Nayar, Vishal; (1991) The photochemical growth and characterisation of thin SiO2 layers. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis reports a new method to grow thin silicon dioxide layers on silicon at low temperatures (<550°C). Oxide growth was induced photochemically by ultraviolet (UV) excimer radiation, a near UV mercury-xenon lamp and a low pressure UV mercury lamp. The latter was found to be most successful and was used to generate ozone and excite the silicon surface electronically. Thin oxide layers of the dimensions required for future microelectronic devices were grown. The growth process and the materials and electronic properties of the oxides were also investigated by a variety of techniques. Oxide growth appeared to follow Cabrera-Mott type kinetics. The capacitance-voltage (C-V) and current-voltage response was measured for metal oxide semiconductor capacitors incorporating the oxide grown by the UV/ozone technique. High breakdown fields (≈10MV/cm) and typical C-V characteristics were observed. Infra-red spectroscopy, X-ray photoelectron spectroscopy and a new technique spectroscopic ellipsometry (SE) were used to assess the chemical and structural properties of the oxides grown. In almost all respects the low temperature oxides were found to be the same as conventional furnace grown (high temperature) layers. Previously thick (>60nm) silicon dioxide on silicon layers have been studied by SE. In the present work the technique has been applied to layers over the range 3-50nm. The accuracy and usefulness of the technique has been studied in detail to reveal hitherto unknown density changes in thin oxides grown at 900 and 1050° C. The capability of multi-angle SE to produce unambiguous results of improved accuracy was demonstrated for the thinnest layers in this investigation. It was found that oxide density increased as the thickness decreased for both oxidation temperatures. This suggests that single wavelength ellipsometry studies of oxide growth kinetics may be invalid because of the failure to take into account oxide density variations. The main contributions of this research are the development of low temperature UV/ozone oxidation of silicon surfaces and the application of SE and multi-angle SE to silicon dioxide/silicon structures. Both these techniques are applicable to silicon microelectronics as the oxide thickness diminishes due to increased miniaturisation and sophistication of integrated circuits.

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