Keenan L. Evans

Work function response of thin gold film surfaces to phosphine and arsine

Abstract The work function changes of thin gold films upon exposure to phosphine and arsine in the concentration range 20–80 parts per billion (ppb) concentrations were studied using the Kelvin probe method under ambient conditions. The work function of gold surfaces decreases significantly in the presence of these gases. This decrease is attributed to charge transfer from these hydride molecules to the gold surface through σ-bonding of their lone-pair electrons. Auger electron spectroscopy and secondary ion mass spectrometry were used to characterize the surface chemical components of thin gold films. The extraordinarily high sub-ppb sensitivity of the work function response for phosphine and arsine on gold surfaces under ambient conditions can be used to detect ultra-trace concentration of these toxic gases.

Be+ and BeF + Implants in GaAs Using Ions Produced from Solid‐Gas Reaction

Be implantation is widely used for p-type doping in III-V semiconductors. Physical sputtering of solid Be may result in some beam instability and low beam current, while solid sources such as BeCl[sub 2] require heating to achieve high vapor pressure. This work discusses GaAs implantation with Be[sup +] and BeF[sup +] ions produced via plasma-etching of solid Be with fluorine-containing gases. Etching of Be with Bf[sub 3] produced Be[sup +] and BeF[sup +] ions with currents 10 times and 55 times higher than that of Be[sup +] from the physical sputtering process, respectively. Activation of Be implanted as Be[sup +] from the new process is comparable to those of the other processes. Activation of Be implanted as BeF[sup +] exhibited higher activation energy and lower activation efficiency. The BeF[sup +] implant still provides reasonable activation for source/drain and buried layer formation under acceptable annealing conditions. The lower effective Be[sup +] implant allows shallow implant depths to be realized.

Texture of gold-palladium couples

The crystal textures of polycrystalline films of gold-palladium couples on an oxidized silicon (100) substrates were investigated via x-ray diffraction (XRD) pole figures. Studies were performed on both as-deposited and thermally annealed films. Scanning electron microscopy (SEM) was used to examine the microstructures of the seed layer thin films as deposited. The {l{underscore}brace}111{r{underscore}brace} texture formation of gold-palladium thin film couples displayed a strong dependence on the nature of the underlying seed layer. Gold films deposited on a palladium seed layer revealed much less degree of {l{underscore}brace}111{r{underscore}brace} texture, than gold films deposited directly on a silicon dioxide surface. In contrast, palladium films deposited on polycrystalline gold films showed a higher degree of {l{underscore}brace}111{r{underscore}brace} texture, compared to palladium films deposited directly on silicon dioxide. The {l{underscore}brace}111{r{underscore}brace} texture of annealed gold-palladium alloy thin films was greater for palladium on gold than for gold on palladium. These results are interpreted in terms of the gold-palladium diffusion mechanism and the interaction of the condensing metals with the oxygens of the SiO{sub 2} substrate surface.

Secondary Ion Mass Spectrometry, SIMS

Secondary ion mass spectrometry (SIMS) is based on the ejection of charged atomic and molecular species from the surface of a solid sample when it is bombarded by a stream of heavy particles. J. J. Thomson1 first observed this phenomenon in 1910. Later Arnot and Milligan2 investigated the secondary ion emission resulting from positive ion bombardment. Herzog and Viehboeck3 provided the basis of modern SIMS instrumentation, using an electron impact primary ion source in 1949. Other pioneers in the field constructed their own unique SIMS instruments.4, 5, 6, 7 The first commercial system derived from Herzog’s work8 was intended for the geochemical analysis of extraterrestrial material captured during the early years of outer space exploration. Since that time, SIMS has become an indispensable tool for the characterization and analysis of semiconductor components and materials. Its ability to detect all elements in the periodic table, excellent elemental sensitivity and inherent depth profiling capabilities make SIMS the appropriate choice for a number of critical semiconductor analysis needs. Dopant profiling, mobile ion monitoring, process contamination diagnosis, thin film characterization, interface analysis and surface analysis are just a few of the areas where SIMS can contribute to the root cause determination of microelectronics failures. In addition to the utilization of SIMS as a tool for the diagnosis of failures, the technique is a very powerful aid in the optimization of semiconductor processes, preventing failures. Typical applications in this preventive mode include the evaluation of the effectiveness of cleaning processes, monitoring the impact of new processing tools on wafer contamination levels and implant matching studies for technology transfer between fabrication sites.

Effect of Poly-Si on Electromigration Behaviors and Microstructure Characteristics of Au Metallization

For BJT and MOSFET, poly-Si is the most critical layer used as an emitter to improve the current gain in BJT and as a gate to improve the gate oxide reliability in MOSFET. In both cases, the poly-Si is then connected to the conductor. It is very important to understand how poly-Si affects the microstructure and the electromigration behavior of conductor. NIST test structures (length = 800μ, thickness = 0.7μ, widths = 1, 5, 10 μ) with Au conductor and TiW/TiWN/TiW barrier were used to study the impact of poly-Si. Two groups of samples were used: one with poly-Si under the barrier and the other without poly-Si. Thermal oxide was used to isolate the substrate from the conductor and Si 3 N 4 , was used as passivation. DC stress was performed at 175, 200, and 225°C. Microbeam X-ray Diffraction (μ XRD) was used to characterize the microstructure of the TiW barrier and Au metallization layers as a function of line length and width. The data indicates that samples with poly-Si have lower electromigration resistance for Au conductors for all widths and temperatures, with higher initial deformation fault densities on poly-Si.