Metrology tool performace guaranteed

02/01/1999

Metrology tool performance guaranteed

Increasingly for sub-50 ? gate films, semiconductor manufacturers are demanding thin-film metrology tools matched to better than 0.5 ?; even a few atoms thicker or thinner than specification can adversely affect the performance of the finished device. Now such performance, even across fabs in different worldwide locations, can be purchased with metrology tools from Rudolph Technologies Inc. (RTI); its Ultrathin Film Support Program sets, maintains, and transfers a baseline for thin-film accuracy from system to system, minimizing frequent recalibrations.

The program guarantees that two tools within a fab will match to ?0.1 ? and that two tools in different fabs across the globe will match to ?0.33 ?.

Briefly described, RTI`s tool matching sets a baseline by measuring a NIST traceable thin oxide calibration wafer of known thickness on a highly accurate research ellipsometer. The customer`s tools are then calibrated to match within 0.1 ? of the standard. Once the tools within a fab are matched, they are routinely checked with a reference wafer. All the systems` measurements within that fab should remain within 0.2 ?. George Collins, director of marketing for RTI, notes, "Although the film thickness of the reference wafer may vary due to environmental conditions, inherently stable instruments will give thickness readings that will go up and down together. If one tool breaks away from the pack, it is an early sign that something is wrong with that instrument. We then repair the problem and bring the tool back into the pack."

Worldwide fab-to-fab matching with Rudolph tools is verified through a wafer exchange procedure. They measure a wafer at fab A (Ta1), send it to fab B (measured as Tb), and return it to fab A (Ta2). The wafer stability is verified (Ta1-Ta2), followed by calculation of fab matching Tb = (Ta1 + Ta2)/2. Fab-to-fab matching can be guaranteed to be ?0.33 ?. - P.B.