Osamu Tanitsu

Development of polarized-light illuminator and its impact

Nikon has developed an illuminator with special options for RET (Resolution Enhancement Technique). For one of the solutions of RET, Nikon has pursued the development of a loss-less polarized illumination system. When the polarization direction is the same as the direction of the printed pattern, this technique improves image contrast and extends the process margin. We have simulated the impact of the RET with polarized illumination, in the case of dipole illumination and phase-shift masks, and we have estimated the dominant parameters for high performance polarized illumination. In addition, we have constructed a polarized-light illuminator and installed it in an ArF full-field scanner. We have measured and optimized the degree and distribution of polarization at the wafer plane with a special tool, and we have investigated image performance with polarized dipole illumination. Results show that the new polarized-light illuminator has extended the process margin, especially with respect to dose latitude. The results of the image simulations and experiments will be reported.

Tolerancing analysis of customized illumination for practical applications of source and mask optimization

Due to the extremely small process window in the 32nm feature generation and beyond, it is necessary to implement active techniques that can expand the process window and robustness of the imaging against various kinds of imaging parameters. Source & Mask Optimization (SMO) 1 is a promising candidate for such techniques. Although many applications of SMO are expected, tolerancing and specifications for aggressively customized illuminators have not been discussed yet. In this paper we are going to study tolerancing of a freeform pupilgram which is a solution of SMO. We propose Zernike intensity/distortion modulation method to express pupilgram errors. This method may be effective for tolerancing analysis and defining the specifications for freeform illumination. Furthermore, this method is can be applied to OPE matching of free form illumination source.

Illumination optics for source-mask optimization

Source Mask Optimization (SMO) 1 is proposed and being developed for the 32 nm generation and beyond in order to extend dose / focus margin by simultaneous optimization of the illuminator source shape and a customized mask. For several years now, mask optimization techniques have been improving. At the same time, the flexibility of the illuminator must also be improved, leading to more complex illumination shapes. As a result, pupil fill is moving from a parametric model defined by sigma value, ratio, clocking angle, subtended angle and/or, pole balance, to a freeform condition with gray scale defined by light intensity in the illuminator. We have evaluated an intelligent illuminator in order to meet requirements of SMO. Then we have confirmed controllability of the pupilgram.

Dosage Control for Scanning Exposure with Pulsed Energy Fluctuation and Exposed Position Jitter

Techniques of dosage control for scanning exposure are introduced and the accuracy of exposure dose achieved by these techniques are discussed. Analytical formulation of the dosage accuracy is performed for the first time under consideration of both pulsed energy fluctuation and exposed position jitter. Actual dosage accuracy was measured by adopting the simplest method. Experimental data from the exposure apparatus are shown and the effectiveness of derived formula for dosage error estimation is confirmed. Application for the exposure system is also discussed.

Performance of Polarized Illuminators in Hyper NA Lithography Tools

Polarized light illumination is essential for hyper-NA imaging such as immersion lithography. This is confirmed by comparison of optical images between unpolarized light illumination condition and polarized light illumination condition. In this paper, we introduce our polarized light illumination apparatus and some experimental results, which confirm the effect of improvement of the imaging performance by utilization of polarized light illumination. In addition, required quality of the polarized light illumination for hyper NA lithography is discussed