DE2 crystal clock pulse

Agree with FvM, most likely the problem is with the measurement, not the signal itself.

The length of the ground wire on scope probes means that it is useless for any sort of high speed measurements, you need to reduce the length of the loop that goes from the driver of the signal, to the probe tip, to the probe ground, to the PCB ground and back to the driver.

One handy tip I've used is to unscrew the sheath of the scope probe and hold an unbent paperclip across the metal of the probe body to a nearby ground point on the PCB. This massively shortens the length of the ground loop. I hear the blade of a craft knife is even better, because a wide strip of conductor has a lower impedence than a thin wire.

Also, reduce the drive strength unless you need it.