Arrays of cone-shaped diamond tip can be fabricated using conventional dry etching using silicon oxide dots as an etch-resistant mask. In this work, we have investigated how the size of the oxide mask dots influences the shape of the diamond cone tips. Silicon oxide dots (2 mum in diameter, 300 x 300 array) were patterned on a polycrystalline diamond film. The thickness of the oxide mask was chosen to be 400 and 800 nm. Under the given etching condition the 800-nm thick mask resulted in tips with better aspect ratio. This suggested that the longer etching time for a thicker mask helped sharpening the diamond tips.