Micheli, Francesca; (1990) Argon laser oxidation of silicon. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The growth of high quality silicon dioxide layers of thicknesses between a few 10's and a few 100's Å is a fundamental step in the development of present and future VLSI technology. The use of optical radiation allows very fast heating times compared to a classical quartz furnace and is therefore well suited to the formation of very thin layers. Our investigation aimed at isolating and quantifying a possible photonic enhancement to the mainly thermal oxidation process, as was suggested in recent years. This could mean lower fabrication temperatures and, therefore, reduced unwanted side effects. Furthermore, laser processing gives the opportunity of very fine scale pattern production either by direct writing or projection imaging. C-Si samples of various orientations and doping levels were oxidized in dry oxygen with an Argon laser as the sole source of energy. By exploiting the thin film interference effect, we succeeded in amplifying small differences in the growth rates induced by the two strongest laser spectral lines and arising by non-thermal effects, thereby confirming the existence of a photonic effect related to incident photon flux. To further improve our technique and measurement facilities, we devised an in-situ, non-invasive, computer controlled monitor capable of measuring oxide thickness and temperature on the irradiated sample. An estimate of the absolute value of this photonic component to the reaction was provided by experiments with double-side polished silicon, which acted as a sort of 'filter' for this non-thermal effect. An empirical mathematical model was obtained for the photonic component of the growth rate. Oxidation of heavily doped samples gave further backing to suggested scenarios of photoexcited carriers induced effects. Our results were finally discussed in the light of the vast amount of literature available in the field of silicon oxidation.

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