Role of the oxidizing agent in the etching of 4H-SiC substrates with molten KOH

Abstract

A novel etching solution using molten potassium hydroxide (KOH) for the identification of dislocation types in a silicon-carbide (SiC) epilayer is identified. Threading screw dislocations (TSDs) and threading edge dislocations (TEDs) are rarely useful for size-based differentiation of etch pits in highly nitrogen (N)-doped SiC through conventional KOH etching. In this study, we report the role of sodium peroxide (Na₂O₂) and potassium dioxide (KO₂) as oxidizing agent additives to the etchant for identifying the dislocation types in highly N-doped 4H-SiC. A Na₂O₂-KOH phase diagram was calculated to predict the chemical composition of the etchant. Solid-phase Na₂O₂ remained in the system when added to the etchant at concentrations greater than 13-wt% Na₂O₂, and it provided excess oxygen to the etchant. We experimentally confirmed that etch pit shapes became more hexagonal and that the etch pit sizes of TSDs and TEDs differed more greatly when more than 20-wt% Na₂O₂ was added to the etchant. We also found that the size distribution of TEDs was much smaller than that of TSDs after etching using Na₂O₂-KOH. Dissolved oxygen played an essential role in enhancing the anisotropic etching of highly N-doped SiC and allowed the dislocation types to be identified.