In non-barrier metal processes aluminum can sit in physical contact with silicon. The silicon will diffuse into the aluminum and the aluminum will pit the silicon. This is a function of temperature and time after the aluminum is put down.
Under ESD events, large currents flowing through a contact can heat the contact up to the point where the aluminum diffuses deep into the silicon shorting out the p-n junction. It no longer is a rectifying junction.
This is what is ment by junction spipking.
Hope this helps....