Hideo Shimizu

Subquarter micron optical lithography with practical superresolution technique

Practical resolution, which is defined as the minimum geometry for a 1.0 micrometers depth of focus, in conventional krypton fluoride (KrF) excimer laser (248 nm) lithography is 0.30 micrometers . A new illumination technique, which uses a weak quadruple effect to enhance the depth of focus and to solve the current problems in the off-axis illumination techniques, has been developed. This new illumination technique is suitable for use with the attenuated phase shifting mask. With this combination technique, a 1.8 micrometers depth of focus using a 0.45 NA KrF excimer laser stepper can be achieved without a secondary peak in the distribution of light intensity for the various duties 0.30 micrometers space patterns. Even for hole patterns, a 2.0 micrometers common depth of focus can be achieved. These results indicate that KrF excimer laser lithography is a powerful candidate for beyond 0.25 micrometers -rule devices. It is also confirmed that i-line lithography is an expectable candidate for the second generation of 0.35 micrometers -rule devices.

Experimental Verification of an Aerial Image Evaluation Method and Its Application to Studies of Attenuated Phase-Shifting Masks

Attenuated phase-shifting masks can improve the resolution of optical lithography, and an accurate aerial image evaluaton method is necessary for optimizing parameters. In a positive-tone chemically amplified resist, WKR-PT2, the actual resist pattern size can be easily estimated from the aerial image. This was experimentally verified by evaluating both binary and attenuated phase-shifting masks, and it was established that the secondary peak resolution limits can also be estimated from an aerial image. Further study indicated that this resolution limit in dense patterns is determined by numerical aperture, wavelength, and target hole size. Optimization of numerical aperture and pattern layout is necessary before attenuated phase-shifting masks can be put to practical use.

New systematic evaluation method for attenuated phase-shifting mask specifications

A new simulation-based approach for specifying an attenuated phase-shifting mask (att-PSM) is proposed with systematically evaluating entire process parameters related to illumination sources, resist development in a wafer and process latitude. Exposure-defocus and mask fabrication latitude (EDM) methodology is adopted for considering the process latitude of exposure, defocus and mask line width. Transmittance and mask bias are targetted in the specifications, because these parameters are essential in the selection of the optimum att-PSM characteristics. The suppression of optical proximity effects by modified beam illumination (MBI) is also verified by the new evaluation method. The technique of combined att-PSMs and MBI can be applied to various types of dense hole patterns with the appropriate transmittance and mask bias.

ArF lithography technologies for 65 nm-node CMOS (CMOS5) with 30 nm logic gate and high density embedded memories

In this paper ArF lithography technology for 65nm-node CMOS with 30nm logic gate and high density embedded memories have been demonstrated. ArF step-and-scan exposure systems with 0.75NA are available under accurate lithography design with level specific focus and does error budgets. Also,the process steps with two kinds of lithography are implemented to fabricate GC pattern.

Estimation of attenuated phase-shifting mask fabrication latitude using an optical exposure-defocus methodology

The performance and practical fabrication latitude of attenuated phase shifting masks have been studied using a newly developed exposure-defocus and mask fabrication latitude (EDM) methodology in which the mask linewidth latitude is taken into account as well as the conventional estimation parameters such as the exposure latitude and depth of focus (DOF). Both isolated and dense 0.3 micrometers contact hole (C/H) patterns have been evaluated using an EDM process window which is obtained by the light intensity profiles with the KrF 248 nm exposure, NA equals 0.45 and (sigma) equals 0.3. When the practical process latitude of within +/- 5% of exposure dose and +/- 0.01 micrometers of mask linewidth are supposed, background transmittances of more than 9.00% and phase error controllability within +/- 2 degrees are required for both isolated and dense C/H patterns. The EDM window is steeply shrunk by the enhanced optical proximity effect for the dense C/H pattern at a pitch of less than 0.90 micrometers .