COPPER SILICIDE PRECIPITATION INFLUENCED BY THE STRAIN OF A GE0.02SI0.98 HETEROEPITAXIAL LAYER

Copper silicide precipitates in silicon by forming elliptical colonies in 11101 planes. In strained Ge0.02Si0.98 heteroepitaxial layers on (001) silicon substrates the colonies prefer {110} planes intersecting the surface under an angle of 45-degrees with zero strain and avoid {110} planes perpendicular to the surface with maximum compressive strain. For the first time copper silicide precipitate colonies lying in (001) surrounded by Lomer dislocations have been observed and studied in detail. They are due to the maximum tensile strain in the [001] direction. The ordering of colonies increases as long as no relaxation via misfit dislocations occurs. The depth of the defect zone containing copper silicide precipitate colonies in the substrate wafer increases with the thickness of a thermal oxide layer on its surface. After annealing in nitrogen the copper silicide precipitate zone remains constant. The morphology of the copper precipitate colonies is first of all determined by the stress of the studied layer system and only to a less extent by the available silicon self-interstitials. Copper silicide precipitate colonies grow below a relaxing heteroepitaxial layer in a patterned arrangement that corresponds to the arrangement of the misfit dislocations. The elastic strain of the heteroepitaxial layer strongly influences the accumulation of copper impurities in the silicon substrate. The smaller the distance between the misfit dislocations becomes, the smaller is the depth of the defect zone containing copper silicide precipitate colonies.