Whole-Wafer Mapping of Dislocations in 4H-SiC Epitaxy

Abstract

A non-destructive technique to image the dislocations and other extended defects in SiC epitaxial layers has been developed. Basal plane dislocations (BPDs) and threading dislocations (TDs) are imaged. Photoluminescence from the dislocations is excited with the 364 and/or 351 nm lines of an argon ion laser and near-infrared light is collected. A computer controlled probe station takes multiple images and the mm-sized images are stitched together to form whole-wafer maps. The technique is applied to a set of four n+ wafers from the same boule with 50 um n- epitaxial layers. The epitaxy was grown with Cree’s low-BPD process. BPDs form as either single, isolated dislocations or as clusters encircling micropipes. The concentration of TDs is on the order 104/cm2 and the local concentration varies more than an order of magnitude. The advantages of mapping dislocations by UV-PL imaging compared to other techniques are discussed.

Structure and Morphology of Inclusions in 4° Offcut 4H-SiC Epitaxial Layers

“…Large-area mapping was performed using the recently developed ultraviolet photoluminescence (UVPL) technique. 19 Various extended defects such as BPDs, in-grown stacking faults, threading dislocations, and more structurally complex defects, such as inclusions, were observed in UVPL images. High-resolution x-ray topography (HRXT) maps provided large-area information on lattice strain, lattice deformation, inclusions, and overall crystalline quality of the sample.…”

“…UVPL mapping was carried out using an Ar-ion laser with primary excitation lines at 351 nm and 364 nm (30 lm and 120 lm penetration depth, respectively), in conjunction with a computer-controlled probe station. 19 Images were digitally acquired using a liquid-nitrogen-cooled chargecoupled device (CCD) detector. HRXT maps were obtained using a 12-kW Rigaku rotating-anode source and a double-crystal arrangement, where an asymmetrically cut Si(111) monochromator crystal was used to obtain Cu K a radiation and provided horizontal magnification of the incident x-ray beam to image a larger area.…”

Examination of In-Grown Stacking Faults in 8°- and 4°-Offcut 4H-SiC Epitaxy by Photoluminescence Imaging

“…19 From the maps, average densities of IGSFs formed during epitaxial growth were estimated. The epitaxial structure of all the samples consisted of an n + buffer layer (thickness of 5 lm to 20 lm, $10 18 cm -3 ) and an n -drift layer (thickness of 10 lm to 120 lm, $10 14 cm -3 ), and some samples intended for fabricating devices had an additional p + layer (thickness of 2 lm, $10 18 cm -3 ).…”

Imaging Surface Pits and Dislocations in 4H-SiC by Forescattered Electron Detection and Photoluminescence

“…It should be noted, however, that PL alone was unable to differentiate between edge and screw dislocations in those studies. [17][18][19] …”

“…15,16 Images recorded by FED of regions containing surface features were compared to corresponding photoluminescence (PL) images of the same areas. PL has been previously utilized to image screw and edge dislocations in both 4H-SiC 17,18 and 6H-SiC 19 with molten KOH etching used for confirmation. It should be noted, however, that PL alone was unable to differentiate between edge and screw dislocations in those studies.…”