Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Metrology tools and techniques for the 65nm node

The main agreed goals of the metrology package could be summarised as follows:
- Feed the whole project with the correct metrological techniques and tools;

- Minimize the reduction of the global process window due to metrological uncertainty.

Both topics were successfully covered, and relevant results made available to all the partners on time.

In particular, as far as the former goal is considered, four techniques were selected and evaluated extensively throughout the project: CD-SEM, CD-Scatterometry, CD-AFM and "Combo" approaches, i.e. the combination of either technique in a single platform. All the techniques were evaluated according to five characteristics: timing (i.e. on-time availability), ultimate resolution, precision, severity of the interaction with measured structured and "universality".

The selected benchmark for resolution and precision was the ITRS roadmap (for 65nm node) in its last released edition. Our analysis brought to the conclusion that:
- CD-SEM, though several improvements are required to match all the requested quality figures, have to be looked at the main tool class for 65nm node;

- CD-scatterometry offers a good and viable secondary solution, mainly due to the lack of universality;

- CD-AFM and "combo" approaches might be used for "niche" applications, especially when very local information are looked for.

Within each class, one or more tool models were evaluated and their performance compared to the benchmark, in order for the partners to be aware of the best metrology solution on the market during the whole project timeframe. Today, neither of them fulfils the requirements for the 65nm node, due to the large tool-to-tool matching component. Nevertheless, considering that in early development phase only a very few wafers have to be measured at ultimate resolution and precision, a single tool strategy for ultra-critical measurements may be applied. This being the case, commercial tools close to the requested performance are available today.

Looking at the latter goal, main part of the work was dedicated to find innovative procedures for the newest considered technologies (scatterometry and "combo", with particular care to FIB+SEM combination) aiming to the optimisation of tool and recipe setups for a fast implementation into a productive environment. Proper experiments were ideated to strengthen the identified weak points of the considered techniques. Whenever any solution to a particular aspect was not available on time, a clear path towards requested minimal characteristics was given.

For the technique (and tool) benchmark pointed out that the most critical aspect related to metrological quality (i.e. the largest component of the precision budget) is the tool-to-tool matching, procedures to reduce this contribution were studied and validated by a thoroughly exercise, carried on using tools owned by different project partners. The study demonstrated that applying the suggested procedure, the contribution could be limited about to the same value of the poorer single tool precision from a value equal to about three times that value. Further improvements are limited by the fact that it is statistically not significant to reach better overall results than those coming form a single tool, unless a larger data collection, not realistic in an early development phase, is available. Some hints were also given about the feasibility of matching tools belonging to different techniques ("combo" FIB+SEM versus CD-AFM and scatterometry versus CD-SEM).

Results coming from the technique and tool benchmark are immediately usable by everyone, helping in taking decisions about the proper metrology tool selection for the 65nm node and avoiding to some extent the usual evaluations each partner is used to carry on before equipment purchase. Metrology procedures described in this summary a few lines above are immediately usable in principle by all the factories. They may require a few changes for a proper optimisation on a generic model. The suggested procedure for tool-to-tool matching, instead, is quite general and even exploitable to other kinds of measurements in semiconductor industry, e.g. the evaluation of thin layer thickness.

The greatest part of the conclusions are valid also if the process choice for the 65nm node is other than an exposure wavelength of 157nm (with the exception of the interaction studies between the probe and the measured target, which of course are typical of the adopted materials), and therefore shall not be repeated in the case the lithography preferred solution is different (as it seems to be today).

All the results were shared with project partners and exploited through two deliverables, which report all relevant data and conclusions. Raw data coming from tool benchmark and related analyses are available as well. Less sensitive material is also subject of a few papers or presentations, accepted at major lithography or metrology conferences.

More information on the UV2LITHO project can be found at:

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Via C. Olivetti 2
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