Fractional Fourier Domain Filtering Applied To Improve Image Quality In Photolithography

With the development of micro-electronics and information processing, microelectronic devices with high density, high velocity and superfrequency have been get rid of the stale and brought forth the fresh, which vastly prompt the development of the micro fabrication technologies to the field of the hyperfine, and put forward the higher requirement for the resolution of the conventional photo 1 i tho graphy.We increased the resolution in the conventional photolithography at the expense of the focal depth. For the coordination of the contradictory, the wavefront technique has been regarded as an effective method to improve the image quality in photolithography by optimizing the image of the mask. It includes: pupil filtering, phase shift mask, off-axis illumination, optical proximity correction, and so on. We can improve the image quality by above method at a certain extent, however there are some limitations in technology and craft. So it is urgent to develop the wavefront engineering, and find a new technology to improve the resolution in photolithography.Fractional Fourier Transform(shortened as FRT) is the generalized Fourier Transform. Fractional Fourier Optical becomes a new ranch of the modern optics after the introduction of FRT from mathematics to optics. It is regarded as the development and extension of Fourier optics. It not only makes us look at optical propagation, optical imaging and information processing from a new point, but also provides us a new tool to treat these problems. It has more functions than the common Fourier transform because of the fractional order, which results in more applications in optics and information process. But at the present time the newresearches about Fractional Fourier Domain Filtering applied to improve image quality in photolithography have not been reported.Based on the theory of partial coherent diffraction and FRT, an approach for Fractional Fourier Domain Filtering is presented as a new wavefront engineering method to improve the image quality in photolithography. Compared with the common Fourier Filtering, Fractional Fourier Domain Filtering adds a new freedom. It can process the filtering operation in non-spectrum surface, which greatly improves the flexibility of the mask design, and which may be layed aside more properly and conveniently.In this paper, the theory and the method of Fractional Fourier Filtering applied to improve the image quality by the partial coherent illumination have been established. We encoded and optimized the filter to design the algorithm for filter. Computer simulation of complete simulation has demonstrated that the new filtering technique can significantly not only reduce the width relative deviation and the area relative deviation of the image, but also improve the resolution and the focal depth. It provides directive basis for the development of the experiment and the practicability of the technology.