EUV was never going to be single patterning
- Thread starter Fred Chen
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Given what happened with 20nm and 16FFL, and the projected 1.1x density for N2; my guess is N2 uses the same BEOL as N3. EUV double has a ways to scale further. I think that EUV double, quad duv, and high-na single are capable of getting to like 19nm feature size (or something like that).
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Remember the primary goal of N2 is GAA and then (possibly in the same initial N2, more likely a year later in an N2B [or whatever name]) BSPD.
Each of these (especially BSPD) will free up some effective density even if they don't increase the absolute maximum density; we may get some minor improvements to minimum cell size but that's not the focus of N2.
The official TSMC pronouncement is the limited "density >1.1x"...
Relaxed upper metal pitches, > 40nm, similar to 10nm node MMP.TSMC says they avoided double patterning on N3E by reducing density:
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Afterthought: these may very well be long single-pitch SADP lines (no cut/self-trim), which also need only a single exposure.
Second thought: the cross section might already show clues.
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Even with ~50 nm pitch, stochastic behavior is still significant (https://www.semanticscholar.org/pap...bert/4773b3807b16e62a1fdb5aba1057b2989136f210), so the yield or throughput would still be impacted. A single exposure illumination also limits the pitch due to shift vs. focus, as well as best focus vs. pitch (http://euvlsymposium.lbl.gov/pdf/2015/Oral_Monday/Session2_EUV Insertion in Manufacturing 2/S2.4_Wittebrood.pdf).
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Not sure how much the pitches will scale. It doesn't look like CGP moved much, and the nanosheets can still be quite wide. Contact resistance can be bigger as well.
The point spread function of 0.55 NA EUV is ~15 nm. The point spread function of 0.33 NA EUV is ~ 25 nm.
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HNSs offer some Lg improvements (reducing CPP), and because you have an effective 1.5 fin device you can shrink cell height. I would assume these alone could provide a >1.1x theoretical density improvement. Maybe it needs N3's BEOL rather than N3E's. But either way I think they might be enough to do the job with some modifications. We probably need to wait two more years before having any indication of whether this is the case though.
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In short, N3 still requires multipatterning for both DUV and EUV.
19 nm (half-pitch) is possible with DUV SADP, but not every expected case.
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38 nm half-pitch is a practical limit for DUV immersion single pass exposure, some tool have gone to 37 nm.
I visually estimated the lower metal pitches from Figure 15 of the N3E IEDM paper 27.5:
The 23 nm pitch layers cannot be single exposure since the pupil fill is too low, which means the EUV system itself is absorbing a lot of the EUV light. There is also cross slit rotation more severely affecting the dipole illumination.
The next few layers I estimated to be around 30 nm pitch. Presumably these would be assumed to be the single exposure layers (edit: should still be double-patterned), but the M3 line gap space is also tight (~30 nm), so a cut is still necessary. It seems cuts are not included in the single exposure description, but the layer should be considered a multi-patterned layer nonetheless, since a cut is an additional exposure. And as far as safe cuts are concerned, SALELE would still be the preferred way.
M5 looks like it may not require cuts since the gaps are wider. Above M5, the pitch jumps up ~2X, so it looks like around 60 nm, very relaxed, like early double patterning days.
The 23 nm pitch layers cannot be single exposure since the pupil fill is too low, which means the EUV system itself is absorbing a lot of the EUV light. There is also cross slit rotation more severely affecting the dipole illumination.
The next few layers I estimated to be around 30 nm pitch. Presumably these would be assumed to be the single exposure layers (edit: should still be double-patterned), but the M3 line gap space is also tight (~30 nm), so a cut is still necessary. It seems cuts are not included in the single exposure description, but the layer should be considered a multi-patterned layer nonetheless, since a cut is an additional exposure. And as far as safe cuts are concerned, SALELE would still be the preferred way.
M5 looks like it may not require cuts since the gaps are wider. Above M5, the pitch jumps up ~2X, so it looks like around 60 nm, very relaxed, like early double patterning days.
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I’m not even going to attempt to figure out how you derived all of that information from one low resolution cross section.
pitch or half pitch? For that to be pitch, with 12 nm wide metal, they would need an LELE process after EUV linear patterning, right?
That or SADP plus cuts.
Recent data https://www.researchgate.net/public...ty_electrical_test_and_voltage_contrast_study shows 28 nm pitch having an 80 nm difference of best focus (for minimal LER) from 32 nm pitch:
The illumination was targeted for 28 nm pitch.
What phenomenon causes LER to improve when focus is off by -70nm? You can see the LER decreases even further at -100nm but Fig. 4(b) shows many other defects by that point (they do not show the images for less than 60 which would have been interesting).
It appears to be a LAM formulation 3-layer dry resist, in which case the resist is only about 20 to 30nm thick, so depth of focus interior to the resist does not seem the reason.