Yoshihiro Shiode

Method of Zernike coefficients extraction for optics aberration measurement

With recent progress in resolution enhancement techniques, requirements for exposure tools, specifically optics aberration, are becoming severer. Some simple ways to allow aberration measurements to be performed on exposure tools have been reported and made commercially available. These methods, however, do not seem to go much beyond monitoring of aberration changes while the accuracy of absolute values is left unclear. This paper describes a new approach of optics aberration measurement. With this approach, an optimum effective light source and patterns to be measured have been designed for analysis of Zernike polynomials that represent the wavefront of optics. By measuring the shift of images printed from the patterns with the light source, specific Zernike coefficients can be extracted. This new technique can also be applied to any conventional lens aberration tests using SEM. Same as the above Zernike coefficients extraction, just measuring the displacement of the images that are formed from optimum mask patterns with an optimum light source will provide a conventional SEM value. Simulations to compare the new technique with the conventional SEM showed a very good correlation with each other as expected. Experimental results are discussed to determine the accuracy of the new technique.

A novel focus monitoring method using double side chrome mask

In order to measure the focus control performance on exposure tools with high accuracy, we developed a novel focus monitoring method, entitled Z-SPIN. The features of this Z-SPIN method are the high resolution focus measurement accuracy of < 1nm and process robustness. We therefore began by quantitatively analyzing the issues exposure tools were having through the use of the Z-SPIN method. From this examination result, we demonstrate a robust focus control solution with Z-SPIN mask. In parallel, through the determination of the focus budget with the new focus control technique, a significant improvement of the focus performance on exposure tools is shown. Finally, by tightening focus control, we examined the viability of extending the lifetime of exposure tools as well as enabling device shrinking.

Study of polarization aberration measurement using SPIN method

High-NA and immersion projection systems require RETs (Resolution Enhancement Techniques) that utilize polarized illumination. Therefore measuring aberrations that are dependent on illumination polarization (polarization aberration) also becomes important. Generally, metrology for polarization aberration measurement consists of polarizer, resulting in a large-scale apparatus and rising cost. Therefore, a simple and accurate metrology method is desired, one that can be easily installed then removed after testing. We have investigated a simple and accurate metrology method for polarization aberration measurement using Canon SPIN. Through this work, we developed a new theory, entitled BLP (Birefringence measurement by Linear Polarization of light), to characterize birefringence of the lens by rotating linear polarization illumination. One of the merits of BLP is its applicability to most of the conventional metrologies for lens aberration measurement. In this paper, we have used the SPIN method for BLP evaluation. We confirmed the accuracy of BLP by achieving 1.0 correlation coefficient with Jones theory for Retardance and Fast-Axis of birefringence. We also evaluated the validity of Pseudo-Jones-Pupil (PJP), which was generated from SPIN-BLP analysis, for imaging performance simulation. This resulted in identical imaging performance with the original Jones pupil for resolution and LRCD. As a polarization aberration monitor, SPIN can be used for qualification, periodic monitoring and evaluation of image performance in the field. Another advantage of SPIN is its portability. Therefore we also consider usage of SPIN as a machine-to-machine calibration tool.

Characterization of imaging performance: considering both illumination intensity profile and lens aberration

Achieving accurate low k1 imaging performance requires that the illumination intensity profile (effective light source profile) no longer be neglected. Simultaneously, simulation techniques have taken on an unprecedented level of importance because it is not practical for all low-k1 imaging applications to be performed experimentally. The impetus is now on the simulation to efficiently narrow down the numerous those options. Moreover, we are concerned that current metrology methods, such as the SEM, will be no longer be used with full confidence in terms of data reliability and accuracy because the specification may reach its measurement limit and the sample reproducibility may dominate the CD budget. We therefore anticipate that a simulation, which incorporates all factors potentially impacting performance, will predict experimental results accurately and repeatedly. We have been newly developing a reticle-based metrology tool, entitled REMT (Reticle Effective light source Measurement Tool), to precisely quantify the illumination shape. The illumination light, which first passes through a pinhole and traverses an optical path within REMT, is then detected by a CCD camera located over the reticle stage to form the illumination intensity profile. The measurement reproducibility of the σ size for REMT is less than ±0.0002. We have developed a lens metrology tool, entitled SPIN (Slant projection through the PIN-hole), to accurately quantify lens aberrations. SPIN is also a reticle-based metrology tool, with repeatability of less than 1mλ. In this paper, we will investigate Left-Right CD Difference (LR-CD), the well-known detection method for coma aberration, comparing experimental results with those from simulations that consider both lens aberrations and illumination shape as measured by SPIN and REMT, respectively. In this discussion, the factors causing LR-CD for dipole illumination will be also analyzed and quantified.

0.85-NA ArF exposure system and performances

At the time when the 90nm node is near at head, the era for ArF exposure tool is expected in the near future. In this paper, the extension possibility to over the 65 nm node with the FPA-6000AS4, which equips a lens with 0.85 of the numerical aperture (NA) and some indispensable functions with the future lithography for extending the patterning capabilities down to 65nm node and beyond it, is discussed. In the development of the 0.85NA exposure system, we would like to introduce the three major topics. Firstly, the exposure tool equips an illuminator providing flexibly variable illumination modes. Secondly, we newly developed a metrology for determining the aberrations on the exposure tool in order to achieve extremely low aberrations, with the method applying Haltman. And lastly, exposure performances, and the flare, are discussed.