IMPROVED HDP-BASED ILD CAPPING LAYER

A cap nitride stack which prevents etch penetration to the HDP nitride while maintaining the electromigration benefits of HDP nitride atop Cu. In one embodiment, the stack comprises a first layer of HDP nitride and a second layer of a Si-C-H compound disposed over the first layer. The Si-C-H compound is for example BLoK, or N-BLoK (Si-C-H-N), and is selected from a group of materials that has high selectivity during via RIE such that RIE chemistry from the next wiring level does not punch through. Carbon and nitrogen are the key elements. In another embodiment, the stack comprises a first layer of HDP nitride, followed by a second layer of UVN (a plasma nitride), and a third layer comprising HDP nitride disposed over the second layer.