Customized off-axis illumination aperture filtering for sub-0.18-μm KrF lithography

Abstract

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.

Evaluating the impact of spherical aberration on sub-0.2-μm contact/via hole patterning

“…The f 00 f 10 and f 10 f 11 terms shift to opposite axis directions. As a result, the focus shift in the superposed intensity is smeared due to the offset of these two cosine terms.…”

“…Since the attenuated PSM diffracts the 0 th order beam f 00 180° out of phase than other diffracted beams, the related cosine terms with coefficients of f 00 f 10 and f 00 f 11 have reverse distributions. As a result, the asymmetry of axis intensity profile is exacerbated.…”

“…The aforementioned discussion suggested the best focus shift in dense hole pattern can be suppressed by a larger portion of lens utilization. Hence, we can customize the illumination configuration to provide better lens utilization without much sacrifice of DOF 10,11 . Figure 13 shows the design of customized illumination, which can be regarded as the combination of conventional highly coherent illumination and quadrupole illumination.…”

Customized illumination aperture filter design for through-pitch focus latitude enhancement of deep submicron contact hole printing

“…The idea of this graphic method has been disclosed in several previous works for source and mask optimization but lacked the detailed derivation of the diagram. [8][9][10][11][12] Here we will give an instructive interpretation of the physical meaning of the illumination chart method and elucidate its application on source element selection. Figure 2 shows the concept and geometry involved in the illumination chart construction, which is the reverse thinking of source-image plots in Fig.…”

“…6,7 With this modified illumination technique, a satisfactory common process window for one-dimensional line/space patterns can be achieved using a conventional binary mask. 8,9 When it comes to two-dimensional window patterns, due to the complexity of the diffraction nature, additional mask shape modification as well as phase-shifting mask ͑PSM͒ technologies are required to manipulate the magnitudes or phases of certain diffraction orders for synergistic combination with a custom illumination scheme. Previous works have described general algorithm of mask and source optimization for two-dimensional regular pattern printing.…”