Chemistry Reference
In-Depth Information
dislocations,
91,304,319,340,387,433,1020
patterns,
dislocation network,
162,319,387
oxide precipitates,
445
swirl
387,433,1023
striations,
311,433
hillock defects,
652
epitaxial defects,
375
epitaxial
alignment,
367
grain boundary,
91,319,455
twin band,
91
diamond saw damage,
391
pn
398,399,410
precipitates,
388,1173
junction,
metallic
and damaged layer
of mechanically
polished surface.
302
319,340,387
Most defect etchants are mixtures of and The preferential
etching of dislocations takes place only at a proper concentration ratio of
HF.
HF.
and
387
These etchants are easy to use and fast, taking only several minutes to reveal
the defect etch features. Agitation is in general not required but it may improve the
quality of etched features in some etchants, such as Wright etch,
433
Yang etch,
387
Secco
etch.
319
etchants are also used for defect etching. For example,
based etchant has been found to be highly sensitive for defects
of polycrystalline materials.
91,993
Etching in a CuSO
4
-
HF solution under anodic bias
reveals surface defects associated with dislocation networks.
162
Etching profile by stain-
ing in Cu
2+
-containing acids at forward bias condition under illumination reveals
pn
junction and doping.
410,576
The copper preferentially is deposited on the
n
region, while
the silicon preferentially dissolves on the
p
region.
The degree of differential etching at defects depends on the orientation of the
crystal. In general, for diamond-type structures such as silicon it is much easier to
reveal dislocations on the {111} planes than on other planes.
289,387
Some etchants, such
as Sirtl etch, reveal sharply the defects on (111) planes but are not satisfactory for (100)
planes.
The defect etching behavior of different silicon crystal planes has been related to
the different surface potentials of the planes.
833
The surface energy of the low-index
surfaces follows the order The potential difference between a
dislocation and its surrounding area is greater on (111) surfaces than on (100) surfaces,
leading to a larger degree of preferential etching of the defects.
The etch pattern of dislocations is determined by the inclination of dislocations
to the surface.
387
For dislocations lying nearly parallel to the surface, dislocation lines
are observed. For dislocations lying at a steep inclination to the surface, etch pits result.
The basic unit of an etch pit is generally bounded by the (111) planes intersecting the
surface. The shape of a dislocation etch pit, which can be viewed as a superposition of
the basic units etched at different intervals along a dislocation, is uniquely determined
by the orientation of wafer surfaces and dislocation lines. Figure 7.61 schematically
illustrates the shapes of etch pits developed on the three major surfaces.
For the formation of a dislocation etch pit it is necessary that the etching rate
along the dislocation line be greater than the rate on the rest of the surface as shown
in Fig. 7.1(c). The increased etching rate along the dislocation line is due to the strain
field associated with the dislocation.
473,1022
Alternatively, the increased reactivity of dis-
locations may be due to the impurities preferentially segregated at dislocations. The
increased reactivity of edge dislocations leading to the initiation and propagation of
etch pits can be understood in terms of the chemical bonding and structure of the atoms
along the dislocation line. The atoms along a dislocation are only triply bonded to the
lattice and thus have dangling bonds. The terminal atom of an edge dislocation inter-
secting the surface may have only two dangling bonds. The sensitivity of an etchant to
defect etching is thus determined by the etch rate at the defects relative to that of the
