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Transmission electron microscopy investigations of the formation of macropores in n- and p- Si(001)/(111)

: Jäger, C.; Finkenberger, B.; Jäger, W.; Christophersen, M.; Carstensen, J.; Föll, H.


Materials Science and Engineering, B. Solid state materials for advanced technology 69/70 (2000), S.199-204
ISSN: 0921-5107
Fraunhofer ISC ()

Morphology and interfaces of macropores in (001)- and (111)-oriented n- and p-type silicon were studied by analytical and high-resolution transmission electron microscopy (TEM) for different stages of their evolution during electrochemical etching with oxidizing and non-oxidizing electrolytes. In n-type Si(001) etched under oxidizing conditions macropores along [100] (diameters~ 1 µm) connected with dendrtic pores (diameters ~ 0.25µm) are formed The dendric pores consist of periodic arrangements od truncated octahedral voids and oxide interface inclusions preferentially at the pore tips, indicating that pore formation proceeds in an oscillatory mode and that the pore nucleation stage in governed by oxidation and subsequent oxide dissulution at the reactive si-electrolyte interface. At later stages of their formation the interfaces of macropores in n- and p-type Si(001) possess {111} facets, and oxide interfaces inclusions are absent thus indicating that {111} fecets are stabilized against further dissolution. In p-Si(001) etched by non-oxidizing organic electrolytes dense arraays of Si fibers and pores with lateral dimensions of a few nanometers form at the surface and inside macropores with preferential [100] pore axes orientation. The presence of this mesoporous Si indicates strongly localized collective direct dissolution processes and a presominance of a direct dissolution mechanism for p-Si etched with a non-oxidizing electrolyte. In (111)-orientated Si Wafers the macropores grow along directions indicating an orientation-dependent growth mechanism.