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Proceedings Paper

A systematic study of process windows and MEF for line end shortening under various photo conditions for more effective and robust OPC correction
Author(s): Qiang Wu; Jun Zhu; Peng Wu; Yuntao Jiang
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Paper Abstract

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.

Paper Details

Date Published: 21 March 2006
PDF: 12 pages
Proc. SPIE 6154, Optical Microlithography XIX, 61543X (21 March 2006); doi: 10.1117/12.655475
Show Author Affiliations
Qiang Wu, Shanghai Huahong NEC Electronics Co., Ltd. (China)
Jun Zhu, Shanghai Integrated Circuit Research and Development Ctr. (China)
Peng Wu, Shanghai Huahong NEC Electronics Co., Ltd. (China)
Yuntao Jiang, Shanghai Huahong NEC Electronics Co., Ltd. (China)

Published in SPIE Proceedings Vol. 6154:
Optical Microlithography XIX
Donis G. Flagello, Editor(s)

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