XPS Studies of SiO<sub>2</sub>/Si System under External Bias

Ülgüt, Burak; Süzer, Şefik

doi:10.1021/jp022003z

Cited by 103 publications

(87 citation statements)

References 37 publications

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“…Some components of the total current can easily be controlled by application of a small (0-10 V) external voltage bias, both in the form of d.c. and/or a.c. pulses, as it has been reported recently [17][18][19][20][21][22][23][24][25][26][27][28][29][30]. The effect of this applied voltage-bias can then be assessed in the measured line positions.…”

Section: Introductionmentioning

confidence: 95%

Methods for probing charging properties of polymeric materials using XPS

Sezen

Ertaş

Süzer

2010

Journal of Electron Spectroscopy and Related Phenomena

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a b s t r a c tVarious thin polystyrene, PS, and poly(methyl methacrylate), PMMA and PS + PMMA blend films have been examined using the technique of recording X-ray photoelectron spectrum while the sample is subjected to ±10 V d.c. bias, and three different forms of (square-wave (SQW), sinusoidal (SIN) and triangular (TRG)), a.c. pulses. All films exhibit charging shifts as observed in the position of the corresponding C1s peak under d.c. bias. The a.c. pulses convert the single C1s peak to twinned peaks in the case of the square-wave form, and distort severely in the cases of the SIN, and TRG forms, and all three of them exhibit strong frequency dependence. In order to mimic and better understand the behavior of these polymeric materials, an artificial dielectric system consisting of a clean Si-wafer coupled to an external 1 M resistor and 56 nF capacitor is created, and its response to different forms of voltage stimuli, is examined in detail. A simple electrical circuit model is also developed treating the system as consisting of a parallel resistor and a series capacitor. With the help of the model, the response of the artificial system is successfully calculated as judged by comparison with the experimental data. Using one high frequency SQW measurements, the off-set in the charging shift due to the extra low-energy neutralizing electrons is estimated. After correcting the corresponding off-set shifts, the XPS spectra of the three different PS films, one PMMA, and one PS + PMMA blend film are re-examined. As a result of these detailed analysis, there emerges a clear relationship between the thicknesses of the PS films with their charging abilities. In the blend film, PS and PMMA domains are electrically separated, and exhibit different charging shifts, however, the presence of one is felt by the other. Hence, the PS component shifts are larger in the blend, due to the presence of PMMA domains, which has intrinsically a larger R eff , and conversely the PMMA component shifts are smaller due to the presence of PS domains.

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Section: Introductionmentioning

confidence: 95%

Methods for probing charging properties of polymeric materials using XPS

Sezen

Ertaş

Süzer

2010

Journal of Electron Spectroscopy and Related Phenomena

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“…The total current is the sum of two opposing currents, resulting from photoelectrons, and secondary electrons going out of the sample, and stray electrons or electrons from the flood gun, going into the sample, which can easily be controlled by application of a small ͑0-10 V͒ external bias, as we have reported recently. 12,13 In this contribution, we extend our application and report simple and noncontact electrical measurements derived form XPS data.…”

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confidence: 97%

X-ray photoelectron spectroscopy for resistance-capacitance measurements of surface structures

Ertaş

Demirok

Atalar³

et al. 2005

Applied Physics Letters

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Cataloged from PDF version of article.In x-ray photoemission measurements, differential charging causes the measured binding energy difference between the Si 2p of the oxide and the silicon substrate to vary nonlinearly as a function of the applied external do voltage stress, which controls the low-energy electrons going into and out of the sample. This nonlinear variation is similar to the system where a gold metal strip is connected to the same voltage stress through an external 10 Mohm series resistor and determined again by x-ray photoelectron spectroscopy (XPS). We utilize this functional resemblance to determine the resistance of the 4 nm SiO2 layer on a silicon substrate as 8 Mohm. In addition, by performing time-dependent XPS measurements (achieved by pulsing the voltage stress), we determine the time constant for charging/discharging of the same system as 2.0 s. Using an equivalent circuit, consisting of a gold metal strip connected through a 10 Mohm series resistor and a 56 nF parallel capacitor, and performing time-dependent XPS measurements, we also determine the time constant as 0.50 s in agreement with the expected value (0.56 s). Using this time constant and the resistance (8.0 Mohm), we can determined the capacitance of the 4 nm SiO2 layer as 250 nF in excellent agreement with the calculated value. Hence, by application of external do and pulsed voltage stresses, an x-ray photoelectron spectrometer is turned into a tool for extracting electrical parameters of surface structures in a noncontact fashion. (c) 2005 American Institute of Physics

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“…Negative bias acts in the opposite way. 23 By controlling the differential charging with external biasing, we were also able to (i) separate otherwise overlapping XPS peaks of the same atom belonging to different chemical entities and (ii) derive information related to the dielectric properties of the layers and the proximity of the atoms within composite multilayers. 24,25 Instead of applying the bias in the dc mode, we can pulse it for time-resolved measurements, which is the main subject of the present contribution.…”

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Time-Resolved XPS Analysis of the SiO₂/Si System in the Millisecond Range

2004

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By applying voltage pulses to the sample rod while recording the spectrum, we show, for the first time, that it is possible to obtain a time-resolved XPS spectrum in the millisecond range. The Si 2p spectrum of a silicon sample containing a ca. 400-nm oxide layer displays a time-dependent charging shift of ca. 1.7 eV with respect to the Au 4f peaks of a gold metal strip in contact with the sample. When gold is deposited as C 12 -thiol-capped nanoclusters onto the same sample, this time the Au 4f peaks also display time-dependent charging behavior that is slightly different from that of the Si 2p peak. This charging/discharging is related to emptying/filling of the hole traps in the oxide layer by the stray electrons within the vacuum system guided by the external voltage pulses applied to the sample rod, which can be used to extract important parameter(s) related to the dielectric properties of surface structures.Charging/discharging is one of the fundamental processes dictating both the thermodynamics and the kinetics of the various physicochemical changes taking place on surfaces. 1 In addition to the standard electrical measurements, STM, AFM, and Kelvin probe techniques are widely used to elucidate the structural changes accompanying these processes. [2][3][4][5][6] When chemical information is also needed, XPS is usually the preferred spectroscopic technique because all elements, except for hydrogen, and their oxidation state(s) can easily be identified. 7 One of the disadvantages of the XPS technique is that additional positive charges are naturally introduced as a consequence of the photoemission process. These charges do not interfere with measurements when the surfaces are electrically conducting but can cause significant binding-energy shifts for poorly conducting samples. [8][9][10][11] Such charges are usually compensated by flooding the sample with low-energy electrons (or sometimes ions) and trying to bring the surfaces to a steady state in terms of electrons going in and out, but the complete elimination of charging is only an ideal. Surfaces can also be negatively charged if more electrons are introduced. This modification, dubbed controlled surface charging (CSC), has been successfully applied to depth profiling in the 1-10 nm range and/or to the lateral differentiation of mesoscopic layers. [12][13][14][15][16] However, prolonged exposure of the surfaces to intense low-energy electrons can cause physical and chemical damage. 9 It was even reported that the surface potential that developed from the added charging caused deintercalation in layered compounds. 17 Lau and co-workers have also utilized the CSC to extract structural and electrical properties of ultrathin dielectrics on semiconductors. [18][19][20][21][22] In a complementary study, we have recently reported that the positive charging developed on the SiO 2 /Si system can also be controlled simply by the application of an external bias to the sample rod to affect the measured binding-energy difference between the Si 4+ overlayer and the...

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XPS Studies of SiO₂/Si System under External Bias

Cited by 103 publications

References 37 publications

Methods for probing charging properties of polymeric materials using XPS

Methods for probing charging properties of polymeric materials using XPS

X-ray photoelectron spectroscopy for resistance-capacitance measurements of surface structures

Time-Resolved XPS Analysis of the SiO₂/Si System in the Millisecond Range

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XPS Studies of SiO2/Si System under External Bias

Cited by 103 publications

References 37 publications

Methods for probing charging properties of polymeric materials using XPS

Methods for probing charging properties of polymeric materials using XPS

X-ray photoelectron spectroscopy for resistance-capacitance measurements of surface structures

Time-Resolved XPS Analysis of the SiO2/Si System in the Millisecond Range

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XPS Studies of SiO₂/Si System under External Bias

Time-Resolved XPS Analysis of the SiO₂/Si System in the Millisecond Range