Simultaneous ion and electron beam etching for charge-free and low-damage silicon processing

There is currently great interest in combining focused ion beam (FIB) and scanning electron microscopy technologies for advanced studies of polymeric materials and biological microstructures, as well as for sophisticated nanoscale fabrication and prototyping. Irradiation of electrically insulating materials with a positive ion beam in high vacuum can lead to the accumulation of charge, causing deflection of the ion beam. The resultant image drift has significant consequences upon the accuracy and quality of FIB milling, imaging and chemical vapour deposition. A method is described for suppressing ion beam drift using a defocused, low-energy primary electron beam, leading to the derivation of a mathematical expression to correlate the ion and electron beam energies and currents with other parameters required for electrically stabilizing these challenging materials.

A thin calcium phosphate film was synthesized on both commercially pure Ti and Si wafers by electron beam evaporation of hydroxyapatite as an evaporant with simultaneous Ar ion beam bombardments. Silver was introduced into an ion-beam-assisted deposition of a calcium phosphate thin film for antimicrobial effect. The amount of incorporated silver ions was controlled by immersing calcium-phosphate-coated samples in different AgNO3 concentrations, and Rutherford backscattering spectrometry (RBS) was employed to measure the amounts of substituted silver. The higher concentration of silver in the calcium phosphate film was more effective in reducing the bacteria of Escherichia coli ATCC 8739 and Streptococcus mutans OMZ 65 on contact with respect to controls.

The metal/semiconductor interface region of in situ deposited Ag thin films prepared on a Si(111) substrate has been investigated using AES sputter depth profiling in conjunction with proton‐induced x‐ray emission (PIXE). Interface regions have been modeled with the interface analysis program LOGIT, developed at the National Institute of Standards and Technology (NIST). Values for the parameters obtained from this model indicate that the rate of ion beam sputtering through samples prepared without simultaneous low‐energy ion activation tended to be noticeably greater than the rate of sputtering through samples prepared with simultaneous ion activation. Further, we found that one effect of the ion beam is temporarily to shift the fractional Ag surface coverage to higher values. The likely mechanism for this shift is sputter redeposition by the ion beam of Ag atoms from large nucleated Ag islands, transporting them to open areas between islands. These results support conclusions from an earlier study, which found that the effect of low‐energy simultaneous ion beam activation during thin‐film deposition was to shift the mode of growth of Ag on an Si(111) substrate from an SK (layer‐plus‐island) to an FM (layer) growth mode, to a degree dependent on the conditions of simultaneous ion co‐bombardment.

We report on the application of low pressure ion beam sputtering combined with simultaneous (neutralized) ion beam polishing to the production of multilayer structures for x-ray optics. Initial examination of these structures by high resolution diffractometry at 0.154 nm indicates that the structures exhibit a high degree of structural perfection.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper investigates the failure causes for slopped through silicon vias (TSV) and presents process improvement for implementing the slopped TSV for 3D wafer level packaging (WLP). IMEC is developing slopped and scaled generic approaches for 3D WLP. Previously we have reported on the integrated process flow for the slopped (TSV) and showed the feasibility of Parylene N as a dielectric material. In the TSV process discussed here, firstly 200mm device wafer is bonded facedown on a carrier using temporary glue layer and thinned by grinding. TSV's are realized by dry etching from the wafer backside, followed by dielectric deposition and patterning. Dielectric patterning is done at the bottom of the via on 100 microns thin silicon device wafer supported by the carrier. Finally, conformal plating is done inside the via to obtain the interconnections.This paper discusses the yield killer or failure causes in the slopped TSV process. There can be many parameter including silicon etch uniformity, dielectric etching at the bottom of the via and resist residue inside the via that can reduce the yield of the process. We report that one of the main factors contributing to the yield loss is silicon dry etching effects including non-uniformity and notching. Using standard Bosch etching process, notching at the interface between landing oxide and silicon has been observed. The notching cause a discontinuity at the bottom of the via resulting in no plating at the bottom interface.In this paper we report on a new via shape that is a combination of slopped and straight etching sequence to overcome the notching problem. Different parameters including influence of grinding marks, mask opening, wafer thickness variation, etching rate and etching profile across the wafer were investigated. The optimized design rules for mask opening and effect of individual etching parameters on the etching profile will be presented. In etching, firstly a sloped via with slope of 60 degrees is optimized with changing different etching parameters including different gasses and pressure. Slope via facilitates in subsequent dielectric deposition and sputtering processes. Secondly, a straight wall etching process based on Bosch process and soft landing step with longer passivation steps were investigated to obtain the notch free etching profile. The optimized etching process is notch free, very repeatable and total variation across different wafers is less then 2 percent for 100 micron target opening.This paper reports the failure analysis of TSV and discuses the processes improvement to obtain higher yielding vias. Different parameters that reduced the yield are discussed with main focus on notching effects during silicon etching. An improved and characterized, notch free uniform silicon etching across the wafer process based on two step etching is presented. An integration flow implementing the above optimized parameters with electrical yield will be detailed in the paper.

The results of a research program concerning the application of the electron beam EB) irradiation, microwave MW) irradiation and simultaneous electron beam and microwave EB + MW) irradiation for removing nitrogen oxides NOX) and sulfur dioxide SO2) in simulated Due gases are presented. Several microwave applicators and reaction chambers used for NOX and SO2 removal tests are also presented. The additional use of MW energy and EB energy or the use of MW energy only proved to be a promising method for removal of pollutants in view of the reduction of power consumption and flue gas treatment process cost. Experiments performed at lower temperature 65-70°C) of the gaseous mixture air, Argon up to 7%, H2O up to 25%, CO2 up to 10%, SO2 up to 2000 ppm, NOX up to 1000 ppm, NH3 added in stoichiometric amounts) demonstrated a higher SO2 removal efficiency with lower absorbed dose. Promising results are obtained especially for SO2 removal efficiency: up to 80% for MW, 85% for EB irradiation and up to 90% for EB + MW irradiation. A considerable amount of SO2 can be separated even without MW, EB or EB + MW irradiation due the spontaneous reaction with ammonia at gaseous mixture temperature below 70°C. The most important conclusion concerning MW irradiation is that efficiency of removal of pollutants strongly depends on microwave applicator structure type, residence time and MW power level.

The properties of titanium nitride prepared by dynamic ion mixing

Standard Ta 2 O 5 30 nm films have been applied for simultaneous Auger electron analysis (AES) and secondary ion mass spectroscopy (SIMS) to characterize and calibrate depth porifles. A combined SIMS/AES‐system (Atomika Kit 3000–30/Perkin Elmer PHI 545) was used applying 2–12 keV Ar + primary beam energy with/without Wien filter at almost normal incidence (2° off normal to avoid neutral particles). The investigated parameters were ion‐beam energy, raster frequency, Wien filter and influence of simultaneous electron beam. Optimum depth resolution at almost normal incidence was found to be 1.7 nm for O–AES and O + (16)‐SIMS peak.

Application of multi-irradiation facilities

A theory of amorphization of ordered intermetallic compounds is applied to the case of simultaneous irradiation by electrons and heavy ions. The theory proposes that the local buildup of radiation-induced defects (interstitial-vacancy complexes) to a critical value destabilizes the crystalline lattice in a small region, causing it to become amorphous. The rate of increase of the complex concentration results from a balance between complex formation (with an athermal component under ion bombardment) and complex annihilation by thermally activated processes. This mechanism explains, in the case of electron irradiation, the existence of a cutoff temperature, ${T}_{e}^{c}$, above which no crystalline-to-amorphous transition occurs due to insufficient complex buildup. In the case of ion bombardment, a cutoff temperature, ${T}_{i}^{c}$, is also obtained, above which no significant complex accumulation takes place, but ${T}_{i}^{c}$ is higher than ${T}_{e}^{c}$. It is shown that simultaneous bombardment with ions and electrons leads to an acceleration of the transition up to temperatures around ${T}_{e}^{c}$ and to a progressive delay and possible suppression of the transition at increasing irradiation temperatures between ${T}_{e}^{c}$ and ${T}_{i}^{c}$. .AE

Modification of polymethylmethacrylate under irradiation of the SEM electron beam

Modification of polymethylmethacrylate under irradiation of the SEM electron beam

The ion beam generation and dynamics of processes in a pulsed straight high-current gas discharge at Iow pressures have been studied. The spatial reversal of a longitudinal con-fining magnetic field is used to stabilize a potential jump. The potential difference of 3–10 kV is applied to the discharge gap filled with a preliminary created plasma. Initially, the precathode potential jump is formed and, thereafter, the auasi-steady double layer arises in the region of magnetic field reversal. Potential difference is concentrated in the double layer, where formation of ion and electron beams occur. A current value of the ion beam formed in the double layer is determined by Bohm's current of the plasma in the anode part of discharge gap (J < 0.6 A/cm2). The ion beam energy is determined by a value of the potential jump (3–10kV) in the double layer. When the plasma with the density higher than the critical one is formed in the system, the magnetic field reversal is self-consistently suppressed; the dou...

Objective.Magnetic resonance (MR) images free of artefacts are of pivotal importance for MR-guided ion radiotherapy. This study investigates MR image quality for simultaneous irradiation in an experimental setup using phantom imaging as well asin-vivoimaging. Observed artefacts are described within the study and their cause is investigated with the goal to find conclusions and solutions for potential future hybrid devices.Approach.An open MR scanner with a field strength of 0.25 T has been installed in front of an ion beamline. Simultaneous magnetic resonance imaging and irradiation using raster scanning were performed to analyze image quality in dedicated phantoms. Magnetic field measurements were performed to assist the explanation of observed artifacts. In addition,in-vivoimages were acquired by operating the magnets for beam scanning without transporting a beam.Main Results.The additional frequency component within the isocenter caused by the fringe field of the horizontal beam scanning magnet correlates with the amplitude and frequency of the scanning magnet steering and can cause ghosting artifacts in the images. These are amplified with high currents and fast operating of the scanning magnet. Applying a real-time capable pulse sequencein-vivorevealed no ghosting artifacts despite a continuously changing current pattern and a clinical treatment plan activation scheme, suggesting that the use of fast imaging is beneficial for the aim of creating high quality in-beam MR images. This result suggests, that the influence of the scanning magnets on the MR acquisition might be of negligible importance and does not need further measures like extensive magnetic shielding of the scanning magnets.Significance.Our study delimited artefacts observed in MR images acquired during simultaneous raster scanning ion beam irradiation. The application of a fast pulse sequence showed no image artefacts and holds the potential that online MR imaging in future hybrid devices might be feasible.

This article describes a model that simulates etching profiles in reactive ion etching. In particular, models are developed to explain the significant lateral etch rate that is observed in many etch profiles. The total etch rate is considered to consist of two superimposed components: an ion-assisted rate and a purely ‘‘chemical’’ etch rate, the latter rate being due to etching by radicals in the absence of ion bombardment. The transport of radicals to the evolving interface is studied for two different transport mechanisms: re-emission from the surface and diffusion along the surface. For the case of transport by surface re-emission, a reactive sticking coefficient is defined for the radicals, and a formulation is developed to simulate etching for any value (between zero and unity) that this sticking coefficient may assume. When the sticking coefficient approaches either zero or unity, the method of characteristics is shown to be useful for profile simulation. Transport of radicals by surface diffusion is also investigated, and it is shown that the important dimensionless parameter governing profile evolution is the Damkohler number. The two models are compared to experiments performed on the etching of silicon in a SF6 plasma, and the surface re-emission model is shown to accurately predict the development of etching profiles.