Amir Raveh

Structural characterization of He ion microscope platinum deposition and sub-surface silicon damage

In this paper we studied helium ion beam induced deposition (HIBID) of Pt on a silicon wafer using the recently commercialized helium ion microscope (HIM) at 25 kV and low beam currents. The motivation of this work was to understand the impact of light, inert helium ions on deposition rate and structure purity, with some implications on the usefulness of HIM nano-machining for circuit modification. Two Pt-rich deposits with sub-micron dimensions were grown with HIBID at different ion beam currents. The pillar and substrate structure were studied using bright and dark field TEM images. The authors analyzed metal purity profile of the HIBID deposit on height using energy dispersive x-ray spectroscopy. The maximum Pt content measured reached 41%, which is the highest measured metal content of a HIBID-grown structure. TEM studies of the sub-surface damage to the Si shows more damage below the deposit grown at a higher beam current. The differences in amorphization layer thickness between the two different beam currents are discussed. A comparison to Pt deposition by Ga FIB and electron beam induced deposition is provided, along with conclusions regarding the usage of HIBID technology for circuit modification.

Characterization of damage induced by FIB etch and tungsten deposition in high aspect ratio vias

In this paper we studied three major issues that have challenged focused ion beam (FIB) circuit edit practices: via overetching, via composition which affects via resistance, and uniformity of via fill. These issues may become critical as minimal circuit dimensions reduce in the future. We investigated the amorphization induced by FIB gas assisted etch and ion beam induced metal deposition in high aspect ratio vias, using bright and dark field transmission electron microscopy images. A simple intuitive model is introduced to explain the differences in amorphization layer thicknesses between the steep FIB via sidewalls and the via floor. We analyze the dependence of FIB via purity on depth using EDS. Directions for future FIB applications are discussed in the paper along with a FIB via fill strategy.

Strategy for focused ion beam compound material removal for circuit editing

Both selective and nonselective focused ion beam (FIB) processes have become critical for enabling fine-scale activities such as nano-machining and nano-fabrication in compound material removal applications. In this paper, we investigate the influence of FIB ion acceleration voltage on gas assisted etch rates for the most frequently used materials in the microelectronic industry, using common FIB etchants. These results can serve as a baseline for FIB process development using various materials for both highly-selective and (almost) nonselective material removal. Etching strategies are suggested. Two test cases are presented here, in which we performed either selective or nonselective material removal processes. The etch rate of different materials was found to be dependent on acceleration voltage, and very specific to the material-precursor system.

Monte Carlo simulations of nanoscale Ne(+) ion beam sputtering: investigating the influence of surface effects, interstitial formation, and the nanostructural evolution.

We present an updated version of our Monte-Carlo based code for the simulation of ion beam sputtering. This code simulates the interaction of energetic ions with a target, and tracks the cumulative damage, enabling it to simulate the dynamic evolution of nanostructures as material is removed. The updated code described in this paper is significantly faster, permitting the inclusion of new features, namely routines to handle interstitial atoms, and to reduce the surface energy as the structure would otherwise develop energetically unfavorable surface porosity. We validate our code against the popular Monte-Carlo code SRIM-TRIM, and study the development of nanostructures from Ne+ ion beam milling in a copper target.

E-beam invasiveness on 65 nm complementary metal-oxide semiconductor circuitry

Postsilicon debug techniques may require e-beam imaging and nanomachining in the vicinity of live metal-oxide semiconductor (MOS) devices. In that context the authors have investigated the invasiveness of e-beam irradiation on MOS devices to 65 nm integrated circuits, tracked as percent change in ring-oscillator frequencies. Device preparation consisted of backside thinning by mechanical polish, local laser chemical etching to 10 μm Si, and finally, focused ion beam gas-assisted etching, leaving 200–2000 nm remaining Si. This was followed by e-beam exposure at various acceleration energies and doses, from a marginally detectable device degradation dose of 10−4 nC/μm2, and beyond a dose causing total transistor failure around 1.25 nC/μm2, at 30 keV. The authors find that relative frequency degradation depends on irradiation dose as a power law which may be applied to limit unwarranted device degradation. E-beam nanomachining is typically performed at low acceleration energies, conveniently reducing the ele...

Avoiding Bias of Focused Ion Beam Edge Resolution Measurements at High Doses

The Focused Ion Beam (FIB) has been an essential tool in the micro-electronics industry for many years, used for failure analysis, circuit modification, and analytical techniques [1,2]. The continual downscaling of minimum features in micro-electronics technology [3] has driven the need for finer machining, and thus FIB probe size (d50) has been steadily decreasing, recently reaching below 10 nm [4]. Several new “cold beam” ion sources are in research with some early implementations, which may eventually reduce FIB probe sizes significantly [5-9]. This development promises better imaging resolution and possibly better machining acuity, i.e., machining of finer features. To assess the goodness of such new ion sources, reliable measurement of beam probe size and beam profile are necessary. This paper addresses a challenge in probe size measurement which arises for small probe sizes.

High resolution TEM analysis of focused ion beam amorphized regions in single crystal silicon—A complementary materials analysis of the teardrop method

The predominant challenge of nanomachining by focused ion beam (FIB) is the generational down-scaling of minimum dimensions of cutting-edge technologies such as very large scale integration (VLSI) process technology. To keep pace with feature size reduction, the state of the art FIB beam profiles must also shrink proportionally. This requirement for FIB profile shrinking necessitates tests that analyze FIB profiles and their characteristics. With such tests in hand, the suitability for VLSI technology applications may be specified, developed, and qualified. The authors present herein various aspects and some fine details of the recently improved beam profile analysis, aka “teardrop” test. This test is based on obtaining real beam characteristics by analyzing amorphization traces produced by scanning the beam in question over a [001] Si single crystal sample, in a series of lines of increasing doses, followed by thorough analysis procedure. To derive the most accurate beam characteristics, the amorphized r...

Monte Carlo simulations of secondary electron emission due to ion beam milling

The authors present a Monte Carlo simulation study of secondary electron (SE) emission resulting from focused ion beam milling of a copper target. The basis of this study is a simulation code which simulates ion induced excitation and emission of secondary electrons, in addition to simulating focused ion beam sputtering and milling. This combination of features permits the simulation of the interaction between secondary electron emission, and the evolving target geometry as the ion beam sputters material. Previous ion induced SE Monte Carlo simulation methods have been restricted to predefined target geometries, while the dynamic target in the presented simulations makes this study relevant to image formation in ion microscopy, and chemically assisted ion beam etching, where the relationship between sputtering, and its effects on secondary electron emission, is important. The authors focus on a copper target and validate the simulation method against experimental data for a range of noble gas ions, ion en...

Energetic Cs+ ion interaction with common microelectronic materials—An investigation of a future FIB candidate source

In this paper, the authors studied the interaction of 14.5 keV accelerated Cs+ ion interaction with commonly used materials in the microelectronic industry. The motivation of this work was to examine the suitability of cesium as a future ion candidate for focused ion beam (FIB) nanomachining applications, from the beam–surface interaction aspect. Since nanometer scale Cs FIBs are uncommon, the authors have used a relatively broad Cs+ beam for this work. Two irradiation configurations were used: 60° and normal incidence with respect to the sample surface. Two sample types were irradiated, a pristine Si wafer piece and layered sample of tungsten over SiO2 on top of a Si substrate. Post Cs+ irradiation, the samples were capped and carefully prepared for transmission electron microscopy (TEM) and scanning transmission electron microscopy/energy dispersive spectroscopy inspection. TEM studies of the subsurface damage to the Si shows a regular amorphization process, without odd microstructural changes even for ...