Mechanical stress problems in integrated circuit devices are becoming more severe as the number of metal interconnect levels increases and new materials such as low-k dielectrics are introduced. We studied dielectric cracking in a four-level Al-Cu interconnect structure that uses hydrogen silsesquioxane (HSQ), a low dielectric constant (low-k) material. The cracks extended down through the passivation layers to the HSQ layer. For the first time we report on passivation dielectric cracks directly related to the level of residual fluorine in a plasma enhanced chemical vapor deposition (PECVD) reactor. It is shown that a silicon nitride pre-coat deposition removes fluorine (F) from the reactor ambient and prevents the dielectric cracks.