Effect Of Backscattered Electrons Research Articles

High-dose exposure of silicon in electron beam lithography

Nowadays, features with sizes smaller than 10 nm can be obtained with electron beam lithography. For such small structures, high exposure doses are required to stay away from the shot noise limit. We investigated the effect of high-dose electron exposure of silicon substrates and subsequent dry development by reactive ion etching. We found that silicon can be directly patterned at electron doses ranging from 0.05 to 3.06 C/cm². The effect of backscattered electrons is seen as a halo around the patterns. In the given dose range, a gradual transition from positive tone low-dose to negative tone high-dose behavior is observed. It is demonstrated that the patterning is likely to be caused by structural changes of the silicon substrate, resulting in different etch rates in exposed and unexposed areas. X-ray photoelectron spectroscopy analysis has been applied to determine if the thickness of the native oxide in the irradiated areas is different from the thickness at a reference position not irradiated. Small but significant differences have been observed, the largest increase being 0.3 nm.

SU-FF-T-320: Observation of Dose Enhancement Between Two Gold Foils with 25MV Photon Beam

Purpose: To study the effect of backscatteredelectrons in enhancing absorbed dose using gold foils. Methods and materials: Tissue equivalent solid phantom and two gold foils with 0.034 mm thickness were used. The first gold foil was placed at 4.5 cm depth and EDR2 film was placed at 6 mm downstream position relative to the gold foil. The second foil was placed at 5.4 mm downstream position relative to the EDR2 film. We used a 25 MV photon beam and 10 × 10 cm2field size. The phantom was set at 100 cm SSD. 200MU was delivered. After the second gold foil was removed, another film was irradiated with the same photon beam, field size, and SSD. Films were analyzed with RIT 113 version 4 (RIT Inc. Colorado Springs, Co). Microsoft Office Excel was also used to analyze the data. Results and discussion: We found that removing the second foil caused a 6% reduction of the dose at the film location. Because the pair production dominates at this energy and with high Z material (gold foil), it is possible that the enhancement was due to the pair production. Pair production generates more electrons and positrons, thereby, increasing backscatteredelectrons as well as annihilation photons. Conclusions: This study showed that there is dose enhancement between two gold foils. The result suggests the possibility of local dose enhancement by using goldnanoparticles.

Effect of backscattered electrons on the analysis area in scanning Auger microscopy

Effect of backscattered electrons on the analysis area in scanning Auger microscopy

Space-charge limited currents in coaxial diodes with electron backscatter

The effect of backscattered electrons on space-charge limited currents of cylindrical (coaxial) diodes with anode center conductors is studied. The scattered electrons are parametrized by a fractional current density α and fractional energy β of the incident electrons. For bipolar flow, current enhancement factors of 2.5 are calculated for α, β≃0.5. Comparison of the model equations to one-dimensional particle-in-cell simulations with fully integrated Monte Carlo scattering algorithms demonstrates very good agreement for a range of energies and anode materials. In the absence of backscattering, the bipolar diode impedance decreases for increasing ratio of cathode to anode radius rc/ra for ratios greater than about 20.

Fabrication of electrode arrays in the quarter micron regime for biotechnological applications

Abstract In the field of biotechnological microsystems there is a strong demand for the fabrication of ultraminiaturised electrodes. Examples are highly sensitive biosensors or electric field induced handling of biological cells and macromolecules. New effects and thus new fields of applications appear when the electrode dimensions reach the 100 nm scale. This paper presents two alternative technologies for the fabrication of biocompatible microelectrodes: a platinum lift-off process and a gold electroplating process. The lithography was performed with a Leica EBPG 4 HR electron-beam writer at 50 kV acceleration voltage. An electrode size dependent exposure dose was calculated from the effect of backscattered electrons (proximity effect). Evaporated platinum lines with 200 nm spaces could be realized. The electrodes are embedded in SiO 2 yielding a nearly planar surface. In the second case 140 nm gold lines with 60 nm spaces were electroplated using a sulphitic plating solution.

Deep submicron contact fabrication by electron beam direct writing with intraproximity effect correction

Electron beam (EB) direct-writing lithography with intraproximity effect correction has been developed for fabricating contact holes having deep submicron size. The dimensional accuracy of contact holes is strongly influenced by the intraproximity effect. In delineating contact hole patterns by using EB direct writing, it is necessary to increase the exposure dose a great deal. This is because the effect of backscattered electrons on the smaller hole patterns is decreasing. It was found that the forward scattering parameter in proximity function should be optimized in order to obtain high dimensional accuracy for contact holes with the minimum feature size of 0.2 μm. The accuracy within ±0.03 μm was realized for contact holes with their dimensions from 1.0 to 0.2 μm at the same time by using present intraproximity effect correction and noncharging trilayer resist process. When this high-performance EB direct writing was applied to fabricate 0.2 μm size contact holes, the yield of the 104 contact hole chains was improved to over 95% by using selectively deposited W film on the bottom of the contact holes.

7356. Monte Carlo simulation of energy dissipation in electron beam lithography including secondary electron generation: Kang-Yoon Lee et al, J Appl Phys, 67, 1990, 7560–7567

A new Monte Carlo simulation including secondary electron generation has been performed to study energy dissipation in electron beam lithography. The simulation of inelastic scattering is calculated from the model of the generalized oscillator strength density distribution determined by a set of resonance energies and oscillator strengths. Varying the polymethylmethacrylate film thickness, the energy dissipation profiles for various electron beam energies are evaluated. The effects of backscattered electrons from the silicon substrate and secondary electrons are studied with respect to film thicknesses and electron beam energies. The backscattered electrons from the Si substrate broaden the profile, especially near the bottom layer, and the secondary electrons broaden the profiles over the whole film.

Monte Carlo simulation of energy dissipation in electron beam lithography including secondary electron generation

A new Monte Carlo simulation including secondary electron generation has been performed to study energy dissipation in electron beam lithography. The simulation of inelastic scattering is calculated from the model of the generalized oscillator strength density distribution determined by a set of resonance energies and oscillator strengths. Varying the polymethylmethacrylate film thickness, the energy dissipation profiles for various electron beam energies are evaluated. The effects of backscattered electrons from the silicon substrate and secondary electrons are studied with respect to film thicknesses and electron beam energies. The backscattered electrons from the Si substrate broaden the profile, especially near the bottom layer, and the secondary electrons broaden the profiles over the whole film.

Introduction of a calibration line for composition determination of a binary alloy by Auger electron spectroscopy (quantitative formalism)

In a complete uniform solid solution of a binary alloy, a theoretical method for constructing a very quantitative calibration line for an AES experiment has been developed. In the method, the following are considered: (i) attenuation of a primary beam, (ii) the effects of backscattered electrons and forwardscattered electrons both from solute and base metals, and (iii) true escape lengths of any electrons. Results of calculations are applied for Ag-Au, Mo-W, and Be-Cu systems.

The effect of backscattered electrons on the resolution of scanning Auger microscopy

Measurements of the spatial distribution of Auger electrons, for the purpose of micro-Auger analysis, are presented. The distributions have been measured as a function of primary energy from 20 kV to 60 kV, and incident angle from 50° to 80°, for silver layers on tungsten, using a field-emission UHVSEM. The comparison of experiment with Monte-Carlo calculations of backscattered lectron distributions is in reasonably good agreement.

Contrast and Resolution in Scanning Electron Microscopes

In scanning electron microscopy, secondary and backscattered electrons play a most important role. When considering these two forms of signal source, it is necessary to treat them separately on the basis of contrast and resolution, since their production processes and energies are different. In practice, the electrons detected by the secondary electron detector consist of secondary electrons excited by a primary electron probe, those excited by backscattered electrons in the specimen and secondary electrons liberated from the specimen's environmental parts during backscattered electron bombardment. Consequently, it is difficult to completely eradicate the effect of backscattered electrons upon the secondary electron image. This paper presents information in regards to the differences in contrast and resolution between the secondary and back- scattered electron image under the condition of optimum secondary/backscattered electron separation. First, it was shown how secondary electron image contrast is affected by secondary electrons liberated by backscattered electrons.