Kenji Yamazoe

Mask optimization for arbitrary patterns with 2D-TCC resolution enhancement technique

In this paper, a new resolution enhancement technique named 2D-TCC technique is proposed. This method can enhance resolution of line patterns as well as that of contact hole patterns by the use of an approximate aerial image. The aerial image, which is obtained by 2D-TCC calculation, expresses the degree of coherence at the image plane of a projection optic considering mask transmission at the object plane. OPC of desired patterns and placement of assist patterns can be simultaneously performed according to an approximate aerial image called a 2D-TCC map. Fast calculation due to truncation of a series in calculating an aerial image is another advantage. Results of mask optimization for various line patterns and the validity of the 2D-TCC technique by simulations and experiments are reported.

Extension of the 2D-TCC technique to optimize mask pattern layouts

The extendibility of 2D-TCC technique to an isolated line of 45 nm width is investigated in this paper. The 2D-TCC technique optimizes mask patterns placing assist pattern automatically. For 45 nm line patterns, the assist pattern width generally becomes much smaller than the exposure wavelength of 193 nm. Thus, the impact of the topography of a mask is examined using an electro-magnetic field (EMF) simulation. This simulation indicates that unwanted assist pattern printings are brought about by assist patterns with a smaller size than expected by the Kirchhoffs approximation. The difference, however, can be easily solved by giving a bias to the main pattern in the optimized mask. The main pattern bias decreases DOF very little. Furthermore, DOF simulated with a thick mask model is roughly the same as that simulated with a thin mask model. Therefore the topography of the optimized mask does not have an influence on the assist pattern position of the optimized mask. From these results, we have confirmed that the 2D-TCC technique can be extended to the optimization of 45 nm line patterns. As one of the notable features, the optimized aperiodic assist pattern greatly reduces MEEF compared with the conventional periodic assist pattern. To verify the feasibility of the 2D-TCC technique for 45 nm line, we performed experiment with an optimized mask. Experimental results showed that DOF increased with the number of assist pattern as simulation indicated. In addition, a defect whose length was twice that of the assist pattern did not have an influence on CD. From these results we have confirmed that the 2D-TCC technique can enhance the resolution of 45 nm line and has practical feasibility.

Computation theory of partially coherent imaging by stacked pupil shift matrix

A theory of partially coherent imaging is presented. In this theory, a singular matrix P is introduced in a spatial frequency domain. The matrix P can be obtained by stacking pupil functions that are shifted according to the illumination condition. Applying singular-value decomposition to the matrix P generates eigenvalues and eigenfunctions. Using eigenvalues and eigenfunctions, the aerial image can be computed without the transmission cross coefficient (TCC). A notable feature of the matrix P is that the relationship between the matrix P and the TCC matrix T is T=P(dagger)P, where dagger represents the Hermitian conjugate. This suggests that the matrix P can be regarded as a fundamental operator in partially coherent imaging.

Quantitative evaluation of mask phase defects from through-focus EUV aerial images

We present an improved method of phase retrieval from through-focus image series with higher precision and reduced sensitivity to noise. The previous method, developed for EUV, actinic mask measurements, was based on the Gerchberg-Saxton algorithm and made use of two aerial images recorded in different focal planes. The new technique improves the reconstruction uncertainty and increases the convergence speed by integrating information contained in multiple images from a through focus series. Simulations characterize the new technique in terms of convergence speed, accuracy and stability in presence of photon noise. We have demonstrated the phase-reconstruction method on native, mask-blank phase defects and compared the results with phase predictions made from AFM data collected after the multilayer deposition. Measurements show that a defects top-surface height profile is not a reliable predictor of phase change in all cases. The method and the current results can be applied to improve defect modeling and to enhance our understanding of the detectability and printability of native phase defects.

Visible light point-diffraction interferometer for testing of EUVL optics

We have built a visible light point-diffraction interferometer with the purpose to characterize EUVL projection optics. The interferometer operates at the wavelength of 532 nm and utilizes two identical pinhole wavefront reference sources for generation of both signal and reference wavefronts. In the simple configuration of our interferometer, the main source of system error is the pinhole reference wavefronts. It is important that the reference wavefronts are calibrated and the calibration is stable. The calibration using our refractive test optic is reproducible to better than 0.1 nm RMS. The interferometer measured the wavefront of our refractive test optic with the repeatability of 0.1nm RMS. This paper will discuss the error sources and removal of the errors with experimental results.

Challenging the limit of single mask exposure

IDEALSmile is introduced as a new exposure technique. Since we have realized k1 equals 0.29, k1 equals 0.32 optical lithography is now achievable. In this paper IDEALSmile is targeted for contact hole patterns. The results validate that it is possible to simultaneously fabricate 110 nm (k1 0.32) half-pitch dense and isolated contact hole patterns using Canon FPA-5000ES3 (KrF, NA equals 0.73). Furthermore, our experimental results also show that it is possible to fabricate different half-pitch patterns at the same exposure dose, which is impossible by conventional methods. Since these results are obtained using binary mask and the modified illumination with single exposure, there are no concerns with regards to decrease in throughput and increase in cost of ownership. By attaining k1 equals 0.32 for contact hole patterns using binary mask with single exposure, printing 100 nm contact hole patterns can be achieved with single exposure using KrF lithography, such as the Canon FPA-5000ES4 (KrF, NA equals 0.80) scanner which will soon make its market debut. ArF or F2 lithography is effective as for contact hole patterns below the 100 nm node. There is no doubt that optical microlithography will continue for some time.

An innovative method for contact hole printing with binary mask and single exposure

In 2002, Canon introduced a new method for contact-hole printing, using a binary mask and single exposure, entitled IDEALSmile (Innovative Double Effective source Aided Lithography with Single Mask Implemented Lithographic Enhancement)). IDEALSmile demonstrated its significant potential for k/sub 1/=0.3 lithography of contact hole patterns. Since then, additional fundamental experiments, such as through-pitch performance, and process applications, were performed to verify the potential effects of IDEALSmile. We have now developed a new type of IDEALSmile by rearranging the dummy patterns and manipulating the diffracted light on the pupil plane. In this paper we will review the principle of IDEALSmile in detail and introduce the new IDEALSmile configuration.

Two models for partially coherent imaging

This paper discusses the physical difference between two image formation approaches for partially coherent imaging. In one approach, the pupil function is shifted according to illumination condition as in the transmission cross coefficient (TCC) approach, whereas in the other approach, the object spectrum is shifted. Although the two approaches result in identical images, they are built on distinct physical models. Eigenfunction analysis reveals that the TCC approach is built on an artificial optical model only for image calculation. Therefore, the two approaches are not interchangeable except for image calculation. Such an example is found in calculating the entropy in an imaging system.

Coherency matrix formulation for partially coherent imaging to evaluate the degree of coherence for image

This paper defines a matrix from which coherence property of imaging by partially coherent Koehler illumination is determined. The matrix termed coherency matrix in imaging system is derived by the space average of a product of a column vector and its transpose conjugate where each row of the column vector represents mutually incoherent light. The coherency matrix in imaging system has similar properties to the polarization matrix that is utilized for calculating the light intensity and degree of polarization of polarized light. The coherency matrix in imaging system enables us to calculate not only image intensity but also degree of coherence for image. Simulation results of the degree of coherence for image given by the coherency matrix in imaging system correspond to the complex degree of coherence obtained by the van Cittert-Zernike theorem.

Full-chip implementation of IDEALsmile on 90nm node devices with ArF lithography

Summary form only given. According to sizes dictated by ITRS roadmap, contact holes are one of the most challenging features to be printed in the semiconductor manufacturing process. To overcome this issue Canon, in 2002, introduced a new technology, entitled lDEALSmile1i2 (Innovative Double Effective source Aided Lithography with Single Mask Implemented Lithographic Enhancement), that was proven to be able to define contacts with high resolution and sufficiently large through pitch? process window using a binary mask, cheap and simple to be manufactured, modified illumination and single exposure, without any negative impact on throughput and no increase of cost of ownership, The technology was further improved in 2003 with the introduction of Enhanced-IDEALSmile4 that, in certain conditions, allows achieving even higher contrast, and increased DOF thanks to three beam interference obtained with special shifted arrangement of dummy patterns without modifying optimized illumination shape.