# 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.
| 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.
|  | The structure is essentially the same, but all layers have been planarized.

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)