Diamond Thermal Conductivity: A New Era in Chip Cooling

> There are hurdles still to overcome. In particular, we still have to figure out a way to make the top of our diamond coatings atomically flat.

Not sure I understand this. Is this a requirement for real-world use? What happens if the outside of the coating isn't atomically flat? What makes this hard to do?

Presumably it's to ensure good contact with the next thermal management layer (heat spreader, heat-sink, etc.)

These are gigantic and interesting questions packed into some pretty tiny boxes :) I will try to capture some of the issues involved.

Caveat: For older processes, built on a larger scale (>1 micron), these kinds of details may not matter, in which you are right to question this point. But if you want to implement on cutting edge manufacturing processes, these details absolutely do matter.

To put this in perspective, in cutting edge process nodes, I've seen senior engineers argue bitterly over ~1 nm in a certain critical dimension. That's (roughly) about 5 atoms across, depending on how much you trust the accuracy of the metrology.

So, if ANY layer isn't "flat" (or otherwise to spec within tolerance), the next layer in the semiconductor patterning stack will tend to translate that bumpiness upward, or cause a deformity in adjacent structure. This is (almost) always bad. These defects cause voids, bad electrical/thermal contacts and characteristics, misshapen/displaced structures, etc, etc

Crystallization in thin-film (especially conformal/gap-filling films) is a tough job which many poor PhD students have slaved over. Poly crystalline material is arguably harder to control in some key ways vs mono crystalline, since you don't have direct control the specific crystal grain orientation and growth direction. That is, some grain orientations will grow quickly, and others growing slowly. You can imagine the challenge then of getting the layer to terminate growth without ending up too jagged on the ~nm scale. After that you also get into the fun world of crystal defects, grain size, and deciding if you need to do some more post-processing (do I risk planarizing?)

Hopefully I have captured some of the pieces involved in an understandable way.

Edit: clarity

All semiconductor manufacturing techniques are based upon precisely flat layers of material that can be stacked and/or drilled into to produce a useful design. All vertical irregularities propogate to the layers above and can cause thinner layers when an upper layer is milled flat

It’s difficult to cmp diamond is the issue I’d assume

This. A quick scan of the wikipedia page for diamond material properties suggests you are very correct. It appears very chemically inert, with some outstanding exceptions: "Resistant to acids, but dissolves irreversibly in hot steel"

https://en.wikipedia.org/wiki/Material_properties_of_diamond

Also, removed/liberated particles of Diamond from the workpiece which failed to fully chemically dissolve into the slurry would then contribute to the abrasive in the slurry. If the slurry abrasive was not also diamond, then that could lead to some serious scratch/gouging of the work surface.

Perhaps not insurmountable, but wow, that sounds like a stiff challenge, especially when accounting for cost.

I wonder if diamond would be machinable with a dry (plasma) etch instead? I am purely speculating here, this is far out of my wheelhouse. But SiO2 is already very chemically inert (though considerably softer vs diamond), but manufacturers regularly dry etch it.