We report on the fabrication and experimental characterization of single crystal diamond diffraction gratings fabricated with crystallographic dry etching. High aspect ratio atomic force microscopy reveals a characteristic V-groove profile exhibiting smooth sidewalls with an angle of 57 degrees. The discrepancy compared to the (111) crystal plane angle of 54.7 degrees can be explained by a directional isotropic etch contribution, which we confirm by etch process modelling based on the continuous automata method. The optical flatness of the diffraction gratings is measured using interferometry and better than lambda/2.