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A Study of Metal Impurities Behavior due to Difference in Isolation Structure on ULSI Devices

We have studied the behavior of metal impurities such as Cu and Ni with different isolation techniques in ULSI devices. We have found by using convergent beam electron diffraction (CBED) that the stress in a shallow trench isolation (STI) structure is larger than that of a local-oxidation-of-silicon (LOCOS) structure. With LOCOS, the highly doped substrate efficiently gettered Cu. However, with STI, a small amount of Cu diffused to the device area because of the high stress. On the other hand, high density of bulk micro defect (BMD) generated with the thermal processing of STI effectively getters Ni impurities. With the LOCOS-based wafer, a large amount of Ni diffuses to the device region because of the low BMD density.