structures have been formed however other isolation structures for instance locos local oxidation of silicon structures could have been formed instead of sti structures regardless of the method used the isolation structures 4 essentially comprise an insulating material such as silicon oxide moreover in the figures references 6 and 8 relate to corresponding layers of masking resist while reference 5 relates to an initial layer formed on both portions 2 and 3 in fig3 d 3 f 4 d 4 g and 5 f references 7 and 9 relate to the final layers formed on the portions 3 and 2 of the substrate respectively in fig4 d 4 f and 5 e references 7 u2032 and 9 u2032 relate to intermediate layers formed on the portions 3 and 2 respectively in the following illustrative embodiments of process flows for forming the devices depicted in the figures are described in fig3 a 3 g according to one embodiment of the present invention the initial layer 5 of for example nitrided oxide is formed on both surface portions 2 and 3 fig3 b the initial layer 5 can be formed by first thermally growing an initial layer of oxide and annealing the initial layer of oxide in a nitrogen containing atmosphere for u2014 instance comprising ammonia nh 3 or nitrous oxide.