Measurement of process-induced defects in Si sub-micron devices by combination of EDMR and TEM

¹ Silicon Systems Research Laboratories, NEC Corporation, Sagamihara, 229-1158, Japan
² Research Center for Knowledge Communities, University of Tsukuba, Tsukuba 305-8550, Japan

Corresponding author: y-mochizuki@az.jp.nec.com

Received: 7 July 2003
Accepted: 28 January 2004
Published online: 15 July 2004

Abstract

Process-induced defects are a serious issue for modern sub-micron Si LSIs. To characterize such defects, two different techniques are useful: electrically detected magnetic resonance (EDMR) and transmission electron microscope (TEM), which can detect small (point) and extended defects, respectively. We applied EDMR and TEM to the issue of defect-induced leakage currents in dynamic-random-access memory (DRAM) cells. For our DRAM samples (a 0.25-μm-rule series), although TEM showed no extended defects, EDMR successfully detected two types of point defects: V₂+O_x (Si divacancy-oxygen complexes) and larger Si vacancies (at least larger than V₆). We confirmed that these defects are the source of DRAM leakage currents. The observed defects were formed by ion implantation processes, but were more thermally stable than those in bulk Si crystals. The origins of this enhanced stability are attributed to the presence of oxygen atoms and a strong mechanical strain in LSIs. To clarify the origin of the complicated strain in LSI structures, we can directly measure the local-strain distribution in DRAM samples by means of convergent-beam electron diffraction (CBED) using TEM, which provides us with a valuable hint for understanding the formation mechanism of process-induced defects.