The document compares the processes for making 2D and 3D chips. For 2D chips, patterns of UV light are focused on a silicon wafer coated with photoresist, exposed areas are etched away, and ions are showered on to dope silicon and make transistors. The process is repeated 4+ times to add metal interconnects and insulators. For 3D chips, the same equipment and materials are used, but additional steps stack polysilicon transistors vertically by repeating photolithography and etching to create active polysilicon regions and adding new layers like polysilicon, tungsten, and antifuse material. The 3D process is repeated 9 times to stack 8 memory cells.

1. GOING 3-D: SAME EQUIPMENT, DIFFERENT STEPS
HOW 2-D CHIPS ARE MADE
1 2 3 4 5
Patterns of ultraviolet Exposed photoresist Ions are showered onto The wafer is coated Chemical-mechanical
light are focused onto is removed, and the wafer, doping areas with insulating polishing flattens the
a silicon wafer coated unprotected areas are of exposed silicon to dielectric or wafer’s surface with
with photoresist etched away by gases make transistors conducting metal 50-nanometer precision
PROCESS IS REPEATED FOUR OR MORE TIMES TO ADD METAL INTERCONNECTIONS AND INSULATING OXIDES
HOW 3-D CHIPS ARE MADE
Additional steps using the same equipment and materials create 3-D microcircuits with many polysilicon transistors stacked vertically
1 2 RETICLE (MASK)
LENS
Photolithography Photoresist
and etching proceed Silicon
just as for 2-D chips, dioxide
above Silicon
nitride
Silicon
substrate
3 PREPARED SILICON
WAFER
Ion implantation
dopes the silicon
to create
transistors
4 5 6 7 8
Three new layers are Photolithography is Memory cells and Chemical-mechanical A layer of “antifuse”
added: polysilicon, repeated to create metal interconnections polishing knocks down material is added; burning
tungsten metal and active regions of are etched; insulation any high spots out an antifuse will store
then more polysilicon polysilicon is added a bit in the memory
PROCESS IS REPEATED NINE TIMES TO STACK EIGHT MEMORY CELLS ON TOP OF ONE ANOTHER