Michael C. Madden

In situ scanning electron microscopy observation of the dynamic behavior of electromigration voids in passivated aluminum lines

The dynamic behavior of electromigration (EM) voids has been studied in situ using a field‐emission scanning electron microscope fitted with a Robinson backscatter detector. A high‐temperature stage has been used to minimize the temperature gradients associated with Joule heating and to allow independent control of temperature and current density. No evidence of pre‐existing voids was found. The formation, growth, and motion of electromigration voids were observed and recorded photographically. The voids moved dynamically against the electron wind. No correlation between void size and void velocity was found. The static growth of EM voids was observed in some instances; however, this did not precede void motion nor did it lead to failure. Moving voids formed late in the test dominated final failure. Comparison of experimental results with void motion models reveals that the models for dynamic void motion are not consistent with experimental observations.

Observations of electromigration induced void nucleation and growth in polycrystalline and near‐bamboo passivated Al lines

Electromigration voiding in passivated pure Al lines was observed in situ using high voltage scanning electron microscopsy. Two different types of lines were investigated; one deposited under high purity conditions with a near‐bamboo microstructure, and one deposited under conventional conditions with a polycrystalline microstructure with stress voids present. The samples were observed while being tested under accelerated electromigration conditions. Samples were then thinned and analyzed with transmission electron microscopy techniques to investigate the relationship between line microstructure and void nucleation. Electromigration voids and stress voids were seen to nucleate at very specific, unique, microstructural sites that require the intersection of a grain boundary with the line sidewall. Void movement after initiation is also dictated by microstructure, with voids only growing into and causing failure in grains oriented with a {111} plane near perpendicular to the line. The conditions for void nu...

Total reflection x-ray fluorescence spectroscopy using synchrotron radiation for wafer surface trace impurity analysis (invited)

Trace impurity analysis is essential for the development of competitive silicon circuit technologies. Current best methods for chemically identifying and quantifying surface and near‐surface impurities include grazing incidence x‐ray fluorescence techniques using rotating anode x‐ray sources. To date, this method falls short of what is needed for future process generations. However, the work described here demonstrates that with the use of synchrotron radiation, total reflection x‐ray fluorescence methods can be extended to meet projected needs of the silicon circuit industry until, at least, the year 2000. The present results represent over an order of magnitude improvement in detection limit over what has been reported previously. A double multilayer monochromator on a high flux wiggler beam line resulted in a detection limit for Ni of 3×108 atoms/cm2. This is to be compared with a detection limit of 5×109 atoms/cm2 obtained with a rotating anode system. This is due to the greatly improved signal to bac...

In situ observations of dc and ac electromigration in passivated Al lines

In situ experiments have been carried out using a field emission scanning electron microscope (Hitachi S‐800) in order to characterize the dynamic behavior of electromigration (EM) voids under high spatial resolution. These experiments have shown how the EM voids move against the electron wind either in passivated or unpassivated lines under dc and low‐frequency ac currents.

Wide band-pass approaches to total-reflection X-ray fluorescence using synchrotron radiation

Abstract Measurement and control of surface and near surface trace impurities on silicon wafers is a critical technology for the development and manufacture of leading-edge silicon VLSI circuits. Among the industry-standard methods for monitoring surface impurities are grazing-incidence X-ray methods employing rotating anode sources. In the semiconductor industry, the X-ray method is referred to as total reflection X-ray fluorescence spectroscopy (TRXRF or TXRF). Conventional-source TRXRF methods are not adequate for future industry needs. Beamline modifications and a special experimental chamber were designed and executed at the Stanford Synchrotron Radiation Laboratory to investigate the performance of synchrotron radiation based approaches to this application. Crystal monochromators, a MoC multilayer mirror, and filtered white light were examined as sources for TRXRF. The best experimental configuration surpassed previous attempts in the field. With it, two different semiconductor industry user groups were able to demonstrate significant improvements in the TRXRF detection limits for 3-d transition metals and for aluminum compared to standard conventional equipment. The design goals, equipment configuration and current performance level of this synchrotron-based TRXRF configuration are described in detail. Aspects of the experimental design under further development for even higher performance are discussed.

Observation of voids induced by mechanical stress and electromigration in passivated Al lines deposited at different purity levels

Two pure Al passivated line samples were prepared under different metal deposition conditions, and were electromigration tested in a high voltage scanning electron microscope (HVSEM). The sample prepared under ultrahigh purity conditions showed a high resistance to void initiation and a very large grain size, while the more conventionally deposited metal displayed comparatively poor electromigration resistance. The sample prepared at lower purity conditions showed initial stress voids, but these were not the site for electromigration damage.

Structure of ionized cluster beam aluminum deposited on (100) silicon

Ionized cluster beam aluminum deposited on (100) silicon has a unique grain structure consisting of only two crystallographic orientations. Both are (110), but are rotated 90° with respect to each other about the (110) axis so that their (220) planes are perpendicular. This structure arises from a close match between the (200) planes in the aluminum and the (220) planes in the silicon along one direction, and the existence of a interfacial superlattice consisting of three (220) planes from the silicon and four (220) planes from the aluminum, along the orthogonal direction. This grain structure contains no triple points and curved grain boundaries.

Transmission electron microscopy for the determination of the microstructure of thin films and interfaces

Abstract The optics and construction of a transmission electron microscope are reviewed, along with electron diffraction and its relation to image contrast. Three general areas of thin film analysis by transmission electron microscopy are discussed: geometric determinations, involving variations in the thickness of thin films, substrate dislocations and grain size; microstructure determination by electron diffraction, using ionized cluster beam deposited aluminum; analysis of an interfacial reaction by a combination of diffraction and X-ray fluorescence, using Inconel 718 and a lithia-silica glass ceramic. Future trends in the use of transmission electron microscopy for the analysis of thin films are discussed.

Synchrotron Radiation for Measurement of Contaminants on Silicon Surfaces

The detection limit for aluminum using total reflection x-ray fluorescence (TXRF) is approximately 100 times lower for a synchrotron source compared to a conventional source. The detection limit for transition metals is approximately 15 to 40 times lower depending on atomic number and energy of the incident radiation.

Thermally activated magnetization and resistance decay during near ambient temperature aging of Co nanoflakes in a confining semi-metallic environment

We report the observation of magnetic and resistive aging in a self-assembled nanoparticle system produced in a multilayer Co/Sb sandwich. The aging decays are characterized by an initial slow decay followed by a more rapid decay in both the magnetization and resistance. The decays are large accounting for almost 70% of the magnetization and almost 40% of the resistance for samples deposited at 35 °C. For samples deposited at 50 °C the magnetization decay accounts for ∼50% of the magnetization and 50% of the resistance. During the more rapid part of the decay, the concavity of the slope of the decay changes sign and this inflection point can be used to provide a characteristic time. The characteristic time is strongly and systematically temperature dependent, ranging from ∼ 1 × 102 s at 400 K to ∼ 3 × 105 s at 320 K in samples deposited at 35 °C. Samples deposited at 50 °C displayed a 7-8-fold increase in the characteristic time (compared to the 35 °C samples) for a given aging temperature, indicating tha...