Since I don't have details on the AMI process, my comments are speculative.rjlittlefield wrote:I was wondering if the lower levels were somehow exposed, versus being seen through transparent stuff.mawyatt wrote:Of course you have the lens effect taking place at the chip surface with the index of refraction for the insulators hovering around 1.5.
If I recall correctly, apparent depth goes as 1/RI, so 3 microns apparent at refractive index 1.5 would be actual depth 4.5 microns.
Your diagram shows about 10 microns.
That discrepancy strikes me as large enough to be interesting, but given the direct measurement method, not large enough to indicate an error. That judgement could change with more info, of course.
While I have you here, I have another question. In JW's images, the top layer of elements, oriented vertically in these images, seems to bump up-and-over the elements that are oriented horizontally. In the diagram that you've provided, I notice that the "metal 5" layer seems actually to be two sets of wires, with one crossing up and over the other. Is that perception correct?
--Rik
Usually the individual metal layers are planarized during processing as they are "built up" by deposition, same for insulator layer. The last metal layer generally is not planarized nor is the final passivation layer, so you expect to see some vertical 3D effects with these layers.
As you mention, in James's images it shows what appears to be metal ridges in the lower layers as they go over other metal lines. I don't think these are actual ridges because of the mentioned layer planarization but an optical effect that caused by a different metal orientation that occurs during the metal deposition process. This might be caused by the metal grain boundaries getting oriented differently when the metal is deposited over another insulated layer that has a metal line underneath. Since the metal may have a slight different surface texture due to the grain boundary orientation it has a different optical micro reflectance.
Best,