Journal ArticleDOI

# A model to study the effect of selective anodic oxidation on ultrathin gate oxides

01 Jan 2005--Vol. 52, Iss: 1, pp 118-121
Abstract: We have studied the effect of selective anodic oxidation on ultrathin (22-31 /spl Aring/) silicon dioxide grown at different temperatures ranging from 600/spl deg/C to 875/spl deg/C, on both p- and n-type substrates. A model based on the concept of filling of pinholes by selective anodic oxidation is presented to quantitatively explain the reduction in the gate leakage current of the MOS capacitors after selective anodic oxidation.
Topics: Gate oxide (54%)
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Abstract: Anodic oxidation in 0.1 M HCl followed by a post-rapid thermal annealing process has been used to repair defects existing in thin thermally grown oxide layers (3 and 6 nm) on a p-type silicon substrate. The improved quality of the insulator layer is particularly useful for applications that require large gate areas in Metal–Insulator–Semiconductor (MIS) or Electrolyte–Insulator–Semiconductor (EIS) devices such as Light-Addressable Potentiometric Sensors (LAPS) and Scanning Photo-induced Impedance Microscopy (SPIM). Different methods have been used to characterize the oxide. High-frequency capacitance–voltage curves and ac impedance spectra showed that there was no significant change of the oxide thickness after repair, and the number of the interface states of the oxide was increased for both types of samples. Ramped voltage stress (RVS) measurements of Metal–Oxide–Semiconductor (MOS) structures with gate electrodes 2 mm in diameter showed leakage currents of 0.75 nA cm −2 for the repaired and annealed 3 nm thick oxide and 1.31 nA cm −2 for the repaired and annealed 6 nm thick oxide at accumulation voltage. XPS measurements confirmed that there was no change of the oxide thickness and no contamination with other ionic species after repair. AFM results showed a good agreement with the other characterization methods.

17 citations

Journal ArticleDOI
01 Jun 2014-Applied Physics A
Abstract: A clear current kinked phenomenon was observed in Al/SiO2/Si(p) structures with nanoscale (<2.5 nm) SiO2 in a forward biased region. It was found that the kinked points are dependent on oxide thickness and are not the same as flat-band voltages. A model regarding the oxide voltage dropping efficiency with the consideration of interface trap density ($$D_{\mathrm{it}}$$) and effective charge number density ($$Q_{\mathrm{eff}}/q$$) was proposed for the observation. It is noted that the kinked point is severely affected by the oxide quality and uniformity. However, Al/SiO2/Si(n) structures in a forward biased region do not exhibit this current kinked phenomenon because the dropping behavior of oxide is absolutely different from Al/SiO2/Si(p) structures.

11 citations

Journal ArticleDOI
Abstract: Negative capacitance (NC) was observed in a MOS capacitor grown on an n-type substrate with ultrathin gate oxide film. The NC effect was studied by considering the oxide thickness, the lateral nonuniformity of oxide layers, the current conduction mechanism, and the minority carrier response. It was found that the NC effect turned on at the flatband voltage and was mainly attributed to local electron-hole recombination occurring at the nonuniform interface. A circuit model including an inductive pathway is proposed to take the local electron-hole recombination into account, and the estimation of the NC response on frequency approximates the experimental observation. Because the device sizes are scaled down continuously, it is important to gain an insight into the NC phenomenon induced from the nonuniform factors in fundamental MOS devices.

10 citations

### Cites background from "A model to study the effect of sele..."

• ...Considering the lower oxidation temperature in N1, it is inferred that the thinner EOT, the more Dit, or the more oxide nonuniformity [9] might be the reasons that the gate capacitance is more negative....

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• ...n-type substrates [9], [10], denoted as MOS(p)s and MOS(n)s, respectively, it was found that the fraction of pinholes in oxide...

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Journal ArticleDOI
Vaibhav G. Marathe
10 May 2006-Thin Solid Films
Abstract: 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.

9 citations

Journal ArticleDOI
Vissarion Mikhelashvili
Abstract: We report a strong negative capacitance effect in back to back combination of a metal-insulator-semiconductor (MIS) structure and a metal-semiconductor junction, which is fabricated on an n type Silicon-on-Insulator substrate. The MIS capacitor comprises a SiO2-HfO2 insulator stack with embedded Pt nanoparticles. The capacitor undergoes a voltage stress process and thereby turns into a varactor and a photodetector. The negative capacitance is observed only under illumination in structures that employ a Schottky back contact. A symmetric double or an asymmetric single negative capacitance peak is observed depending on the nature of illumination. The phenomenon is attributed to the modulation of the semiconductor conductance due to photo generated carriers and their incorporation in trapping/de-trapping processes on interfacial and post filamentation induced defects in the insulator stack. The frequency range of the observed effect is limited to 100 kHz. Large ratios of light to dark and maximum to minimum ...

8 citations

##### References
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Journal ArticleDOI
Abstract: In this paper, we present a model for silicon dioxide breakdown characterization, valid for a thickness range between 25 /spl Aring/ and 130 /spl Aring/, which provides a method for predicting dielectric lifetime for reduced power supply voltages and aggressively scaled oxide thicknesses. This model, based on hole injection from the anode, accurately predicts Q/sub BD/ and t/sub BD/ behavior including a fluence in excess of 10/sup 7/ C/cm/sup 2/ at an oxide voltage of 2.4 V for a 25 /spl Aring/ oxide. Moreover, this model is a refinement of and fully complementary with the well known 1/E model, while offering the ability to predict oxide reliability for low voltages. >

518 citations

### "A model to study the effect of sele..." refers methods in this paper

• ...Now, the leakagecurrentdensity canbe modeled using an expression for a direct tunneling current [7] given by...

[...]

Journal ArticleDOI
Abstract: Thin‐oxide (40–50 A) metal oxide semiconductor (MOS) structures are shown to exhibit, prior to large levels of electron tunnel injection, the near‐ideal behavior predicted for a uniform trapezoidal barrier with thick‐oxide properties. The oscillatory field dependence due to electron‐wave interference at the Si/SiO2 interface indicates an abrupt, one‐monolayer barrier transition (∼2.5 A) consistent with earlier work. After tunnel injection of 1017 –5×1018 electrons/cm2, the barrier undergoes significant degradation leading to enhanced tunneling conductance, with reproducible behavior observed among different samples. This effect is consistent with the generation of positive states in the region of the oxide near the Si/SiO2 interface (<20 A), where the tunneling electrons emerge into the oxide conduction band. Densities of positive‐charge and interface‐state buildup are also observed from capacitance‐voltage (C‐V) measurements and are found to be consistent with the observed tunneling dependence on positiv...

266 citations

### "A model to study the effect of sele..." refers result in this paper

• ...415 corresponding to oxidation temperature of 875 C agrees very well with the values reported previously for ultrathin oxides with minimum defect density [8], [9]....

[...]

Journal ArticleDOI
Abstract: Electron transport in ultrathin (tox<40 A) Al/SiO2/n−Si structures is dominated by direct tunneling of electrons across the SiO2 barrier. By analyzing the tunneling currents as a function of the SiO2 layer thickness for a comprehensive set of otherwise identical samples, we are able to extract an effective mass for the tunneling electron in the SiO2 layer. Oxide films 16–35 A thick were thermally grown in situ in a dry oxygen ambient. The oxide thicknesses were determined by capacitance–voltage measurements and by spectroscopic ellipsometry. The tunneling effective mass was extracted from the thickness dependence of the direct tunneling current between an applied voltage of 0 and 2 V, a bias range that has not been previously explored. Employing both a parabolic and a nonparabolic assumption of the E−κ relationship in the oxide forbidden gap, we found the SiO2 electron mass to be mP*=0.30±0.02me, and mNP*=0.41±0.01me, respectively, independent of bias. Because this method is based on a large sample set, t...

253 citations

### "A model to study the effect of sele..." refers result in this paper

• ...415 corresponding to oxidation temperature of 875 C agrees very well with the values reported previously for ultrathin oxides with minimum defect density [8], [9]....

[...]

Journal ArticleDOI
Abstract: The rate of formation of very thin films thermally grown on [111] and [100] oriented silicon wafers was studied using ellipsometry to measure oxide thickness. Film thicknesses from 10–300Aa were obtained by varying oxidation time, oxidation temperature (700°–1000°C), and oxygen concentration in O2‐N2 mixtures at 1 atm total pressure. The applicability of ellipsometry for such a study is discussed. Reproducibility of oxide films grown to thicknesses of 20–30Aa was approx. ±1.0Aa. Under otherwise equal conditions the oxide thickness grown differs for [100] and [111] oriented wafers. The pressure and temperature dependence of the linear rate constant, klin, show that the growth reaction is more complicated than was suggested earlier. In particular, a different pressure dependence for the two substrate orientations used indicates that several oxygen species participate in the rate determining steps.

95 citations

### "A model to study the effect of sele..." refers background in this paper

• ...With lower growth temperature it is possible to obtain better control over the thickness of silicon dioxide [1], [2] but at the cost ofmore number of pinholes and defects in the oxide, resulting in increased leakage and unreliable performance [3]....

[...]

Journal ArticleDOI
Abstract: The formation of voids on the thermally grown (650 °C) ultrathin (∼1 nm) silicon oxide films on the Si(100) surface was investigated by using ultrahigh vacuum scanning tunneling microscopy. Voids form randomly on the ultrathin oxide film upon thermal annealing at 750 °C. In contrast to void formation observed on thicker (>5 nm) thermal silicon oxide films and that observed on ultrathin (∼1 nm) oxide films formed by room temperature O2 adsorption, the number of voids increases during annealing. We find that Si monomer creation and SiO production compete kinetically in the void formation process.

69 citations

### "A model to study the effect of sele..." refers background in this paper

• ...With lower growth temperature it is possible to obtain better control over the thickness of silicon dioxide [1], [2] but at the cost ofmore number of pinholes and defects in the oxide, resulting in increased leakage and unreliable performance [3]....

[...]

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