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This work combines focused ion beam sputtering and ultra-precision machining as a first step in fabricating metal alloy microcomponents. Micro-end mills having ∼25 μm diameters are made by sputtering cobalt M42 high-speed steel and C2 micrograin tungsten carbide tool blanks. A 20 keV focused gallium ion beam is used to define a number of cutting edges and tool end clearance. Cutting edge radii of curvature are less than or equal to 0.1 μm. Micro-end mill tools having 2, 4 and 5 cutting edges successfully machine millimeter long trenches in 6061-T4 aluminum, brass, 4340 steel and polymethyl methacrylate. Machined trench widths are approximately equal to the tool diameters, and surface roughnesses (Ra) at the bottom of micromachined features are ∼200 nm. Microtools are robust and operate for more than 6 h without fracture. Results from ultra-precision machining aluminum alloy at feed rates as high as 50 mm/minute and an axial depth of 1.0 μm are included.

The relationship among the grain structure, texture, and electromigration lifetime of four Al-1% silicon metallizations produced under similar sputtering conditions was explored. The grain sizes and distributions were similar and the grain structure was near-bamboo for all metallizations. All metallizations exhibited a near-(111) fiber texture, as determined by the pole figure technique. Differences in electromigration behavior were noted. Three of the metallizations exhibited a bimodal failure distribution while the fourth was monomodal and had the longest electromigration lifetime. The electromigration lifetime was directly related to the strength of the (111) fiber texture in the metallization as anticipated. However, whereas the grain size distribution has an effect on the electromigration lifetime when metallization lines are several grains wide, the electromigration lifetime of these near-bamboo metallizations appeared independent of the grain structure. It was also observed that a number of failures occurred in the 8 μm interconnect supplying the 5 μm wide test lines. This apparently reflects an increased susceptibility of the wider interconnect lines to electromigration damage.

The effects of irradiation from a focused ion beam (FIB) system on MOS transistors are reported systematically for the first time. Three MOS transistor technologies, with 0.5, 1, and 3 /spl mu/m minimum feature sizes and with gate oxide thicknesses ranging from 11 to 50 nm, were analyzed. Significant shifts in transistor parameters (such as threshold voltage, transconductance, and mobility) were observed following irradiation with a 30 keV Ga/sup +/ focused ion beam with ion doses varying by over 5 orders of magnitude. The apparent damage mechanism (which involved the creation of interface traps, oxide trapped charge, or both) and extent of damage were different for each of the three technologies investigated.

We report on recent studies of the effects of 50 keV focused ion beam (FIB) exposure on MOS transistors. We demonstrate that the changes in transistor parameters (such as threshold voltage, Vt) are essentially the same for exposure to a Ga+ ion beam at 30 and 50 keV under the same exposure conditions. We characterize the effects of FIB exposure on test transistors fabricated in both 0.5 μm and 0.225 μm technologies from two different vendors. We report on the effectiveness of overlying metal layers in screening MOS transistors from FIB-induced damage and examine the importance of ion dose rate and the physical dimensions of the exposed area.

Both the increased complexity of integrated circuits, resulting in six or more levels of integration, and the increasing use of flip-chip packaging have driven the development of integrated circuit (IC) failure analysis tools that can be applied to the backside of the chip. Among these new approaches are focused ion beam (FIB) tools and processes for performing chip edits/repairs from the die backside. This paper describes the use of backside FIB for a failure analysis application rather than for chip repair. Specifically, we used FIB technology to prepare an IC for inspection of voided metal interconnects (“lines”) and vias. Conventional FIB milling was combined with a superenhanced gas assisted milling process that uses XeF2 for rapid removal of large volumes of bulk silicon. This combined approach allowed removal of the TiW underlayer from a large number of M1 lines simultaneously, enabling rapid localization and plan view imaging of voids in lines and vias with backscattered electron (BSE) imaging in a scanning electron microscope (SEM). Sequential cross sections of individual voided vias enabled us to develop a 3D reconstruction of these voids. This information clarified how the voids were formed, helping us identify the IC process steps that needed to be changed.

The electrical and chemical properties of insulators produced by codeposition of siloxane compounds or TEOS with oxygen in a focused ion beam (FIB) system were investigated. Metal-insulator-metal capacitor structures were fabricated and tested. Specifically, leakage current and breakdown voltage were measured and used to calculate the effective resistance and breakdown field. Capacitance measurements were performed on a subset of the structures. It was found that the siloxanebased FIB-insulators had superior electrical properties to those based on TEOS. Microbeam Rutherford backscattering spectrometry analysis and Fourier transform infrared spectroscopy were used to characterize the films and to help understand the differences in electrical behavior as a function of gas chemistry and deposition conditions. Finally, a comparison is made between the results presented here, previous results for FIB-deposited insulators, and typical thermally-grown gate oxides and interlevel dielectric Si02 insulators.

This report describes the first practical, non-invasive technique for detecting and imaging currents internal to operating integrated circuits (ICs). This technique is based on magnetic force microscopy and was developed under Sandia National Laboratories` LDRD (Laboratory Directed Research and Development) program during FY 93 and FY 94. LDRD funds were also used to explore a related technique, charge force microscopy, for voltage probing of ICs. This report describes the technical work performed under this LDRD as well as the outcomes of the project in terms of publications and awards, intellectual property and licensing, synergistic work, potential future work, hiring of additional permanent staff, and benefits to DOE`s defense programs (DP).

High gain Optical Beam Induced Current (OBIC) imaging has been used for the first time to examine the internal structural effects of electrical stress on thermally-isolated polysilicon resistors. The resistors are examined over a wide range of current densities, producing Joule heating up to /spl sim/1200/spl deg/C. Throughout this current density range, the OBIC images indicate a clustering of dopant under dc stress and a more uniform distribution under ac conditions. The OBIC images also reveal areas that are precursors to catastrophic resistor failure. In addition to OBIC imaging, conventional electrical measurements were performed, examining the polysilicon resistance degradation and time-to-failure as a function of electrical stress. The electrical measurements show a monotonic increase in polysilicon resistor lifetime with frequency (up to 2 kHz) when subjected to a bipolar ac stress. The enhanced lifetime was observed even under high temperature (from Joule heating) stress conditions previously reported to be electromigration-free. The dopant redistribution indicated by the OBIC images is consistent with an electromigration stress experienced by the polysilicon resistors. The implications for thermally-isolated polysilicon resistor reliability are examined briefly.

Thin films of Al-l%Si were sputter deposited on Si under a variety of pressures of atmospheric impurity gases. The effect of the impurity gases (oxygen, nitrogen, and water), and deposition temperature (15° and 300° C), on the microstructure and properties of the aluminum thin films were studied. The gas pressures introduced during deposition varied from 5 × 10s−6 Torr (6.7 × 10s−4 Pa) to 1 × 10s-10 Torr (1 × 10s−8 Pa). The thin films were investigated by transmission electron microscopy and were found to have a columnar microstructure with an even distribution of silicon precipitates. Both the grain size and silicon precipitate size increased at the higher deposition temperature. A smaller grain size was found in samples that were deposited under the higher impurity gas pressures tested. The specular reflectance of the films was found to be dependent upon the amount of impurity gases present during deposition, the greater the partial pressure the greater the surface roughness. This study also investigated the possibility of using a Resistivity Ratio (RR) measurement to evaluate the grain size of the Al thin films. It has been previously observed that a small Al grain size has poor electromigration resistance. This study found that the correlation between Al grain size and RR values was good indicating that RR tests may be used as a quick, non-destructive measure of film quality.

The precipitation of Pb3Au from dilute Pb(Au) alloys and the subsequent Ostwald ripening of the precipitate phase have been studied. The Au diffusivity which limits the precipitation from Pb(500 at. ppm Au) specimens is in good agreement with Dp = 45 exp[(−20.8 kcal/mol)/RT], found previously to control the precipitation rate in Pb(900–1000 at. ppm Au) alloys (Rossolimo and Turnbull, 1973). In contrast, precipitation from Pb(100 at. ppm Au) alloys and Ostwald ripening in the Pb(500 at. ppm Au) specimens appear to be governed by the high temperature Au tracer diffusivity, DAu = 0.0041 exp[(−9.35 kcal/mol)/RT], which is about 103 times greater than Dp at the temperatures of interest, 75 to 112°C, and is attributed to the motion of a Au interstitial defect. In the 100 ppm alloys the Au is incorporated most easily at the ends of the Pb3Au crystals and a ribbon- or whisker-like morphology results. The particles which form at the grain boundaries in the 500 ppm Au alloy specimens are at least six times larger in volume than the matrix particles and ripen at their expense. The Ostwald ripening kinetics of the grain boundary particles scale with t1/2 rather than with t1/3 as is usual. The Pb3Au formed whiskers, blades, ribbons, or equiaxed particles depending upon the Au concentration and precipitation temperature. The precipitation and ripening kinetics are critically dependent on the morphology of the second phase.