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.
16Mbit DRAM
cross section 
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.

With frame With frame as PDF

go to 6.4.1 Physical Processes for Layer Deposition

go to 5.1.5 Integrated CMOS Technology

go to 6.3.3 CVD for Poly-Silicon, Silicon Nitride and Miscellaneous Materials

go to 6.6.2 Resist and Steppers

go to Poly-Silicon

© H. Föll (Electronic Materials - Script)