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060804: Knowing Where Your Atoms Be
Ed’s Threads 060804
Musings by Ed Korczynski on 4 August 2006

Knowing Where Your Atoms Be
I had the chance to meet with some of the good folks at KLA-Tencor this week, and they gave me a good overview of the evolutionary changes in metrology for leading-edge semiconductor manufacturing. We must measure ever smaller particles and defects, and combine random defect data with other data-streams to perform yield analyses. Sub-wavelength lithography for complex structures induces systematic layout-dependent second-order and third-order yield losses due to opens and shorts, to name just a couple of examples.

You must ensure high levels of manufacturing yield in multibillion-dollar fabs where the depreciation in capital equipment cost is over $1M per day! Everything is too expensive and too complex to casually react to potential problems, and it’s too late for a re-do when you have to meet the back-to-school selling season. You simply need to know what’s going to happen before it happens. You really want confidence that the new mask-set that’s being delivered will yield well the first time through the line.

One of the fundamental axioms of materials engineering is that to achieve desirable final material properties you must have proper microstructures, which requires controlling manufacturing processes. The more complex properties invariably require more complex structures, which can only be created with more control on manufacturing. Even without the incorporation of new materials, leading-edge ICs today use very complex structures with atom-scale control needed to ensure acceptable final yield.

What used to be a single material is now two phases (i.e., low-k dielectrics with nano-pores). What used to be a homogeneous layer is now complex (i.e., transistor gate dielectrics). And everything must occur within tighter windows. KLA-Tencor shows data indicating that the number of metrology inspections has necessarily increased with the basic complexity of ever smaller manufacturing nodes. The need for more data is felt throughout the line, from mask fabrication to transistor formation to interconnect. Yield enhancement teams need ever more information to keep production moving up the curve.

Coupling between metrology and other production processes invalidates the old mind-set that metrology is not “value-added” like processes that are supposed to move atoms around. While it’s certainly true that moving atoms around is basic to IC fabs (whether by ion implantation, rapid thermal annealing, atomic layer deposition, etc.), it’s significant that we’re now living in a world measured in atoms -- not grams, not even milligrams. To make yielding nanometer-era ICs you must control on the atomic scale, and that means you must measure on this scale. To me, metrology must be seen as an intrinsically value-added function when you need to control the locations of individual atoms, especially considering that just existing at 298°K (room temperature) provides enough thermal energy for atoms to bounce around.

Companies such as Imago (see SST feature article) or the Balazs Labs division of BOC-Edwards (see another SST feature article) provide the ability to count individual atoms in 3D, but these amazing technologies are destructive and unsuitable for routine line-monitoring. Non-destructive metrology companies such as KLA-Tencor, Nanometrics, Rudolph, and n&k (and others) have spoken with me in the last few months about known technologies to provide atomic-scale control in production.

Fab people who grew up in the relatively casual world of >0.25-micron nodes may need to re-examine their concepts about metrology itself. It may sound a bit philosophical, but it’s of the utmost practical importance to think of nanometer-scale metrology steps as vital and intrinsically value-added to production. Besides (as the old saying goes), if it isn’t adding value, then why are you even doing it?

— ed

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060804: Knowing Where Your Atoms Be

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Ed's Threads is the weekly web-log of SST Sr. Technical Editor Ed Korczynski's musings on the topics of semiconductor manufacturing technology and business. Ed received a degree in materials science and engineering from MIT in 1984, and after process development and integration work in fabs, he held applications, marketing, and business development roles at OEMs. Ed won editorial awards from ASBPE, including interviews with Gordon Moore and Jim Morgan, and is not lacking for opinions.