E. K. Broadbent

Interactions of thin Ti films with Si, SiO2, Si3N4, and SiOxNy under rapid thermal annealing

Thin Ti films sputter deposited onto single‐crystal Si, thermal SiO2, and low‐pressure chemical vapor deposited Si3N4 and SiOxNy (x≊y≊1) substrates have been rapid thermal annealed in N2 or Ar, with and without an amorphous Si overlayer, and the reactions followed using Auger elecron spectroscopy, transmission electron microscopy, electron diffraction, and sheet resistance measurements. A multilayer film is created in practically every case with each layer containing essentially a single reaction product, viz.,TiSix, TiOx, δ‐TiN, or TiNxO1−x. The results are discussed in light of published Ti‐Si‐O and Ti‐Si‐N phase diagrams.

Excimer laser processing of Al-1%Cu/TiW interconnect layers

Planar thin-film stacks comprising 750-nm Al-1%Cu/100-nm TiW/100-nm SiO/sub 2/ were subjected to a 25-ns excimer laser pulse (XeCl, 308 nm) at an optical fluence of 3.5 to 5.0 J/cm/sup 2/ at a substrate temperature of 250 degrees to 400 degrees C, and a number of the important film properties were measured. Resultant grain sizes ranged from 2 mu m to in excess of 300 mu m, the largest grains corresponding to the highest fluence/temperature condition. The melting of the Al-Cu films was found to eliminate hillock growth completely during subsequent furnace annealing (450 degrees C). Laser processing at the higher fluence condition (5.0 J/cm/sup 2/) produced large (>30%) increases in layer resistivity. Ultramicrohardness was found to range from 39 to 52 kg/mm/sup 2/ for the treated films. Accelerated stress testing revealed no significant difference in open-circuit electromigration resistance between the as-deposited and the majority of the laser-processed Al-Cu films. However, one particular group of laser-melted samples (3.5 J/cm/sup 2/, 400 degrees C) demonstrated lifetimes at least 10 times greater than those of the other sample groups. Specular reflectivity, impurity distribution, and layer morphology were also examined.<<ETX>>

Application of self-aligned CoSi/sub 2/ interconnection in submicrometer CMOS transistors

CoSi/sub 2/ interconnection layers of 0.14-0.40- mu m thickness were applied in a self-aligned manner to 0.75- mu m-gate-length n-channel and p-channel transistors in a complete CMOS device fabrication flow. The sheet resistance above the active regions ranged from 1.6 to as low as 0.46 Omega /square for the four CoSi/sub 2/ thicknesses examined. Using an Al-Cu/TiW metallization, the resistance per contact for 1- mu m-diameter openings to CoSi/sub 2/ was >

Formation and high‐temperature stability of CoSix films on an SiO2 substrate

A thin α‐Co layer with an amorphous Si underlayer has been sputter deposited onto a thermal SiO2 substrate, rapid thermal annealed in N2 at 700–1050 °C, and the phases formed examined using Auger electron spectroscopy, transmission electron microscopy, electron diffraction, and sheet resistance measurements. A CoSix film results where x is constant with depth and determined by the relative amounts of Co and Si deposited. With increasing x, phases identified are α‐ and β‐Co containing dissolved Si, Co2Si, CoSi, and CoSi2. At high temperatures, the CoSi2 film agglomerates and thins the underlying oxide probably on account of excess Si in the silicide film. Furthermore, in an N2 atmosphere, the CoSi2 globules are converted into CoSi in accordance with the phase diagram.

Range distributions of 11B+ in Co, CoSi2, Ti, and TiSi2

The range distributions of 10–120 keV 11B+ in polycrystalline Co, Ti, CoSi2, and TiSi2 targets have been measured by secondary ion mass spectrometry. The obtained projected ranges Rp and projected range stragglings ΔRp are within 25% and 10%, respectively, of those predicted using the Monte Carlo computer program trim. By comparison the one‐dimensional Boltzmann transport calculation in suprem‐3 tends to overestimate Rp by as much as 300% at the highest ion energies.

Electromigration-induced short-circuit failure in aluminum underlaid with chemically vapor deposited tungsten

Electromigration was studied in Al conductors underlaid with chemically vapor deposited W, and the results compared to the more conventional Al/TiW metallization. In Al/TiW conductors electromigration results in Al whisker growth, causing metal short rather than open‐circuit failure. Contrary to expectations, the Al/W metallization was found to be more susceptible to the formation of whiskers during current stress, with Al/W lifetimes reduced by about one‐half compared with Al/TiW. The temperature and current density failure dependencies were not significantly affected by the composition of the underlayer. The mechanical stress in the underlayer was not found to significantly affect the stress distribution in the overlying Al film.

Effect of post‐silicidation annealing on TiSi2/p+‐n Si junctions

The reverse‐bias leakage of TiSi2/p+‐n Si junctions is <10 nA/cm2 for 0.1‐μm‐deep p+‐Si with a TiSi2 sheet resistance of 1.7 Ω/sq, and is essentially independent of carrier concentration, and the amount of B consumed during silicidation. Forward‐bias current characteristics show that the TiSi2 contacts are ohmic with significant recombination currents and high‐level injection at voltages below the series resistance limit. Post‐silicidation annealing for 30 min at 920 °C, with or without an overlayer of borophosphosilicate glass, increases the majority‐carrier concentration and does not cause B to diffuse out of the Si. Also, minority‐carrier lifetimes show a twofold increase after annealing and this results in nearly ideal junctions with leakage that is dominated by diffusion currents. Thus, TiSi2/p+‐n Si is thermally stable under conditions that are compatible with glass flow and reflow processing.

The high-temperature stability of chemically vapor-deposited tungsten-silicon couples rapid thermal annealed in ammonia and argon

A rapid thermal anneal (RTA) in an NH3 ambient has been found to increase the thermal stability of W films chemically vapor deposited (CVD) on Si. W films deposited onto single‐crystal Si by low‐pressure CVD were rapid thermal annealed at temperatures between 500 and 1100 °C in NH3 and Ar ambients. The reactions were studied using Rutherford backscattering spectrometry, x‐ray diffraction, Auger electron spectroscopy, transmission electron microscopy, and four‐point resistivity probe. High‐temperature (≥1000 °C) RTA in Ar completely converted W into the low resistivity (31 μΩ cm) tetragonal WSi2 phase. In contrast, after a prior 900 °C RTA in NH3, N inclusion within the W film and at the W/Si interface almost completely suppressed the W‐Si reaction. Detailed examination, however, revealed some patches of WSi2 formed at the interface accompanied by long tunnels extending into the substrate, and some crystalline precipitates in the substrate close to the interface. The associated interfacial contact resistance was only slightly altered by the 900 °C NH3 anneal. The NH3‐treated W film acted as a diffusion barrier in an Al/W/Si contact metallurgy up to at least 550 °C, at which point some increase in contact resistance was measured.