Ning Zhang and Michael Dudley

1
4th Dr. Mow Shiah Lin Scholarship Award
Strain/Stress and Defects Analysis in Silicon
Carbide
Ning Zhang and Michael Dudley Department of
Materials Science and Engineering, Stony Brook
University
Defects Analysis
Strain/Stress Mapping
While the general picture of defect
propagation/conversion from the substrate may be
understood to a certain extent, the nucleation of
defects near the interface between the substrate
and epilayer has not received much attention.
Surface scratches, residual from polishing, are
generally accepted as dislocation nucleation
sites during the epitaxial growth although no
detailed mechanism for this process has been
reported. We present a study of defect nucleation
at substrate surface scratches.

• When the crystal is subjected to a displacement
  field

Plane normal before/after distortion
Displacement field associated with the distortion
Magnitude of the displacement field along .
the vector pointing the direction of the greatest
rate of increase of its magnitude is
the greatest rate of change of .
Commercially available 4H-SiC wafers grown by the
PVT technique with an 8off-cut angle toward the
11-20 direction were used as the substrates for
chemical vapor deposition (CVD). After CVD
growth, synchrotron x-ray topographs were
recorded from the epilayer. The samples were
etched in molten potassium hydroxide (KOH) at
600C for 10 min. following the x-ray topography.
The etch patterns were recorded for
further comparison with x-ray topographs.
the vector perpendicular to the plane after
deformation.
Nucleation of TEDs and BPDs
Synchrotron White Beam X-ray Reticulography
(SWBXT)
Residual damage associated with scratches on the
substrate surface are expected to have
dislocation half-loops associated with them and
their surface intersections act as sites from
which dislocations propagate via replication
during homo-epitaxial growth. Scratches parallel
to the off-cut direction create half-loops whose
surface intersections are mostly edge in
character which propagate into the epilayer as
TEDs. As the inclination between the scratches
and the off-cut direction increases so does the
probability that the associated half-loops will
have one surface intersection can have
significant screw character leading to
propagation into the epilayer as screw character
BPDs.
Figure 1. X-ray topographs (a, c and e) and
corresponding etch pit patterns (b, d and f)
recorded from epilayers grown on a scratched
substrate surface. (a)-(b) show a scratch
parallel to the off-cut direction while (c)-(f)
show scratches inclined to the off-cut direction.
Strain Mapping Results
Figure 2. (a) Enlarged x-ray topograph recorded
from a region similar to Fig 1(c) (b)
Corresponding etch pit pattern showing six pairs
of TEDs (hollow arrows) and a single paired TED
and BPD (solid arrows) which have propagated from
the scratch to the epilayer surface.
Figure 3. Schematic diagrams show (a) generation
of dislocation loops near the substrate surface
due to the scratch, and (b) Two possibilities for
replication of the loop surface intersections
during CVD epitaxial growth.
Figure 1. Figure 4. Strain mapping of a 20 mm x
27 mm region in a 3-inch SiC wafer. (a) (f) are
3D mapping of the six strain components exx, eyy,
ezz, exy, exz and eyz, respectively.