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Comment by pcunite | Hacker News Reader

Copper is used for electrical traces, I take it. If technology allows for light (laser) based switching, could less metals be used in the construction?

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Odd place to ask this question. As it happens, inside chips it's either (doped) silicon, aluminium (metal layers), or gold (bond wires).

There's a reason why copper isn't used in chip manufacture; something to do with reacting with or diffusing into silicon dioxide.

There's a reason why copper isn't used in chip manufacture; something to do with reacting with or diffusing into silicon dioxide.

Huh?

A number of years ago when I was still doing chips, copper was quite popular. Wikipedia claims it still is[1]: copper-based processes continue to be the state of the art for the semiconductor industry today.

As Wiki explains, the key is "dual-Damascene". They inlay copper into trenches.

[1] https://en.wikipedia.org/wiki/Copper_interconnect

Expanding on above, Al-based BEOL interconnects were used until the process for making the more-difficult Cu interconnects matured around the turn of the millennium. Without precautions, Cu will diffuse into Si badly and generate tons of traps. TiN is a typical barrier material, but increasingly exotic materials are now being used in cutting edge nodes.

Copper allows creating a movement of electrons, which is what you usually call electricity. Any kind of light, while it allows transferring a signal, does need to have the signal transformed from electricity to light on one end, and from light to electricity on the other.

Replacing a very long cable with a fiber that allows transferring the same signal using light is a way to save on copper. But in appliances themselves, having signals transformed to and from light is too expensive. So you won't find lots of light fibers inside of appliances.

I think the person you're replying to meant having the computing be done optically (switching by some optical rather than transistor means), so in theory if you could do that you wouldn't need any copper except to provide power to your optical computer. I doubt we'll ever get to the point where optical computing is more cost effective than what we currently have though.

Silicon photonics is changing this dynamic some, right?

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