Chemistry Reference
In-Depth Information
Primary and Branched Pores.
The branched pores are significantly smaller
than the primary pores.
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The hierarchical pore structure has been found to be
universal to the PS formed on all types of substrates.
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Pore Arrays.
Straight large pores with smooth walls can be formed by back side
illumination of
of (100) orientation.
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Using micropatterning for pore initia-
tion sites (micro processed pits), regularly spaced pore arrays can be produced. Pro-
n
-Si
duction of pore arrays of
in diameter up to
deep on a 6-inch wafer has
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been reported.
Well-aligned pore arrays have not been obtained on [111] and [110]
wafers due to the misalignment between the direction of pore growth and that of the
hole source.
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Under given formation conditions, the pore diameter beyond the surface region
reaches a certain size determined by the formation conditions (i.e., HF concentration,
current density, potential, and doping concentration) and is generally constant with
increasing depth. According to Lehmann and Gr
ing
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as shown in Fig. 8.25, the
smallest possible pore diameter for a regular pore array is about below which
branching at the side of the pore bottom occurs. The largest pores are found to be about
above which formation of straight and smooth pores becomes a problem due to
hydrogen bubble formation. The diameter of the macropores formed on
ün
n
-Si
is pro-
portional to
Because
