YIELD Engineering Systems Inc.

When copper is annealed some of its molecules want to diffuse into the dielectric; unfortunately, this diffusion reduces the insulation and degrades mechanical and thermal properties. To prevent Cu diffusion, “cap” layers of another metal are placed as a barrier between the copper and polyimide. These metal barriers also enhance the copper-polyimide adhesion.

Because an oxide quickly forms on copper exposure to air, post-CMP cleaning and stripping of the oxide is necessary before the next process step. It’s also essential to remove all copper residues from the surrounding dielectric field to keep residues from acting as troublesome nucleation sites.

Thorough copper oxide removal can be achieved through plasma cleaning, utilizing a product such as the YES-CV200RF or the YES-G1000.