Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 70: Methods: Atomic and Electronic Structure III

O 70.7: Talk

Friday, March 30, 2007, 11:45–12:00, H42

Geometric Analysis of Etch Pits for Intrinsic Defect Studies in Optical Crystals — •Christian Motzer and Michael Reichling — Fachbereich Physik, Universität Osnabrück, Barbarastr. 7, 49076 Osnabrück

Calcium fluoride is the material of choice in optical devices applying deep ultraviolet light. Intrinsic crystal defects, e.g. dislocations, may cause birefringence and reduce the laser damage threshold. Such defects, therefore, impose major limitations on optical lithography in the semiconductor industry. By etching the crystal surface such defects exhibit an enhanced reactivity and a characteristic etching figure remains that allows a characterisation of defects in the crystal. We have investigated the dimensions and geometry of etch pits created with hydrochloric and phosphoric acid on (111) CaF₂ cleavage plates by means of contact mode scanning force microscopy (SFM). By comparing geometric data, we can differentiate between two basic types. One etch pit type is related to dislocation defects terminating on the surface. Our measurements showed that the depth of those etch pits relates to the angle between the surface and the direction of dislocations. The other etch pit type is related to nm-sized local defects and has a typical geometric characteristic which differs from that of dislocation etch pits. High resolution SFM images reveal that there is a distinct transition when the core of these defects is dissolved. By comparing geometric data, we can differentiate between combinations of dislocations and these local defects.