Chemical Etching of SiC

The procedure involves placing a solid salt in a Pt (platinum) beaker and bringing it up to the required temperature. The salt crystals liquefy and the SiC sample to be etched is placed in a Pt mesh basket and is then lowered into the molten salt for the required time. All of the molten salts to be used for this procedure need oxygen for etching [1]. The oxygen can be supplied by the molten salt, as in the case of KOH, or by the surrounding atmosphere. The following molten salts have been used to etch SiC and reveal various surface features  

In the 6H polytype, with the stacking sequence ABCACB, the (0001) carbon face and the (0001) silicon face etch differently because the SiC bond is slightly ionic. Many researchers use this fact to determine the difference between the two faces. Koga et al [9] used KOH to study three kinds of etch pits in 6H-SiC single crystal grown by the sublimation method. They observed that by increasing the pressure they could reduce one type of etch pit. 

Chlorine and fluorine-based gases at high temperature attack SiC [1]. If one uses pure chlorine and/or fluorine a layer of carbon is left on the surface. This layer of carbon can be removed by adding oxygen to the mixture. Fluorine and chlorine based gases are highly reactive to many materials and in many applications are not practical. 

Hydrogen [1] and HC1 [10] at high temperatures, above 1350°C, etch SiC. Hydrogen etching is useful in cleaning the surface prior to epitaxial growth and appears to be non-preferential. 

HC1 etching at 1350°C has been used to study defects [10] and decorated defects in a similar way to that of molten salts. 

---

W. Kem, Wet-chemical etching of SiC>2 and PSG films, and an etching-induced defect in glass-passivated integrated circuits, RCA Rev. 47, 186, 1986. 

---