In this work, we have correlated the electrical characteristics of ultrathin oxide with the presence of pinholes by C-AFM studies. Ultrathin gate oxide has been grown thermally as well as by chemical treatment with HNO 3, followed by selective anodic oxidation. The results of C-AFM studies confirm that the improvement in the gate leakage current in thermally grown oxide is indeed due to the filling of pinholes by selective anodic oxidation, while the absence of pinholes in the chemically grown oxide explains why there is no improvement in the gate leakage current after selective anodisation. © 2005 Elsevier B.V. All rights reserved.

Nandita Dasgupta

Department of Electrical Engineering

Vaibhav G. Marathe

Anodic oxidation

Atomic force microscopy

Leakage currents

C-AFM

PINHOLES

SELECTIVE ANODIC OXIDATION

ULTRATHIN GATE OXIDE

silica

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

Thin Solid Films

In this paper the effect of selective anodisation under ac bias on ultrathin (1.5-2.75 nm) silicon dioxide grown at two different temperatures, viz. 700 °C and 800 °C have been studied. It is shown that ac anodisation is much more effective in improving the electrical properties of the ultrathin oxide compared to selective anodisation carried out under dc condition. Unlike dc anodisation, which only repairs the pinholes but does not improve the interfacial properties, ac anodisation is found to reduce the density of interface states. The parameters during ac anodisation, e.g. signal frequency and dc offset are found to have a major role in the degree of the improvement and have been optimised carefully. Best results have been obtained when ac anodisation has been carried out using a 260 mV peak-to-peak signal of frequency 5 kHz and dc offset of 70 mV. © 2007 Elsevier Ltd. All rights reserved.

Solid-State Electronics

Optimisation of ac anodisation parameters for the improvement of electrical properties of thermally grown ultrathin gate oxide

In this paper, electrical and reliability properties of ultrathin silicon dioxide, grown by immersing silicon in nitric acid solution have been studied. It is observed that the temperature, oxidation time, and concentration of the nitric acid solution play important roles in determining the thickness as well as the quality of the oxide. Prolonged exposure to nitric acid degrades the quality of the oxide. However, it was found necessary to reduce the oxidation temperature and the concentration of nitric acid to grow oxide of thickness < 2 nm. In these conditions, the leakage current and fixed oxide charge in the chemical oxide were found to be too high. However, when this chemical oxidation was followed by anodic oxidation using ac bias, the electrical and reliability characteristics of metal-oxide-semiconductor (MOS) devices showed tremendous improvement. MOSFETs with gate oxide grown by this technique have demonstrated low subthreshold slope, high transconductance and channel mobility. It is thus proposed that chemical oxidation followed by ac anodization can be a viable alternative low-temperature technique to grow thin oxides for MOS application. © 2007 IEEE.

IEEE Transactions on Device and Materials Reliability

Electrical and reliability characteristics of MOS devices with ultrathin SiO2 grown in nitric acid solutions

In this paper we have studied the effect of selective anodisation under ac bias on ultrathin (2–2.75 nm) silicon dioxide grown at 800°C. It is shown that ac anodisation is more effective in improving the electrical properties of the ultrathin oxide compared to selective anodisation carried out under dc condition. Unlike dc anodisation, which only repairs the pinholes but does not improve the interfacial properties, ac anodisation is found to reduce the density of interface states. The efficacy of ac anodisation is found to depend on the ac signal frequency and best results have been obtained at a frequency of 5 kHz. © 2006 Taylor & Francis Group, LLC.

IETE Journal of Research

Improvement in the interfacial properties and electrical characteristics of ultrathin SiO2 by selective AC anodisation

The presence of weak spots and pinholes in ultrathin gate oxides significantly increases the leakage current, thereby degrading the device performance. This paper proposes a method, which identifies the weak spots in thermally grown gate oxide and repairs them by selective anodization. By controlling the applied voltage, it is ensured that current flows only through the weak spots in the oxide during anodization. Anodic oxide therefore grows over these weak spots, improving the reliability of the oxide without increasing the gate oxide thickness. Significant improvement in electrical characteristics was observed in the gate oxides treated by anodic oxidation.

IEEE Electron Device Letters

Improvement in electrical characteristics of ultrathin thermally grown SiO2 by selective anodic oxidation

Journal of Applied Physics

Nitric acid oxidation of Si to form ultrathin silicon dioxide layers with a low leakage current density

Enhancement of the effective tunnel mass in ultrathin silicon dioxide layers

IEEE Transactions on Electron Devices

Determination of deep ultrathin equivalent oxide thickness (EOT) from measuring flat-band C-V curve

Study of pinholes in ultrathin SiO2 by C-AFM technique

Journal	Thin Solid Films
ISSN	00406090
Open Access	No