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Thread: How important is cobalt?

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    How important is cobalt?

    At IEDM Intel revealed that they will use cobalt in on the bottom two layers of its 10-nm interconnect to get a five- to ten-fold improvement in electromigration and a two-fold reduction in via resistance: ​https://www.eetimes.com/document.asp?doc_id=1332696

    What sort of advantages will Intel get from using cobalt compared to TSMC, or Globalfoundries 7nm, which are using old-fashioned copper?

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    First guess: slower electromigration because of the much higher melting point suggesting stronger bonds in the lattice

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    Some benefits to using Cobalt in the lower two layers of metal interconnect:

    • Lower resistance wires means higher clock speeds because of faster switching times on the interconnect
    • Better electromigration means interconnect lasts longer before wearing out, causing high resistance and possible open circuits


    Of course, there has to be a downside, which is probably higher cost and longer times in the fab with more steps added for depositing the Cobalt. Maybe even more time to QA the new 10nm process using Cobalt as a new part of interconnect.

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    Blogger Scotten Jones's Avatar
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    Quote Originally Posted by lefty View Post
    At IEDM Intel revealed that they will use cobalt in on the bottom two layers of its 10-nm interconnect to get a five- to ten-fold improvement in electromigration and a two-fold reduction in via resistance: ​https://www.eetimes.com/document.asp?doc_id=1332696

    What sort of advantages will Intel get from using cobalt compared to TSMC, or Globalfoundries 7nm, which are using old-fashioned copper?
    I will be blogging about these two processes shortly.

    Cobalt has a higher bulk resistivity than copper but at very narrow lines cobalt can have a lower line resistance because copper suffers from scattering and requires relatively thick barrier layers. Intel has a 36nm minimum metal pitch while GLOBALFOUNDRIES has a 40nm minimum metal pitch and therefore Intel may need cobalt where GLOBALFOUNDRIES doesn't. Cobalt is more expensive.

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    Quote Originally Posted by Scotten Jones View Post
    I will be blogging about these two processes shortly.

    Cobalt has a higher bulk resistivity than copper but at very narrow lines cobalt can have a lower line resistance because copper suffers from scattering and requires relatively thick barrier layers. Intel has a 36nm minimum metal pitch while GLOBALFOUNDRIES has a 40nm minimum metal pitch and therefore Intel may need cobalt where GLOBALFOUNDRIES doesn't. Cobalt is more expensive.
    I think the thing most people are interested in is to what extent this is a unique (and important) Intel advantage.

    My understanding is that IBM pioneered this, meaning that presumably such patent barriers as exist are somewhat porous... So the real issue is what are the costs (to the foundry, and on a per chip basis), and what are the benefits?

    (a) Would it make sense for Apple (or QC or ...) to call up TSMC and say "we want cobalt ASAP", or would that make no sense yet because it's only helpful for chips running at 5GHz+ and generating 150W+?

    (b) Assuming it would be useful for some segment (mobile? GPUs? AMD, IBM, or Oracle large server chips?) how long would it realistically take TSMC/Samsung/GloFo to offer it as an option? My guess is that they're both researching it as part of the usual on-going development, and with customer demand they could deliver it as an option within a year; but of course I've no idea if there is some subtle problem with using Cobalt that makes it a much tricky prospect than it appears.

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    Quote Originally Posted by name99 View Post
    I think the thing most people are interested in is to what extent this is a unique (and important) Intel advantage.

    (a) Would it make sense for Apple (or QC or ...) to call up TSMC and say "we want cobalt ASAP", or would that make no sense yet because it's only helpful for chips running at 5GHz+ and generating 150W+?

    (b) Assuming it would be useful for some segment (mobile? GPUs? AMD, IBM, or Oracle large server chips?) how long would it realistically take TSMC/Samsung/GloFo to offer it as an option? My guess is that they're both researching it as part of the usual on-going development, and with customer demand they could deliver it as an option within a year; but of course I've no idea if there is some subtle problem with using Cobalt that makes it a much tricky prospect than it appears.
    GLOBALFOUNDRIES knows how to use cobalt and in fact makes use of it in their 7nm technology, just not as widely as Intel does. There are trade offs to cobalt and whether it benefits a process depends on the details of the process. GLOBALFOUNDRIES uses cobalt in their process where it makes sense for the process and Intel uses cobalt in their process where it makes sense for that process, the two processes are different and have different requirements. At the end of the day you have to compare the processes on their density and performance and cobalt is just one element building up to that.

    I will discuss this in detail in my blog but just having cobalt in a process doesn't really mean anything, it is what the process achieves overall that is important.

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    Quote Originally Posted by Scotten Jones View Post
    GLOBALFOUNDRIES knows how to use cobalt and in fact makes use of it in their 7nm technology, just not as widely as Intel does. There are trade offs to cobalt and whether it benefits a process depends on the details of the process. GLOBALFOUNDRIES uses cobalt in their process where it makes sense for the process and Intel uses cobalt in their process where it makes sense for that process, the two processes are different and have different requirements. At the end of the day you have to compare the processes on their density and performance and cobalt is just one element building up to that.

    I will discuss this in detail in my blog but just having cobalt in a process doesn't really mean anything, it is what the process achieves overall that is important.
    Totally agree. I am looking forward eagerly to reading your analysis of both Intel 10nm and GF 7nm.

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    Quote Originally Posted by Scotten Jones View Post
    GLOBALFOUNDRIES knows how to use cobalt and in fact makes use of it in their 7nm technology, just not as widely as Intel does. There are trade offs to cobalt and whether it benefits a process depends on the details of the process. GLOBALFOUNDRIES uses cobalt in their process where it makes sense for the process and Intel uses cobalt in their process where it makes sense for that process, the two processes are different and have different requirements. At the end of the day you have to compare the processes on their density and performance and cobalt is just one element building up to that.

    I will discuss this in detail in my blog but just having cobalt in a process doesn't really mean anything, it is what the process achieves overall that is important.
    Thanks for the answer. That pretty much matches my conclusions.
    I phrased the questions the way I did in response to the level of hype that's building up in some quarters regarding Intel's use of cobalt, a level that seems to me detached from precisely the sort of analysis you provided.

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    From what is published I share Scotten conclusion. The two solutions are not so radically different anyhow and cobalt is there to have more conductive lines in the end.
    Cobalt is not a new beast in the fab, some with a good memory may remember that the first chips with a silicide contacts where with Co and that process lasted many nodes.
    If I remember correctly some SEU where related to its presence in the process. Would be nice to see if anybody looked into it or at these nodes it is not an issue.

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    Last edited by SPQR54; 12-14-2017 at 01:50 AM.
     

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    Quote Originally Posted by SPQR54 View Post
    From what is published I share Scotten conclusion. The two solutions are not so radically different anyhow and cobalt is there to have more conductive lines in the end.
    Cobalt is not a new beast in the fab, some with a good memory may remember that the first chips with a silicide contacts where with Co and that process lasted many nodes.
    If I remember correctly some SEU where related to its presence in the process. Would be nice to see if anybody looked into it or at these nodes it is not an issue.
    Yes cobalt has been used in fabs for silicide for a long time, there are also cobalt liners and caps for copper interconnect that have been used for at least a few years.

    It is really using cobalt fill of contacts, vias and interconnect lines that is new and therefore presents new fill and planarization requirements.

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