Research On Simulation Of Proximity UV-Lithography

UV-LIGA technology uses ultraviolet source instead of X-ray generated in synchrotron radiation accelerator, and thus obtains large aspect ratio microstructures at relatively cheaper price. It is of great potential of micro fabrication technology. Whereas pattern distortion caused by the diffraction affects its process of high accuracy. It makes some limitation in its practical application. In order to fabricate high-precision micro-structure of resist, a project supported by the National Natural Science Fund (NO. 60473133) is going along to research the countermeasure of error correction. As part of the project this thesis gives an in-depth investigation of the theoretical basic issues in proximity lithography. Based on the theory of partially coherent light the lithography process is studied, and a mathematical model for lithography simulation is created to analyze the photoresist pattern distortion. The research is mainly focused in the following aspects:In the lithography, light from extended quasi-monochronmatic light source transmits though the illuminating system, the mask, the gap between the mask and the resist, and at last reaches the substrate through the resist. So lithography simulation involves intricate multidisciplinary research. Optical propagation is one of the core theories. Based on the partial coherent light theory the mathematical model for proximity lithography simulation is built. The mutual intensity in the propagation process is analyzed. A precise model is established to calculate the coherence of the light on the mask. On this basis the distribution of light intensity on the resist is obtained by use of mutual intensity propagation theory. Rayleigh-Sommerfeld scalar diffraction theory is used to calculate the light intensity in the near-field and nonparaxial region. The result is of higher accuracy than Fresnel approximationIntensity distribution on the resist and its affection on the profile shape of the resist is analyzed. Several important factors, such as the gap between resist and mask, the mask shape error, the interaction between neighboring patterns, are discussed to evaluate their contributions on the diffraction intensity distribution. Some patterns with particular shapes are also analyzed. Various approximate methods for partial coherent light model and their limitations are discussed. How to improve computational efficiency under the permissible error is very important, especially for patterns of large area, and for some algorithms based on computational intelligent. A simple and effective approximation method of partial coherent simulation model is presented. With this method the four-dimensional integral is reduced to two-dimensional, thus the computational efficiency is greatly improved.The propagation of light in the absorption media is discussed to simulate the deep lithography, and a unified expression is given for the proximity and contact lithography. The reflection and refraction of light on the interface of the different mediums is considered. The transmission and reflection of light on the air/resist/substrate interface are studied to investigate how they affect on the intensity distribution in the interior of the resist. In this model, the extinction coefficient is changed with depth. All the considerations make the model more reasonable.Some work and ideas about a self developed MEMSCAD is discussed also. A collaborative platform for mask design, high-precision lithography 3D data reconstruction, high-fidelity 3D simulation, and visualization of the lithography errors in quantitative analysis are presented.Experimental results prove the validity of the method and make know that the intensity distribution can be accurately calculated to detect the graphics defects in lithography. The work provides a basis to explore methodology for error correction.