In an effort to improve the silicon carbide (SiC) substrate surface, a new electrochemical mechanical polishing (ECMP) technique was developed. This work focused on the Si-terminated 4H-SiC (0001) substrates cut 8°off-axis toward <1120>. Hydrogen peroxide (H 2 O 2 ) and potassium nitrate (KNO 3 ) were used as the electrolytes while using colloidal silica slurry as the polishing medium for removal of the oxide. The current density during the polishing was varied from 10 µA/cm 2 to over 20 mA/cm 2 . Even though a high polishing rate can be achieved using high current density, the oxidation rate and the oxide removal rate need to be properly balanced to get a smooth surface after polishing. A two-step ECMP process was developed, which allows us to separately control the anodic oxidation and removal of formed oxide. The optimum surface can be achieved by properly controlling the anodic oxidation current as well as the polishing rate. At higher current flow (Ͼ20 mA/cm 2 ), the final surface was rough, whereas a smoother surface was obtained when the current density was in the vicinity of 1 mA/cm 2 . The surface morphology of the as-received wafer, fine diamond slurry (0.1 µm) polished wafer, and EMCP polished wafer were studied by high-resolution atomic force microscopy (AFM).
A new electro-chemical mechanical polishing (ECMP) process was developed for SiC. This work focused on the n-type Si-face 4H-SiC (0001) substrates, with 8 ° off axis toward <1120>. Hydrogen peroxide (H 2 O 2 ) and potassium nitrate (KNO 3 ) solutions were used as the electrolytes while using colloidal silica slurry as the polishing medium for removal of the oxide. The current density during the polishing is varied from 10µA/cm 2 to over 20mA/cm 2 . At higher current flow (>20mA/cm 2 ), the final surface was rough whereas a smoother surface was obtained when the current density was in the vicinity of 1mA/cm 2 .
Selective growth of SiC on SiC substrate was demonstrated in a chemical vapor deposition (CVD) reactor using a new high temperature mask. Bulk 4H-SiC with 8 o miscut (0001) Si-face wafers were coated with the high temperature mask and patterned using standard photolithography. The pattern consisted of window stripes as spokes of a wheel. Epitaxial growth of SiC was carried out in a conventional, horizontal, rf-heated cold wall reactor at temperatures in the range 1450-1550 o C. When the window stripes are oriented along <1120> miscut direction, the growth on the exposed area followed the substrate orientation, and the top surface was smooth and specular. However, when the window stripes are aligned along <1100> direction (perpendicular to the miscut direction), the growth on the window stripes developed (0001) facets on the surface. Epitaxial lateral overgrowth over the mask was also studied by cross sectional scanning electron microscopy (SEM). It was found that the extent of lateral growth varied with the stripe orientation. Effects of growth temperature as well as silane flows on the selective growth were also studied. Higher temperature or lower silane flow results in the etching of exposed SiC instead of growth. The etched surfaces developed orientation dependent facets similar to the growth. Importantly, the mask could be easily removed after the growth.
Selective nitrogen doping of 4H-SiC by epitaxial growth using TaC as the hightemperature mask has been demonstrated. Nomarski optical microscopy and scanning electron microscopy (SEM) were used to characterize selective growth of SiC. In addition, 250-µm, square-shaped, p-n junction diodes by selective n-type epitaxial growth on a p-type epilayer were fabricated. The refilled fingers with different width were designed to vary the periphery/area (P/A) ratio. The effects of P/A ratio on the current-voltage (J-V) characteristics have been investigated. The ideality factor extracted from J-V characteristics is Ϸ2 at a temperature range of 25-275°C, which indicates that the ShockleyRead-Hall recombination is the dominant mechanism in the conduction region. The reverse leakage current does not show dependence on P/A ratio for trench-refilled diodes. The room-temperature reverse leakage-current density at 100 V is less than 3.5 ϫ 10 Ϫ7 A/cm 2 for all diodes. Also, the reverse leakage current does not increase significantly with temperature up to 275°C. The breakdown voltages measured at room temperature are about 450 V and 400 V for diodes without and with fingers, respectively.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.