How can I type a backtick on an Estonian keyboard?
Looking through the keybindings in the Estonian keyboard layout that ships with Mac OS X, it appears (amazingly) that the backtick character (`) cannot be produced with any of the unmodified keys, nor with any combination of option, shift, or control, despite the fact that most of the option-character key combinations are left unmapped on this layout. There are many ways to modify it to produce this key combination.

You could create a modified Estonian layout using Ukelele, you could use a program like Keyboard Remap for Macbook, or even TextExpander.