Effect of temperature on the Fowler-Nordheim barrier height, flat band potentials and electron/hole effective masses in the MOS capacitors
Introduction
The Metal-Oxide-Semiconductor (MOS) structures are the most useful devices in the study of semiconductor surfaces. Since most practical problems in the quality of reliability and stability of all semiconductor devices are strongly related to their surface conditions, an investigating of the surface physics with the help of MOS capacitors is of great importance to device operations. The Metal/SiO2/Si structure remains the most ideal and most practical MOS structure to date [1]. Thermally grown silicon dioxide (SiO2) has excellent properties as a gate dielectric in MOS structures due to its process advantages, high energy barrier and low trap density at the Si/SiO2 interface [[2], [3], [4]]. The energy band diagram of a Metal/SiO2/p-type Silicon (MOS) structure before and after the contact is shown in Fig. 1. It illustrates the different energy's level characterizing the interface state between the different regions. After the contact, the deformation of the interface state is illustrated by the bending of the energy's level (CB: Conduction Band) of the silicon dioxide SiO2 and of all the energy's level (CB, VB: Valence Band) of the p-type Si semiconductor.
The characteristics of high-field currents through the oxide layer (ie: SiO2) of the MOS structures have been studied extensively for many years, notably by Lenzlinger and Snow in 1969 [5]and continuously until the present [[6], [7], [8], [9], [10], [11], [12]].
Fundamentally, in insulators like SiO2, the mechanism of the carrier charge transport is arranged into six regimes called respectively as tunneling, thermionic emission, Frenkel-Poole, ohmic mechanism, ionic conduction and space-charge-limited[13]. Nevertheless, tunneling is the most common conduction mechanism under high fields. It can be divided into direct tunneling and Fowler-Nordheim (FN) tunneling process.
For oxide layers thicker than 6 nm, the current-voltage (I–V) behavior of the structure has been well explained by Fowler-Nordheim field emission [14]. However, a detailed investigation of the influence of temperature on the current-voltage characteristics is still of great interest for applications issues as well as for basic purposes.
In this work, we characterize the FN I–V curves of the MOS structures biased in accumulation and in inversion in the range of temperature of [303−423] K. Initially, we extract simultaneously the four FN parameters (mox, msc, ϕB, Vcorr) by means of the optimization method (as described below in the theoretical back ground) using just the measured I–V-T. Secondly, we perform a comprehensive study of the temperature dependence of the four FN characterized parameters (mox, msc, ϕB, Vcorr) extracted previously of the MOS structures.
Section snippets
Theoretical background
According to Good and Müller [15], the Fowler-Nordheim (FN) current density J through silicon dioxide is dependent on the temperature T and the corresponding electric field F and can be calculated from the following equation:q is the elementary charge, k is the Boltzmann constant, E is the hole/electron energy, mox is the hole/electron effective mass in the oxide band gap, msc is the hole/electron effective mass in the
Structure fabrication and characterisation
The MOS structures used in this study have a SiO2 dielectric with a thickness of 9.6 nm grown via dry oxidation on p-type Si substrates (1–6 Ωcm). The gate contacts with an area of 104 μm2 consisting of 20 nm TiN and 300 nm Al stacks are deposited via plasma sputtering and patterned via photo lithography and dry etching, respectively. Finally, a Forming Gas Annealing (FGA) at 430 °C for 30 min is performed. The temperature dependent I–V measurements are performed in the range of [303−423] K
Fowler-Nordheim curves
Fig. 2 illustrates the I–V-T measurements for the studied MOS capacitors for both inversion and accumulation.
Using the optimization process described in the theoretical background section on the I–V-T measurements, we have extracted simultaneously the four FN characterizing parameters (mox, msc, ϕB, Vcorr). The FN plots for the real MOS in comparison with the simulated FN plots using the four extracted parameters, in the inversion mode for different temperatures are shown in Fig. 3, while those
Discussion
The maximum variation obtained of , and with temperature are summarized in Table 1 (where is the difference between the maximum and the minimum values of the extracted parameters expressed in percentage). As shown in Fig. 5 and Table 1, the variation of the charge carrier effective mass of hole/electron in the oxide for both accumulation/inversion denotes a decrease but with different percentage with an increase of the temperature. It is well known that the charge carrier
Conclusions
The current voltage characteristics versus temperature were measured in Metal/SiO2/p-type Si MOS capacitor structures in the range of [303−423] K. These measurements were investigated by FN tunneling current characterized by the FN parameters such as: the effective mass of the charge carrier in the oxide mox, the effective mass of the charge carrier in the semiconductor msc, the barrier height of the charge carriers ϕB and the corrected oxide voltage Vcorr. Our process enables us a simultaneous
Credit author statement
Below a list assigning the author's name against the following roles conception or design of the work.
Structure fabrication and characterization: Pr k. Murakami.Data collection: Pr Z. Ouennoughi.Data analysis and interpretation: Dr S. Toumi.Drafting the article: S. Toumi.Critical revision of the article: S. Toumi.Final approval of the version to be published: Dr S. Toumi
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
One of the authors S. Toumi is very grateful to Dr T. Guerfi for the valuable and the fruitful discussions and for the correction of this manuscript.
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