OVERVIEW ON SURFACE MICROSTRUCTURING BY PHOTODESORPTION ETCHING OF CHLORINATED SILICON

Developing a mechanistic interpretation of complex dynamical chemical systems such as halogen photoetching requires correlated microscopic data on the kinetics, dynamics, surface composition and microstructure of prototypical and real surfaces. This overview is concerned especially with two important variables which significantly influence the microetching mechanisms and structures; (I) the role of electronic point defects induced by substitutional doping in producing site-specific reactions and, (II) the quantum mechanical enhancement of chemical reaction induced by uv-radiation at low fluences and temperatures.

From uv-photoetching and photodesorption studies of heavily doped Si(100) and Si(111) with chlorine beams at low laser fluences, the mechanisms of photostimulated desorption is analyzed based primarily on the kinetics of chemisorption and surface layer microanalysis obtained from core-level photoemission. These results are coupled with time-of-flight dynamical measurements on the energetics of the photodesorption process to provide a more unified understanding of anisotropic photon-stimulated microetching.

Substantial alterations of the etching mechanisms occur when selective surface molecular processes are driven quantum mechanically by low level photon radiation rather than thermally. This is clearly reflected in the dynamical mechanisms for photodesorption which become strongly site- and atomic process-selective illustrated by the energetics of the processes. Creation and transport of charged carriers, especially at high doping levels by photoionization coupled with field-induced charge transport, introduces new reaction channels into the surface chemistry leading to resultant changes in the microstructure on an atomic scale. The results from the kinetics, velocity dynamics and film composition measurements are combined in terms of the dependency of chlorine adsorption on doping at high carrier levels and low laser fluences, to provide an improved interpretation of the anisotropic microetching in terms of field-promoted electron-hole activation.