Influence of the Wafer Edge on Defect Formation in P/P+ Silicon Vapor Phase Epitaxy
P. Feichtinger, B. Poust, H. Fukuto, M.S. Goorsky,
Dept of Materials Science and Engineering, University of California, Los Angeles;
D. Oster, J. Chambers, and J. Moreland,
Wacker Siltronic Corporation, Portland, OR.
An essential issue associated with optimizing substrates for devices
is the reduction of strain-relaxing defects. A challenge in the fabrication
of large diameter epitaxial silicon wafers is the heterogeneous nucleation
of misfit dislocations at crystal imperfections around the wafer edges.
Our prior investigations in the evolution of misfit dislocations in the
low-mismatch p/p+ silicon system showed that different edge treatments
of the highly boron doped substrates can help eliminate the misfit segments.
We investigated the nucleation process of misfit dislocations in boron
doped p/p+ silicon wafers. The samples were 150 mm Czochralski grown
wafers with boron concentration 2.6.1019 cm-3. Lightly
boron doped (1015 cm-3), compressively strained epitaxial layers
were deposited via vapor phase epitaxy at ~ 1100°C in a single wafer
reactor. The strain in the system is about 1.6* 10-4.
Three different thicknesses beyond the thermodynamically predicted critical
one (~ 1.2 mm) were employed. Double axis
x-ray diffraction was used to determine the off-orientation of the substrate
and the tilt of the epitaxial layer with respect to the substrate due to
misfit dislocation density differences. Double crystal x-ray topography
and defect etching were used to measure the length, density and properties
(Burgerís vector and thus glide plane) of the misfit dislocation segments
around the wafer periphery. Using high temperature annealing of wafer
pieces, the nucleation activation energy for misfit dislocations could
be determined in addition to the glide activation energy. Electrical
measurements were done in regions where the misfit or threading segments
existed to quantify the relationship between the defects and device performance.
All results suggest that edge treatments have the potential to impede the
formation of strain-relaxing defects in strained epitaxial systems.