the starting material for the cvd deposition during the processing step for the deposition of the undoped silicon oxide layer 4 so that during the subsequent deposition process at 635 u00b0 c for 45 minutes a doped silicate glass fill 3 is deposited in the trench 1 and on the mask nitride layer 6 with reference to fig2 first a varnish fill 7 is poured into the trench next the varnish fill 7 is sunk into the trench 1 to between one tenth and one half the trench depth the sinking can be carried out with a plasma process that utilizes acid and or nitrogen at 175 u00b0 c next the silicate glass fill 3 and undoped silicon oxide layer 4 are also sunk into the trench buffered hydrofluoric acid bhf in a ratio of 88 10 2 of water ammonia hydrofluoric acid h 2 o nh 4 hf can be applied for 30 seconds to accomplish the sinking with reference to fig3 first the varnish fill 7 is completely removed from the trench which can be carried out with piranha this being a matter of concentrated sulfuric acid h 2 so 4 95 with a temperature of 110 u00b0 c next an oxide cover layer 8 is deposited in the trench 1 and on the mask nitride layer 6 the oxide cover layer 8 is realized with a cvd method that utilizes teos as the starting material fig4 represents the result of a temperature step at approximately 1 000 u00b0 c for 90 minutes in.