SPECIFIC PREPARATION PROCEDURES FOR FAILURE ANALYSIS OF (SUB)MICRON AREAS IN SILICON DEVICES

Special preparation techniques have to be applied for trans-mission el ectron microscope (TEM) failure analysis of ULSI devices as well as fo r technology characterization of non-periodic test patterns to obtain information from volumes as small as 1 x 1 x 1 mum3. These regions may be prepared either as thin cross sections or as planview specimens by making use of a well established precision polishing technique. In th is article strategical preparation steps are described which have to b e thought of and carried out depending on the specific problem before the specimen is actually thinned. This comprises the choice of localiz ation and marking techniques for the area of interest and the consider ation whether layers which cover the surface of the Si substrate and i mpede TEM observation should be removed by either chemical or mechanic al means. Precise ion milling of planview specimens becomes necessary to remove thin residual polycrystalline layers on the Si substrate whi ch disturb TEM observation of, defects in the silicon near-surface zon e due to diffraction contrast. Particular problems require specimens a few micrometers thick, to be studied in an 1 MV TEM first in order to locate the exact position of the interesting features. Further ion mi lling may then provide a thin specimen usable for characterization by imaging and composition analysis. The various approaches and procedure s will be illustrated by numerous examples taken from memory and logic device technology.