MicroLED Device Fabrication And Its Application In Maskless Patterning

With the rapid development of integrated circuits(IC)and the continuation of Moore’s Law(ML)in the semiconductor industry,the integration level of integrated circuits is getting higher and higher,which means that on a chip of the same size,the integration size needs to be smaller and more for this reason,more masks are needed for lithography experiments when preparing highly integrated chips.However,the manufacturing cost of masks is very high,so researchers are working hard to study another lithography technology-maskless lithography,which uses an image generator’s virtual pattern in place of a mask.This dissertation mainly focuses on the maskless patterning technology of digital optical core and the fabrication process of light-emitting diode microdisplay(MicroLED).First,the development of maskless lithography technology at home and abroad is introduced,the advantages and disadvantages of maskless lithography technology and masked lithography technology are compared,and then several mainstream maskless lithography technologies are listed.Secondly,several common lithography light sources are compared,and then the front-end lighting system in the lithography system is introduced in detail,and the importance of the collimating lens and the homogenizing lens in the lighting system is expounded,and then the light source without these two kinds of lenses is explored.Photolithography experiments.Finally,the problem of manually adjusting the optimal exposure focal length(the distance from the projector’s objective lens to the photoresist surface)in the exposure experiment is studied.Then,how to make the display chip MicroLED is described in detail.The main technological process of chip fabrication and the corresponding instruments are introduced.The chip is turned on at a voltage of about 2.74 V.When the forward voltage is+4 V,the corresponding current is 109.70 mA and the current density is2.50 A/cm~2.The luminescence peak wavelength of the chip is 407 nm.When the current density is 9.00 A/cm~2,the external quantum efficiency(EQE)of the chip is0.36%.Finally,the cathode ray luminescence(CL)problem of the chip is analyzed.Furthermore,in the experimental exploration of maskless lithography,when the average power of the chip is 2.50 mW/cm~2,the optimal exposure time of the pattern lines is 40 s and the optimal development time is 35 s,and the circular exposure time is also analyzed.Pattern rasterization and spherical aberration.At the same time,the problem of the jagged edge of the image after exposure and development was deeply explored,and a new digital mask pattern was finally designed to reduce the jaggedness of the image.Finally,the grab-and-release method and the laser lift-off method are introduced,and then the two methods of transferring single pixels in the experiment are studied.The first is to use a crystal expander to expand the chip whose Si substrate has been completely removed;The second is to perform gold plating on the chip whose N-GaN layer has been cut,and then perform laser bonding on the Au-Au surface with the gold-plated Si wafer,and finally transfer a single pixel.