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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.

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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In the IC industry the mask cost and cycle time have increased dramatically since the chip design has become more complex and the required mask specification, tighter. The lithography technology has been driven to 65-nm node and 90-nm product will be manufacturing in 2004, according to ITRS's roadmap. However, the optical exposure tools do not extend to a shorter wavelength as the critical dimension (CD) shrinks. In such sub-wavelength technology generation, the mask error factor (MEF) is normally higher. Higher MEF means that tighter mask specification is required to sustain the lithography performance. The tighter mask specification will impact both mask processing complexity and cost. The mask is no longer a low-cost process. In addition, the number of wafers printed from each mask set is trending down, resulting in a huge investment to tape out a new circuit. Higher cost discourages circuit shrinking, thus, prohibits commercialization of new technology nodes.How to reduce the mask cost and cycle time? Robust mask processes will play a crucial role but it is an extreme challenge for the mask-processing people. For example, the blank mask provided by the vender has been coated with the resist. Each batch of blank masks needs to find an optimal dose to meet the rigorous CD specification, since these coating blanks are sent out to the mask house in different periods and through different transportation conditions. The cycle time and the data size also increase drastically when higher transistor density is demanded and smaller pattern jags are created by the aggressive OPC. The vacuum, heating and fogging effects will worsen the process control of the e-beam writer due to a long writing time. The well-controlled transmission and phase shift changes after the cleaning process also become crucial, when an Att-PSM consisting of lines and spaces is fabricated. Dry cleaning may be one possible solution. The mask cost contributed from the defect inspection process has risen significantly, since the price of next generation tool increased but the throughput decreased. After the implementation of model-based OPC, the circuit layout is full of small jig and jag patterns making the failure rate of defect repair higher. In order to reduce cycle time and mask cost, the optimization of both OPC Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/21/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx algorithm and circuit design needs the closer cooperation between designers, wafer process engineers and mask makers. A close linking of wafer processing, mask making, and OPC as found in captive mask houses is becoming indispensable.