The time and temperature dependent mechanisms underlying the relaxation of thermally induced stresses in Al-films on quartz substrates have been investigated for film thicknesses in the range between 0.4 and 4.2 μm. Film stresses were determined by a high resolution capacitive technique from the bending displacement of the specimens. By employing a lamp furnace heating rates of 10°C/sec could be achieved. This test equipment allowed the investigation of thermally induced film stresses between room temperature and 450°C and in the time range between 10 sec and several hours. Similar temperature programms were run in situ in a scanning electron microscope in order to observe the concommitant changes of the surface morphologies.
The experiments show that a major fraction of 50 to 70% of the thermal stress recovers instantaneously by plastic flow. This defines a yield stress for the Al-films which is found to be inversely proportional to the film thickness and to vary linearly with temperature. The magnitude of the yield strength under tension is larger by a factor 1.7 compared to that under compression.