Study on the effect of polarized light on off-axis illumination space imaging

Modern microelectronics technology is developing toward ultra-fine integration, high-density, high-speed and ultra-high-frequency devices, which promotes the development of information highways, information exchange networks, global mobile communication technologies and multimedia technologies. In order to meet the needs of larger scale integrated circuit devices, and to advance the limits of lithography, and to extend the life of lithography, various methods have been proposed to improve lithography resolution and improve depth of focus. In the conventional method, a method of increasing the numerical aperture of the lithography objective lens and shortening the exposure wavelength is generally adopted, but as the resolution is improved, the depth of focus is rapidly shortened, which has an extremely adverse effect on optical lithography processing. In order to get better resolution and greater depth of focus, phase shift mask (PSM) technology, off-axis illumination (OAI) technology, optical proximity correction (OPC), standing wave effect correction (SWC), surface Imaging multi-layer resist technology, spatial filtering and other wavefront engineering methods, and many techniques have been used in projection lithography, which has achieved high resolution. Polarization is an important aspect of light. This paper mainly studies the influence of polarization characteristics of light on the imaging of off-axis illumination space.

It is well known that for light waves that are easily polarized, the distribution of point spread functions is asymmetrical, as in the case of high numerical aperture systems where the intensity distribution spreads along the direction of polarization.

The traditional model used for imaging simulation is a scalar diffraction model in the case of Fraunhofer's approximation. This model has not been applied to high numerical aperture optical lithography systems, and it is not able to handle the polarization characteristics of light. The expression of the electromagnetic field in the focal region of the lithography optical system has been studied by vector diffraction theory, and one of the formulas is applicable to the simulation. In this paper, the effect of the polarization characteristics of illumination light on spatial imaging in off-axis illumination is studied.

2 The number of imaging mathematical models can be expressed as: the polarization direction distribution, 3 simulation results After determining the polarization state of the incident wave, the polarization distribution of the diffracted light at the exit pupil can be determined by a specific optical system through ray tracing. . In order to simplify the tracing process, the following processing is performed: a meridional plane is assumed for each diffracted ray, and the polarization direction and the angle of the standard meridional plane remain unchanged throughout the optical system, in order to determine the polarization of each diffracted ray at the exit pupil The direction, the angle with the light is set to P/2. In the case of off-axis illumination imaging, the imaging consists mainly of - and 0 or 0 and + 丨 diffracted light. In the analog computational optical imaging, the numerical aperture NA used is 0.63, the exposure wavelength K is 365 nm, and the lithography objective magnification is U5. These parameters are fixed in all calculations; the mask pattern used is A one-dimensional line pattern consisting of equal lines; the illumination used is linearly polarized and perpendicular to the ey direction (as shown in the figure, the entire optical imaging system is the ideal optical system. Proceedingsof

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