“Bulk Micro Defects,” is a term commonly used to refer to oxygen precipitates in silicon. In fact, many imperfections in the silicon lattice create defects, and BMDs could be any imperfections including oxygen precipitates, voids, inclusions, slip lines, etc.
BMDs go by many names, referring to the problems they cause, how they were created, or their physical characteristics. Examples include COPs (Crysal Originated Particles) and Grown-In Defects.
Imperfections in the lattice of a semiconductor and impurities create energy states in the bandgap, decrease carrier lifetime, and increase junction leakage. They also act as gettering sites at which impurities tend to concentrate. The profile of BMDs is often controlled as shown in the figure above, via a complex series of high temperature processes, to create a “denuded zone,” so that the surface layer silicon, where the MOS transistor action takes place, is free of oxygen precipitates, and the oxygen precipitates in the underlying silicon acts as a gettering site to keep impurities away from the MOS transistors.
IR light penetrates most semiconductor materials, and since BMDs alter the local optical properties of a semiconductor, BMDs can be detected by illuminating a sample with IR light and looking at it with a camera that is sensitive to IR. Both the LST-300a Light Scattering Tomography system and the SIRM-300 Scanning Infrared Microscope system detect BMDs. The respective technologies they use are Light Scattering Tomography and Scanning Infrared Microscopy.
