4 ms·

This is really fascinating. I apologize if this is a silly question but under the Fabrication section there is a pic titled "physical structure(Texas Instrument

This is really fascinating. I apologize if this is a silly question but under the Fabrication section there is a pic titled "physical structure(Texas Instruments, 1997.)" My question is why do all of the components always look so "puffy" or "fuzzy" in these chip zoom-in pics? I guess I'm always surprised that such a precision process produces something with such imperfect looking shapes. Or are these slightly amorphous shapes just a distortion produced by a scanning electron microscope? EDIT: This is the pic I was asking about: http://sam.zeloof.xyz/wp-content/uploads/2018/04/na_1.png http://sam.zeloof.xyz/wp-content/uploads/2018/04/na_1.png

Kirby64 7y ago
You're referring to the fact that the edges aren't really sharp and are kind of 'soft', right? Like, everything isn't 90 degree angles and is kinda rippley in places? If so, that's not an SEM issue, that's just what it looks like. Photo exposure by it's very nature doesn't edge things 100% properly, diffraction or tiny misalignments causes stuff to end up being 'soft'. Also, keep in mind that was from 1997. Fab tech has gotten way better; although we don't have a scale reference, I imagine if you were to make the same device on modern tech everything would look a lot 'sharper'. You still can't get away from some softness though.
- bogomipz 7y ago
  >"You're referring to the fact that the edges aren't really sharp and are kind of 'soft', right? Like, everything isn't 90 degree angles and is kinda rippley in places?" Yes to both of these questions. "Soft" is probably a better way to articulate this, thanks. I'm not following the explanation of this being caused by photography however. Is this specific to photography at this scale? >"I imagine if you were to make the same device on modern tech everything would look a lot 'sharper." I don't have an example handy however I have seen more recent micrographs and they display the same "softness" and lack of true 90 degree angles etc.
  - marcosdumay 7y ago
    > Is this specific to photography at this scale? Yes. A smaller scale makes it worse, a larger scale makes it better. If you reduce things enough, everything will become so blurred that you won't be able to see anything (that's why we can't photograph atoms using visible light), and if you make things large enough your camera will become the bottleneck so a very small amount of blur is added to any object, whatever the size.
    - bogomipz 7y ago
      Ah I see, when you say "photo" you are referring to the photolithography used in the chip making and not the captured photo of the finished chip is that correct?
      - marcosdumay 7y ago
        I mean the captured photography of the chip. Most of the time it is not done with ultraviolet light or electron microscopes, just with normal visible light cameras ans some very good lenses.
  - Kirby64 7y ago
    By photography, I meant the photolithography, as you mentioned to another replier. This inherently will cause softness as described since there's always going to be light leakage and the masks you use will never be truly perfect. Given the sizes though, they're pretty damn good. As for 'modern tech' vs. old tech, I'm referring to if you made the same size silicon structure on newer tech. When you get down to 7nm or whatever, the same problems show up (or even new ones) because the sizes get smaller. I wouldn't be surprised if the image from 1997 is 180nm or larger nodes. Also, unlike the other replier, I don't think there's any meaningful diffraction (causing softness) by the actual SEM images... they don't use glass lenses like traditional cameras.
    - bogomipz 7y ago
      Thanks for the clarification. Agreed, given the scale of these they're pretty damn good :) Cheers.
- deleted 7y ago
  [deleted]
PhaseLockk 7y ago
I can't see the image you're referring to at the moment, but I imagine the fuzziness you are seeing is due to this fact: chips perform better if the features are smaller. Because of this, manufacturers want to make chip features as small as they can without causing failures, which means that you are manufacturing things at the scale that your manufacturing precision is barely sufficient, which means that the components look ugly, but they (mostly) work.
- fengazer 7y ago
  This. Every step in fabrication has limits on its resolution beyond the resolution of the machine exposing the polymer resist. The resist has a finite thickness (often comparable to the size of the feature you are trying to make). The developer solution works downwards through the exposed resist, but also outwards at the edges (where you will have some proximity effect in the exposure). Deposited metal or insulator sometimes sticks to both the bottom of the pit and the top of the resist without a clean break, or contains chunks or grains that make the coating uneven. Wet chemical etchants don't etch straight down, and often create rounded corners in cross-section. Every aspect of this has decades of optimization behind it, and its success in any one fabrication run is vulnerable to a frustrating number of variables. If there's an SEM cross-section of a device in a paper, it's likely because fabricating it was an accomplishment, and/or the design is in some way new (not ruling out other reasons of course: there's also "we have an SEM and not a lot else to put in the paper"). TL;DR: I agree. These things are very small and if we could make the corners sharper, that would remove one major barrier to making them even smaller. And then they wouldn't look so tidy anymore.
  - bogomipz 7y ago
    >"This. Every step in fabrication has limits on its resolution beyond the resolution of the machine exposing the polymer resist." I didn't quite understand what you meant here. Could you elaborate on this? What are some of those limits? >"These things are very small and if we could make the corners sharper, that would remove one major barrier to making them even smaller. And then they wouldn't look so tidy anymore." Aren't these contradictory? Did you mean to say "And then they would look so tidy"?
pjc50 7y ago
Necessarily it is operating at the limit of precision. If it wasn't blurry, you'd keep making it smaller until the blurring starts to become a problem again.
- fengazer 7y ago
  This sums it up best.
Junk_Collector 7y ago
As mentioned in other posts, the process of making these types of devices tend to produce rounded structures. This is a byproduct of using Ion beams, deposition, lithography, etc in manufacture. BUT, the image is also made worse by how the image is captured. The picture you are looking at is a FIB (Focused Ion Beam) cut cross-section of a transistor which is then imaged by a SEM (scanning electron microscope). Probably in one of their fancy dual source beam devices. Depending on how you cut with the FIB, you can also push material downwards into lower layers and create a waterfall effect that will blur edges. It's can be very noticeable in rookie cuts but doesn't look like a major impact here. Imaging with the SEM itself can also cause distortion and blurring as trapped charge accumulates on the surface and deflects the electron beam slightly. You can see this where the edges get increasingly bright because charges gather and become trapped at the boundary of the conductive and insulating layers. The image isn't sharp enough for me to tell if that is poly-silicon or aluminum contact traces.
- bogomipz 7y ago
  >"As mentioned in other posts, the process of making these types of devices tend to produce rounded structures. This is a byproduct of using Ion beams, deposition, lithography, etc in manufacture." Thanks for the detailed response. Might you have a link to one of those other posts or some other resources that talks about how these processes tend to produce rounded structures?
  - Junk_Collector 7y ago
    In the manufacturing process you have several methods that are used each with their own issues. Photo-lithography suffers from diffraction at the edges of features. Chemical processes undercut, overcut, and generally move around. They eat away faster at edges because of surface space and eat along different crystal lattice vectors at different rates. Plasma processes are effectively a hose of charged particles and have a sort of Gaussian distribution vs location of particle impact depending on your focus. And during the whole process, diffusion is trying to move everything around to boot. These effects exist at all scales, but when you get to IC scales, the effects can be dominant.

Kirby64 7y ago

You're referring to the fact that the edges aren't really sharp and are kind of 'soft', right? Like, everything isn't 90 degree angles and is kinda rippley in places? If so, that's not an SEM issue, that's just what it looks like. Photo exposure by it's very nature doesn't edge things 100% properly, diffraction or tiny misalignments causes stuff to end up being 'soft'. Also, keep in mind that was from 1997. Fab tech has gotten way better; although we don't have a scale reference, I imagine if you were to make the same device on modern tech everything would look a lot 'sharper'. You still can't get away from some softness though.

bogomipz 7y ago
>"You're referring to the fact that the edges aren't really sharp and are kind of 'soft', right? Like, everything isn't 90 degree angles and is kinda rippley in places?" Yes to both of these questions. "Soft" is probably a better way to articulate this, thanks. I'm not following the explanation of this being caused by photography however. Is this specific to photography at this scale? >"I imagine if you were to make the same device on modern tech everything would look a lot 'sharper." I don't have an example handy however I have seen more recent micrographs and they display the same "softness" and lack of true 90 degree angles etc.
- marcosdumay 7y ago
  > Is this specific to photography at this scale? Yes. A smaller scale makes it worse, a larger scale makes it better. If you reduce things enough, everything will become so blurred that you won't be able to see anything (that's why we can't photograph atoms using visible light), and if you make things large enough your camera will become the bottleneck so a very small amount of blur is added to any object, whatever the size.
  - bogomipz 7y ago
    Ah I see, when you say "photo" you are referring to the photolithography used in the chip making and not the captured photo of the finished chip is that correct?
    - marcosdumay 7y ago
      I mean the captured photography of the chip. Most of the time it is not done with ultraviolet light or electron microscopes, just with normal visible light cameras ans some very good lenses.
- Kirby64 7y ago
  By photography, I meant the photolithography, as you mentioned to another replier. This inherently will cause softness as described since there's always going to be light leakage and the masks you use will never be truly perfect. Given the sizes though, they're pretty damn good. As for 'modern tech' vs. old tech, I'm referring to if you made the same size silicon structure on newer tech. When you get down to 7nm or whatever, the same problems show up (or even new ones) because the sizes get smaller. I wouldn't be surprised if the image from 1997 is 180nm or larger nodes. Also, unlike the other replier, I don't think there's any meaningful diffraction (causing softness) by the actual SEM images... they don't use glass lenses like traditional cameras.
  - bogomipz 7y ago
    Thanks for the clarification. Agreed, given the scale of these they're pretty damn good :) Cheers.
deleted 7y ago
[deleted]

PhaseLockk 7y ago

I can't see the image you're referring to at the moment, but I imagine the fuzziness you are seeing is due to this fact: chips perform better if the features are smaller. Because of this, manufacturers want to make chip features as small as they can without causing failures, which means that you are manufacturing things at the scale that your manufacturing precision is barely sufficient, which means that the components look ugly, but they (mostly) work.

fengazer 7y ago
This. Every step in fabrication has limits on its resolution beyond the resolution of the machine exposing the polymer resist. The resist has a finite thickness (often comparable to the size of the feature you are trying to make). The developer solution works downwards through the exposed resist, but also outwards at the edges (where you will have some proximity effect in the exposure). Deposited metal or insulator sometimes sticks to both the bottom of the pit and the top of the resist without a clean break, or contains chunks or grains that make the coating uneven. Wet chemical etchants don't etch straight down, and often create rounded corners in cross-section. Every aspect of this has decades of optimization behind it, and its success in any one fabrication run is vulnerable to a frustrating number of variables. If there's an SEM cross-section of a device in a paper, it's likely because fabricating it was an accomplishment, and/or the design is in some way new (not ruling out other reasons of course: there's also "we have an SEM and not a lot else to put in the paper"). TL;DR: I agree. These things are very small and if we could make the corners sharper, that would remove one major barrier to making them even smaller. And then they wouldn't look so tidy anymore.
- bogomipz 7y ago
  >"This. Every step in fabrication has limits on its resolution beyond the resolution of the machine exposing the polymer resist." I didn't quite understand what you meant here. Could you elaborate on this? What are some of those limits? >"These things are very small and if we could make the corners sharper, that would remove one major barrier to making them even smaller. And then they wouldn't look so tidy anymore." Aren't these contradictory? Did you mean to say "And then they would look so tidy"?

pjc50 7y ago

Necessarily it is operating at the limit of precision. If it wasn't blurry, you'd keep making it smaller until the blurring starts to become a problem again.

fengazer 7y ago
This sums it up best.

Junk_Collector 7y ago

As mentioned in other posts, the process of making these types of devices tend to produce rounded structures. This is a byproduct of using Ion beams, deposition, lithography, etc in manufacture. BUT, the image is also made worse by how the image is captured. The picture you are looking at is a FIB (Focused Ion Beam) cut cross-section of a transistor which is then imaged by a SEM (scanning electron microscope). Probably in one of their fancy dual source beam devices. Depending on how you cut with the FIB, you can also push material downwards into lower layers and create a waterfall effect that will blur edges. It's can be very noticeable in rookie cuts but doesn't look like a major impact here. Imaging with the SEM itself can also cause distortion and blurring as trapped charge accumulates on the surface and deflects the electron beam slightly. You can see this where the edges get increasingly bright because charges gather and become trapped at the boundary of the conductive and insulating layers. The image isn't sharp enough for me to tell if that is poly-silicon or aluminum contact traces.

bogomipz 7y ago
>"As mentioned in other posts, the process of making these types of devices tend to produce rounded structures. This is a byproduct of using Ion beams, deposition, lithography, etc in manufacture." Thanks for the detailed response. Might you have a link to one of those other posts or some other resources that talks about how these processes tend to produce rounded structures?
- Junk_Collector 7y ago
  In the manufacturing process you have several methods that are used each with their own issues. Photo-lithography suffers from diffraction at the edges of features. Chemical processes undercut, overcut, and generally move around. They eat away faster at edges because of surface space and eat along different crystal lattice vectors at different rates. Plasma processes are effectively a hose of charged particles and have a sort of Gaussian distribution vs location of particle impact depending on your focus. And during the whole process, diffusion is trying to move everything around to boot. These effects exist at all scales, but when you get to IC scales, the effects can be dominant.