Effects of substrate temperature on copper distribution, resistivity, and microstructure in magnetron-sputtered Al-Cu films

Abstract

The depth distribution of copper in Al-Cu (4% by weight) films has a strong influence on the electrical properties and microstructure. Magnetron-sputtered films were deposited on tantalum silicide substrates with substrate temperature ranging from ambient to 510°C with a fixed r.f. bias voltage at a typical deposition rate of 1 μm min-1. The copper distribution in a 1 μm thick film deposited at ambient temperature is very non-uniform, with a peak concentration of 6.7% atomic) near the film-substrate interface and 0.6% distributed uniformly over the top half of the thickness. As the temperature increases, the copper peak near the interface decreases while the copper level in the upper portion of the film increases gradually. At 510°C the copper distribution becomes almost uniform with 2% near the interface and 1.8% near the top surface. The resistivity of the ambient film is typically 3.4μΩ cm with a standard deviation of 2% across the 130 mm diameter probed. As the temperature increases, the resistivity increases gradually to 4.1 μΩ cm at 510°C accompanied by decreasing standard deviation to less than 1%. Cross-sectional transmission electron microscopy reveals θ-Al2Cu precipitates concentrated near the interface in films deposited at ambient temperature, thus confirming the results obtained from Rutherford back-scattering. By contrast, in films deposited at higher temperatures, many single-oriented precipitates were found to be distributed uniformly throughout the film and identified as θ'-Al2Cu. © 1987.