Strain effects in multi-layers

High stress levels can cause problems for both electronics and micromechanics. It is therefore important to characterize the stress and strain of the different mechanical layers used for processing. In order to predict the properties of a multi-layered structure it is not sufficient to know the mechanical properties of each independent layer. The deposited layers may have a considerable effect on the mechanical properties of the underlying layer. This paper discusses the importance of the effect of each layer on underlying layers and on the total structure, using poly-silicon and silicon-nitride as the mechanical layers. The measurements show that at an anneal of 850 degrees C the influence of nitride on the underlying poly is considerable. At an anneal of 1000 degrees C this effect disappears. We also examined the stress in poly-nitride-poly layers in order to find out the influence of annealing in between the deposition of the layers. Measurements show that the temperature of the anneal is the dominant factor.