Focused Ion Beam induced material deposition and removal is nowadays well established for IC device modification and local sample preparation for failure analysis. The technique fulfills most of the demands required for today's IC modification. The limits of the technique can be seen in some cases, when devices are of leading edge technologies with new materials and small and complex structures. Fundamental restrictions of the technique will become more obvious, when FIB is applied for generation of nanostructures with dimensions in the sub 100nm range.
In this contribution we will discuss shortly what we consider state of the art FIB machining for device modification. Furtheron, FIB generation of small structures and beam induced effects limiting the lateral and vertical dimensions will be discussed. The impact on defect generation and gallium implantation will also increase with decreasing dimensions and higher aspect ratios and models of the physical processes behind ion beam induced deposition and etching become rather inaccurate. Finally, we will show examples of nanoscaled devices, like SNOM probes, where these effects play an important role.
The presentation will overview some of the limitation encountered during FIB device modification and solutions proposed to the problem of the high resistance of FIB interconnections. Emphasis will be given on resistance limitation observed on contacts of deep metal levels on technologies using 5 or 6 levels of interconnection. One problem is the time required to make a void free filling of the via at low current and also the intrinsic resistance of Pt or W deposited by « ion beam decomposition ». One solution of improving this limitation consists of filling the vias by nickel plating before platinum strap deposition. The advantage of using nickel instead of copper plating, already reported [1,2], is that the chemical deposit is electroless. The presentation will include electrical characterisation of these vias. We will also give some results on Ni plating of FIB deposited Pt straps in order to reduce their resistivity.
[1] How to use Cu-plating for low Ohmic long distance FIB connections, K. Van Doorselaer and L. Van Den Bempt, ISTFA 94
[2] How to Prepare golden devices using lesser materials. K. Van Doorselaer and L. Van Den Bempt and J. Whitney, ISTFA93
Download the presentation FIB process optimisation for complex integrated circuits modification (pdf-file, 612 kB).
The modification of IC interconnects has become a routine process for chip repair and rapid prototyping. However, FIB-deposition of complex multilayer structures is typically avoided due to the immature state of ion induced deposition of dielectrics. This study demonstrates the application of FIB-deposited insulators for interlayer and interline dielectrics with sub-µm spacing between deposited metal structures. The complex influence of deposition parameters such as exposure times and delay times on obtained material properties is discussed on bias of the chemical composition obtained by Auger-spectroscopy and Secondary Ion Mass Spectroscopy. The influence of total pressure and gas phase composition is illustrated with exemplary structures. The feasible application of FIB-deposited dielectrics for electrical applications is demonstrated with capacitor test structures. The correlation between material qualities and electrical properties is corroborated
Whether an ion-milled wafer can be returned to line or not is a matter of great concern. We have investigated for Ga distribution around the milled spot on a silicon wafer by several analysis methods such as TRXPS, TXRF, AES, WDX, and ICPMS. Combining all the results, the following picture was derived. In the case, where 2 x 1013 Ga ions (corresponding 1 nA x 71 min) were irradiated over 10 m m x 10 m m area, Ga spread over the area of 200 to 300 m m in diameter and 50% of injected Ga particles (=1 x 1013) remain in the wafer. 4.5 x 107 injected particles remain in the very thin surface layer down to 2.5 nm from the surface and 2 x 1011 particles in the layer down to 1.4 m m. Most of the injected particles will exist in/under the bottom of crater. Also, a gas assisted deposition layer was investigated.
An overview of the research activities of the FIB group in the Research Centre Rossendorf is given. More in detail the fabrication technology of alloy LMIS as well as their characterization is discussed. The FIB system IMSA-100 is briefly introduced and typical applications are presented: writing implantation of Co ions into a heated Si target in order to create maskless sub-micron CoSi2 structures, bombardment of semiconductor materials with different ions in a wide range of current density, dose and temperature allows to study the damage creation and dynamic annealing process.
Download the presentation Mass separated Focused Ion Beams using alloy Liquid Metal Ion Sources (pdf-file, 401 kB).
As semiconductor device dimensions are shrinking, there is a growing demand for Transmission Electron Microscope (TEM) analyses in routine support of IC manufacturing, low-yield analysis or process development. From a production point of view, the shift from SEM/EDX to TEM/EELS/EDX techniques is problematic given the time consuming TEM sample preparation methods that are needed.
While clear improvements are made with the introduction of Focused Ion Beam (FIB) systems as alternative to the conventional TEM sample preparation method that includes mechanical polishing and Ar ion milling, the sample preparation remains elaborative and requires significant operator attention. To arrive at time efficient and optimised FIB TEM-sample preparation techniques, automation methods are now proposed by FIB equipment manufacturers.
To assure a correct analytical support to both production and research groups, an industrial FIB-TEM line is set-up that includes automatic wafer sample cleavage tools, automatic FIB systems for lamellae thinning and state-of-the-art but at the same time easy-to-operate TEM systems for High Resolution imaging and chemical analysis.
Here, we will present our results obtained on a FEI200 TEM FIB system equipped with the AUTOFIB software package. Using pattern recognition, the integrated software package automatically drives the wafer stage to its correct position and controls the metal deposition, milling and final polishing steps by means of recipe driven beam parameter settings. Quality of the final lamellae (thickness, wall flatness and degree of amorphisation) obtained with this automated FIB method as well as accuracy, repeatability and throughput of this method will be presented and discussed. Further, the 'destructive' pre-thinning technique and the lift-out technique which eliminates the need for any sample treatment prior to the FIB preparation and that allows to extract a sample from a full silicon (device) wafer are compared. Finally, the automated "FIB only method" is compared with the more sophisticated but currently manually operated "dual beam FIB-SEM method" and the respective application domains of both methods are discussed.
This study is focused on the question of how the FIB technique damages samples during cross section preparation. Especially, surface amorphization and ion implantation during ion bombardment have been investigated for pure sputtering as well as for gas assisted platinum deposition. It is well known that FIB milling leads to a thin amorphous surface layer on the sample and also to ion implantation. In case of TEM sample preparation the thickness of the amorphous layer can become crucial because for very thin lamellas the ratio between undistorted bulk material versus amorphous material decreases.
An already FIB-prepared TEM lamella was cross-sectioned again for sample damage investigation. Before all cross sections were cut, platinum protection layers had been deposited.
The TEM investigation showed a homogeneous amorphous layer of several nm on both sides of the lamella. Using EFTEM (Energy Filtered TEM) it could be revealed that the concentration of Ga ions incorporated into the amorphous layer and into the bulk material is increasing from the upper to the lower part of the lamella. The amorphous film on top of the lamella, which had been formed during the platinum deposition, was also investigated. To explain this effect in more detail, several platinum layers were deposited on a silicon substrate at different conditions and modes. Subsequently these samples were TEM cross-sectioned and investigated.
Download the presentation FIB induced damages of SEM/TEM samples of semiconductor devices (pdf-file, 1817 kB).
Now, at the dual beam FIB of the Fraunhofer EADQ Dresden an alloy source (AuGeSi) is available for sputter applications. Additionally to process parameters as ion energy and incident angle this also allows to change the sort of ions in order to minimise damaging by amorphisation and contamination. An important point for successful optimisation is the ability to measure the resulting parameters especially the amorphisation depth. A suitable method for such studies, which is based on Raman scattering and has been successfully tested recently, will be described. The penetration depth of ions has been determined by extensive Monte-Carlo simulations varying the sort of ions (Au, Ge, Si, Ga), the ion energy and the incident angle. A comparison with the amorphisation depth determined by Raman scattering gives a good agreement, so optimisation with respect to penetration depth should lead also to an optimisation with respect to amorphisation depth.
Download the presentation TEM specimen preparation by focused ion beam sputtering – optimisation of the process (pdf-file, 5290 kB).
Scanning Electrochemical Microscopy is a powerful technique to obtain in-situ information of a wide range of processes occurring at interfaces. However, one major drawback of this technique is the lack of high spatial resolution compared with AFM or STM, due to the interference of the currents originated by the topographical and the electrochemical effects, respectively. Hence, a simultaneous but independent sensing of both, the topographical and the electrochemical information with high spatial resolution is a major issue in the field of scanning electrochemical microscopy (SECM). In this paper, we present a focused ion beam (FIB) based technology, which, for the first time, enables the realisation of an independent, simultaneous sensing of both, the topography and the electrochemically active interface. By remodelling an AFM-cantilever, an isolated ring-shaped electroactive metallic surface was integrated in the probe, whereas the residual AFM-tip was applied to gain the topographic information.
Download the presentation FIB Based Micro Fabrication Technique for a Novel Type of Scanning Electrochemical Microscopy Probes (pdf-file, 98 kB).
Focused ion beam systems are ideally suited to the micro-machining of 3-D shapes such as embossing tools, scanning probe tips and microelectromechanical structures. The possibility of tilting the stage and milling curved surfaces enable shapes to be made which are difficult by conventional wet and dry etching.
We discuss our work using a focused ion beam system for the milling of 3-D shapes. An algorithm has been written which corrects for the variation of the sputter yield with incidence angle and profile of the ion beam. To assess the milled shapes either stereo imaging or reconstruction from a series of focused ion beam cross sections through the milled shapes is used.
Download the presentation Application of a Focused Ion Beam System to the Micromachining of 3-D Shapes (pdf-file, 186 kB).
The problem is that the near-earth space environment where most satellites, the Shuttle, Mir, and the coming International Space Station orbit the earth is cluttered with man-made debris and naturally occurring meteoroids. Hypervelocity impacts between any spacecraft and this particulate environment can lead to catastrophic failure. In this short presentation, we will briefly describe this problem and how FIB help us for space debris and meteorites studies. Because most or the debris are smaller than 10µm, it is possible to study their origin, their density and their evolution on small surfaces in order to assess the risk by choosing the right material, the right orbit, the right shield and how to manage the satellite end of life. We use FIB for fine impact analysis (cross sectioning to analyse the mass / velocity ratio...). The main advantages of FIB for this application is the ability to analyse a lot of impacts on the same sample and to improve material analyses (residues coming from the debris at the bottom of the hole impact). FIB is used for satellite damages (LDVF : Long Duration Exposure Facility), to design new MOS impact detectors and to validate impact simulation according to the target material, the mass the nature and the velocity of the debris.
Download the presentation Spatial and Special FIB application: The debris issue (pdf-file, 1118 kB).
