ADVANCED IMAGING AND OVERLAY PERFORMANCE OF A DUV STEP & SCAN SYSTEM

Transcription

1 ADVANCED IMAGING AND OVERLAY PERFORMANCE OF A DUV STEP & SCAN SYSTEM Jan van Schoot, Bert Koek, Chris de Mol, Peter van Oorschot. ASML Veldhoven, The Netherlands This paper was first presented at the Semicon/ Japan 97, SEMI Technology Symposium, December1997, Makuhari Messe, Chiba, Japan.

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3 ADVANCED IMAGING AND OVERLAY PERFORMANCE OF A DUV STEP & SCAN SYSTEM Jan van Schoot, Bert Koek, Chris de Mol, Peter van Oorschot. Abstract The ASML PASx5500/500 DUV Step & Scan system is being used in early production of next generation devices. Larger field size requirements and tighter overlay specifications have pushed the development of Step & Scan systems for optical lithography. In this paper, we present recently obtained imaging and overlay results from the PASx5500/500 DUV Step & Scan system. We will show that the /500 has mass production capabilities for both 0.25/0.22 µm and 0.18 µm device generations. Depth of focus (DoF) and CD uniformity results of 0.25 µm contact holes and 0.22/0.18 µm lines are shown. CD uniformity numbers below 10 nm across the field for 0.18 µm lines have been observed and nm over a focus range of 0.6 µm. For 0.22 µm dense lines, a common corridor DoF across the field (UDoF) of 1.6 µm was measured. The single machine overlay, being 36 nm, and matched overlay results between 50 and 70 nm are within the overlay requirements for 0.22 to 0.18 µm device technology. Finally, SEM pictures of 0.16 µm and 0.10 µm lines demonstrate that imaging, scan synchronization and vibrations are controlled extremely well in the PASx5500/500 DUV Step & Scan system. 1. Introduction Step & Scan lithography is the next generation of optical photolithography equipment. Larger field size, tighter design rules, smaller resolution and low operating costs are the main driving forces for the competitive semiconductor industry. In Step & Scan lithography, the image is not projected completely in one flash, as in Step & Repeat, but the image on the reticle is scanned by the illuminated slit and simultaneously projected on the scanning wafer [1,2]. Lower aberrations in a Step & Scan system, allowing reduced critical dimension and machine-to-machine matched overlay control, enable device manufacturers to produce future device generations with sufficient process latitude using optical lithography. The challenge in Step & Scan technology is to scan the reticle and wafer rapidly and accurately. Fast stages are essential for high productivity and, consequently, low operational cost. Accurate reticle and wafer stage synchronization and system vibration control at high stage speeds are required to print sub 0.25 µm features. In this paper, we will start with a theoretical analysis of the performance of the system with 0.22 µm dense lines and spaces. We optimized the and partial coherence (σ) for maximum DoF and best CD uniformity. The simulations are followed by experimental results. We investigate the imaging capabilities for the 0.25/0.22 µm (for example 256 Mb/P6) and 0.18 µm (1 Gb, P7) design rules. We compare Step & Repeat and Step & Scan systems. The CD uniformity and UDoF for 0.25 µm dense lines and spaces from a PASx5500/300 DUV Step & Repeat and a PASx5500/500 DUV Step & Scan are compared to each other. For the Step & Scan system, ED-windows, UDoF and CD uniformity through focus for lines and spaces with resolutions of 0.22 µm down to 0.18 µm are measured for several illuminator settings. In addition to dense lines and spaces, other geometries (contact holes, isolated lines and semi-isolated lines and spaces) are characterized and the results are compared to theoretical data. Ultimate resolution is shown with pictures of 0.16 µm and 0.10 µm lines and spaces. Overlay and matching data is presented. Because Step & Scan systems are to be operated side by side with existing Step & Repeat systems, data is shown with the PASx5500/500 matched to both to a PASx5500/300 4x DUV Step & Repeat and PASx5500/200 5x i-line Step & Repeat system. 2. Process window optimization It is generally known that the selection of and σ can have large effects on the imaging performance in advanced semiconductor applications [6]. With the improved resolution and the subsequent decrease of process windows, it becomes more and more important to use the available optical enhancement techniques (variable partial coherence, off-axis illumination, pupil filtering, phase shift masks etc.) to maximize the process window for a given application. Optimum settings depend on which process parameter is considered most critical, i.e. the process must be optimized for either depth of focus, exposure latitude (EL), CD uniformity etc. This section investigates how process parameter optimizations influence the and σ setting using simulations. The parameters used are listed in Table 1. 1

4 Parameter Three metrics are investigated: Value Lumped contrast (γ) 9.0 Table 1 Resist thickness µm Absorption 0.2 µm -1 Wavelength Model 248 nm High scalar Flare 2% Parameters used for the simulations. Simulations are performed with the lumped parameter model of Prolith 2 [4]. 1) Optimizing DoF at a given fixed exposure latitude One technique to examine imaging performance is to analyze UDoF values. This is a generally accepted method. The maximum DoF can be found with no requirements placed on exposure latitude. A more realistic approach is to assume an exposure latitude criterion. In these simulations, 10% is used. 2) Optimizing CD uniformity at a fixed focus range Another viewpoint is that a focus budget can be made, from which the practical maximum defocus situations, and, thus, the required UDoFs can be derived. Such evaluations [3] typically result in required focus latitudes of around 0.6 µm. Using this focus range, the CD uniformity across the image field can be optimized. The simulations are a good prediction for the CD uniformity over 0.6 µm focus range, as presented in the experimental sections. In our simulations, 0.2 µm for image plane deviation is assumed and hence a minimum DoF of µm is required. With this boundary condition, an optimization for CD uniformity can be made. Within our simulations, we assume that this point is reached when the exposure latitude over a focus range of µm, is at a maximum. 3) Optimizing CD uniformity with normal distributed energy/focus deviations In a normal production mode, the actual exposure energy and focus errors have a normal distribution. This can be simulated by Monte Carlo techniques [3]. The simulations incorporate a 6 sigma range of 14% on the energy distribution and 0.66 µm on the focus distribution which are realistic production values. Simulations are run to demonstrate the and σ parameter space for all three metrics, 0.22 µm dense lines and spaces and annular illumination with a ring width of 0.3 σ are used. The results are illustrated in Figures 1, 2 and 3 for metric 1, 2 and 3 respectively. As can be seen in Figure 1, if DoF is optimized, the optimum /σ combination has a tendency towards lower and extreme annular settings. In Figure 2, it can be observed that, as the CD uniformity is optimized according to metric 2, the extreme annular setting is still preferred, but the selected makes no significant difference. This is in contrast to the most production oriented metric 3, in which a clear trend towards high and very moderate annular settings is seen. The conclusion here is that the applicable evaluation metric for optimum exposure conditions should be chosen carefully because it can drive the optimum and σ settings to completely different values. σ outer Figure µm Dense Lines 10% Exposure Latitude (µm) Simulation of DoF at 10% exposure latitude for different and σ settings, annular illumination. 3. Experimental conditions Experiments were executed using the ASML PASx5500/500 DUV Step & Scan system. This system has a projection lens with a continuously variable in the range of The AERIAL illuminator [2] enables continuously variable partial coherence in the range of , and also continuous variable annular illumination. For experiments performed with annular illumination, the ring width was kept constant at 0.3 and the position of the ring was varied. The PASx5500/500 has been described in more detail by de Zwart et al [2]. APEX-E was used as the photoresist material for imaging dense and isolated lines, at a nominal film I ILL 2

5 thickness of 0.63 µm. A Shipley RTC top coat was applied with a thickness of µm. Contact holes were exposed in TOK DP015 photoresist at a film thickness of 0.68 µm. The lines and spaces were examined using an OPAL7830i automated top-down CD SEM, contact holes were analyzed on a Hitachi 8840 top-down CD SEM. The Hitachi 8840 SEM was used for the printed pictures of the contact holes. The top-down SEMs were operated at low voltage mode. Tilted pictures of the lines and spaces were obtained from a Philips XL50 high voltage SEM using gold coated wafers. Overlay was measured using the PASx5500/500 s metrology system and a KLA 5011 overlay measurement tool. σ outer Figure 2 Simulation of Exposure latitude at µm DoF for different and σ settings, annular illumination. σ outer Figure µm Dense Lines Exposure µm DoF (%) 0.22 µm Dense Lines CD uniformity 6 σ (nm) Simulation of CD uniformity for different and σ settings with annular illumination. A focus distribution of 6σ = 0.66 µm and an exposure distribution of 14% are used. I ILL I ILL Imaging Performance 4.1. Device generation micron To benchmark the imaging performance of the Step & Scan system with the current production standard, 0.25 µm imaging tests were executed on the PASx5500/500 and ASML s PASx5500/300 DUV Step & Repeat system [8]. This directly compares the scanning technique to the traditional full field technique. Table 2 shows a comparison between the /500 and /300 for UDoF and CD uniformity. Field size for comparing both systems is 22 x 22 mm 2 and the same reticle was used. Projection tool UDoF CD uniformity 0.6 um Step & Repeat (/300) 1.3 [8] Step & Scan (/500) Table µm dense lines and spaces imaging comparison between PASx5500/500 Step & Scan and PASx5500/300 Step & Repeat systems. CD uniformity data is shown at best focus (BF) and over a focus range of 0.6 µm. From Table 2, it can be seen that both systems have sufficient UDoF and CD control for 0.25 µm device technology. The PASx5500/500, however, has a larger UDoF, probably due to the lower aberrations in the Step & Scan system. The significantly smaller area of the projection lens actually used for imaging allows for a tighter aberration control. Aberration is also partially averaged out, due to the scanning principle. The CD uniformity difference between both systems is within the noise of the measurements. In section 4.2 it will be shown that the CD uniformity is dominated by the reticle contribution. Comparison of Table 2 to measurements performed on the /500 Step & Scan with 0.22 µm dense lines, as given later on in Table 3, show that the CD range does not increase if the entire imaging field of 26 x 33 mm 2 is used. The PASx5500/500 is specified at a resolution of 0.22 µm. In Figure 4, the experimentally measured depth of focus as function of and σ for dense features is shown. In Figure 5 the data of the isolated features is shown for conventional illumination. With annular illumination a similar flat response is observed. The larger DoF values are obtained for low and high σ values, which is in accordance with the simulations as shown in Figure 1. The experimentally determined DoF is shown for the condition when there is 10% exposure latitude. DoF at 2% and 10% exposure latitude, UDoF and the iso-dense 3

6 overlapping depth of focus (ODoF) values are summarized in Table 5. ODoF is important especially where isolated and dense features have to be printed at the same time as in embedded RAM or logic devices. Figure 6 shows the ODoF for 0.22µm dense and isolated features. Values around 0.9 µm are obtained for low and low σ. In a µm chip design rule, a typical contact hole size is 0.30 µm. The imaging performance of 0.25 µm contact holes has been investigated for different and σ settings. σ outer Figure 4 σ µm Dense Lines 10% Exposure Latitude (µm) Measurement of the DoF@10%EL with 0.22 µm dense lines and spaces for different and σ settings, annular illumination µm Isolated Lines 10% Exposure Latitude (µm) I ILL I ILL σ outer 0 0, Figure 6 σ 5 Figure µm Dense & Isolated Lines 10% Exposure Latitude (µm) Measurement of the overlapping DoF of 0.22 µm dense and isolated lines for different and σ settings, annular illumination Measurement of the DoF@10% EL with 0.25 µm contact holes for different and σ settings, conventional illumination. Figure 7 shows the experimentally obtained DoF as function of and σ, where the exposure latitude is 10%. The optimum DoF values were found for =0.50, σ=5. Similar measurements using annular illumination show an optimum DoF value also an of 0.50, σ inner =, σ outer = µm Contact Holes 10% Exposure Latitude (µm) I ILL I ILL Figure 5 Measurement of the DoF@10%EL with 0.22 µm isolated lines and spaces for different and σ settings, conventional illumination. 4

7 Away from the lens 1.4 µm DoF Towards the Lens BF BF BF BF BF Figure 8 SEM pictures of 0.22 µm dense lines and spaces. =0.54, σ inner =0.45, σ outer =. To show the actual quality of the image printed, sample photos were taken. Figure 8 shows SEM pictures of 0.22 µm dense lines. The images were taken at =0.54 with an annular setting of σ inner =0.45, σ outer =. This setting was found to be the optimum for DoF (see Figure 4). The figure shows five focus settings, best focus, -0.6 and -0.7 µm defocus and +0.6, +0.7 µm defocus. Figure 9 shows 0.25 µm contact holes exposed at the optimum optical settings for maximum DoF for both conventional and annular illumination. Imaging performance is shown at best focus and in maximum defocus. As explained in section 2, there can be different metrics for optimizing the imaging performance of a lithography tool. The above figures show the DoF performance for 0.22 µm features. Tables 3 and 4 show an overview of the measured CD uniformity for 0.22 µm dense lines, isolated lines and 0.25 µm contact holes. The reticles used for these experiments are specially designed to minimize the reticle CD variation contribution using the Picked CD technique [9]. The reticle CD range for the dense lines is 34 nm. The expected CD range at wafer level due to the reticle is (34 nm/4)*1.35=11 nm. The value of 1.35 is the litho factor and has been determined experimentally with a set of constant pitch, variable line width lines and spaces. A typical value for CD uniformity in BF is 13 nm so it is obvious that the reticle contribution of 11 nm is dominant in the observed CD range. This is consistent with the observations of 0.25 µm features on a /300 DUV Step & Repeat system as described by Ingen Schenau and Kuijten [5]. The isolated features on the reticle were defined in the same way as the dense, but the CD distribution across the reticle has not been measured yet. The reticle CD range for the contact holes was measured to be 37 nm at reticle level. The litho factor for the 0.25 µm dense contacts is 1.8 so the expected CD range at the wafer is 17 nm. So, for the contact holes, we can also draw the conclusion that the reticle CD contribution dominates. Away from the lens 1.7 µm DoF Annular illumination f Towards the Lens BF BF BF µm DoF Conventional illumination BF - Figure 9 BF BF SEM pictures of 0.25 µm dense contact holes. Annular illumination =0.50, σ inner =, σ outer =5. Conventional illumination =0.50, σ=5. 5

8 From Table 5 we can see that the UDoF values lie approximately 250 nm below the DoF values. This difference corresponds very well to the image plane deviation [2]. Setting CD unif DL [nm] CD unif iso [nm] um 0.54 / / * Table 3 CD uniformity measured over 26 x 33 mm 2 field for 0.22 µm dense and isolated features at best focus and over a focus range. *0.4 µm focus range used. Setting UDoF CD unif [nm] 0.4 um 0.6 um / Table 4 CD uniformity of 0.25 µm contact holes at best focus, over 0.4 µm and 0.6 µm focus range Imaging performance at 0.18 micron Research and development for shrink versions of the current 256 Mb generations and for pilot production of 1 Gb generations is in progress. The PASx5500/500 has been used in some preliminary 0.18 µm imaging. First, the linearity of the tool and process has been investigated. Figure 10 shows the CD linearity for the standard APEX-E process for both conventional and annular illumination, dense and isolated lines. From the graph, it can be seen that the PASx5500/500 prints the dense lines linearly down to 0.18 µm features within ±10% from nominal CD. The isolated lines are printed linearly down to 0.16 µm. In Figure 10, both the dense and isolated lines are printed with the same dose. A negative bias of 5% has been applied. The graph does not show the ultimate resolution of the tool being used. Smaller features and pitches can be printed when the exposure dose is increased and the process will be adapted to the higher demands. Figures 11 and 12 show the experimentally obtained depth of focus for 0.18 µm dense and isolated features as function of and annular ring position. The DoF values are shown for the condition where there is 10% exposure latitude. Figure 11 shows that larger DoF values are obtained for high and high σ which is in line with theoretical expectations. Setting Dense Lines Isolated Lines σ DoF@2%EL DoF@10%EL UDoF DoF@2%EL DoF@10%EL UDoF ODoF@7%EL 0.54 / / / / / Table 5 Different DoF values for 0.22 µm dense and isolated lines. 6

9 Figure 12 shows that the isolated line performance is rather flat around the data points. CD [nm] Isolated Lines. Size Linearity =0.63 σ=0.50/0.20 =0.63 σ= % -10% σ outer µm Isolated Lines 10% Exposure Latitude (µm) 0, I ILL I ILL Figure 10 Dense Lines CD nominal [nm] Size linearity of dense and isolated lines measured with an annular (=0.63, σ inner =0.20, σ outer =0.50) and conventional (=0.63, σ=0.63) illumination. Figure 12 Measured DoF@10% exposure latitude of isolated lines for different and σ settings, annular illumination. Also, the overlapping depth of focus (ODoF, defined as the overlapping region of the dense and isolated process windows, see Figure 14) has been measured. Figure 13 shows the ODoF for 0.18 µm dense and isolated features as function of and annular ring position. The ODoF values are measured at 10% exposure latitude. Maximum ODoF is obtained for high and low σ settings. The reason for this is that the iso-dense bias is around zero in this region. σ outer Figure µm Dense Lines 10% Exposure Latitude (µm) Measured DoF@10% exposure latitude of dense lines and spaces for different and σ settings, annular illumination. I ILL σ outer 5 0 Figure µm Dense & Isolated Lines 10% Exposure Latitude (µm) Measured ODoF between dense and isolated lines for different and σ settings, annular illumination. See text I ILL 7

10 The maximum ODoF for 0.18 µm dense and isolated lines is µm. This is the case where we applied a negative bias of 10%. Strategies for improving the ODoF by reticle bias and -σ optimization are described in detail by Vandenberge et al [6] and Rogoff et al [7]. Figure 15 shows SEM pictures of 0.18 µm dense and isolated lines. The images of the dense lines were taken at an of 0.62 and an annular setting of σ inner =, σ outer =5. This setting was found to be the optimum for DoF from Figures 11 and 12. For the isolated lines, the setting used was =0.54, σ=/0.45. The figure shows five pictures through the entire acceptable focus range. Initial 0.18 µm testing across the field has been performed to give an impression of the 0.18 µm imaging capabilities. A 22 x 22 mm 2 reticle with semi-dense and isolated lines has been used. As in the 0.22 µm application, CD uniformity was measured for 0.18 µm. Table 6 shows an overview of the measured CD uniformity for 0.18 µm semi-dense and isolated features. The semi-dense features have a line space ratio of 1:2.5 to represent a microprocessor application. Dose [mj/cm 2 ] I ILL Figure 14 7% EL isolated lines dense lines µm ODoF Defocus [µm] Definition of the overlapping depth of focus between 0,18 µm dense and isolated lines. 0.5 µm ODoF has been obtained with =0.63, σ inner =0.35, σ outer =. See text. Setting CD uniformity [nm] σ Semi Dense] um / / * Table 6 CD uniformity for 0.18 µm semi-dense (1:2.5) and isolated features at best focus and over a focus range of 0.6 µm. *Levenson type Phase Shift Mask. The CD uniformity of 0.18 µm dense and isolated features through focus is as good as the 0.22 µm features but CD control at best focus is better. The cause for this improved CD control is the better reticle quality. The reticle has been manufactured with extremely tight specifications for the 22 x 22 mm 2 field. These results again indicate that we can expect even better CD control for the 0.22 µm lines and spaces with superior reticles. This is in line with the previous conclusion that the reticle error is the main contributor to the CD uniformity at BF. This semi-dense reticle has also been used to measure the CD uniformity of the PASx5500/300. The limitations of imaging with the PASx5500/500 have also been investigated. Figure 16 shows an example of 0.16 µm horizontal and vertical dense lines. The exact DoF of these features was difficult to determine since the quality of the 0.16 µm features on the test reticle was suspect. Figure 17 shows an image of 0.1 µm semi-dense structures. These images were obtained using a Levenson type hard phase shift reticle. Figure 16 and 17 show the resolution quality in both horizontal and vertical direction, which demonstrates that imaging, scan synchronization and vibration of the PASx5500/500 are controlled extremely well. 8

11 Away from the lens 1.3 µm DoF Towards the Lens +BF BF BF BF BF µm DoF Figure 15 +BF BF BF BF BF SEM pictures of dense and isolated 0.18 µm lines. Dense lines: =0.62, σ inner =, σ outer =5. Isolated lines: =0.54, σ inner =0.45, σ outer =. 5. Matching Figure 16 Figure 17 Horizontal Vertical SEM pictures of 0.16 µm dense lines and spaces using a binary mask. =0.63, σ inner =0.45, σ outer =5 Horizontal Vertical SEM pictures of 0.1 µm semi isolated lines and spaces using a Levenson type phase shift mask. In addition to imaging, the overlay performance is also crucial for the applicability of the PASx5500/500 in production applications. The overlay requirements for 0.25 µm technology are approximately nm for critical layers and nm for non-critical layers. These will be reduced to nm for critical layers and nm for non critical layers for 0.18 µm technology. The single machine overlay of the /500 is the basis of all overlay and matching experiments. The short term overlay performance of the /500 has previously been reported by de Zwart et al [2]. Figure 18 shows the long term single machine overlay performance. The figure shows the results of nine wafers which were exposed over a period of three days. The overlay for 99.7% of the data points is better than 36 nm. The first Step & Scan systems delivered to customers are used in combination with existing Step & Repeat systems. To investigate the expected performance in the field, matching experiments have been executed between the /500 and the 5X PASx5500/200 i-line Step & Repeat and 4X PASx5500/300 DUV Step & Repeat systems. In these experiments, the intrafield parameters of magnification, rotation and translation and interfield parameters scaling, rotation and translation were corrected. 9

12 The /300 and the /500 both have a double sided telecentric lens with moveable lens elements, allowing on site aberration control. In these systems, additional third order lens distortion can be optimized. Furthermore, unlike the 5X /200 Step & Repeat, the /300 and /500, being 4X systems, do not have to take additional reticle error into account. This improves the intrafield matching performance. The matching performance between the two /500s benefits from the maximum flexibility and the low distortion of the Step & Scan systems. The overlay was measured over multiple wafers, with 20 exposures on each wafer, including eight edge dies. Matching to the Step & Repeat systems was executed over a 22 x 22 mm 2 field. The matching between two /500s was executed over the full 26 x 33 mm 2 field. Table 7 shows the typical matching results between the /500 and the /200 or /300. The reference systems in these experiments were systems used in a production environment. The set-up of these reference systems was typically matched to an internal fab standard. From the table, it can be seen that the additional correction parameters in the /300 and /500 and the use of the same reticle, result in a better matching performance. The matching performance is affected by the selection of the reference grid and the degrees of freedom to correct for grid errors. By selecting a more square grid as a reference, the expected matching performance is better. An example of a better grid is given in Figure 19, plot a. Matched overlay (nm) Table 7 PASx5500 /200 PASx5500 /300 PASx5500 / Maximum matched overlay of a /500 to two Step & Repeat systems and a Step & Scan system. This figure shows the non correctable image distortion over the whole 26 x 33 mm 2 field. The maximum error in the image field is only 12 nm. Based on this grid it can be expected that the matching between a /300 and /500 will improve by approximately 5 nm. Another contribution to the overlay in device applications is the change in image distortion due to different /σ settings. In the final adjustment of the lens at Carl Zeiss, Oberkochen, Germany, the effect of /σ on lens aberrations is minimized. This typically results in a small aberration difference between different illumination modes. Figure 19 shows a vector plot of the distortion difference between conventional and annular illumination. The maximum distortion difference between the two settings is only 5 nm. The measured system overlay using the two different illumination modes is 25 nm, which is very similar to the standard, one setting overlay. number of registrations dx dy Three day overlay I ILL Figure distortion difference [nm] Three day single machine overlay result. 10

13 Nominal Position Y (mm) Nominal Position Y (mm) nm Nominal Position X [mm] a Distortion b Distortion difference I ILL 6. Conclusions The PASx5500/500, DUV Step & Scan system has been characterized for the applicability in µm device applications. The image quality, DoF, exposure latitude, and CD uniformity of 0.25 and 0.22 µm features result in large process window for 256 Mb/P6 applications. A UDoF of 1.6 µm for 0.22 µm dense lines has been measured. Performance at 0.18 µm has also been investigated. DoF values for dense lines of 1.1 µm and for isolated lines of 0.7 µm have been observed. For 0.18 µm lines CD uniformity numbers below 10 nm across the field and between nm over a 0.6 µm focus range are demonstrated. Although more optical enhancement techniques can be applied, the process window for dense and isolated features is large enough for mass production application with 0.18 µm design rules. The resolution experiments show that features down to 0.1 µm can be resolved which proves that scan synchronization and vibrations of the system are controlled extremely well and do not affect the imaging quality even at these small features. The three day single machine overlay, being 36 nm, and matched overlay results between 50 and 70 nm are within the overlay requirements for 0.22 to 0.18 µm device technology. To keep sufficient overlay margin, system improvements, the development of new matching algorithms, process and reticle control have to be continued to follow the device technology road map nm Nominal Position X [mm] Figure 19 Distortion for =0.57, σ=(a) and the difference plot of the distortion for =0.57, σ= and =0.54, σ=/0.45 (b). Note the different scales. 11

14 ACKNOWLEDGMENTS The authors would like to thank all involved in the PASx5500/500 project. Thanks also to the prototype tester personnel of the PASx5500/500, without them, no system test could have been run. Special thanks also to Corine Buijk, Yin Fong Choi, Frank Duray, Mariette Hoogendijk, Koen van Ingen-Schenau, Ingrid Janssen, Ted der Kinderen, Toine de Kort, Angelique Nachtwein, Jan-Chris van Osnabrugge, Jenny Swinkels and Marty Vermeulen for generating an enormous amount of data. Also we would like to thank John Jeuken and Jeremy Collin for their assistance in the writing of this paper and Cecile van der Riet for the illustrations and preparation of the SEMI slide presentation. We would like to express our gratitude to Paul van Attekum, Donis Flagello, Paul Luehrmann, Danu Satriasputra, Steef Wittekoek and Gerard de Zwart for reviewing the paper and giving valuable comments. REFERENCES [1] M. van den Brink et al. Step-and-scan and step-and-repeat, a technology comparison, SPIE Vol. 2726, Santa Clara, March 1996, pp [2] G. de Zwart, M. van den Brink, R. George, D. Satriasaputra, J. Baselmans, H. Butler and J. van Schoot, Performance of a step and scan system for DUV lithography, SPIE Vol. 3051, Santa Clara, March 1997, pp [3] Kurt Ronse et al., Characterization and optimization of CD control for 0.25 µm CMOS applications, SPIE Vol. 2726, March 1996, pp [4] Chris A. Mack, Inside Prolith, Finle Technologies Inc., Austin, Texas, USA. [5] K. van Ingen Schenau and J-P.Kuijten, Investigation of key components to intrafield CD variation for sub-quarter micron lithography, OLIN-Interface, October 1997, pp [6] Geert Vandenberge et al., 248 nm lithography for the 0.18 µm generation OLIN interface, October 1997, pp [7] R. Rogoff, G. Davies, J. Mulkens, J. de Klerk and P. van Oorschot, Photolithography using the AERIAL illuminator in a variable wafer stepper, SPIE Vol. 2726, Santa Clara, March 1996, pp [8] J. Stoeldraijer et al., A high throughput DUV wafer stepper with flexible illumination source, Semicon/Japan, December [9] J. Waelpoel, J. van Schoot and A. Zanzal, Demonstrating next generation CD uniformity with today s tools and processes, SPIE Vol. 3236, Redwood City, September

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