Definitions for "ROOT CAUSE"
The ultimate reason for an event or condition.
The root cause is the event or combination of events that initiate a failure. Although root cause is the ultimate goal of failure analysis, the root cause may not be obvious even though the defect mechanism is known. For example, analysis may show the failure resulted from distorted deposition of layers around a foreign particle. The particle is the cause. However, when the fabrication process is fully understood, the particle and many like it may occur normally in the process. The root cause might be the cleaning process that should have removed the particle. Even at this level of understanding, possibilities are many. The clean might be inherently inadequate, the chemicals may be overused, the temperature may be too low, or the content of the particles may have changed.
To prevent continuing recurrence of an undesirable outcome, problem-solvers need to "peel back the layers" to find the underlying or "root" causes. One technique for doing this is to ask "why did this happen?" And then to the reply to that question, ask "why?" Again. By the process of asking "why?" Several times in this fashion, one gets closer to the root cause. The early answers to the inquiries are more likely to be symptoms of more fundamental problems.