Effect of annealing on the mechanical behaviour of Au/Cu and Cu/Au bilayers on silicon

Abstract

The realtime evolution of stress during deposition of Cu/Au and Au/Cu bilayers was studied by an in-situ curvature measurement optical technique and annealing in the temperature range from room temperature to 400 °C. The Au/Cu and Cu/Au bilayers attached to silicon substrate with total thickness equal 12 nm and individual film thicknesses equal 6 nm Cu and 6 nm Au; 4 nm Cu and 8 nm Au; and 8 nm Cu and 4 nm Au, respectively, were examined. During deposition, an increase in tensile stress with increasing the total thickness of a system for both Au/Cu and Cu/Au bilayers were observed. Deposition of Au layer on Cu layer resulted in a change in compressive direction, whereas no change was observed for Cu deposition on Au. This difference is explained by lattice parameter mismatch. Significant stress evolution during the first cycle of heating was observed for all samples. It was found that irreversible modifications occur in systems during the first cycle of annealing. A change in the slope of the elastic part of stress curve during heating indicates a change in the coefficient of thermal expansion of metallic layers.

Stress Evolution During Annealing of Cu/Au, Cu/Ag and Au/Ag Bilayers

“…In our previous work, we focused on deposition and annealing of Au/Cu bilayers with different thicknesses of individual films. 14 …”

Electron migration behavior of Au/Cu multilayer films on Si substrates under UV radiation

“…Such Au/Cu thin films are also common in micro-electromechanical systems (MEMS) that are vastly used as intelligent integrated electrical systems in contacts, relays, actuators, RF circuits, hybrid switches. [6][7][8] These intelligent integrated electrical systems are the essential composition parts in spacecrafts, and their reliability is the key factor to the high cost of their fabrication, launching, operation and maintenance. [9][10][11] The electrical systems work in the low earth orbit (LEO) environments and suffer from ultraviolet (UV) radiation, thermal cycles or/and atomic oxygen attack, [12][13][14] which may lead to the destruction of seals, fracture of pins and breakage of inner bonding sites and finally cause failures of the devices even the whole system.…”