2N7000 Mosfet destroyed during soldering?
What kind of soldering iron are you using?

If you use a soldering iron powered directly from mains, instead of a proper soldering station, its tip will be connected, for safety reasons, to the earth ground of the electrical system of your building.

Although MOSFETs like 2N7000 are fairly rugged, compared to discrete parts of 20 years ago, they might get damaged by phantom voltages coming from the ground connection of your electrical system.