978-1-4244-7199-7/10/$26.00 © 2010 IEEE PROC. 27th INTERNATIONAL CONFERENCE ON MICROELECTRONICS (MIEL 2010), NIŠ, SERBIA, 16-19 MAY, 2010 Probing the Electrical Properties of the Si Nitride/Si Interface C. Tsonos, A. Kanapitsas, A. Karagounis, I. Stavrakas, D. Triantis, C. Anastasiadis, P. Photopoulos, V. Em. Vamvakas and P.Pissis Abstract - The present publication employs Dielectric Relaxation Spectroscopy for the examination of the relaxation mechanisms in silicon nitride MIS structures. These results are combined with capacitance and conductance measurements in order to give a more complete picture of the dielectric behaviour of silicon nitride. The analysis concludes with a method based on Dielectric Relaxation Spectroscopy for the calculation of the depletion layer width. IINTRODUCTION Silicon nitride is material widely used in microelectronics. Some of its applications include Si 3 N 4 films as gate dielectrics in MOS transistors [1] or in MOS ICs in the form of thin nitride-oxide layers [2] for memory applications. Because of these and other applications the dielectric properties of Si 3 N 4 have been extensively studied [3,4]. The calculation of the depletion width for an MIS structure, a p-n or a Schottky diode, is based on the solution of the Poisson equation by making some approximations based on the relative magnitudes of the carrier concentrations and the impurity concentrations in the depletion region. In all these cases the depletion width w of the induced space charge depletion region, is proportional to 2 / 1 V , where V is the build in voltage bi V for the case of p-n diodes or the potential drop across the semiconductor, usually denoted by s < , for the case of a MIS structure [5]. The above dependence assumes a crystalline and uniformly doped semiconductor, and finds that in the full depletion approximation the magnitude of the net charge density in the depletion region is equal to the product of the unit charge and the dopant density. Nonetheless determining the width of the depletion region is not always straight forward especially for some novel structures and devices. One example is organic semiconductor structures. This is because of the fact that density of the trapped charges in such structures is not constant within the depletion region and changes with the bias voltage; consequently Poisson’s equation has to be solved numerically to obtain the depletion width [6]. To do so, the density of states in the organic is required, which is strongly dependent on the molecular order in the semiconductor. An experimental method has been recently proposed by Takshi et. al. [7] where it was found that the depletion width does not follow the square root law dependence on applied voltage. In a different type of application, the width of the depletion region affects the efficiency of solar cells. In a recent publication Eun-Chel Cho et. al. [8] reported the fabrication of silicon quantum dot/crystalline silicon solar cells. In such devices the calculation of the depletion width is not a straightforward issue but it does play a critical role in the efficiency of the solar cells. Finally, accurate knowledge of the depletion layer width is also necessary in the case of reliability tests in MOSFET devices. II DEVICE LAYOUT AND EXPERIMENTAL TECHNIQUES MIS devices were fabricated by Al deposition (11 mm in diameter), over a 99 nm thick Si 3 N 4 layer grown on a 380ȝm thick n-type Si substrate. Ohmic contacts were formed on the Si-substrate by aluminum alloying. Detailed description of the growth of the Si 3 N 4 film has been reported in previous work [10]. A Novocontrol Alpha Analyser in combination with the Novocontrol Quatro Cryosystem was used for the Capacitance – Voltage (C-V), Conductance – Voltage (G-V) and Dielectric Relaxation Spectroscopy (DRS) measurements. For the C-V and G-V measurements the applied voltage ranged from -15 V to +15 V with steps of 0.5 V (and 0.1 V in depletion region) in the frequency range 1 kHz – 100 kHz, while the DRS measurements were carried out in the frequency range 10 Hz – 1MHz. All measurements have been carried out at room temperature, 300 K. III RESULTS AND DISCUSSION In order to identify the accumulation-depletion- inversion regions of the device, the capacitance-voltage and conductance-voltage characteristics for various frequencies were determined simultaneously. Fig. 1 depicts the C-V curves for the silicon nitride MIS structure with C. Tsonos, A.Kanapitsas, and A. Karagounis are with the Electronics Department, Technological Educational Institute of Lamia, 35100 Lamia, Greece, E-mail: tsonos@teilam.gr, I. Stavrakas, D. Triantis, C. Anastasiadis, P. Photopoulos are with the Electronics Department, Technological Educational Institute of Athens, 12210 Athens, Greece, V.Em. Vamvakas is with the HelioSphera S.A. Building Block 8, Street 5, Industrial Area of Tripolis, 22100, Tripolis, Greece, and P. Pissis is with the Physics Department, National Technical University of Athens, 15780 Zografou, Athens, Greece.