Ken Shirriff has posted a teardown of the beloved 555 timer IC. He sawed the top of a metal can packaged 555 to expose the die underneath.
On top of the silicon, a thin layer of metal connects different parts of the chip. … Under the metal, a thin, glassy silicon dioxide layer provides insulation between the metal and the silicon, except where contact holes in the silicon dioxide allow the metal to connect to the silicon. At the edge of the chip, thin wires connect the metal pads to the chip’s external pins.