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Politics : Formerly About Advanced Micro Devices
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To: Bill Jackson who wrote (82655)12/12/1999 1:16:00 AM
From: Saturn V  Read Replies (1) of 1572865
 
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I also wonder how they etch those thin point? Do they implant some sodium at an earlier stage in deposition, laying down a thin layer with a few extra sodium atoms in the mix? ( just a few) since it is well known that sodium in glass makes it dissolve faster in an alkaline etch bath? Probably those sodium atoms would make the SiO2 act funny, unless they deposited it only on the surface in the trenches where they wanted the extra etching by shadow mask type deposition? so it went away at the end. Does anyone know just how they do it within the process methodology? >

Bill your statements are not applicable to Silicon Technology. Sodium is the last thing you want in a silicon wafer.It is not clear which is worse Copper or Sodium. Sodium is an enormous reliability hazard, and Andy Grove made a name as a Silicon Technologist in the 60's for his role in identifying Sodium as the biggest culprit for MOS devices.So several process steps exist for gettering and removing any trace amounts of Sodium.

The biggest process variable which affects speed of a part on a wafer is the polysilicon line width, which is reasonably stable on a wafer.Overall speed on a wafer should not change by more than ten percent on a well controlled process
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