608Chapter 9Figure 9.16 2009:Full-field exposure tool EUV1 by SELETE.The SEM image shows30-nm dense and isolated lines.NA =0.2539(source:SELETE).Figure 9.17 2010:Full-field exposure tool NXE:3100 by ASML.NA =0.25.40 The SEMimages show from left to right 27 nm L/S at 11 mJ/cm2 and 16 nm L/S at 33 mJ/cm2(source:ASML).two realized systems were installed at the research institutes IMEC andSEMATECH and used for early process and resist development.The systemsupported the 32-nm node.One year later,Nikon introduced their EUVIexposure tool.3 This system was installed at SELETE (Fig.9.16).In 2010 ASML introduced the NXE:3100 (Fig.9.17),40 a twin stagesystem with a NA of 0.25 targeted for early production.In total,six of thesesystems were built.The next generation was targeted for the 16-nm node andhas a NA of 0.33.With advanced off-axis illumination,the resolutions ofthese systems can be extended down to 13 nm.Going farther in resolutionrequires a larger NA.Figure 9.18 shows possible POB designs for the differentNAs.Table 9.3 provides an overview of the early full-field tools.Table 9.3 Overview of the early full-field toolsToolETS4-43ASML ADTNikonASML NXE:3100NA0.10.250.250.25Sigma0.70.50.80.8Field size24×3226×3326×3326×33Resolution70m32 nm30m22nmFundamentals of EUVL Scanners609NA0.25NA0.33NA >0.4,no obscurationNA >0.5,obscuredreduces angleperturered NADesignexamplesWatUs6.710.917B2W02006/069725Figure 9.18 Possible POB designs for different NAs(source:ASML).9.2.3 Full-field tools:current 0.33 NAThe current-generation EUV tools (Table 9.4)are intended for use in massproduction.With a NA of 0.33,they are capable of printing lines and spacesdown to 13 nm(Fig.9.19).The most recent system,the NXE:3400B(Fig.9.20),has an improved,loss-free highly flexible illuminator.More details are given inSection 9.3.2.2.Table 9.4 Overview of the current full-field production tools.The pupil fill ratio (PFR)describes the minimum relative area of the pupil that can be used without light loss.ToolASML NXE:3300BASML NXE:3350BASML NXE:3400BNA0330.330.33Sigma0.2-0.9/flexible0.2-0.9/flexible0.06-1/highly flexiblePFR40%40%20%Field size26×33mm226×33mm226×33mm2Resolution18 nm16m13 nmThroughput125 wph145 wphFigure 9.19 2013:Full-field exposure tool NXE:3350B by ASML.NA 0.33.45 Theexposures are carried out with a nanopartide resist.46 The SEM images show from left toright 16 nm L/S at 18.5 mJ/cm2 and 13 nm L/S at 31 mJ/cm2(source ASML).610Chapter 9Figure 9.20 2017:Full-field exposure tool NXE:3400B by ASML45 NA 0.33.Theilluminator has a smaller pupil fill ratio (PFR)to increase aerial image contrast (seeSection 9.3.2.2).The exposures are carried out with a nanoparticle resist(source ASML).9.2.4 Full-field tools:future 0.55 NATo further improve the resolution,the NA of future-generation EUV tools(Table 9.5)will be 0.55.47-51 This allows for a resolution of 8-nm lines andspaces.A further increase in the NA would result in large mask shadowingeffects.In order to circumvent this,the printable field size can be reduced to26 mm x 16.5 mm.The reason for this will be explained below.For any projection system with a given NA at the image plane (wafer),there is also a NA at the object plane (mask),where the relation between thesetwo NAs is given asNA waferN Amask=MAG’(9.6where MAG is the demagnification of the projection system.In all modernlithography scanners,MAG=4x,meaning that the image is a 4x reducedcopy of the image at the mask.Figure 9.21 a schematic overview of such asystem.In order to increase the NA,the NA at the mask will need to increase,absent a change in magnification.Given the so-called chief ray angle at object(CRAO)of 6 deg,the incoming and outgoing cones of light will overlap if theTable 9.5 The projected high-NA half-field production.ToolASML High-NANA0.55Sigma0-1/highly flexibleField size26×16.5mm2ResolutionThroughput185 wph