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The effects of laser marking on silicon wafers were studied by oxidation and preferential etching for structure characteristics. Scanning electron microscopy (SEM) and optical microscopy were used to study cleanliness and epitaxial growth characteristics. Laser marking not followed by etching is seen to cause dislocations and slip patterns in the vicinity of the mark after an oxidation. If the wafer is etched after marking in either caustic (KOH) or acid (HF/nitric/acetic) no dislocations or slip patterns develop after an oxidation cycle. Marking done in dot matrix mode exhibits slag around the dots which is above the plane of the polished surface. It is shown that epitaxial growth on this slag is slower than on the polished surface. No epitaxial spikes are observed on marks engraved before polishing. No contamination is observed on finished polished slices. However, at high magnification (×4000 and ×20 000) particulate matter is seen after a photoresist has been applied, baked, exposed, developed, and stripped.
laser marking, contamination, structure damage, epitaxial spike, process automation
Product Development Director, Dynamit Nobel-SMIEL, Cupertino, Calif.
SMIEL Spa Dynamit Nobel Group, Novara,