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My question simply is why ICs are made using layers? Why they have used this method specifically ?

AAAA
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    How else do you propose to make them? – Hearth Mar 28 '20 at 20:30
  • Somewhat related queston, doesn't answer "why" but explains how in some detail: https://electronics.stackexchange.com/questions/67598/how-are-integrated-circuits-fabricated – MarkU Mar 28 '20 at 23:47
  • Because we can't reach in between little gaps in between parts of the IC to place things like you can with a car engine. – DKNguyen Mar 29 '20 at 06:12

2 Answers2

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An IC is a kind of 'additive manufacturing' approach where the various features are deposited on a base material, the silicon wafer (or germanium, etc.)

Each type of added material that makes up a semiconductor - doping, diffusion, poly, metallization, contacts, oxide insulators and so forth - needs a different set of chemicals and process parameters for that material. Because of their differences, it's not possible to combine them in one step without them interfering with each other.

Using layers separates the types of materials used at each process stage so that each additive step can work its best.

hacktastical
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fundamentally, the various structures on an IC need to be isolated, as if built on a PCB or white board.

One method of isolation is depositing layers of glass; to make connections up and down, any previous layers will have small pedestals of extremely clean aluminum; small holes will be etched in the glass, so the following layer of metal can make contact with the tiny metallic pedestal.

Another method of isolation is between opposingly-doped or implanted_by_high_energy_ionic_bombardment silicon layers.

All these layers are like assembling a pineapple upside cake--the order of layers does matter.

analogsystemsrf
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