MRS 1999 Fall Meeting

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.