I got the G, S, D part.
but what are end pads? and why do you scale up from nm to um as you move top the layers?
There are these two classic images by, if I'm not mistaken, intel and IBM:
Intel, 11 metal layers. Clearly shows how metals are getting thicker. Green is a low-k dielectric, used to reduce capacitance (due to the high \$\epsilon_{R}\$ of silicon, the parasitic capacitance would be very high if SiO would be used all the way to the top layers): ...
There are these two classic images by, if I'm not mistaken, intel and IBM:
Intel, 11 metal layers. Clearly shows how metals are getting thicker. Green is a low-k dielectric, used to reduce capacitance (due to the high \$\epsilon_{R}\$ of silicon, the parasitic capacitance would be very high if SiO would be used all the way to the top layers): ...
This is mind bogglingly amazing!!
How on earth do you get such great images?!
Interesting thing that you talk about the repeatable pattern. And there also seems to be a pattern on the upper half of the thick substrate layer (the bottommost one).
What patterns are those?
Are the substrate and the 2 layers above it, the transistors?
With regards to the bottom most image what kind of program generates such kind of design, is it a CAD program or a specialized IC design software?
Fin-Fets, which is what you see in the second picture, involves growing fins. It's these fins I think you are talking about.
The transistors are completely in the bottom layers. For a planar process (bulk CMOS, not FINFET), the transistors look like this (source):
This is all made before the first metal layer is deposited. There are some small differences between processes (metalgate, self-aligned transistors) but that would take us too far. Everything is built out of the original silicon, with exception of the two bumps. After this is made (everything up to this point is called front-end-of-line) we start with metals (back-end-of-line).
The transistors are completely in the bottom layers. For a planar process (bulk CMOS, not FINFET), the transistors look like this (source):
This is all made before the first metal layer is deposited. There are some small differences between processes (metalgate, self-aligned transistors) but that would take us too far. Everything is built out of the original silicon, with exception of the two bumps. After this is made (everything up to this point is called front-end-of-line) we start with metals (back-end-of-line).
1. For NMOS why make a p-Si well when a P-Si already exists?The main reason is that the doping profile of each well can be individually tailored. Also provides isolation benefitsQuote2. What is punch stop?Not sureQuote3. What is STI?Shallow Trench Isolation
This technique replaces the old LOCOS techniqueQuote4. The silicide layers are used as conductors? But then why the gate has n+poly also where as the drain and source has only silicide and no n+ poly?Yes, silicide is a refractory metal--a conductor.
Polysilicon is the preferred material to make defect-free gates. Metal is terrible as the gate-oxide interface
There is no need for poly at the source and drains.
Just a few questions that come to my mind while contemplating on the topic
1. Why is the silicon wafer when its being manufactured from a liquid kind of state not 100% pure silicon?. Why is it doped to become an N type or a P Type substrate? I mean some dopants are added to the mix when the wafer is being manufactured?
2. Why is an epitaxial coating done over the silicon wafer before any other processes are done?
3. Is there a comprehensive list of steps for silicon chip fabrication?
3. Is there a comprehensive list of steps for silicon chip fabrication?
An N-channel transistor needs N+ source and drain (the "+" indicates heavy doping of donor atoms) diffused into silicon doped with acceptor atoms so that the underlying material is doped P type. In order to achieve desired transistor performance, that material is very lightly doped...we call it P- where the "minus" means lightly doped. In the above, Phosphorous is typically used as a donor dopant, and Boron is used as an acceptor dopant.
An N-channel transistor needs N+ source and drain (the "+" indicates heavy doping of donor atoms) diffused into silicon doped with acceptor atoms so that the underlying material is doped P type. In order to achieve desired transistor performance, that material is very lightly doped...we call it P- where the "minus" means lightly doped. In the above, Phosphorous is typically used as a donor dopant, and Boron is used as an acceptor dopant.The "diffused" term that you use here what does that do? I heard that ion implantation is used to for adding impurities (doping) to the silicon wafer. What does diffusion do?
Secondly you refer to the wafer being lightly doped either N- or P-.
Is that it because from what I had read so far is that the subtrate is heavily doped P+ or N+ and on top of this there is a lightly doped epitaxial layer grows P- or N-.
What about Maskless Lithography systems or Direct Write systems like Mapper https://mapper.nl/.
The say that it does patterning without a mask.
So does this system only replaced the mask?
Because transistor fabrication would still need Diffusion / Ion Implanting and other processes involved in chip fabrication? How does Mapper achieve that?
Would additional equipment be needed in addition to Mapper?
TIA
What about Maskless Lithography systems or Direct Write systems like Mapper https://mapper.nl/.
The say that it does patterning without a mask.
So does this system only replaced the mask?
Because transistor fabrication would still need Diffusion / Ion Implanting and other processes involved in chip fabrication? How does Mapper achieve that?
Would additional equipment be needed in addition to Mapper?
...The cost of masks, and the time to requalify, is a huge deterrent to fixing things right now.
Quote...The cost of masks, and the time to requalify, is a huge deterrent to fixing things right now.
Spare gates!
Requal still needed though.
Quote...The cost of masks, and the time to requalify, is a huge deterrent to fixing things right now.
Spare gates!
Requal still needed though.Everyone adds spare gates these days, and they do reduce the number of ALRs considerably. They are seldom able to fix more than simple logic errors, though.
Quote...The cost of masks, and the time to requalify, is a huge deterrent to fixing things right now.
Spare gates!
Requal still needed though.Everyone adds spare gates these days, and they do reduce the number of ALRs considerably. They are seldom able to fix more than simple logic errors, though.
Yes, indeed.
Spare analog can save an ALR from time to time as well.
Another useful feature is spare metal runs...wonder why???
Quote...The cost of masks, and the time to requalify, is a huge deterrent to fixing things right now.
Spare gates!
Requal still needed though.Everyone adds spare gates these days, and they do reduce the number of ALRs considerably. They are seldom able to fix more than simple logic errors, though.
Yes, indeed.
Spare analog can save an ALR from time to time as well.
Another useful feature is spare metal runs...wonder why???I wonder what the overall ratio of metal fixes to ALRs is, across the semiconductor industry?
These days even a single layer fix is getting so expensive, it can be hard to get managers to commit to them.
I wonder what the overall ratio of metal fixes to ALRs is, across the semiconductor industry?
These days even a single layer fix is getting so expensive, it can be hard to get managers to commit to them.Good question. My last node was 180nm, so I have been out of the industry for awhile.
At my last company (which I started), I dont think we ever did an ALR--maybe one. That was out of about a dozen base platforms. Tools are just so good, and with a solid methodology, you can get it mostly right (tweak with metal fix) every time. Now, doing RF or extreme precision...perhaps another story.
At my last company (which I started), I dont think we ever did an ALR--maybe one. That was out of about a dozen base platforms. Tools are just so good, and with a solid methodology, you can get it mostly right (tweak with metal fix) every time. Now, doing RF or extreme precision...perhaps another story.
At my last company (which I started), I dont think we ever did an ALR--maybe one. That was out of about a dozen base platforms. Tools are just so good, and with a solid methodology, you can get it mostly right (tweak with metal fix) every time. Now, doing RF or extreme precision...perhaps another story.
I agree with this. Maybe some analogish problem, but there's not much excuse for bad digital design now, especially if you don't overly complicate the design with seldom-used features.
At SiFive we use "agile hardware design". You can see Dave Paterson talking about it here
You can test fundamentals in tools such as Verilator, but pretty quickly you want to get into an FPGA where you can run at 50 MHz or 100 MHz and boot up Linux, build and test any software you want, even run SPEC in a week. You should be able to exercise the design enough that when it gets moved into an ASIC there are no show-stoppers.
I had my team synthesize all of the digital to FPGA back in 1999. We were certain of the logic. When pushing speed, a little different story.
You cannot do a lot with analog spares, but there was one occasion where a designer was expecting a low-side bias current but the verilog model (which drove the hookup) had high-side bias. Obviously did not work. Solution? I had designed an analog spare block that allowed for an easy turn-around mirror. Saved an all-layer rev. plus it was quick...and on VC money, time is everything.
1. This sounds interesting. How does one make a one size fits all spare block. Because in the end anything could go wrong or have a bug.
2. Was this bug discovered after the masks were made?
3. Did you have to redo some masks after correcting this?
it was an easy FIB to fix and verify.