ning zhang and michael dudley department of materials science and engineering, stony brook...

Ning Zhang and Michael DudleyNing Zhang and Michael Dudley

Department of Materials Science and Engineering, Stony Brook University

Ning Zhang and Michael DudleyNing Zhang and Michael Dudley

Department of Materials Science and Engineering, Stony Brook University

While the general picture of defect propagation/conversion from the While the general picture of defect propagation/conversion from the substrate may be understood to a certain extent, the nucleation of defects substrate may be understood to a certain extent, the nucleation of defects near the interface between the substrate and epilayer has not received much near the interface between the substrate and epilayer has not received much attention. Surface scratches, residual from polishing, are generally accepted attention. Surface scratches, residual from polishing, are generally accepted as dislocation nucleation sites during the epitaxial growth although no as dislocation nucleation sites during the epitaxial growth although no detailed mechanism for this process has been reported. Wedetailed mechanism for this process has been reported. Wepresent a study of defect nucleation at substrate surface scratches.present a study of defect nucleation at substrate surface scratches.

Introduction

Figure 1. X-ray topographs (a, c and e) Figure 1. X-ray topographs (a, c and e) and corresponding etch pit patterns (b, d and corresponding etch pit patterns (b, d and f) recorded from epilayers grown on and f) recorded from epilayers grown on a scratched substrate surface. (a)-(b) a scratched substrate surface. (a)-(b) show a scratch parallel to the off-cut show a scratch parallel to the off-cut direction while (c)-(f) show scratches direction while (c)-(f) show scratches inclined to the off-cut direction. inclined to the off-cut direction.

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.

Commercially available 4H-SiC wafers grown by the PVT technique with an Commercially available 4H-SiC wafers grown by the PVT technique with an 8°off-cut angle toward the [11-20] direction were used as the substrates for 8°off-cut angle toward the [11-20] direction were used as the substrates for chemical vapor deposition (CVD). After CVD growth, synchrotron x-ray chemical vapor deposition (CVD). After CVD growth, synchrotron x-ray topographs were recorded from the epilayer. The samples were etched in topographs were recorded from the epilayer. The samples were etched in molten potassium hydroxide (KOH) at 600°C for 10 min. following the x-ray molten potassium hydroxide (KOH) at 600°C for 10 min. following the x-ray topography. The etch patterns were recorded for furthertopography. The etch patterns were recorded for furthercomparison with x-ray topographs.comparison with x-ray topographs.

Experiment

Nucleation of TEDs and BPDs

Figure 3. Schematic diagrams show (a) Figure 3. Schematic diagrams show (a) generation of dislocation loops near the generation of dislocation loops near the substrate surface due to the scratch, substrate surface due to the scratch, and (b) Two possibilities for replication and (b) Two possibilities for replication of the loop surface intersections during of the loop surface intersections during CVD epitaxial growth.CVD epitaxial growth.

Residual damage associated with Residual damage associated with scratches on the substrate surface scratches on the substrate surface are expected to have dislocation are expected to have dislocation half-loops associated with them half-loops associated with them and their surface intersections act and their surface intersections act as sites from which dislocations as sites from which dislocations propagate via replication during propagate via replication during homo-epitaxial growth. Scratches homo-epitaxial growth. Scratches parallel to the off-cut direction parallel to the off-cut direction create half-loops whose surface create half-loops whose surface intersections are mostly edge in intersections are mostly edge in character which propagate into the character which propagate into the epilayer as TEDs. As the inclination epilayer as TEDs. As the inclination between the scratches and the off-between the scratches and the off-cut direction increases so does the cut direction increases so does the probability that the associated half-probability that the associated half-loops will have one surface loops will have one surface intersection can have significant intersection can have significant screw character leading to screw character leading to propagation into the epilayerpropagation into the epilayeras screw character BPDs. as screw character BPDs.

44thth Dr. Mow Shiah Lin Scholarship Award Dr. Mow Shiah Lin Scholarship Award

Defects AnalysisTheoretical Background

Experiment

Strain Mapping Results

Strain/Stress Mapping

When the crystal is subjected to a displacement field:

)( 00 unnn

:/0 nn

Plane normal before/after distortion :u

Displacement field associated with the distortion

0n u

the vector pointing the direction of the greatest rate of increase of ; its magnitude is the greatest rate of change of .

0n u

0n u

0 0n n u the vector perpendicular to the plane after deformation.

un

0Magnitude of the displacement field along .

0n

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 εxx, εyy, εzz, εxy, εxz and εyz, respectively.

Synchrotron White Beam X-ray Reticulography (SWBXT)