon is exposed to a hydrogen plasma
and subsequently annealed. The effects of such a treatment vary and will be discussed
later. Here we will show the formation of the so-called platelet (Fig. 3.3).
A platelet is a two-dimensional case of a bubble, i.e., atoms from one or two
lattice positions are removed and filled with hydrogen, so that a disk-like structure
is formed (Fig. 3.4).
The proof of H 2 molecules and Si-H bonds shown in Fig. 3.4 can be done by
means of Raman spectroscopy. This is an optical procedure during which the
sample is irradiated with laser light. The energy of the laser quantum is increased
or decreased by the interaction of quasi-free molecules with the incoming light.
The modified reflected light is analyzed in terms of molecular energies which act
as finger print of the material and its specific defects.
p-type Czochralski (Cz) Si is plasma-treated for 120 min at 250 °C and annealed
in air for 10 min at temperatures between 250 °C and 600 °C. The Raman
shift is measured in two spectral regions [22, 23]. At energies around 4150 cm 1
the response due to H 2 molecules is observed (Fig. 3.5a), and around 2100 cm 1
that due to Si-H bonds (Fig. 3.5b).
Fig. 3.3 Formation of a (100) platelet in Si by hydrogen plasma at 385 °C [21].
The image has been acquired by the transmission electron microscopy.
Fig. 3.4
Platelets filled with H 2 molecules and Si-H bonds (schematic)