A method of manufacturing a plurality of through-holes in a layer of first material by subjecting part of the layer of said first material to ion beam milling.For batch-wise production, the method comprises after a step of providing the layer of first material and before the step of ion beam milling, providing a second layer of a second material on the layer of first material, providing the second layer of the second material with a plurality of holes, the holes being provided at central locations of pits in the first layer, and subjecting the second layer of the second material to said step of ion beam milling at an angle using said second layer of the second material as a shadow mask.