Mr. Jun Zhu Profile

Jun Zhu

at Shanghai Hua Hong NEC Electronics Co Ltd

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Publications (5)

Proceedings Article | 27 March 2007 Paper

A study of double exposure process design with balanced performance parameters for line/space applications

Jun Zhu, Peng Wu, Qiang Wu, Hua Ding, Xin Li, Changjiang Sun

Proceedings Volume 6520, 65202H (2007) https://doi.org/10.1117/12.712793

KEYWORDS: Optical proximity correction, Photoresist materials, Photomasks, Line edge roughness, Binary data, Neodymium, Scanning probe lithography, Logic, Critical dimension metrology, Photoresist processing

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As the semiconductor fabrication groundrule has reached the 32nm node, in general there are several possible approaches for the photolithography solution such as the double exposure with 1.35 NA immersion, the high refractive index immersion, the extremely ultra violet (EUV) lithography, nanoimprint lithography etc. Among the four, the easiest approach seems to be the double exposure method at an effective numerical aperture (NA) of 1.35. However, there are still challenges in the design and optimization of the process, such as, the use of appropriate illumination condition, the choice of a good photoresist, and the design of an optical proximity correction (OPC) strategy. Besides these considerations, there is a question as whether we really need the double etch process. To study the double exposure mechanism, we have used a 248 nm deep-UV exposure tool and several well chosen photoresist (one is for Space application and the other is for Line application) to study the photo performance parameters in the merge of two photo exposures. At a numerical aperture (NA) around 0.7, the minimum groundrule we can achieve is the one for a 75 nm logic process with minimum pitch around 220 nm. One approach will be that the features with pitches wider than 440 nm are completed in a single exposure, which includes various isolated lines and spaces, line and space ends, two-dimensional structures, etc. This strategy essentially puts the single exposure pattern under the 0.18 um logic like pitches where mild conventional illumination can produce a balanced performance. Under typical illumination conditions, the photolithographic process under 0.18 um like ground rule is well understood and the optical proximity correction is not complicated. The remaining issues are in the dense pitches, where the double exposure kicks in. We have demonstrated that the double exposure with single development can achieve a process window large enough for a 75 nm logic like process and the OPC behavior such as line through pitch is manageable although OPC correction strategy may require substantial improvement to accommodate two individual exposures. In this paper, we will demonstrate the result of our study of the basic photolithographic performance indicators, such as the exposure latitude (EL), the depth of focus (DOF), the CD through pitch, the line edge roughness (LER) and the mask error factor (MEF) for the optimized process. And we will discuss the choice of photoresists for this special application. It seems that a photoresist with a balanced performance for both the line and space is necessary to realize a good double exposure process. In this paper, we will also present our simulation result of effective resist diffusion length to explore the limit of such approach.

Proceedings Article | 26 March 2007 Paper

The improvement of photolithographic fidelity of two-dimensional structures through double exposure method

Qingqing Wenren, Hua Ding, Xin Li, Changjiang Sun, Jun Zhu, Qiang Wu

Proceedings Volume 6520, 65202I (2007) https://doi.org/10.1117/12.711979

KEYWORDS: Semiconducting wafers, Photomasks, Lithium, Optical proximity correction, Diffusion, Electroluminescence, Photoresist materials, Silicon, Point spread functions, Optical lithography

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Proceedings Article | 26 March 2007 Paper

A study of process window capabilities for two-dimensional structures under double exposure condition

Qiang Wu, Peng Wu, Jun Zhu, Hua Ding, Xin Li, Changjiang Sun, Chaoqun Peng

Proceedings Volume 6520, 65202O (2007) https://doi.org/10.1117/12.712089

KEYWORDS: Photomasks, Semiconducting wafers, Diffusion, Lithium, Optical proximity correction, Critical dimension metrology, Photoresist materials, Testing and analysis, Point spread functions, Electronics

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Proceedings Article | 21 March 2006 Paper

A systematic study of process windows and MEF for line end shortening under various photo conditions for more effective and robust OPC correction

Qiang Wu, Jun Zhu, Peng Wu, Yuntao Jiang

Proceedings Volume 6154, 61543X (2006) https://doi.org/10.1117/12.655475

KEYWORDS: Diffusion, Point spread functions, Scanners, Photomasks, Semiconducting wafers, Optical proximity correction, Photoresist processing, Optical lithography, Image resolution, Electronics

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Line end shortening (LES) is a classical phenomenon in photolithography, which is primarily caused by finite resolution from the optics at the position of the line ends. The shortening varies from a couple tens of nanometers for processes with a k1 around 0.5 to as much as 100 nanometers for advanced processes with more aggressive k1 numbers. Besides illumination, the effective resist diffusion has been found to worsen the situation. The effective diffusion length for a typical chemically amplified resist, which has been demonstrated to be critical to the performance of the photolithographic process, can be as much as 30 to 60 nm, which has been found to generate some extra 30 nm LES. Experiments have indicated that wider lines have less LES effect. However, under certain CD through-pitch condition, when the lines or spaces are very wide, the opposing line ends may even merge. Currently, two methods have been widely used to improve the situation. One method to fix this problem is to extend the line ends on mask, or to make them move closer toward each other to compensate for the shortening. However, for a more conservatively defined minimum external separation rule, this method itself may not be enough to fully offset the LES. This is because it has been found that there is a limit when the line ends are too close to each other on mask, any perturbation on the mask CD may cause line ends to merge on wafer. The other way is to add hammerheads, or to add wider endings. This is equivalent to the situation of an effectively wider line ends, which has less shortening effect and can also live with a rather conservative minimum external separation. But in some design, this luxury may not have room to implement, i.e., when the line ends are sandwiched by dense lines with minimum ground-rules. Therefore, to best minimize the effect of LES or to completely characterize the LES effect, one will need to study both the process window and mask error factor (MEF) under a variety of photo process conditions, such as, illumination conditions and resist parameters. However, no such systematic study has been reported so far. Our data indicate that the better the latent image contrast, the better the control of line end shortening. In this paper, we will present our systematic studies in the effects of illumination condition and resist parameters to the behavior of LES.

Proceedings Article | 20 March 2006 Paper

A systematic study of the dip in the CD through-pitch curve for low-k1 processes

Jun Zhu, Peng Wu, Yuntao Jiang, Qiang Wu

Proceedings Volume 6154, 61543P (2006) https://doi.org/10.1117/12.655470

KEYWORDS: Scanners, Diffusion, Photomasks, Critical dimension metrology, Semiconducting wafers, Optical proximity correction, Deep ultraviolet, Tolerancing, Bismuth, Photoresist processing

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Optical proximity correction has been widely used to correct line width variation in various different environments. The most important correction will be the CD through-pitch variation. For deep-UV (DUV) photo processes, it is observed that the CD will have a reduced trend at certain intermediate pitch range around 1.1 to 1.4 wavelength / NA (numerical aperture), also called "forbidden pitch". The process windows within this pitch range are small. In this case, even though we can use OPC to print the CD correctly, the process window can still be limited, which can generate a bottleneck for the entire process. In order to make OPC more effective, we find it necessary to be able to design an optimized process with enough process windows for all pitches. Although this may mean that we need to map out the entire parameter space spanned by relatively unknown parameters in resist, exposure tool quality, mask tolerance, etc, recent developments in the understanding of the effect of illumination selection, scanner lens aberration, and resist blur have provided us with new hints in realizing it. Such new developments include the optimization of off-axis illumination (OAI) condition, the characterization of the effect of lens aberration, and the selection of resists with appropriate effective acid diffusion length. We have studied the effect of illumination, lens aberration, and resist diffusion to the CD and process window at the above described intermediate pitch range both in theory and experiment. We have found that the effective resist diffusion, whose range is from 10nm to 50nm, can affect the process window at the intermediate pitch range, to as much as a few tens of nanometers. We will show that, in general, longer diffusion correlates to a deeper "dip". However, according to the experience in the use of photo resists, short diffusion length can also affect process window through the reduction of depth of focus. Therefore it is important to find an optimized resist diffusion length under various ground-rule and illumination conditions. But there has been no studies reported so far as to how much diffusion that can be tolerated for a given process at the intermediate pitch range. We have also performed experiments on the effect of the scanner lens aberration, we found that the lens aberration, which may be largely ignored in the past, may affect the process performance, causing mask error factor to rise significantly. In this paper, we will present the result of our experiments and theoretical investigations in how much resist diffusion and lens wave front error that can be tolerated for a given photolithographic process with certain CD tolerance. Insight will be provided for the choice of illumination conditions, resolution enhancement techniques, and the resist in realizing the best CD through-pitch performance under any given ground-rule condition.

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