Chemistry Reference
In-Depth Information
generally are single crystalline (with some deviation from the substrate for very fine
structures) over a wide range of thicknesses.
649,650
For two-layer PS formed on illuminated
n
-Si the top micro PS may have very
different crystal structures varying from amorphous to polycrystalline to distorted
single-crystalline structure. For example, micro PS formed in 5% HF under illumina-
tion on
n
-Si with a doping range from 10
15
to 10
18
/cm
3
is single crystalline with the
same orientation as the substrate.
247,767
On the other hand, amorphous structure is found
in the micro PS formed on illuminated heavily doped
n
-Si.
640,651
The surface crystalline
structure of the PS formed on
n
-Si under illumination varies from single crystalline to
amorphous depending on the silicon resistivity and the condition of anodization as sum-
marized in Fig. 8.55.
36
Distortion of the crystalline structure of PS from that of substrate silicon is cor-
related with the size of the morphological structure and can be associated with a number
of causes. The extent of change in lattice spacing depends on the type of PS formed.
It has been found that the lattice spacing of the silicon atoms in PS is slightly larger
than in the Si substrate and the expansion is about 0.04% for degenerately doped
p
-Si
