The formation of copper microcrystallites on a Cu/Fe/Cu(100) sandwich due to annealing at temperatures between 500 K and 600 K was studied. For the crystallites to form, the iron film thickness must be more than 10 monolayers (bcc-Fe) and the copper film thickness must be in the range of 3-10 monolayers. The formation process of the crystallites was investigated using a newly developed apparatus allowing scanning electron, scanning Auger and scanning tunneling microscopy on the same sample position and repeated repositioning to a given position. The crystallites were found to form mainly at step bunches and predominantly oriented along the <110> directions of the copper substrate. A large number of screw dislocations are visible on top of the crystallites. The growth of the crystallites was observed by sequential measuring/annealing cycles. The results are discussed in terms of the structural transformation of the Cu/Fe/Cu sandwich.