Transient interferometric mapping of carrier plasma during external transient latch-up phenomena in latch-up test structures and I/O cells processed in CMOS technology

Substrate current distribution as trigger for external latch-up (LU) and transient latch-up (TLU) is analyzed by optical transient interferometric mapping (TIM) technique. The transient free carrier (plasma) concentration related to substrate current flow is studied for various guard-ring configurations and injection carrier type on special test structures and real I/O cells. TIM uncovers proximity effects in I/O cells causing substrate current crowding which are important for the definition of effective LU protection concepts.