Cross Section of 16 Mbit DRAM and 64 Mbit DRAM

Below a large SEM micrograph showing the cross-section of an (early) 16 Mbit DRAM.
 
Cross-section 16Mbit DRAM
cross section 16Mschematic
 
       
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.
Below the successor of the 16 Mbit DRAM, the 64 Mbit DRAM from a development stage around about 1996.
 
Cross-section 64MDRAM
 
The structure is essentially the same, but all layers have been planarized.
 

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© H. Föll (Semiconductor - Script)