First, the technique of using sulfuric and nitric acid is described and illustrated:
But the really bit interesting bit is what comes out. Here’s the ATmega8:
(both pictures were copied from that site, i.e. zeptobars.ru – I hope that’s ok)
The size of this chip is 2855 x 2795 µm, i.e less than 3 x 3 mm.
Fascinating! I wonder what all the different bits and pieces are…