Optimizing reticle based high throughput i-line grayscale projection lithography for 3D structures with low surface roughness

In this work a reticle based i-line projection grayscale stepper lithography is applied, the patterning results are analyzed and the lithographic process is optimized to obtain low surface roughness grayscale pattern. Here the low contrast resist ma-P 1211G, one type of the ma-P 1200G grayscale resist series, from micro resist technology and tailored grayscale reticles from benchmark technologies are used. The spin curve, contrast curve and layer homogeneity of the resist were measured. A low surface roughness of the generated grayscale structures is important, because the roughness will be transferred during subsequent etching steps as pattern transfer. The impact of the pixel size (within the reticle) on the resist roughness and structure fidelity after resist development was investigated. Therefore, to measure the roughness of exposed and developed structures by AFM, dedicated roughness pads were integrated into the reticle design. After evaluation of the resist roughness a DOE study for different annealing steps in order to smoothen the resist surface after development was conducted. The ideal annealing or smoothening temperature was determined to reduce the resist roughness and preserve/ retain the structure fidelity at the same time.