We have demonstrated a new planarized all-refractory technology for low Tc superconductivity (PARTS). With the exception of the Nb-AlOx-Nb trilayer preparation, the processing is done almost exclusively within an advanced Si technology fabrication facility. This approach has allowed us to leverage highly off of existing state-of-the-art lithography, metal etching, materials deposition, and planarization capabilities. Using chemical-mechanical polish as the planarization technique we have fabricated Josephson junctions ranging in size from 0.5–100 μm2. Junction quality is excellent with the figure of merit Vm typically exceeding 70 mV. PARTS has yielded fully functional integrated Josephson devices including magnetometers, gradiometers, and soliton oscillators.
We have investigated the interaction between Ti and SiO2 in the temperature range of 400° to about 1000°C. The reaction proceeds in a layer‐by‐layer fashion and consists of SiO2 reduction followed by the formation of a Ti‐rich silicide at the interface. At higher temperatures, a Ti‐rich oxide is formed near the surface. The reaction starts at approximately 400°C, and the loss of SiO2 becomes significant above 500°C. A strong interaction between Ti and SiO2 takes place at 700°C and above. The thicker the SiO2 , the higher resistance it has to degradation due to elevated temperature effects.
We have investigated reactively sputter',d ZrN, the most thermally stable of the refractory metal nitrides, for its applicability as a submicron gate electrode. One would require for such gate electrode in addition to the lowest possible resistivity, a metal work function that will tailor the threshold voltage of metal/oxide/semiconductor (MOS) field effect transistor in such a way as to minimize the channel implant. Having these requirements in mind, we have measured the temperature dependence of resistivity, its dependence on the annealing temperature and work function of ZrN films. Our best films have resistivity, p of 20 A2-cm, comparable to TiSi. We find that p of as-deposited films being nearly stoichiometric, decreases about 20% after 1000°C anneal. Such anneal does not significantly alter the average grain size, which remains about 300 A even at this temperature. The temperature dependence of p at low temperatures indicates phonon scattering mechanism and we suggest that small amounts of oxygen are re- sponsible for residual resistance. The films undergo superconducting transition at 7.5-8 K and this transition provides an additional check on the compositonal homogeneity of the films. The work function, determined from the capacitance-voltage (C-V) characteristics of ZrN capacitors with various thicknesses of Si02, has value 0. = 4.6 Volts, at the midgap between n+ and p+ polysilicon and thus is applicable to 0.5 1m N-MOS and submicron C-MOS.
We have studied the properties of reactively sputtered TiN films used as diffusion barriers for Al-Cu metallization in submicron bipolar transistors. Emitter-base diodes with shallow junctions were fabricated to monitor the integrity of the barrier via junction leakage measurements. Scanning and transmission electron microscopy were used to study the morphology and step coverage of these films, and also for barrier failure analysis. The effectiveness of the barrier depends on both the nominal thickness of the TiN layer and on the device dimensions. For thin TiN layers (∼47 nm), high junction leakage was observed on narrow emitters (0.5 μm) but not on wide emitters (5 μm). These observations highlight the reliability and yield concerns associated with the use of sputtered TiN films for deep submicron technologies. In some cases, low-temperature (500 °C) epitaxial alignment of the emitter polysilicon was observed, associated with Al penetration of the barrier. This indicates that the Al provides an enhancement of the tendency towards epitaxial alignment of the polysilicon grains. For thicker TiN layers (∼83 nm), low leakage was observed on both narrow and wide emitters, and no unusual epitaxial alignment was observed.
In situ sputtering of TiN/Ti liners into high aspect ratio (six to eight) sub-half-micrometer contacts with step coverages more than 40% on the side as well as on the bottom is demonstrated for the first time. The process utilizes a collimator, honeycomb-like structure through which atoms are directed into contact holes. A study of step coverages, deposition rates, contact resistances, and junction leakages for Ti and TiN layers as a function of the aspect ratio of the collimator is carried out. The extendibility of collimation beyond 0.25 μm contact geometries is demonstrated. The optimum deposition rate is achieved based on the aspect ratio of the collimator. The structures formed with chemical vapor deposition (CVD) of W on TiN/Ti liners exhibit an order of magnitude improvement in contact resistance over the structures formed without collimated liners, especially for geometries below a critical geometry. The reverse leakages using the shallow junctions (0.12–0.14 μm) remain unchanged.
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