Research Of Characters Of Maskless Digital Lithography Based On 365nm LED Light Source

Since 1958,the United States has made the first successful use of lithography technology in manufacture of integrated circuit,lithography technology is developing.Lithography technology is used to make semiconductor devices and integrated circuits,which determines the development of semiconductor industry.With the increasing of the line width accuracy,the cost of traditional mask lithography is becoming higher and higher.Digital lithography technique based on the DLP projection technique using DMD instead of the mask as spatial light modulator.Becauce no need to make a mask for each lithography pattern,thus reduce the manufacturing cost of lithography,and surface scanning mode can greatly improve the production efficiency,digital lithography technique based on the DLP projection technique can achieve real-time,high efficiency and low cost of graphic transfer.The traditional light sources such as high-pressure mercury lamp or excimer laser,some light is expensive,some light is not enough environmental protection,some light is not enough energy conservation,and their volume is relatively large,it is difficult to realize the miniaturization of the lithography illumination system.And the new generation lighting source of UV-LED not only has the advantages of long life,low energy consumption,high efficiency,good safety,stable performance and so on.Compared to other traditional light sources,centimeter size of the UV-LED makes it an ideal light source for small lighting systems.In this paper,the optical system of digital lithography technique based on the UV-LED light source and the dynamic mask DMD are studied.The optical system is mainly composed of two parts.The first part is the illumination system,including the light source,the collimating unit and the uniform light unit,the other part is the projection system,which is also called projection lens.Firstly,the development process,structure and working principle of DMD are introduced briefly.Then,the gray level,structure and optical properties of DMD are studied.Secondly,we study the illumination system.The advantages of UV-LED light source are defined,and the characteristics of UV-LED light source are studied.Then,we analyze the pros and cons of the common alignment mode,introduce two kinds of common uniform device in Kohler illumination mode,understand the key parameters of the lighting system.Thirdly,select and take the lens as the collimating unit,fly's-eye lens as the uniform unit.In this case,365 nm LED is designed by using fly's-eye lens.The lens is arranged in a nearly hexagon array structure,which can basically cover the circular light.The nearly hexagon array can reduce the number of invalid lens compared with the traditional square structure,so that the lens can be more effectively used to develop uniform light efficiency.The illumination systems with nearly hexagon array and 9×9 square fly's-eye lens array are simulated respectively by software,and their irradiance maps are compared.Results show that the illumination system with nearly hexagon array is more uniform.Finally,the characteristics of the projection lens is studied.According to the lighting system and DMD,we design a matched projection lens group with Zemax software,the resolution can reach 2 ?m,NA is 0.158,magnification is-0.15,optical path difference is less than ?/20,distortion is less than 0.016%.And the illumination system designed with nearly hexagon array is combined with digital micro mirror device(DMD)and lithographic lens,and a digital lithography experiment with 2 ?m precision is carried out.It's found that the image surface illumination is uniform,line is clear and not disconnected.The effectiveness of the designed nearly hexagon array illumination system and the projection lens is verified.