A theoretical analysis to estimate the effect of shot noise on CDU is induced from optical imaging perspectives combined with quantum theory, and is studied for 193-nm, EUV, and electron beam lithography. We found the CDU variation from shot noise is related to the number of particles absorbed in the printed area and to the image log slope (ILS). Hence, the CDU variation contributed by shot noise gets worse when the technology node advances from 45-to 32-, 22-, and 15-nm, EUV with higher ILS is no exception. For e-beam lithography, we are interested in the values of ILS calculated from array structures with different pitches, backscattering, wafer-stage movement, and raster-scan writing.

A completely new concept for designing the illumination aperture filter is suggested. From experimental or simulative methods, we have extracted the performance of every individual beam component on the illumination plane. The optimal apertures are then obtained by superimposing the best components that meet the requirements demanded by the specific photo processes. Different kinds of optimal apertures were successfully implanted to deal with different process problems. Therefore, it is called the customized illumination aperture filter (CIF). The zero 1D OPE CIF, as a proof of concept, was designed to eliminate the OPE of low k process. Without any OPC, O.6.tm DOF ofthe common ED window was obtained, where ki 0.39 for our NA0.55 stepper to print 0. 18.tm line patterns. To push to smaller ki, another CIF was designed to maximize the individual DOF and overcome the reduced power problem accompanied with the typical aggressive OAI.Using this CIF, we achieved I . Im common DOF with 7% EL for 0. 1 8.tm line patterns. The CIF doubles the power of the Nikon's strong quadrupole, shrinc. An ultimate resolution limit of 0. 1 1.tm line pattern was reached as well with the CIF. Finally, a contact/via CIF was designed combined with a half-tone PSM (6%). The CIF gives about O.8im common DOF with 7% EL for O.2.tm holes and O.7.tm DOF for 0. l7prn holes using thinner resist. The CIF approach is, therefore, proven to be a cost effective and relatively easy realizable alternative to the alternating PSM for extremely low ki process applications.

ArF-resist-shrinkage and line-edge roughness-induced CD errors are the two main challenges for CD SEM. The requirement of measurement precision for the 65-nm node is less than 0.5 nm. The current CD SEM ADI precision is between 0.7 to 0.9 nm after shrinkage curve correction. Optical CD (OCD) has provided three major advantages. That is more sampling (> 2500:1), insensitivity to line edge roughness, and less resist damage. These advantages facilitate much better measurement precision (< 0.3 nm) than CD SEM and make OCD a potential APC metrology candidate. However, the recipe and library generation of OCD is more complicated and time consuming than CD SEM. Any thin-film variation will disturb the CD accuracy and recipe coverage range of OCD. For different pitches and film combinations, new OCD libraries need to be generated. Matching through all pitches between CD SEM and OCD is also very difficult. We propose a new concept on optical-CD-like CD SEM measurement, i.e. average line width (ALW) and contact hole diameter (ACD) measurement at high resolution and low magnification (HRLM) CD SEM. The resolution chosen is below 2nm and the magnification is 50KX. The low magnification CD measurement can average the e-beam dosage and reduce the ArF shrinkage. Several repeated patterns such as line/space and hole arrays are measured to get an averaged CD under lower magnification condition. These low magnification average CDs increase the sampling size and they are insensitive to the line edge roughness. The CD linearity of ALW/ACD and the CD matching to current CD SEM methodology will be presented. Small step FEM CD by low magnification and high magnification CD measurement will be studied. The difference between low/high magnification SEM and optical CD will be also studied.

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ArF immersion lithography is essential to extend optical lithography. In this study, we characterized the immersion process on production wafers. Key lithographic manufacturing parameters, overlay, CD uniformity, depth of focus (DOF), optical proximity effects (OPE), and defects are reported. Similar device electrical performance between the immersion and the dry wafers assures electrical compatibility with immersion lithography. The yield results on 90-nm Static Random Access Memory (SRAM) chips confirm doubling of DOF by immersion as expected. Poly images of the 65-nm node from a 0.85NA immersion scanner are also shown.

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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.

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