Feed-forward control for a lithography/etch sequence

Feed-forward and feedback control are used to compensate for variations caused by processes or equipment. The variations may be due to e.g. aging or shift and they may occur within a single process step or within a process sequence. The application of advanced process control methods offer the possibility to reduce deviation of process centering and, therfore, improving process capability. In this work, we investigated the feed-forward concept applied for a litography/etch sequence to control the deviation of the critical dimension (CD) of polysilicon wires an also the implmentation of feed-forward control into existing manu facturing execution systems. The process sequence investigated consists of pho toresist on a polysilicon layer and an intermediate antireflective coating (ARC). The aim was to reduce the variability of the polysilicon wire. The antireflective coating is structured by a dry etching step followed by etching the polysilicon layer performed in the same process chamber. The overetch of the ARC serves as process step where corrective actions for the development demensioncan be conducted. The CD is controlled after photoresist development and after etching of the polysilicon, but not after ARC etching. Therefore, a model was created to calculate the overetch time as a function of the development dimension and polysilicon dimension. Additionally, a concept was developed to integrate the feed-forward control into proprietary manufacturing execution systems used and allowing a fully automated compensation of the CD Variability of polysilicon. In summary, it could be proven that the intruduced feed-forward concept can be used to correct CD variability by a subsequent ARC etching process step.