4 Metal, 350 nanometer fabrication process, EAL4+ smart card. A device fabricated in 2002 and yet, today the latest ST19W/N series only main differences are the ROM data bus output width into the decrypt block and the fabrication process (180nm and 150nm shrink).
The device was dipped into a HydroFluoric (HF) bath until the active shielding fell off. The result of this saved about 10 minutes of polishing to remove the surface oxide and Metal 4 (M4). This also helps begin the polishing process on the lower layers fairly evenly.
The oxide thickness of a layer once the passivation oxide is removed requires less than 2 minutes per layer to remove. We purposely stop just before the Metal 3 (M3) surface is exposed leaving the vias visibly clear (there are several gates tied to the ground of the mesh on Metal 4 (M4) as well as the active shield’s begin and end vias.
As Metal 3 (M3) was removed exposing the M2 layer, the device is beginning to not look so complicated.
Metal 1 (M1) shows us all the transistors. We did not polish down to the poly. Most of the gates are understandable without it for the purposes of finding the clear data bus.