Control of Resistivity, Microstructure, and Stress in Electron Beam Evaporated Tungsten Films

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Abstract
We have investigated the capability of the electron beam evaporation technique for producing thin W films having properties suitable for application as first-level metallization in refractory MOS (RMOS) devices. The apparatus consisted of a sputter-ion pumped 18-in. diam UHV station, 6-kW e gun, and a quartz crystal rate monitor. The evaporation process employs low background pressures (1−3×10−7 Torr), substrate heating (200–700 °C), a preevaporation step, and evaporation at rates of 100–500 Å/min. Maximum throughput is 16 1(14)-in. diam silicon slices per run. Using substrate temperatures of 500–700 °C, we have been able to produce mechanically stable, adherent films having a resistivity of 7–8 μΩ cm and a sheet resistance of ∼ 0.08 Ω/□ (for 9000-Å film). “Cold”-deposited films (> 1000 Å thick) having a high resistivity of 40–50 μΩ cm can be annealed at 1000 °C to resistivity of 10–15 μΩ cm. The films are single-phase bcc W with a small grain size of 0.1–0.2 μ. Low resistivity films (deposited above 550 °C) are associated with a large degree of microstructural perfection, and have small tensile stresses (3−7×109dyn cm−2). The films possess, excellent high-resolution etchability, and were found to be compatible with MOS structures provided care is exercised during the deposition.

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