Formation of U-shaped diamond trenches with vertical {111} sidewalls by anisotropic etching of diamond (110) surfaces

U-shaped diamond trenches with vertical {111} sidewalls for power devices were successfully obtained by anisotropic etching of diamond (110) surfaces using Ni films in high-temperature (1000 °C) water vapor. The etching rate for the diamond (110) surfaces was estimated to be 3.8 mm/min on the basis of the relationship between etching time and etching depth of diamond trenches with (110) bottoms. These (110) bottoms gradually disappeared as the etching progressed. Finally, they completely vanished and each diamond trench was surrounded by four vertical {111} sidewalls and two slanted {111} sidewalls. The formation mechanisms of the U-shaped diamond trenches are also discussed on the basis of the experimental results.