Proceedings Paper193-nm lithography and resist reflow for the BEOL
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This paper presents data obtained in developing a lithography process for the metal and via levels using a first generation 193 nm stepper and first generation 193 nm photoresist. For the line/space levels, process windows obtained using chrome on glass (COG) and phase shift masks are presented. The effect of print bias (wafer - mask dimension) on process window is shown. At 280 nm pitch, process windows for COG and phase shift masks are compared. When using a phase shift mask to print 245 nm pitch, thinner resist is shown to increase the process window. Results are shown for printing 245 nm pitch with a COG mask. For contact hole and via levels, a resist reflow process was investigated with the same resist used for the line/space levels. In this process contact holes are printed larger than required and then reduced in size by heating the resist and causing it to flow. The results obtained with different mask dimensions and different wafer critical dimension (CD) targets are discussed. Results show that a process could be developed for printing 150 nm contact holes with 400 nm depth of focus at 5% exposure latitude. Finally, the through-pitch behavior as a function of reflow bake temperature is shown. Although the more isolated vias tend to show more shrinkage than the nested vias, it is shown that the deviation in size through pitch can be controlled by adjusting the mask dimension.