Stress Behavior of High Density Plasma Chemical Vapor Deposition Oxide Deposited on a Metal-Patterned Wafer

Abstract

A high density plasma chemical vapor deposition (HDPCVD) oxide was used as an inter metal dielectric (IMD) due to its good gap-fill properties for compensating the tensile stress of Al metal layers. When the HDPCVD oxide was deposited on a metal patterned wafer, however, the oxide showed tensile stress. In order to understand the mechanism of the characteristic stress behavior of the HDPCVD oxide on a metal patterned wafer, the change in magnitude of the wafer bow was measured as a function of oxide thickness, and was modeled quantitatively using the density of metal patterns and the stress change of the metal film. In the model, the oxide deposited between metal lines was assumed to have tensile stress due to the relatively high shrinkage of the neighboring metal pattern. When the deposited HDPCVD oxide thickness was thinner than that of the metal film, only the stress of the lower parts of the metal film, which was connected to the oxide, could affect the change of the wafer bow value. When the deposited oxide thickness was greater than that of the metal film, the stress of the oxide above the metal film was assumed to be compressive. Using the above assumptions and a simple mathematical model, the change in magnitude of the wafer bow was calculated and compared with experimental results. The calculated data were in good agreement with the experimental values.