Mechanistic understanding of the stress-induced failure of Si₃N₄ metal-insulator-metal capacitors

The failure of Si₃N₄ metal-insulator-metal (MIM) capacitors fabricated by plasma enhanced chemical vapor deposition (PECVD) was investigated using cross-sectional transmission electron microscopy (XTEM) and residual stress analysis. As a result we noted that the failure of the Si₃N₄ MIM capacitors originated from the microvoids formed over the Si₃N₄ dielectric and the TiN interlayer. The microvoid of the MIM capacitor, particularly in case of having a very thin Si₃N₄ of less than 50 nm-thick, caused it to leak out much of the current to the extent of a few microamperes even at bias of 3 volts. The formation of microvoids was explained by the residual stress of the constituent layers at a mechanistic point of view. The stress analysis showed that the absolute stress normalized by the thickness of the Si₃N₄ layer should be less than 31 MPa/nm to avoid microvoiding. In this research it was noted in conclusion that the stress state of not only the dielectric but also the interlayer should be taken into account for the successful design of high capacitive Si₃N₄ MIM capacitors.