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.

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With the next technology nodes 193nm lithography is pushed to its utmost limits. The industry is forced to print at low k1 factor which goes along with a high MEEF. Additionally, new blank materials are being introduced for smaller nodes. From 4x node and beyond, global CD uniformity on wafer is getting more critical and becomes key factor to ensure a high yield in chip production. Advanced process control is required and correction strategies are applied to maintain tight wafer CD uniformity. Beside other parameters, like scanner and etch process, mask CD uniformity is one main contributor to the intra-field CD on wafer. To enable effective CDU correction strategies it is necessary to establish a mask CD uniformity metrology which shows a good correlation to wafer prints. Especially for logic pattern mask uniformity measurements to control intra-field CD uniformity becomes challenging.In this paper we will focus on mask CD uniformity measurement for logic application utilizing WLCD, which is based on aerial image technology. We will investigate 40nm node and 28nm node gate masks using 6% MoSi phase shifting mask and MoSi binary mask respectively. Furthermore, we will correlate the mask CD uniformity data to wafer data to evaluate the capability of WLCD to predict the intra-field wafer CD uniformity correctly in order to support feedforward correction strategies. We will show that WLCD shows an excellent correlation to wafer data. Additionally, we will provide an outlook on logic contact-hole masks showing first CD uniformity data and wafer correlation data.

Continuously shrinking designs by further extension of 193nm technology lead to a much higher probability of hotspots especially for the manufacturing of advanced logic devices. The CD of these potential hotspots needs to be precisely controlled and measured on the mask. On top of that, the feature complexity increases due to high OPC load in the logic mask design which is an additional challenge for CD metrology. Therefore the hotspot measurements have been performed on WLCD from ZEISS, which provides the benefit of reduced complexity by measuring the CD in the aerial image and qualifying the printing relevant CD. This is especially of advantage for complex 2D feature measurements.Additionally, the data preparation for CD measurement becomes more critical due to the larger amount of CD measurements and the increasing feature diversity. For the data preparation this means to identify these hotspots and mark them automatically with the correct marker required to make the feature specific CD measurement successful. Currently available methods can address generic pattern but cannot deal with the pattern diversity of the hotspots. The paper will explore a method how to overcome those limitations and to enhance the time-to-result in the marking process dramatically. For the marking process the Synopsys WLCD Output Module was utilized, which is an interface between the CATS mask data prep software and the WLCD metrology tool. It translates the CATS marking directly into an executable WLCD measurement job including CD analysis.The paper will describe the utilized method and flow for the hotspot measurement. Additionally, the achieved results on hotspot measurements utilizing this method will be presented.