An evaluation of the ASML ATHENA alignment system was performed using marks placed in the scribeline of an Intel test chip used for 130 nm node processing. Exposures were performed using two ASML scanners at IMEC at the isolation, gate, contact and first metal layers, with extreme process splits performed at Intel at critical steps in between. The splits were arranged as factorials in order to evaluate the process sensitivity of the alignment system. The modeled overlay terms with the largest sensitivities are discussed. In addition, data taken by the scanners on various mark/recipe combinations is analyzed to provide insight into overlay optimization and potential alignment system limitations.
The phase shift focus monitor technique is based on the fact that phase shift structures which utilize a non-180 degree(s) shift exhibit asymmetric imaging which is proportional to defocus. This asymmetry results in a lateral displacement of the printed features, which can be measured quickly at a number of locations across the field and across the wafer with a registration measurement tool. The monitor provides a means of evaluating focus effects such as lens tilt, chip leveling, astigmatism, and field and wafer flatness. This paper presents a detailed investigation of the focus monitor. Experiments were performed to evaluate the effects of linewidth and exposure dose on the sensitivity of the monitor. An alternative measurement structure was also evaluated. Monitor repeatability was assessed, indicating that wafer-to-wafer variation is the largest source of repeatability error. Unexpected variation in sensitivity and calibration curve offset across the field was observed. These effects make interpretation of the focus data problematic. Potential factors which might contribute to the variability of the monitor were analyzed. Partial coherence uniformity appears to have a significant impact on the monitor, but does not entirely explain the observed effects. Potential use of the monitor as a coherence mapping tool is proposed.
A process is described in which OCG-895i resist is exposed using both e-beam and i-line optical exposures. This dual exposure allows efficient writing of patterns requiring both fine geometries and large areas in a single lithographic layer. The unique aspect of this process is that the two exposure methods use completely independent developers. This allows the optical exposures to be aligned directly to the e-beam exposed resist, eliminating the need for 'zero- level' alignment marks. E-beam features as small as 200 nm lines and spaces, connected by large photo-exposed pads, have been fabricated. The process presented here results in e-beam contrast of 4.8, with insignificant unexposed film loss. The photo-exposure characteristics are unchanged by the e-beam exposure and develop process. The application of this process to the fabrication of surface acoustic wave devices is discussed.
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