Improving wafer level CD uniformity for logic applications utilizing mask level metrology and process

Critical Dimension Uniformity (CDU) is one of the key parameters necessary to assure good performance and reliable functionality of any integrated circuit (IC). The extension of 193nm based lithography usage combined with design rule shrinkage makes process control, in particular the wafer level CDU control, an extremely important and challenging task in IC manufacturing. In this study the WLCD-CDC closed loop solution offered by Carl Zeiss SMS was examined. This solution aims to improve the wafer level intra-field CDU without the need to run wafer prints and extensive wafer CD metrology. It combines two stand-alone tools: The WLCD tool which measures CD based on aerial imaging technology while applying the exact scanner-used illumination conditions to the photomask and the CDC tool which utilizes an ultra-short femto-second laser to write intra-volume shading elements (Shade-In Elements™) inside the photomask bulk material. The CDC process changes the dose going through the photomask down to the wafer, hence the wafer level intra-field CDU improves. The objective of this study was to evaluate how CDC process is affecting the CD for different type of features and pattern density which are typical for logic and system on chip (SOC) devices. The main findings show that the linearity and proximity behavior is maintained by the CDC process and CDU and CDC Ratio (CDCR) show a linear behavior for the different feature types. Finally, it was demonstrated that the CDU errors of the targeted (critical) feature have been effectively eliminated. In addition, the CDU of all other features have been significantly improved as well.