Cross Section of 16 Mbit DRAM and 64 Mbit DRAM
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Below a large SEM micrograph
showing the cross-section of an (early) 16 Mbit DRAM. |
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Some explanations:
- The two deep "trenches" (they are
really
holes) contain the capacitors. There dielectric (with ca. 7 nm far too
thin to be visible) is "ONO", a triple layer of Oxide -
Nitride - Oxide.
- The trench os lined with poly-Si as a first electrode and as the
second electrode.
- To the left and right two transistor gates are visible. The sources of both
transistors is the (poly-Si) electrode lining the trench and the
diffused areas being contacted by the "Polizid bitline".
"Polizid" means a double layer of poly-Si and
MoSi2 Molybdenum-silicide.
- The "poly-Si wordline" runs perpendicular to the picture
and connects the gates of the transistors
- The "BPSG" layers denote SiO2 doped with
B and P that serves as insulating dielectric. It is essentially a
glass.
- Parallel to the word lines are Ti/TiN/AlSiCu lines. They contact the
wordlines every once in a while to decrease the ohmic resistance. The consist
of a layer sequence: Ti, TiN, and Al doped with about
0,5% of Si and Cu.
- On top of this first metal layer is another one running across the picture.
- The metals are insulated by the intermetal dielectric composed of
plasma-oxide (PO) that contains spin-on-glass (SOG) in the
interstices.
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Below the successor of the 16 Mbit DRAM,
the 64 Mbit DRAM from a development stage around about 1996. |
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The structure is essentially the same, but all
layers have been planarized. |
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With frame

6.4.1 Physical Processes for Layer Deposition
5.1.5 Integrated CMOS Technology
6.3.3 CVD for Poly-Silicon, Silicon Nitride and Miscellaneous Materials
6.6.2 Resist and Steppers
Poly-Silicon
© H. Föll (Electronic Materials - Script)