Off-axis illuminalion (OAT) has been shown as one of the most practical resolution enhancement techniques (RET) available for optical lithography. A customized off-axis illumination aperture ifiter (CIF) was designed to gain the benefits of OAI and keep the optical proximity effect (OPE) in a manage-able range for sub-0. 18im line and space patterns. The performance of the filter comparing with conventional, annular and quadrupole illuminations in terms of depth of focus (DOF), OPE, throughput, dose and power unifonnity for both 0. 18im and 0. l5jnn on a 0.55 NA Nikon KrF excinier laser stepper with a maximum partial coherence factor of 0.8 is presented in the paper. A brief description of the design principle of the ifiter is also given. A summarized conclusion on the weakness ofthe ifiter and possible improvements is also presented in the paper.

Three parameters, measurement times, charging distances, and charging area, are studied with respect to measurement of the local charging effect. We found that the effects of measurement times and charging distances to the local charging is under observation limit and the measured CD deviation is very small. However, the charging area is found to be the most dominant parameter for local charging. A 7-nm CD deviation from this local charging is observed. After the root cause of the local charging is understood and controlled, we use an extra charging area at the opposite side of the measurement site to compensate for the charging effect. The SEM image and CD deviation are greatly improved after this compensation. At last, a novel measurement algorithm is introduced to deal with the actual OPE evaluation. From simulation, the net Coulomb force experienced during the measurement is greatly reduced with the new algorithm compared with that used in the normal measurement sequence. The comparison of the global charging and local charging effects is also discussed in this report.

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The mechanism of focus latitude enhancement for contact/via hole printing is explained by approximating the axis intensity distribution of an image as a series of cosine functions to characterize the interference between each pair of diffraction beams. It is found that a phase-shifting mask ͑PSM͒ with symmetrical assist features improves the depth of focus ͑DOF͒ by introducing destructive interference to counterbalance the intensity fluctuation from constructive interference as defocus. A simple formula was derived to represent the capability of focus latitude enlargement. It shows that the extent of enhancement depends on the exposure wavelength and numerical aperture of a projection lens only. Increasing the degree of partial coherence degrades the focal range enlargement because a larger illumination angle elongates the destructive interference pattern in the optical-axis direction to weaken its ability for intensity compensation. On the other hand, the lack of constructive interference in dense hole imaging fails the mask pattern transfer, which limits the application of the phase-shifting method to pattern pitch greater than ͱ2/NA. A tiny amount of spherical aberration results in prominent asymmetrical defocus behavior because the wave deformation in the projection lens shifts the distribution of constructive and destructive interference patterns to opposite defocus directions. The printing characteristics of 0.17 m contact using an 18% transmission, rim-type attenuated phase-shifting mask are investigated to corroborate our analysis of defocus behavior. The dependence of depth of focus on pattern duty is stressed to elucidate the difference in mechanisms of focus latitude improvements for a sparse hole and periodic dense hole.

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Several super resolution techniques, such as phase-shifting mask (PSM) and off-axis illumination (OAI), have been reported to extend the resolution limit and increase the depth-of-focus (DOF) of optical lithography. However, these techniques provide less immunity to spherical aberration than the conventional approaches like chrome binary mask and low coherent illumination. Best focus position shift is the most well known anomalous phenomenon resulted from spherical aberration. In this paper, the origin of best focus shift is explained in pictorial and analytical forms. The phenomenon is evaluated by observing the exposure-defocus windows of sub-0.2µm hole patterns from an 18% transmission rim-type attenuated PSM combined with several types of illumination. Under high coherent illumination, severe focus shift was observed in sparse patterns as strong phase-shifting effect is applied. For dense hole patterns, OAI results in abrupt focus position variation at specific pattern pitch. The experimental results show that spherical aberration would induce best focus shift, distortion of process windows, loss of DOF, and shrinkage of iso/dense process window overlap. Two approaches were proposed to suppress the impact of spherical aberration. One is introducing proper amount of phase bias in attenuated PSM to adjust the wave aberration in the lens. The other more feasible method is using a customized illumination. A synthesized illumination aperture was proposed to compensate the focus shift. Excellent lithographic performance was obtained in the experiment from this method.

193-nm immersion lithography is the only choice for the 45-nm logical node at 120-nm half pitch and extendable to 32-and 22-nm nodes. The defect problem is one of the critical issues in immersion technology. In this paper, we provided a methodology to trace the defect source from optical microscope images to its SEM counterparts after exposure. An optimized exposure routing was also proposed to reduce printing defects. The average defect count was reduced from 19.7 to 4.8 ea/wafer.

This paper reports the water-leakage mechanism of the immersion hood in an immersion scanner. The proposed static analysis reveals the immersion hood design performance in defect distribution. A dynamic water-leakage model traces the leaked water and identifies its position on the wafer, during exposure. Comparing simulation to experimental results on bare-silicon and resist-coated wafers, the defect type, source of residuals, and critical settings on the immersion system were clearly identified. 1.INTRODUCTIONImmersion lithography is the only viable choice to produce 65-nm and 45-nm half-pitch circuits. Although 193-nm immersion lithography is being developed at an unprecedented pace, it still needs enormous efforts to meet the extremely tight requirements for the 45-nm node. 1,2,3 One of them is defect density. It needs to be as low as 1 defect per wafer pass, especially when many device layers are exposed with immersion scanners.The immersion hood (IH) is an important component of the immersion scanner for supplying, confining, and draining the water during exposure. Unfortunately, the fluid will leak from the IH due to insufficient constrain and the droplets left will produce watermark defects. Besides watermarks, the liquid coupling medium is more likely to carry particulates than the air coupling medium, no matter these particles are from materials, the wafer, or the exposure system itself. The particulates may be left through water leaking from the IH during wafer movement and cause printing and fall-on defects.Hence, preventing water leakage is one of the most critical issues for immersion defect reduction. This paper reports a static residuals analysis to monitor the IH design performance and define the correlation between airflow instability and water leakage in the IH. Furthermore, a dynamic water-leakage model has been setup, basing on the mechanism discussed in Section 3. This dynamic model traces the water-leakage trajectory during exposure routing.