Assessment of Polishing-Related Surface Damage in Silicon Carbide

Abstract

The subsurface damage generated by the polishing of silicon carbide crystals was investigated by measuring dislocation densities in sublimation grown SiC layers and through the use of high-resolution X-ray diffraction. Physical vapor transport growth on silicon carbide seeds, with a typical polishing finish using 1 m diamond paste, leads to the nucleation of threading edge dislocations of density on the order of 10 7 cm Ϫ2 and threading screw dislocations of density on the order of 10 6 cm Ϫ2 . Chemical mechanical polishing lowered the dislocation density by four orders of magnitude for threading screw dislocations and two orders of magnitude for threading edge dislocations. Controlled high temperature hydrogen etching was used to determine the depth of damage produced by mechanical polishing and it was found to be 700 Ϯ 300 Å. Diffuse scattering from mechanically polished, chemical mechanically polished, and hydrogen etched SiC crystals were quantified by triple axis high-resolution X-ray diffraction. A consistent trend of decreasing diffuse scattering intensity was observed in mechanically polished, chemical mechanically polished, and hydrogen etched surfaces. Root mean squared ͑rms͒ roughness measurements of the surface finishes, obtained with atomic force microscopy, were in agreement with the high-resolution X-ray diffraction results. The mechanically polished surfaces had an rms roughness that was two to three times larger than the chemical mechanically polished surfaces.

Optimizing reactive ion etching to remove sub-surface polishing damage on diamond

“…13,21,22 HRXRD was performed here after repeated etching steps had removed materials from the surface. This technique has been reported in the literature to study polishing damage in silicon carbide 23 and was applied here to determine the effectiveness of the RIE process and estimate the extent of the polishing damage (as a function of depth). This approach offers a nondestructive qualitative assessment of polishing damage depth on diamond substrates.…”

Dislocation nucleation in 4H silicon carbide epitaxy

“…Similar flat-bottomed circular etch pits are frequently observed along scratches on mechanically polished SiC wafers. The dislocations along a scratch have very limited length and typically do not extend for more than a fraction of a micron from the surface [19]. Thus, it can be inferred that the threading dislocations of the array P extended down to no more than 3 mm from the epilayer surface.…”

Synchrotron X-ray topography analysis of local damage occurring during polishing of 4H-SiC wafers

“…[6][7][8][9][10][11][12][13][14][15][16][17] There are also reports on the quality of epi-films investigated from the view-point of surface preparation before starting the epi-film growth. 18,19) However, most of those works are based on the assumption that damage is introduced uniformly on the wafer surface, but not locally.…”