Focused ion beam tools are available since gallium ion sources have been reproducibly fabricated with stable characteristics and incorporated in an accelerating and focusing electrostatic column. The operator running this column has a key role by handling the ion source, which is composed of a tungsten tip covered by liquid gallium. He also has to maintain the electrostatic column in good shape mainly under vacuum and without particles, in order to use all the capability of the focused ion beam tool. He has to understand the interaction of ions with a surface giving secondary ions or electrons used to form images and extract some atoms from the surface allowing drilling holes. The capability of new software running on very fast computer allows real time control of the ion beam. This gives new possibilities to the operator and new words like: pixel time, dwell time, raster scan, line scan, image scan, refresh time, ... are used and needed to be defined. Quantitative knowledge of the beam substrate interaction to control deposition and etching process of the ions is important to give to the operator the possibility to forecast what he will obtain. From all this, the operator can apply focused ion beam for a wide range of applications: Circuit repair, optical mask modification, trimming of resistor, magnetic head adjustment, cutting and observation of integrated circuit, defect identification in silicon technology, sample preparation for SEM or TEM observation.
The need for IC repairs and modifications with Focused Ion Beam continue to be in increasing demand. Furthermore, image visibility on the FIB is drastically reduced, making accurate positioning and milling operations on the area of interest more difficult and thereby putting the success of FIB operations at risk. We will present an innovative approach which brings optical microscopy inside the FIB vacuum chamber. With this approach it is possible to visualise the area of interest with FIB secondary emission microscopy and with optical microscopy. The advantage of this approach is that it solves FIB intrinsic positioning limitations for backside approaches as well as for planar circuits. It also makes it possible to reduce FIB irradiation damage since the optical system alone can be used to navigate on the circuit and locate the area of interest for FIB modifications. Another non-negligible aspect of using optimal microscopy consists in checking the result of FIB modifications. After demonstrating how this approach can be implemented, we will extend this work to the use of a laser cutter (plugged onto the optical system) which can be used for rapid ablation to prepare work for precise FIB circuit modifications from the frontside or the backside.
With each semiconductor technology generation, new interconnect schemes have evolved to meet the rapidly increasing performance demands. The interest in tungsten for applications in IC metalization results mainly from the high activation barrier for self diffusion with high resistance to electromigration under high current densities. With our Micrion 2500 FIB-System (50 keV, 5 nm) we have achieved high spatial resolution of the FIB deposited tungsten. In the presence of nickel we obtained highly pure tungsten films with superior electrical properties compared to those based on the W(CO)6 precursor only. The electrical properties (conductivity, electromigration resistivity) as a function of process parameters (dose, acceleration voltage, pixel spacing), the nickel content and the hydrogen to hexacarbonyltungsten ratio was investigated
The deposition of dielectric layers by gas-assisted processes is an important aspect for device modification by focused ion beam. Low layer thickness and a robust insulating features of the FIB-deposited film are often demanded simultaneously. This study focuses on the optimization of the deposition process of Silicon dioxide layers using a Micrion 2500 FIB-system. Dielectric layers of silicondioxide were deposited at varying process parameters such as dwell time, refresh time and composition of the precursor gas mixture. Novel material systems such as metal oxides and salicides were exploited by using alternative metalorganic precursors. The deposited dielectric layers were characterized by electric testing biasing on the concept of an capacitor setup implementing the generated insulator structure.
In the next generations of high performance semiconductor devices copper will replace the present aluminum metallurgy in the metallization layers. Therefore the effects of FIB gas assisted etching on these samples have to be investigated. Up to now there are no new gas processes offered by the equipment vendors. The results of the experiments with the existing gas chemistry on Cu samples are discussed. For the exposure of copper the insulator enhanced etching process with XeF2 seems to work. In the case of iodine the removal characteristics of the metal etch process is disastrous. There is a spontaneous reaction of iodine with exposed copper similar to the well known reaction of XeF2 with exposed polysilicon or si-substrate. Bromine is for the same reason not usable for the removal of copper. For chlorine this fatal reaction with exposed copper was not observed. For all etch processes the long term corrosion on the exposed metallization has to be investigated. The contact resistance of deposited tungsten and platinum pads on copper is similar to the according pads on aluminum. The values for tungsten on copper are one order of magnitude lower than for Pt on Cu.
The passive voltage contrast in the secondary electron image of an FIB is much better visible than in conventional SEMs. It can be used for several applications in physical failure analysis of semiconductor products. The basic mechanisms are shown and it It will be discussed, how the the generation of VC is influenced by many parameters such as ion beam current, scan speed, sample orientation and sample preparation. The operator has to adjust them carefully and has to have a detailed knowledge of the design in order to get the expected result. Three examples of investigations on test structures will illustrate the facts.
Due to reduction in structure size, conventional electrical measurements in DRAM failure analysis becomes more and more difficult. Passive voltage contrast with focused ion beam (FIB) turned out to be a convenient and quick method to detect and localize leakage path in DRAM cell arrays. Therefore a detailed knowledge of the circuit design is necessary to explain the visible voltage contrast and to modify the circuit for exact failure localization. In three examples the charging mechanism and the influence of a leakage path is explained out of the circuit design. On BL-BL shorts the effect of positive charge on involved electrical devices is demonstrated. With CB-GC shorts the possibility to emphasis the passive voltage contrast by choosing a special analysis strategy is shown. In the third example passive voltage contrast and in-situ preparation by selective etching are combined for analysis of node dielectric leakages.
In-fab analytical methods are of increasing interest for wafer monitoring and physical failure analysis in advanced semiconductor device manufacturing. In particular, the installation of FIB tools in the clean room has been discussed recently. One of the key issues of the FIB application is the Ga-beam induced wafer surface contamination. This study is focused on the question of how FIB application contributes to wafer surface contamination. TOF SIMS measurements were performed to investigate distribution and level of surface contamination on 8" wafers which had been modified by FIB. Several sputter conditions for ion beam milling were chosen to cover typical FIB applications like cross section preparation. The angle of incidence, beam current, milling box size and sputter time were varied. In addition, the use of chemically assisted sputtering or deposition was considered. The mechanism for sputter induced redeposition will be discussed. Investigated sources for contamination comprise redeposition of secondary ions, sputtering from the chamber environment by elastic recoils and scattering at residual gas atoms. Acknowledgment: The authors thank Ercan Adam (AMD Inc. Sunnyvale/CA) for stimulating discussions.
In this work, some of the possibilities of focused ion beam for application in microsystem technology are explored. More precisely, the deposition of silicon oxide was investigated, since it enables three-dimensional structures to be made on a small scale. The key to this is the possibility to deposit "overhang" features, i.e. features that extend beyond the already present or previously deposited structures underneath. In this way, a number of interesting micromechanical structures can be formed, e.g. oxide "bridges", hollow bended pipes, spiral shapes and so on. Furthermore, investigations into the mechanical properties (Young's modulus) of the deposited silicon oxide were carried out.
A new method for the preparation of cross sections for transmission electron microscopy (TEM) using a focused ion beam (FIB) system is presented. The new technique consists of micro-machining a free-standing cantilever into which a TEM membrane is milled. Advantages of this approach over the conventional FIB trench method for the preparation of TEM cross sections are that, for a given beam current, the total milling time is reduced since less material is milled away and the resulting samples can be tilted through large angles (45º) without the electron path becoming obstructed.
In Delft a unique dual beam instrument has been designed, and partly built, in which a focused ion beam column is combined with a transmission electron microscope. The objective is to investigate the physical limits to nanofabrication with focused ion beams. For non-destructive imaging of structures smaller than 10 nm it becomes necessary to use electrons instead of ions. The ion beam is brought onto the axis of a conventional Philips EM-420 STEM. The optics has been optimized such as to minimize the Coulomb interactions in the ion beam, and the objective lens has been designed such that it focuses both electrons and ions onto the specimen. The spotsize aimed for is 2 nm in diameter. The resolution for fabrication is also determined by the size of the ion-specimen-interaction volume. Monte Carlo simulations of the interaction process show that FIB-fabricated structure sizes below 10 nm are feasible.
