How do they make the chips so incredibly thin? Surely they're not using 75µm/120µm wafers throughout the entire production process - that's literally the thick

How do they make the chips so incredibly thin? Surely they're not using 75µm/120µm wafers throughout the entire production process - that's literally the thickness of a human hair! Can a 200/300mm wafer of that thickness even support itself, let alone all the stresses in the production process?