It says screwdriver unlocked when you level up, but I have yet to see a single screwdriver at level 5.
Some ideas:
-Screws take multiple clicks to unscrew.
-You can spend screws to buy new screwdrivers that decrease the amount of clicks needed to unscrew a screw.
- Have stages you can go back and forth between, the higher the stage, the more screws there are and the harder they are to unscrew.
-If possible, add 'screwdriver skins' that change the player's mouse to look like various screwdrivers.