Thermal stresses in Cu damascene submicron line structures

Abstract

Thermal stress in passivated blanket Cu and in passivated 0.2 μm wide damascene Cu lines have been characterized using x-ray diffraction and compared with that measured for 0.2 μm AlCu line structures. The microstructure plays an important role in controlling the thermal stress behavior, particularly for Cu due to its elastic anisotropy. Microstructural analysis of the blanket Cu revealed a strong (111) fiber texture. The damascene Cu lines had a strong (111) texture along with a weak in-plane (110) texture component that can be explained by surface energy considerations. The grain size of damascene Cu is constrained by the linewidth. The observed stress behavior of blanket Cu films shows stress hysteresis and plastic deformation. Under thermal cycling, the 0.2 μm wide Cu lines show a nearly hydrostatic triaxial stress state with linear elastic behavior. Compared with 0.2 μm wide AlCu lines, the principal stresses are generally lower in Cu lines and the difference can be attributed to the thermoelastic properties and confinement effect of the line structures. This indicates a weaker driving force for stress-induced void formation in Cu.