For immersion lithography with aggressive polarization illumination settings, it is important to newly construct two
systems for diagnosing lithography tools; Stokes polarimetry of illumination and Mueller matrix polarimetry of
projection lenses. At the SPIE conference on Optical Microlithography XXI in 2008, the authors had already reported on
the former Stokes polarimetry. True polarization states of several illumination settings emerged. On the other hand, the
latter Mueller matrix polarimetry is thought more complicated than the Stokes polarimetry. Therefore, the Mueller
matrix polarimetry is reported separating into two papers. A theoretical approach to realizing the polarimetry has
reported at the SPIE conference on Lithography Asia 2009.
The test mask for the Mueller matrix polarimetry also comprises thin-plate polarizers and wide-view-angle quarter-waveplates,
both which are developed by collaboration with Kogakugiken Corporation in Japan. Mueller matrices of the
sample projecting optics are reconstructed by sixteen measurements of Stokes parameters of a light ray that reaches the
wafer plane though the test mask and the projecting optics. The Stokes parameters are measured with a polarization
measurement system already equipped on a side stage lying at the wafer plane. It took about seven hours to capture all
the images at five image heights within the static exposure field. Stokes parameters are automatically calculated from the
images and outputted from the lithography tools as a text file, and Mueller matrices are calculated by homebuilt software
in a short time. All the images were captured under the identical illumination condition that the tool manufacturer calls
It will be required for more accurate lithography simulation of complicated mask patterns then ever, under hyper-NA
(numerical aperture) projection lens and aggressive small-aperture polarized-light illumination, to construct two systems
of polarimetry; one is polarimetry for illumination, and the other is Mueller matrix polarimetry for projection lenses. The
former polarimetry already reported by the authors is necessary for us to appreciate how the true polarization state of
illumination is. The polarimeter mask described in the paper determines illumination polarization states by Stokes
parameters. The latter polarimetry is the main subject of this paper. A Mueller matrix is a translation matrix of the input
Stokes parameters to the output Stokes parameters. With the full elements of the Mueller matrix of a projection lens, the
Stokes parameters of a light at the wafer plane can be easily predicted from the Stokes parameters of any illumination
conditions. This paper proposed a new method of Mueller matrix polarimetry and a monitor mask used for 193-nm
immersion lithography tools with a polarization monitor at the wafer plane.
Fluoropolymers have been successfully utilized for pellicle manufacturing in 248 and 193nm lithography. Moreover, the pellicle using such fluoropolymers will make a large contribution to the development of 193nm immersion technology that is now expected as NGL for 65nm and 45nm node. On the other hand, 157nm lithography is also considered to be a desirable solution as a future manufacturing technique. However, no fluoropolymers show good laser durability to 157nm irradiation. This is one of major obstacles for implementing 157nm lithography. It follows that the purpose of this research is to find out a polymer that has outstanding durability, and would therefore promote wider use of the 157nm technology. Through this research, we had synthesized some kinds of fluoropolymer platform and investigated their durability. From the investigation, we have found several criteria to control their photo-induced degradation. Based upon these criteria, we have synthesized several new fluoropolymers and investigated their durability. As the result of these evaluations, these polymers showed good initial transmission as expected. Moreover, some polymers showed good mechanical durability when exposed to over 100J/cm2 irradiation. In addition, some new copolymers between monomer containing tert-hydrogen and perfluorinated monomer showed poor mechanical durability, however the polymers showed higher transparency during irradiation. To investigate these phenomena, we have analyzed these polymers using FT-IR and XPS. From these analyses, we estimate and propose possible degradation mechanism of these polymers.
We reported the Guideline(Ver. 1) of Reticle Data Management(RDM) Activity in 2001. Among we have been focused SoC(System on Chip) Business, we have been improved the efficiency over Design technology, Mask manufacturing and Wafer manufacturing. Especially, these subjects have been the lithography Cost including Reticle Cost, shorter life cycle of product, more difficult technique, lower cost and shorter total TAT from design to chip shipping. Guideline Ver 1.0 announced the standardization of interface contents over Design to Mask manufacture, and to wafer manufacture. Guideline Ver 2.0 will announce this RDM activity has been developed the optimization of a new engineering chain management in addition to the pattern data and the linkage to EDA in 2003.
Measurement by AIMS is the final step of mask defect control, and its accuracy is the critical issue to make guaranty and improve the mask quality. AIMS157 has developed by Carl Zeiss SMS GmbH and is expected to make a contribution to accelerate the 157nm lithography technology development. AIMS157 has been challenging to solve 157nm specific optical issues with accuracy for 65nm node photomask specifications. This paper discusses the defect measurement by AIMS157. Evaluation using programmed defect mask, repeatability is analyzed changing the optical parameters. Static and dynamic measurements were evaluated and the result shows the improved accuracy. It shows the possibility to be applied on 65nm node and smaller feature size.
We reported the Guideline (Ver.1) of Reticle Data Management (RDM) Activity in 2001. While focusing on SoC (System on Chip) business, we have improved the efficiency in design technology, mask manufacturing and wafer manufacturing. Especially, these subjects have been the lithography costs including a reticle cost, a shorter life cycle of products, more difficult techniques, a lower cost and shorter total TAT from design to chip shipping. The Guideline Ver1.0 announced the standardization of interface contents from design to mask manufacture, and to wafer manufacture as well. According to the Guideline Ver2 in 2003, RDM activity has developed the optimization of a new engineering chain management that added the pattern data and the linkage to EDA. The unique characteristics of standardization proposed in Ver2 is that apart from standardization of the data format of the pattern data itself, expression of referencing pattern data and other additional information that are associated in case pattern data is utilized should be standardized. The difference between "expression" and "format" could be understood. These expressions include knowledge, view, property for retrieve, annotation, reference and relation about pattern data. These relations will be considered from a user's view of utilizing pattern data. The purpose of this expressions is to combine various standards relating to reticle. For example the linkage between RDM and UDM that is standardization of a data model relating to EDA tools and their applications is assumable. These two layers of standardization will make creative associations of applications possible.
In modern mask manufacturing, a successful defect mitigation strategy has been become crucial to achieve defect free masks for high-end lithography. The basic steps of such a strategy include inspection, repair, and subsequent post-repair qualification of repair sites. For the latter task, actinic aerial image measurements have been proven to be the technique of choice to assess the printability of a repaired site. In the last three years, International SEMATECH in cooperation with Infineon/AMTC-Dresden and SELETE, funded a joint development project at Carl Zeiss to develop an AIMS tool operating at the 157nm wavelength. The three beta tools were shipped in 2003 to the three beta customer sites. In this paper are presented the first results obtained with these beta tools, including measurements on binary as well as alternating phase shift masks. The technical properties of the tool were discussed with regards to the capability of the tool for defect qualification on photomasks. Additionally, preliminary results of the evaluation of alternating phase shift masks will be discussed, including measurements performed on dense lines-and-spaces structures with various pitch sizes.
At the panel discussion of Photomask Japan 2003, we discussed about Mask cost and specification. The topics are (1) Mask price trend and its impact, (2) How to reduce the mask costs; solutions from a mask shop, mask writing tool and mask inspection tool 3) Partnering mask suppliers with mask users; reasonable mask specification and OPC strategies. The choice of DUV laser writer instead of e-beam writer is one solution for reduction of mask cost. The continuous improvement of e-beam writer and resist sensitivity for high throughput is another solution. The partnership between designer, EDA vender, mask maker and wafer lithographer becomes more important.
Direct phase-shift measurement is one of the key technologies to realize Phase-Shift-Mask (PSM) application. Most mask makers are developing practical PSMs for 157nm lithography. Final tuning of the optical parameters and quality assurance of them require accurate measurement tool of phase-shift and transmittance with 157nm light
illumination. In this paper, we will report the development of the system, which measures the phase-shift and transmittance of 157nm PSM at wavelength. This system has a 157nm F2 laser as a light source of the illumination and CaF2 optics with a CCD camera for the imaging. Key component is the interferometer, which has a function of lateral image shearing and phase modulation. The same technology is used in the current UV and DUV tools already exist. N2 purge and vacuum environments are newly introduced for the optical path to minimize attenuation of 157nm light by O2 and H2O. A fluctuation of the attenuation in the optical path significantly affects the short-term measurement repeatability. A new measurement algorithm, which uses two measurement spots on a PSM image, gives better repeatability than using single measurement spot under such unstable condition. Because most fluctuations are common elements to both of the two spots, they can be canceled out by the new calculation algorithms for phase-shift and transmittance measurements. The system with new techniques shows enough performance for the requirement of 157nm PSM measurements with new techniques.
Because 157 nm light energy is two or more times of C-C bonding energy, the main bonding of organic materials, pellicle membrane material decomposes if it absorbs light at 157 nm. Therefore, in order to ensure the durability of the pellicle membrane, it is very important that the membrane material absorbs 157 nm light as little as possible. We researched high transmittance polymers at 157 nm by using simulation technology. In conclusion, we estimated that polymers with high transmittance at 157 nm are possible, and several companies were asked to develop it. As a result, we obtained a polymer in which 157 nm transmittance is 98.5% at 0.8 um [157 nm absorbance is 0.008 um-1, 10 base] from Asahi Glass Co., Ltd. We carried out various 157 nm irradiation tests by using the above polymer, and obtained the result showing durability of 15 J/cm2 in nitrogen + 1000 ppm oxygen environment. Furthermore, we examined the environment during F2 Excimer Laser irradiation and found that transmittance loss of membrane and also oxygen addition quantity to irradiation environment may be improved substantially by adopting irradiation environment of Helium.
The challenge to achieve an early introduction of 157 nm lithography requires various advanced metrology systems to evaluate the 65 nm node lithography performances, equipments and processes. Carl Zeiss AIMS tool based on the Aerial Image Measurement Software is the most promising approach to evaluate the mask quality in terms of aerial image properties, in order to assess post repair quality. Selete has joint activities with Carl Zeiss, International SEMATECH and Infineon to accelerate the development of an AIMS tool operating at the 157 nm wavelength. The alpha tool phase of the project has been completed, and beta tools are currently being built. This paper is discussing the results from measurements on the alpha tool of some 157 nm attenuated phase shift masks (Att-PSM). Resolution results and CD evaluation with respect to these measurements will be presented.
Carl Zeiss is currently in the final phase of an AIMS 157 development program in cooperation with Selete, Infineon and International SEMATECH. Based on Carl Zeiss' proven AIMS (Aerial Image Measurement System) technology, the new tool can optically emulate the aerial image generated in any given 157 nm scanner. Beta tools will be shipped throughout 2003. In this work the AIMS fab 157 hardware concept will be described. Latest measurements show that
compared to first measurements CD repeatability and illumination uniformity could be significantly improved.
We reported the Guideline(Ver.1) of Reticle Data Management (RDM) Activity in 2001. Among we have been focused SoC(System on Chip) Business, we have been improved the efficiency over Design technology, Mask manufacturing and Wafer manufacturing. Especially, These subjects have been the lithography Cost including Reticle Cost, shorter life cycle of product, more difficult technique, lower cost and shorter total TAT from design to chip shipping. Guideline Ver1.0 announced the standardization of interface contents over Design to Mask manufacture, and to wafer manufacture. Guideline Ver2.0 will announce this RDM activity has been developed the optimization of a new engineering chain management in addition to the pattern data and the linkage to EDA in 2003.
The worldwide first Aerial Image Measurement System (AIMS) for 157 nm lithography has been used to measure binary chrome and attenuated phase shift masks at 157 nm wavelength. The AIMS measurements were done for line structures from 200 nm up to 400 nm and for 500 nm contacts. Through focus series have been conducted to calculate the process windows for various structures and feature sizes.
We have developed a new mask patterning system, which can fabricate 130nm generation masks by means of a stitching exposure technique. We call this system the Photomask Repeater (PR)1,23,4. The PR is a 5x i-line stepper modified for mask manufacturing with a field size of 22x22mm in a single exposure. However, the device size on a 4x mask is larger than 22x22mm. Furthermore, excellent mask CD uniformity is required. For this purpose the exposure field size was extended with the use of “seamless stitching technology”. This is clearly the key to obtaining a practical, accurate mask patterning system. Results have been achieved on masks with this system showing CD variation of less than +/- 7nm at a stitching area by means of a “gradation filter”. Moreover, overall CD uniformity is 10.36nm (3?), while image placement accuracy is 17.8nm (3?) and 2nd alignment accuracy is 24.1nm (3?). PR is an attractive system for System on Chip mask manufacturing, and is also effective in reducing Turn Around Time.
A Device mask of 180nm generation was fabricated by Photomask Repeater system and the performance of it proved to be high by the results of fabricated mask. Great margins between the results of the fabricated mask and specifications suggest that lower graded masks can be used as master masks. From this point of view, error budgets were estimated about CD uniformity and pattern placement. The required specifications for master mask were estimated for 180nm and 130nm lithography. In CD uniformity the specification is 50nm(3?) for 180nm and 30nm(3?) for 130nm lithography. In pattern placement the specification is 75nm(3?) for 180nm and 50nm(3?) for 130nm lithography. In defect size the specification is lOOOnm for 180nm and 900nm for 130nm lithography. The requirements of master mask are rather rough even for 130nm lithography and enough realistic.
Proc. SPIE. 4066, Photomask and Next-Generation Lithography Mask Technology VII
KEYWORDS: Lithography, Kinematics, Scanning electron microscopy, Printing, Photomasks, Optical proximity correction, Critical dimension metrology, Semiconducting wafers, System on a chip, Process engineering
New pattern generation system, Photomask Repeater, based on i-line stepper has been developed. This system can transfer device patterns from master masks onto a photomask plate with 22mm field size. To print a chip larger than the 22mm field, stitching technology has been developed. Critical dimension error in the region where fields are stitched is the key issue of this technology. Quantification of critical dimension deviation induced by field misplacement was carried out by calculation. Introducing exposure dose gradation, it was reduced less than 1.5nm. From measurements of a real exposed mask this technique proved to be able to stitch fields seamlessly. Major two specifications, pattern placement accuracy and critical dimension uniformity, were evaluated. Both specifications required for 150nm photomasks were fully satisfied. Availability of the photomask repeater to memory device and system on chip is discussed.
We have developed a new reticle exposure system, which can fabricate 150nm generation masks by means of a stitching exposure technique. We call this exposure system the Photomask Repeater, or high accuracy repeater (HR). HR is a modified i-line stepper for mask manufacturing with a field size of 22 by 22 mm in a single exposure. However, the device size on a 4x mask is larger than 22 by 22 mm. Furthermore the improvement in mask CD uniformity is required. For this purpose the exposure field size was extended with the use of 'seamless stitching technology'. This is the key to obtaining a feasible exposure system with the use of this method. Results have been achieved with this system showing CD variation of less than +/- 5 nm across a 1D seam band by means of a 'gradation filter'. Moreover, overall Cd uniformity is less than 13nm, while image placement accuracy is less than 24nm. HR is an attractive system for SoC mask manufacturing, and is also effective in reducing TAT.
To extend the life of photolithography, it has been proceeded the development of the strong PSMs which has no printing 'phase shifter' defects. At PMJ '98 a defect inspection algorithm for phase shifter defects of 60 degrees on i-line multi-phase alternating PSMs was discussed. At BACUS '99, a defect printability and inspection sensitivity of multi-phase shifter defect for KrF exposure had also discussed. It was reported that the inspection tool combing \9MD84SR and STARlight had enough sensitivity for quartz bump defect that caused +/- 10 percent CD-error on 150nm L and S pattern. But, the delay of ArF exposure tool and process required DUV low-k1-lithography for next generation devices. And the, we tried to evaluate defects printability and inspection sensitivity for Logic-Gate pattern mask, that lien width is narrower than the line width evaluated by precede researchers.
New pattern generation system, Photomask Repeater, based on i-line stepper has been developed. This system can transfer device patterns from master masks onto a photomask plate with 22mm field size. To print a chip larger than the 22mm field, stitching technology has been developed. Critical dimension error in the region where shots are stitched is the key issue of this technology. Quantification of critical dimension deviation induced by shot misplacement was carried out by calculation. Introducing exposure dose gradation, it was reduced less than 1.5nm. Form measurements of real exposed mask this technique proved to be able to stitch shots seamlessly. Major two specifications, pattern placement accuracy and critical dimension uniformity, were evaluated. Both specifications required for 150nm photomask were fully satisfied. Availability of the photomask repeater to memory device and system on chip is discussed.
Defect specifications were studied for 0.200 and 0.175 micrometer rule memory cell patterns. Furthermore, we evaluated whether current inspection systems were capable of satisfying the defect specifications. For our evaluation, test masks with programmed defects in 0.200 and 0.175 micrometer rule memory cell patterns were fabricated using a variable shaped electron beam writing system and reactive ion etching. Recently, 0.250 micrometer rule devices have entered the mass- production phase using the defect specification based on the SIA roadmap. Accordingly, we assumed that the ratio of CD variations, corresponding to the defect size based on the SIA roadmap, to nominal sizes has no influence upon action of devices for 0.250 micrometer rule devices. Then, we also assumed that the ratio of CD variations has no influence upon action of not only 0.250 micrometer rule devices but also 0.200 and 0.175 micrometer rule devices. For 0.200 and 0.175 micrometer rule memory cell patterns, defect specifications were obtained by lithography simulations and exposure experiments for the criteria of the ratio of CD variations based on the assumption. We also evaluated whether current inspection systems were capable of satisfying the defect specifications.
In electron beam writing with high accelerating voltage on photomask blanks, resist heating effect, which is the main factor of CD error in a localized area, is one of the serious problem that must be solved or ameliorated. In this study, the dependence of CD error on the types of resists and the dependence of CD error on the writing conditions of EB writer, were investigated. In this experiment, ZEP7000 (Nihon Zeon), a typical standard of non-chemically amplified resist for electron beam and two chemically amplified resists (CARs) were selected. As a result, the CD error caused by the resist heating effect for the CARs was smaller than that for ZEP7000. The efficiency of multi-pass writing for all of the evaluated resists was observed. The multi-pass writing was very effective in reducing the CD error for both ZEP7000 and the CARs, and especially so for ZEP7000. The dependence of the CD error caused by the resist heating effect on the various writing parameters was investigated using Ralf's model simulation, which is the calculation tool of the temperature rise during the exposure of electron beam including the heat diffusion equation. The CD error for the CARs was smaller and more stable than that for ZEP7000 in various writing conditions. Current density and shot size influenced CD error in sub-field strongly, however, settling time of each shot don't almost influence CD error in sub-field for ZEP7000. The fact that the results for CARs, which have high sensitivity, didn't depend on the current density and shot size indicates the ability to fabricate more accurate mask with higher throughput.
Recently, next-generation mask fabrication processes have been actively examined for application with Electron Beam writing tools and chemically amplified resists. In this study, we used a variable shaped electron beam writing system with an accelerating voltage and chemically amplified resist to investigate the dependence of the CD error in a localized area of a 6025 mask on the process factors, with the goal of fabricating more accurate masks with improving sensitivity. Our results indicated that CD error in a localized area did not depend on the resist thickness. Higher sensitivity and CD uniformity were achieved simultaneously. Moreover, we could isolate the CD error caused by the resist heating effect is more apparent for higher doses than lower doses. However, a higher dose gives rise to a small CD change rate. In this experiment, the effect of the lower CD change rate at a higher dose counterbalances the resist heating effect. By decreasing CD error in a localized area, we obtained a CD uniformity of 14 nm in a 100 mm area on the mask.
The etch-back and laser-explosion process was proposed and reported for Levenson mask repair before. If convex defects and leveling film were etched by physical sputtering and remaining leveling film was removed by laser explosion in the etch-back and laser-explosion process, quartz (Qz) substrate was over-etched because the Ga implanted layer of Qz substrate was also removed by the laser explosion due to the transmittance decrease of the Ga implanted layer. In this paper, gas assisted etching with the mixture of XeF2 and O2 was applied to the etch-back and laser-explosion process. The coincident etching rate of Qz (phase shifter) with C film was obtained, which is an indispensable requirement for the etch-back process. The optical transmittance of Qz substrate after the repair was 95% for the light of 250 nm wavelength. The transmittance was sufficient to avoid over-etching of Qz substrate.
CD uniformity to be patterned by electron-beam (EB) writing system with a variable-shaped beam was evaluated. The experimental EB writing system, EX-8D, was used under conditions of current density of 20 A/cm2 and acceleration voltage of 50 keV. Quartz reticles coated with positive tone resist ZEP7000TM (Nippon Zeon Co., Ltd.) were applied. Test patterns of 1-micrometer-width design were written by shaped beam shots of 1 micrometer square with different exposure doses. Since higher measurement repeatability was confirmed, line width of test patterns without shot stitching points was measured by Nikon XY-3I with a circle-spot probe of 1 micrometer. Line width of clear patterns on resist film was measured after development, and line width of clear patterns on chrome (Cr) film of one mask was measured at same points after wet-etching. The other mask was measured at the same points after dry-etching process by conventional reactive ion etching (RIE). Certain comparisons in this study indicate the importance of evaluating CD uniformity on Cr film after dry- etching process. Expect for resist heating contribution by four-pass writing method, the uncertainty of CD error was quantified as follows: 4 nm (3(sigma) ) on resist film at the applied dose of 19 (mu) C/cm2, and 4 nm (3(sigma) ) on Cr film at the applied dose of 27 (mu) C/cm2.
The effect of phase shift and transmittance fluctuation in a mask plate have been studied. The differences of these optical properties of halftone phase shift masks result in critical dimension(CD) error on a wafer so that these fluctuation in a plate reduce the process window across the exposure field. In considering CD error budget, such factors as phase shift and transmittance has to be taken into account. To estimate this budget, a set of test masks were fabricated, in which phase shift and transmittance are varied, and the exposures using these masks under the same conditions were performed.
At the first stage of defect repair on masks with focused ion beam (FIB), it is necessary to recognize defects by imaging. One of the problems in halftone mask imaging by FIB is that the contrast between halftone (HT) film and quartz (Qz) substrate is not sufficient to recognize material. We investigated the methods of the defect area distinction in deep UV silicon nitride (SiNx) single-layer halftone masks to avoid the transmittance decrease of masks induced by FIB irradiation. The cause of the difficulty in the area distinction is that the difference between the mean secondary electron intensity of HT area and that of Qz area is small in comparison with the width of the secondary electron intensity distributions. A conventional filter was found to be effective to narrow the intensity distributions and the area of defects on halftone masks could be recognized by means of the image filter in the images obtained with a low FIB dose.
The critical dimension uniformity required in the fabrication of photomasks for 1 gigabit DRAMs will be more stringent that 20 nm in terms of 3 sigma. High-voltage variable-shaped e-beam (VSB) writing is advantageous because of its high resolution, linewidth stability, and throughput performance. However, stitching errors in VSB writing have been a critical problem in the fabrication of advanced photomasks. In this paper, an improved method to calibrate the size of a VSB shot and reduce shot stitching errors is proposed. The accuracy of the calibration method depends on that of the linewidth measurement system, and shot-size calibration with an accuracy of +/- 10 nm can be achieved using existing measurement systems. The positioning accuracy of VSB shots was enhanced by a multiple pass exposure scheme. With these procedures applied to a 50 kV VSB system, the linewidth variation of a photomask in a local area such as a square region of 200 micrometers X 200 micrometers was reduced to less than 20 nm.
A set of deep UV attenuated phase shift masks (PSMs) was fabricated to clarify the correlation between PSM optical characters and the printing performance. A SiNx single-layer film was adopted as a phase shifter which works as an attenuator simultaneously. We fabricated nine PSM test masks in which both phase shift and transmittance were varied. In these masks, phase shift ranges from 176 to 205 degrees and transmittance ranges from 6.4 to 13.1%. The target feature size of the experiment was set to that of 256 M DRAM. Line/space patterns under 0.25 micrometer and the contact holes under 0.3 micrometer have been evaluated. The evaluation was made using an exposure-defocus window analysis from measured aerial images. Each mask was compared by the calculated depth of focus (DOF) at 10% exposure latitude. The experimental results show that shifter optical characters do not play an important role in case of line/space patterns. However, the phase shift error leads to serious reduction of DOF for hole patterns. In using high transmittance PSM, mask bias is inevitable to print under -0.30 micrometer hole patterns because of the side-lobe peak. To obtain the maximum DOF, mask bias should be decided with meticulous care.