silicon nitride the masking layer 90 is formed by thermal oxidation by thermal nitriding or by low pressure chemical vapor deposition lpcvd the masking layer 90 is formed for example with a thickness of between 0 3 and 10 nanometers referring now to fig3 nanocrystallites 95 are then deposited on the masking layer 90 by way of example an lpcvd step is suitable for such a purpose the nanocrystallites 95 may for example be formed as silicon containing crystallites with a lateral extent of between 5 nanometers and 100 nanometers the free distance between adjacent nanocrystallites 95 is preferably of the same order of magnitude as their lateral extent in such a case the nanocrystallites 95 cover a first part 100 of the masking layer 90 and leave clear a second part 105 of the masking layer 90 referring now to fig4 the masking layer 90 is patterned using the nanocrystallites 95 as etching mask the first part of the masking layer 90 below the nanocrystallites 95 remains in place and the second part 105 of the masking layer 90 is removed if the nanocrystallites 95 are for example of silicon the masking layer which is of silicon nitride or silicon oxide can be etched selectively with respect.