Using X-ray photoelectron spectroscopy, the chemical state of a silicon surface treated with hydrofluoric acid and the resulting contaminant species (fluorine, carbon and oxygen) were studied as a function of the etchant concentration (2-48%). The surface contamination was quantified as a function of the etchant concentration using a submonolayer coverage theory. It was seen that the carbon level had a minimum value (≈ 4.5×1013 atoms cm-2) for 5% HF concentration, whereas the oxygen level was almost constant (i.e. the variation was from 2×1013-4×1013 atoms cm-2), and the fluorine level showed a steady increase (2×1013-12×1013 atoms cm-2) with the concentration of the etchant. So, by selecting a suitable concentration of the etchant it is possible to create a silicon surface which is relatively free from contamination. Also one can modulate the amount of fluorine incorporation on the silicon surface. © 1992.

E. T Paul Benny

J. Majhi

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

An X-ray photoelectron study of the dependence of HF concentration on an etched silicon surface

Journal of Electron Spectroscopy and Related Phenomena

Our earlier XPS and UPS studies have shown that etching a silicon surface with 5% HF concentration produces a stable surface with minimum contamination and low density of surface states. This has prompted us to study the I-V and C-V characteristics of MIS diodes fabricated on silicon surfaces treated with 5% HF. Tunnel oxides of approximately 20 angstroms are grown on p-type (100) surfaces by a high-pressure (2 atm) and low-temperature (250 °C) method. Aluminum dots are vacuum evaporated through metal masks onto the oxide to fabricate MIS diodes. For photovoltaic measurements the gate electrode is made semitransparent by reducing its thickness to approximately 120 angstroms. From the variable-illumination current-voltage characteristics it is observed that the ideality factor n = 1.25, density of interface states Dit = 9×1011cm-2 eV-1, effective barrier height Vb = 0.74 V, open-circuit voltage Voc = 0.28 V and density of fixed oxide charges Q0 to approximately 1011 cm-2 of 5% HF treated diodes are lower than those of untreated devices where n = 1.54, Dit = 2×1012 cm-2 eV-1, Vb = 0.78 V, Voc = 0.42 V and Q0 to approximately 1012 cm-2. This is attributed to the removal of the native oxide and passivation of silicon dangling bonds by HF treatment. C-V characteristics of the MIS diodes also confirmed the reduction in barrier height on HF treatment. An increase in negative charges with increasing HF concentration, possibly due to excess of fluorine ions which may be responsible for the reduction in barrier height, is found in the interfacial layer.

Semiconductor Science and Technology

Effect of preoxidation treatment on the I-V and C-V characteristics of Si/SiO2/Al MIS diodes

Ultra-thin tunnel oxides(SiOx) were grown on silicon, pretreated with 5% hydrofluoric acid, using high-pressure low-temperature oxidation. These oxides were characterized using variable illumination current-voltage measurements on semi-transparent metal gate metal-insulator-semiconductor diodes. The open-circuit voltage, short-circuit current, ideality factor and reverse saturation current are studied as a function of oxidation time. The interface state density for the HF-treated sample was found to decrease from 2.0×1012cm-2eV-1 to 9.0×1011cm-2eV-1. The HF-treated wafers and those which were not treated were studied with X-ray photoelectron spectroscopy. The treated surfaces were found to contain fluorine in the region of 3-5 ×1013 atoms cm-2 and free of the native oxide layer. Highly reproducible good-quality ultra-thin oxides were obtained by pre-oxidation treatment of the wafer in hydrofluoric acid. It is also seen that the HF treatment induces a negative charge in the oxide grown. © 1991.

Journal	Journal of Electron Spectroscopy and Related Phenomena
ISSN	03682048
Open Access	No