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Vital Control in Fab Materials Supply-Chains

By Ed Korczynski, Sr. Technical Editor

The inaugural Critical Materials Council (CMC) Conference, co-sponsored by Solid State Technology, happened May 5-6 in Hillsboro, Oregon. Held just after the yearly private CMC meeting, the public CMC Conference provides a forum for the pre-competitive exchange of information to control the supply-chain of critical materials needed to run high-volume manufacturing (HVM) in IC fabs. The next CMC Conference will happen May 11-12 in Dallas, Texas.

At the end of the 2016 conference, a panel discussion moderated by Ed Korczynski was recorded and transcribed. The following is an edited excerpt of the conversation between the following industry experts:

  • Jean-Marc Girard, CTO and Director of R&D, Air Liquide Advanced Materials,
  • Jonas Sundqvist, Sr. Scientist, Fraunhofer IKTS; and co-chair of ALD Conference, and
  • John Smythe, Distinguished Member of Technical Staff, Micron Technology.

KORCZYNSKI:  Let’s start with specifications: over-specifying, and under-specifying. Do we have the right methodologies to be able to estimate the approximate ‘ball-park’ range that the impurities need to be in?

GIRARD:  For determining the specifications, to some extent it doesn’t matter because we are out of the world of specs, where what matters is the control-limits. To Tim Hendry’s point in the Keynote yesterday [EDITOR’S NOTE:  Tim G. Hendrey, vice president of the Technology and Manufacturing Group and director of Fab Materials at Intel Corporation provided a conference keynote address on “Process Control Methods for Advanced Materials”], what was really interesting is instead of the common belief that we should start by supplying the product with the lowest possible variability, instead we should try to explore the window in which the product is working. So getting 10 containers from the same batch and introducing deliberate variability so that you know the process space in which you can play. That is the most important information to be able to reach the most reasonable and data-driven numbers to specify control limits. A lot of specs in the past were primarily determined by marketing decisions instead of data.

FIGURE 1: Jonas Sundqvist, Sr. Scientist of Fraunhofer IKTS, discusses collaboration with industry on application-specific ALD R&D. (Source: TECHCET CA)

SUNDQVIST:  Like the first introduction of what were called “super-clean” ALD precursors for the original MIS DRAM capacitors, Samsung used about 10nm of hafnium-aluminate and it would not matter if there was slight contamination in the precursors because you were not trying to control for a specific high-k phase. Whereas now you are doping very precisely and you have already scaled thinness so over time the specification for high-k precursors has become more important.

SMYTHE:  I think it comes down to the premise that when you are doing vapor transport through a bubbler that some would argue that that’s like a distillation column. So it’s a matter of thinking about what is transporting and what isn’t. In some cases the contaminant you’re concerned about is in the ampule but it never makes it to the process chamber, or the act of oxidizing destroys it as a volatile byproduct. So I think the bigger issue is change-management not necessarily the exact specification. You must know what you have, and agree that a single adjustment to improve the productivity of chemical synthesis requires that ‘fingerprinting’ must be done to show the same results. The argument is that you do not accept “less-than” as part of a specification, you only accept what it is.

AUDIENCE QUESTION:  The systems in which these precursors are used also have ‘memory’ based on the prior reactions in the chamber and byproducts that get absorbed on walls. When these byproducts come out in subsequent processing they can alter conditions so that you’re actually running in CVD-mode instead of ALD-mode. Chamber effects can wash-out a lot of value of having really pure chemicals moving through a delivery system into a chamber and picking up contaminants that you spent a whole lot of money taking out at the point of delivery. What do you think about that?

GIRARD:  Well, this is a ‘crisis!’ When something like this starts to happen in a fab or even during the development cycles, you can’t prioritize resources and approaches you just have to do everything. Sometimes it’s the tool, sometimes it’s the chemical, sometimes it’s the interaction of the two, sometimes it’s back-streaming from the vacuum sub-system…there are so many ways that things can go wrong. Certainly you have to clear up the chemistry part as early as possible.

SUNDQVIST:  We work with zirconium precursors for ALD, and you can develop a precursor that gives you a very pure ALD process that really works like an ALD process should. However, you can still use the TEMA-Zr precursor, that in processing has a CVD component which you can use that to gain throughput. So you can have a really good ALD precursor that gives low particle-counts and good process stability and ideal thermal processing range, but the growth rate goes down by 20% so you’re not very popular in the fab. Many things change when you make an ‘improved’ molecule to perfect the process, and sometime you want to use an imperfect part of the process.

FIGURE 2: John Smythe, Distinguished Member of Technical Staff of Micron Technology, explains approaches to controlling materials all the way to point-of-use. (Source: TECHCET CA)

SMYTHE:  What we’re doing a lot more these days is doing chamber finger-printing, where we’re putting a quad-filtered mass-spec on each chamber—not a cheap little RGA, but real analytical-grade—and it’s been enlightening. If you look at your chemistry moving through a delivery line using something like the Schrødenger software, it’s not a big deal to see that you can use the mass spec to see some synthesis happening in the line. We joke and call it ‘point of use synthesis’ but it’s not very funny. We are used to having spare delivery lines built-in so we can install tools to try to gain insights to prevent what we’ve been talking about.

KORCZYNSKI:  John, since Micron has fabs in Lehi and fabs in Singapore and other places, while they do run different product loads, do you have to worry about how long it takes things to travel on a slow boat to Singapore? Do you have to stockpile things more strategically these days, and does that effect your receiving department?

SMYTHE:  What we really need are a few good ocean-going hydrofoil ships! The most complete answer is we first identify which things need ‘batch-qual’ so if we do a batch-qual in Virginia and know that material is going to Taiwan that we have confidence it will pass batch-qual in Taiwan. There are certain materials that we require information on which synthesis batch, which production batch, and sometimes which bottling batch. Sometimes you take a yield hit because you didn’t have the right vision, and then you institute batch qual.

I think most of you are familiar with the concept of ‘ship-to-stock,’ when you have enough good statistical history and a good change management process with the supplier then you can do ship-to-stock and that reduces the batch-qual overhead. On a case by case basis you have to figure out how difficult that is. A small story I can tell is that with Block Co-Polymer (BCP) self-assembly we found one particular element that in concentration above 5 ppm prevented the poly-styrene from self-assembling in the same way, whereas other metal trace contaminants could be a hundred times higher and have no effect on the process. So this gets back to some of our earlier discussion that it’s not enough to know that your trace elements are below some level. Tell me the exact atoms and the exact counts and then we’ll talk about using them. The BCP R&D taught us that in some situations just changing from one batch to the next could increase defects a thousands times. So we will see a bigger push to counting atoms.

[DISCLOSURE:  Ed Korczynski is co-chair of the CMC Conference, and Marketing Director of TECHCET CA the advisory services firm that administers the Critical Materials Council (CMC).]

—E.K.

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