Research On Digital Lithography Optical System Based On DMD

As the core technology of semiconductor devices,lithography has experienced the development from contact lithography to scanning lithography.New lithography technology has been explored and how to reduce cost has become a research hotspot due to the high production cost.Digital lithography based on digital micromirror devices describes the use of DMD as a substitute for mask.Digital lithography does not need to make mask plates for lithography graphics every time,which reduces the cost of lithography,realizes real-time and efficient lithography,and improves the flexibility of lithography technology.After the working principle of DMD digital lithography system has been studied,the components of optical system have been determined to include three parts: illumination system,light splitting system and projection system.Fly's-eye lens is used as beam homogenizers and shaping devices in illumination systems.The Gauss light source is used as an analog light source with a wavelength of 405 nm.The illumination system of shaping uneven circular spot into uniform square spot is designed.The 9-point sampling method is used to measure the uniformity,and the simulated uniformity can reach 97.6%.According to the working characteristics of DMD,three total reflection prisms are designed to separate the "on" and "off" state beams of DMD.The designed total reflection prism can be used for projection lithography by vertically connecting the illumination path with the projection path,which is more convenient for the mechanical structure design when the two are integrated.The design theory of DMD spectroscopic prism is inherited and perfected.The design results are simulated and verified by optical software.It is shown that the separation of DMD "on" and "off" beams can be achieved by connecting the prism with the illumination system.A fixed-focus zoom lens that magnifies a 0.9-inch DMD by 10-14 times is designed to achieve a larger lithographic scale.The lens is a telecentric image system consisting of nine spherical mirrors.The working wavelength of the lens ranges from 385 nm to 415 nm,the focal length is 50 mm,the F number is 3,and the total length of the lens is 150 mm.The lens object distance and the corresponding image distance can be adjusted to achieve high precision,small format;low precision,large format lithography requirements.The image quality is evaluated by modulation transfer function,spot diagram,field curvature and distortion which proves that the image quality meets the design requirements.The tolerance analysis of the system is carried out.It is shown that the system has practical machinability on the basis of satisfying the imaging requirements.The designed lens is tested and the digital lithography system is assembled to verify and realize digital lithography.