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To achieve high volume manufacturing, EUV photoresists need to push back the "RLS trade-off" by simultaneously improving Resolution, Line-Width Roughness and Sensitivity (exposure dose). Acid diffusion in chemically amplified resist is known to impact these performances. This work studies the diffusion of acid in chemically amplified resist by varying the post exposure bake duration while monitoring the evolution of CD and LWR for 6 chemically amplified EUV photoresists (CAR). We observed a first regime where both CD and LWR quickly decrease during the first 30s of post exposure bake (PEB). This can be related to the deprotection reaction taking place in the exposed part of the resist. After 60s the decrease in CD and LWR slows down significantly, likely related to a regime of acid diffusion from exposed to unexposed region, and acid-quencher neutralization at the interface of these two regions. We tested two resists with different protecting group and the one having lower activation energy shows a faster CD change in the second regime, resulting in a worsening of LWR for longer PEB time. On the contrary, a resist with a high quencher loading shows reduced net diffusion of acid towards the unexposed region and controls the resist edge profile. In other words longer PEB does not degrade LWR, but as it reduces the line CD, sensitivity is impacted. With an appropriate ratio selection of quencher to PAG, an EUV dose reduction of up to 12% can be achieved with a change from a standard 60 second to a 240 second PEB time, while keeping LWR and resolution constant and therefore pushing the RLS performances. Finally, we confirmed that the observations on positive tone development (PTD) resist could be applied to negative tone development (NTD) resist: with a high quencher NTD resist we observed a dose reduction of 8% for longer PEB time, keeping LWR and resolution constant.

Irresistible Materials (IM) is a UK company spun out of the University of Birmingham. It is developing novel resist systems based on the Multi-trigger concept, and spin-on-carbon hardmask materials. IM has developed a new EUV resist that is nonmetal based, does not need a post exposure bake (PEB), and delivers high sensitivity, excellent contact hole resolution, with low LER. It is being readied for HVM through a partnership with Nano-C, Inc. (the Massachusetts based manufacturer of advanced electronic materials and chemicals). The transition to scalability will be the highlight of this discussion.

Simulation of negative tone development (NTD) resist has become a challenge for physical resist modeling. Traditionally, resist modeling was mainly limited to reaction-diffusion models for post exposure bake (PEB) and standard development rate models for simulating the pattern formation during the final development step. With some minor extensions, this simulation approach sufficiently predicted resist CDs and resist profile shapes that were in agreement with experimental data.3 For the latest NTD resists, this situation has changed. In contrast to positive tone development (PTD) resists, resist shrinkage is strongly impacting resist profile shapes. Furthermore, NTD resists induce strong proximity effects that require consideration of additional chemical resist properties in modeling and model calibration. In this paper we experimentally characterize and model the main properties of NTD photo-resists.

In semiconductor manufacturing, as the design rule has decreased, the ITRS roadmap requires crucial tighter critical dimension (CD) control. CD uniformity is one of the necessary parameters to assure good performance and reliable functionality of any integrated circuit (IC) [1] [2], and towards the advanced technology nodes, it is a challenge to control CD uniformity well. The study of corresponding CD Uniformity by tuning Post-Exposure bake (PEB) and develop process has some significant progress[3], but CD side to side error happening to some line/space pattern are still found in practical application, and the error has approached to over the uniformity tolerance. After details analysis, even though use several developer types, the CD side to side error has not been found significant relationship to the developing. In addition, it is impossible to correct the CD side to side error by electron beam correction as such error does not appear in all Line/Space pattern masks. In this paper the root cause of CD side to side error is analyzed and the PEB module process are optimized as a main factor for improvement of CD side to side error.

The acceptable tolerance level for CD signatures induced by any process step in the mask manufacturing process has been dramatically reduced with each technology node. Chemical amplified resists (CAR) are used extensively for first layer mask imaging. Therefor a post exposure bake (PEB) process is required after resist exposure, adding yet another potential source of CD signatures. Consequentially, the thermal imprint of the bake process must be further reduced to meet the requirements of future technology nodes. The influence of the measurement devices (wireless and wired sensor arrays) used to optimize the hotplate, on the performance of the Post Exposure Bake (PEB) process is discussed in [1,2]. A concept of utilizing two wired sensor arrays, with wire connections attached in opposite locations on the sensor array surface, called “Mirror Bake” is introduced. Based on the individual hotplate optimization for each of those two sensor arrays, a combined bake recipe for the multi-zone hotplate is calculated. This method eliminates the systematic temperature non-uniformity introduced by the sensor array hardware, when optimizing the recipes with only one sensor array. In this paper the “mirror bake” concept is validated by comparing the CD uniformity data of masks manufactured with a PEB process, optimized using a single standard sensor array vs. the “mirror bake” concept. The “mirror bake” concept achieved a CD uniformity improvement of up to 30% (CD range). During this work additional hardware influences from the sensor arrays were identified.

Strong correlation between de-protection induced thickness reduction and amplified chemical reaction in the exposed area of the chemically amplified resist (CAR) during post-exposure bake (PEB) has been established. The optical properties of the resist film due to the thickness reduction can be detected using a spectroscopic ellipsometer. In this paper, a rotating polarizer spectroscopic ellipsometer is developed and a proposed control scheme is presented for signature profiles matching. With the implementation of the control scheme, wafer-towafer critical dimensions (CD) uniformity is improved by 5 times.

Chemically amplified photoresists require a post exposure bake (PEB) to induce deprotection using a UV generated acid-catalyst. While reaction pathways for deprotection have been proposed, key challenges remain in modeling the reaction kinetics. In this work, we used a scanning line-focused laser beam as an alternate PEB method, to quantify the deprotection reaction kinetics of an ESCAP-type and a 193 nm model resist system at high temperatures in millisecond time frames. Results were compared with conventional PEB at 115°C for seconds time frames. Results show that the deprotection kinetics follow simple first-order reaction models only under laser PEB conditions, with more complex kinetics observed under hot plate PEB. FT-IR and NMR spectroscopies were used to characterize the reaction byproducts. Results suggest potential differences in deprotection mechanisms between the two PEB temperature and time regimes. The deprotection behavior obtained using this l-PEB technique enables a deeper understanding of the reaction kinetics of photoresists, critical for current DUV and future EUV technologies.

The transcanal LLLT was found to recover noise induced hearing loss (NIHL) but the LLLT was performed immediately after the induction of NIHL. The aim of this study was to find an optimal window time to treat and recover a NIHL with LLLT. Bilateral ears of 6SD rats (12ears) were exposed to noise. Left ears of the rats were irradiated with a LLLT (830 nm, 594 J/cm2 per day) for 12 days, starting 3 days and 7 days post exposure to noise. Right ears were used as control ears. The hearing levels were measured at each frequency of 4, 8, 12, 16, and 32 kHz before and after the noise exposure and post 12th irradiations. The initial hearing levels in all frequencies before and after the noise exposure were 26.5, 24.5, 24.0, 24.0 and 24.5 dB SPL and 63.5, 64, 71.5, 73.5 and 67.5 dB SPL in 4, 8, 12, 16 and 32 kHz, respectively in 6 ears. After 12th irradiation, the thresholds of the LLLT treated left ears of the 3-day group recovered significantly compared to those of the untreated right. However, for the 7 day group, the recovery of the LLLT treated left ears was not significantly improved compared to that of the untreated right. The results of this study suggest that the optimal window time to treat NIHL with LLLT was within 3 days from the exposure to noise but the hearing failed to recover if the LLLT was started 7 days post exposure to noise.

Exceptional post exposure delay (PED), CD stability, up to 72 hours was reported. This study was conducted using two negative resist formulations identical in their composition except for their PAG type. A mechanism by which the photoacid is protected from relatively moderate levels of airborne amines is proposed. Evidence of room temperature interaction between the resist components and the acid during post exposure delay was also suggested. Therefore, the PED outcome could be the result of two opposing mechanisms.

ArF water immersion lithography is expected to be used down to the 22nm hp node or below. However, such advancements in technology nodes have led to extremely small process margins. This necessitates more accurate means of process control. CD uniformity of the photo-resist (PR) image is affected by many sources. In the case of the exposure tool-CD error on the reticle, as well as exposure dose and focus errors are the key factors. For the PR process, heterogeneity of the stacked PR film thickness, post exposure bake (PEB) plate temperature, and development have an impact. Further, the process wafer also has error sources that include under-layer uniformity and wafer flatness. Fortunately, the majority of these factors is quite stable in a volume production process and can be compensated for by adjusting exposure dose and focus in the scanner. A technique to calculate exposure dose and focus correction values simultaneously from the measured PR image feature was reported previously [1]. In addition, a demonstration of a correction loop using a neural network calculation model was reported in SPIE 2010 [2], and the corrected CD uniformity was less than 1.5 nm (3-sigma) within the wafer. In this paper, we will report the latest CD uniformity correction results achieved with the NSR-S620D ArF immersion scanner using correction values estimated by scatterometry and CD-SEM. The method of correction using CD-SEM is newly developed. A maximum of nine parameters extracted from the PR profile are used in this correction. In general, the CD variation of an isolated line pattern caused by focus error is more sensitive than that of a dense pattern. Thus, we estimate the focus error from the isolated pattern, with the dose error estimated using both isolated and dense patterns. The Nikon CDU Master then derives the optimal control parameters for each compensation function in the scanner using the exposure dose and focus correction data, and the NSR-S620D is able to control higher order dose and focus distribution. This advanced level of control capabilities enables precise correction of the complicated CD error distribution that is caused by heterogeneities in the process.

This work is the summary of improvements in processing capability implemented and tested on the LITHIUS ProTM -i / TWINSCANTM XT:1950Hi litho cluster installed at ASML's development clean room at Veldhoven, the Netherlands. Process performance with regards to CD uniformity (CDU) and defectivity are investigated to confirm adherence to ITRS roadmaps specifications. Specifically, imaging capabilities are tested for 40nm line 80nm pitch with the new bake plate hardware for below hp 3Xnm generation. For defectivity, the combination of Coater/Developer defect reduction hardware with the novel immersion hood design will be tested. For CDU improvements, the enhanced Post Exposure Bake (PEB) plate hardware was verified versus performance of the previous technology plate. Additionally, after the PEB improvement, a remaining across wafer signature was reduced with an optimized develop process. The total CDU budget was analyzed and compared to previous results. Finally the optimized process was applied to a non top coat resist process. For defectivity improvements, the effectiveness of ASML's new immersion hood and TEL's defect reduction hardware were evaluated. The new immersion hood performance was optimal on very hydrophobic materials, which requires optimization of the track hardware and process. The high contact angle materials could be shown to be successfully processed by using TEL's Advanced Defect Reduction (ADR) for residues related to the high contact angle and optimized bevel cut strategy with new bevel rinse hardware. Finally all the optimized processes were combined to obtain defect counts on a highly hydrophobic resist well within manufacturing specifications.

The rapid expansion in the number of semiconductor manufactures using immersion imaging systems confirms the acceptance of immersion lithography for critical layer imaging. One of the early concerns in the development of immersion lithography was defect levels. These defects levels have been dramatically reduced with each new system, and are now approaching defect levels similar to dry systems. Continued reduction of defects will be required as smaller critical dimensions are pursued on immersion systems with NAs well over one. In this work have studied new ways to further reduce the number of defects. For this investigation an ASML 1150i a-immersion scanner was used for both ultra pure water soaking and for image exposure. Previous pre-exposure and post-exposure rinse/soak tests have been conducted on coater/developer tracks; however using the track causes a significant time delay from soak to exposure, and vice-versa. For this experimentation a dynamic soak of coated wafers immediately before exposure and immediately after exposure was performed on the immersion scanner with controlled soak times. The wafers were then processed as normal on a TEL-Lithius coater/developer track. Defect type and size were analyzed to determine the interactions which reduced defects. The findings showed that an immediate pre-exposure soak of 14 seconds reduced image expansion defects by 38%, compared to no pre-exposure soak. Test results also indicated that the most frequent defect, bridging, was not produced by water droplets.

LER (line edge roughness) is becoming increasingly critical for manufacturers and efforts to understand and control it have given disappointing results. We propose that LER is due to a combination of coherent optical effects, mask LER, and chemical processes during exposure, PEB (post exposure bake) and development. Different sources of LER have similar scaling laws and PSD (Power spectral density) distribution, and the causes of LER are easily misidentified. High sensitivity, thin resist, and low image log-slope generally give more LER. No single-effect model is going to be adequate to give quantitative predictive guidance how to reduce LER. Since LER is shared between chemistry, optics and metrology, a cross-disciplinary model is needed. We propose such an LER budget model with a unified analysis of the metrology and consequences of LER, but with models for source effects plugged in by experts from the relevant domains.

In the current optical lithography, the resolution is being pushed for 45 nm half-pitch, and the chemically amplified resist will be used for wide variety of applications incl uding immersion lithography. So far the chemical amplification has brought high performance for lithography. In the future , for the ArF lithography beyond 45nm half-pith, it will be important to control pattern size. On the other hand, chem ically amplified resist whic h utilized acid catalyzed de-protecting reaction is sensitive to physical and chemical f actor. Thus, there are various factors in the each process (Resist coating, Pre bake, Exposure, Post exposure bake, Deve lopment and Rinse) to cause th e resist blur. For example, it’s acid diffusion on PEB. The influence of these factors for the resist blur is a significant issue for lithography beyond 45 nm half-pitch. Therefore the need to reduce these factors on the resist blur b ecomes higher in order to extend the ArF lithography beyond 45 nm half-pith. In this paper, acid diffusion coefficient ( D ) and resist blur with changing anion size of PAG, size of protecting group in typical ArF resist was reported. The relationship between acid diffusion coefficient and resist blur was discussed on the basis of their difference in structure and characteristics. Keywords: acid diffusion length, resist blur, ArF lithography

In previous investigations of minimal spot, q-switched laser visible (532 nm) on-line pulsed laser exposure, non-human primate (NHPs) required up to 13 times the retinal damage threshold for the emergence of permanent visual acuity dysfunction. In the present experiment, a Landolt ring contrast sensitivity task, employing 4 NHPs trained on a Landolt ring contrast sensitivity task, was employed to determine the effect of threshold retinal damage (532 nm, 3 microjoules, 20 Hz, PRF) on the slope of the NHP Landolt ring contrast sensitivity function measured under repeated threshold exposure conditions. All four animals initially showed uniform deficits in contrast sensitivity requiring about 6 to 16 min post exposure for complete recovery. Over several months of repeated exposures made in 3 NHPs, a steepening of the contrast sensitivity slopes appeared, manifested by an inability to measure sensitivity for the finest Landolt ring spatial frequencies and an associated enhancement in the mid and lower spatial frequencies. In one animal that had undergone a longer period of repeated threshold laser exposure, the slope of its contrast sensitivity function shifted to a uniform deficit relative to pre exposure with an inability to provide sensitivity measurements above 20 Hz/deg, demonstrating an abrupt loss in the ability to measure the higher spatial frequencies associated with maximal optimal visual acuity. Ophthalmic retinal observations demonstrated the presence of punctate lesions induced by minimal spot foveal exposure. These data support measurements of high contrast acuity undergoing repeated q-switched exposure at damaging levels. While the acuity in such exposure situations eventually undergoes a permanent deficits, measurements of the entire contrast sensitivity function, in which acuity function maybe obtained at and above 60 Hz/deg, may reveal enhanced lower spatial frequency sensitivity as well as permanent a permanent deficits in higher spatial frequencies.

Post exposure bake temperature sensitivity (PEB sensitivity) becomes important as the pattern pitch size shrinks gradually. There are several factors affecting the PEB sensitivity including acidity and diffusion of photogenerated acid, activation energy for deprotection reaction, free volume of base polymer, and so on. Our works were conducted as a part of the basic study for searching influential parameter of PEB sensitivity. We found that PEB sensitivity relies largely on not only acid diffusion parameter, but also the hydrophilicity of base polymer and protection group ratio. Also, we observed that bulkiness of deprotection group has great influence on PEB sensitivity. Detailed results will be reported in this paper.

It is well known that within wafer Critical Dimension (CD) uniformity is especially affected by baking temperature variation during Post Exposure Baking (PEB) process of 193nm photolithography. To develop new baking unit for better CD uniformity, it is important to understand Dynamic Temperature CD Sensitivity (DTCS) of PEB processing at each baking process step. This paper studies the DTCS in the PEB process applying unique experimental procedures. We have added an intentional temperature tilt within wafer at particular processing time during PEB, and we have estimated DTCS from CD and temperature deviation within wafer. Using those scattered data, DTCS curves during PEB process were obtained. The high values of DTCS curve appeared just before the temperature of the wafer reaching the setting temperature of the hot plate. This fact indicates that temperature variation within wafer on this particular step has a large impact on CD uniformity. Therefore, the key to secure highly accurate CD uniformity is to improve temperature controllability within wafer on this processing period in PEB process. Based on these results, we have conducted three optimizations of bake plate for the improvement of the temperature controllability within wafer. CD uniformity was also evaluated with 193nm photoresist.

Top coat process is required for immersion lithography in order to prevent both the chemical contamination of scanner optics with eluted chemicals from resist material and the formation of residual droplet under the immersion exposure with high scanning speed. However, defect density of ArF immersion lithography with alkaline developer soluble type top coat material is much higher than that of ArF dry lithography. Mimic immersion experiments comprised of soaking of exposed conventional dry ArF resist with purified water followed by drying step were performed in order to study the immersion specific defects. It was suggested that the origin of immersion specific defects with alkaline developer soluble type top coat was the remaining water on and in the permeable top coat layer that might interfere the desired deprotection reaction of resist during post exposure bake (PEB). Therefore, application of post exposure rinse process that can eliminate the impact of the residual micro water droplets before PEB is indispensable for defect reduction. Post exposure rinse with optimized purified water dispense sequence was noticed to be valid for defect reduction in mimic immersion lithography, probably in actual immersion lithography.

Background and purpose: The purpose of this study is to determine th e impact of melanin on skin response to single 3.8 micron, eight microsecond laser pulses and the di fference in lesion formation th resholds for input into laser safety standards. Williams et al., performed a study ex amining laser tissue interaction from 3.8-micron lasers in lightly pigmented Yorkshire pigs ( Sus scrofa domestica ). 1 However, studies performed by Eggleston et alcomparing pigmented and lightly pigmen ted skin with human skin found that the Yu catan mini-pig is a superior model for laser skin exposures. 2 Methods: Five Yucatan mini-pigs under general anesthesia were exposed to 3.8 micron laser pulses ranging from 0.8 J/cm 2 to 93 J/cm . Gross examinations were done acutely and 24 hours after laser exposure. Skin biopsies were then collected at various times post exposure, and histologic examinations were conducted. Results: The 24 hour ED 50 was determined to be 4.5 J/cm 2 with fiducial limits of 6.2 and 2.2 J/cm . As deposited energy was increased, the lesio n presentation ranged from whitening of the epidermis (4 J/cm

Progress towards 65 nm next-generation lithography requires unprecedented global CD uniformity, with the actual ITRS 2002 roadmap proposing 4.2 nm 3/spl sigma/ (dense lines) for 65 nm binary masks. Since resolution requirements are satisfied only by using chemically amplified resists (CARs), exposure and post-exposure bake (PEB) are key processes to successful mask making, both introducing global CD errors. Develop and etch processes potentially contribute further global CD errors. The global CD uniformity can be improved significantly by adaptive PEB, especially for CARs showing moderate to strong PEB sensitivity, like NEB22. With the 25-zone hotplate of the APB5500 bake system, facilitated through a novel calibration mask with 25 equidistant temperature sensors within the resist plane, an appropriate temperature profile can be applied during PEB. This temperature profile is automatically calculated by an adaptive optimization algorithm, based on 2-dimensional spline fitting of a CD measurement. A CD-uniformity improvement (dense lines) from 4.8 nm 3/spl sigma/ to 3.9 nm 3/spl sigma/ (/spl cong/20%) on a state-of-the-art production mask is achieved for the chrome layer (ASI, after strip inspection).

Five male Yorkshire pigs were exposed on their flank to 4 microsecond pulses of laser light from a Deuterium Fluoride 3.8 micron Laser at varying energies. A preliminary ED50 threshold for various skin reactions was determined for this laser exposure combination. The animal’s skin was assessed for injury immediately, 1 hour, 24 hours and 72 hours post exposure. In general, energies below 3.2 J/cm2 leave no lasting skin reaction. As energy increased above the threshold, erythema or skin reddening was easily visualized. High-energy pulses appear to produce a “rug burn” erythema without evidence of punctate hemorrage (bleeding) or coagulation. Laser exposure sites on the pigs were also biopsied to obtain histopathological results. These findings suggest that the principal effect of this type of in-vivo laser exposure is removal of the epithelium, while not damaging the papillary dermis or structures beneath the Basement Membrane Zone (BMZ).

Keeping post exposure bake (PEB) sensitivity low has become one of the most crucial factors for implementing the 193nm resist process into mass production. In a previous report, we have demonstrated that the nature of the photo acid generator (PAG) has a strong effect on the PEB sensitivity of 193 resists. Based on our findings, we decided to extend our studies to the other important resist components, such as polymers prepared with various monomer compositions, and casting solvents. Also, in an effort to investigate whether PEB sensitivity can be reduced by process optimization, the influence of soft bake and post exposure bake conditions was studied. This paper describes our new findings on some of the important factors that affect the PEB sensitivity of 193 resists.

It was found that the structure of a matrix polymer has strong influence on the PEB sensitivity of 193nm photoresists. As reported, photoresists containing CO polymers exhibited superior property in terms of PEB sensitivity to photoresists formulated with more popular 193 nm photoresist polymers such as VEMA, COMA and methacrylates. In addition, CO polymers exhibited little variation (< 1 nm/°C) in PEB sensitivity when formulated with different PAGs and/or bases. VEMA polymers exhibited PEB sensitivity in the range of 4 ~ 6 nm/°C. VEMA polymers with less leaving group (or lower blocking ratio) exhibited lower PEB sensitivity, but the nature of a leaving group (i.e., lower or higher temperature leaving groups) had little effect on PEB sensitivity. The most pronounced effect was found with functional monomers. For example, VEMA polymers prepared with novel functional monomers exhibited PEB sensitivity in the range of 3 ~ 4 nm/°C. Photoresists formulated with methacrylates exhibited significant variation in PEB sensitivity ranging from 4 ~ 15 nm/°C depending on the backbone chemistry and composition. For instance, with lower blocking ratio as well as lower temperature leaving group, PEB sensitivity of methacrylates were significantly improved by 40~45%. Again, the most pronounced effect was found with functional monomers with methacrylates and PEB sensitivity of methacrylates with novel monomers resulted in the range of 3 ~ 5 nm/°C.

In this work, the effect of exhaust condition during Post Exposure Bake (PEB) on the critical dimension (CD) performance has been investigated for different DUV resists. Two kinds of PEB chamber cover designs have been tested to see the influence of exhaust flow on CD. It has been found that cleaning and adjusting of PEB exhaust flow will change the resist CD. To confirm the impact of PEB exhaust condition on production, resists for both lines and contact holes are verified by scanning electron microscope (SEM).

This paper describes a systematic and rigorously controlled set of experiments showing the effectiveness of the Electric Field Enhanced Post Exposure Bake (EFE-PEB) with 248nm KrF(ASML) exposures on Apex-E photoresist (IBM) where feature sizes ranged from 0.3 um to 0.5 um. Experimental results showed a significant improvement in process latitude and resist sensitivity for features with a k1 technology factor of 0.68 and below. The experiments were executed using a 248nm KrF stepper (ASML), NA 0.5, and Apex-E photoresist (IBM), which has a relatively high acid diffusivity. An improved experimental setup rigorously controls PEB time, PEB temperature, development time, focus drift, and other environmental variables. Cross sectional SEMs of five line arrays with L=S ranging from 337nm to 500 um show deeper trenches when the electric-field treatment was used. Exposures that were intentionally out of focus cleared 600nm deep in 1um thick photoresist in the control group, but did clear the full 1um with the application of the Electric Field during the PEB. A dose matrix experiment showed an 8% decrease in the dose to clear and two-fold increase in focus latitude. This comprehensive study demonstrated an increase in anisotropic acid diffusivity with the application of the electric field and confirmed that the EFE-PEB offers a relatively inexpensive and simple method for improving photoresist performance.

193nm(ArF) photoresist used for 90nm to 65nm nodes has shown many significant characteristics. Especially, higher sensitivity to PEB (Post Exposure Bake) temperatures compared to 248nm(KrF) photoresist is critical in CD control. We classified CD budget of each process in coater/developer regarding 193nm photoresist to examine each factor’s influence. As a result, it’s found that PEB makes up about 70% of the track-related CD factors. This fact indicates the importance of PEB in 193nm process. We made improvements to inter and intra wafer for enhancing CD control in the 193nm process. Controlling chamber temperature in PEB process made 68.9% of improvement in CD variation of inter wafer. As for the intra wafer, the CD variation was improved 28.6% by modifying thermal history that has a great influence on PEB process. However, we assume that there are cases that don’t apply this budget since there are influences of the warped wafer and of flare in the exposure tool. In these cases, using a divided heater-type hotplate that we have been working on the development enables to make adjustment and results in 38.3% of improvement in intra wafer.

International SEMATECH(ISMT) has operated a 157nm Resist Test center since June of 2000. During this time, we have processed hundreds of 157nm photoresist samples from major resist suppliers and research organizations. Almost all of these of these early 157nm resists have demonstrated unusual susceptibility to airborne molecular contamination (AMC). Tests were completed at ISMT comparing post exposure delay stability of 157nm fluoropolymer resists to production level 193 and 248 nm resists. The 157nm resist samples were approximately 5X more sensitive to AMC. We have implemented extensive AMC control measures including the introduction of mini-environments and filtered wafer carriers to mitigate the AMC sensitivity of these resists. The effectiveness of the control measures was measured using a real time airborne base monitor, grab samples, and resist delay studies. 157nm resists were severely affected by relatively low airborne base concentrations of approximately 1 ppbv NH3. Hold time stability was significantly improved when the airborne base concentrations was reduced to < 0.5 ppbv using carbon filtration. Small variations in of +/- 0.2 ppbv NH3 appear to be influencing resist profiles and delay response.

As for CD (Critical Dimension) control, we classified factors of CD variations in each process. We quantified the factors occurred in the devices such as exposure tool, coater/developer and CD-SEM in 193nm lithography. In the coater/developer, influence of PEB (Post Exposure Bake) on CD variation was notably found and made up about 70% of the Track-related factors. This fact indicates that a great importance of PEB in 193nm process. Regarding the exposure tool, we quantified the CD variations caused by Flare using Kirk method. We determined that this issue was influenced by the exposure field layout, and the variation of intra wafer was 1.58nm. As for a CD-SEM, we measured the CD variations caused by the electron beam-induced CD shrink, and LWR (Line Width Roughness). The LWR accounts for about 40% of the total measurement errors, and affects CD variations higher as finer line pattern. We reduced influence of LWR on CD variations by extending measurement points and averaging. Thus we acquired the CD uniformity close to the actual CD.

Improvements in the final uniformity of masks can be shrouded by error contributions from many sources. The final Global CD Uniformity (GCDU) of a mask is degraded by individual contributions of the writing tool, the Post Applied Bake (PAB), the Post Exposure Bake (PEB), the Develop sequence and the Etch step. Final global uniformity will improve by isolating and minimizing the variability of the PEB and Develop. We achieved this decoupling of the PEB and Develop process from the whole process stream by using “dark loss” which is the loss of unexposed resist during the develop process. We confirmed a correspondence between Angstroms of dark loss and nanometer sized deviations in the chrome CD. A plate with a distinctive dark loss pattern was related to a nearly identical pattern in the chrome CD. This pattern was verified to have originated during the PEB process and displayed a (Final CD)/ (Dark Loss) ratio of 6 for TOK REAP200 resist. Previous papers have reported a sensitive linkage between Angstroms of dark loss and nanometers in the final uniformity of the written plate. These initial studies reported using this method to improve the PAB of resists for greater uniformity of sensitivity and contrast. Similarly, this paper demonstrates an outstanding optimization of PEB and Develop processes.

Negative-tone chemically amplified resists (nCARs), like NEB22 are promising candidates for next-generation lithography, e.g. 90 nm and 65 nm technology node and next-generation lithography. For these resists, e-beam exposure and post-exposure bake (PEB) are most critical processes, since these resists show a strong sensitivity to post-exposure delay (PED) in vacuum during e-beam writing of about 0.5 nm/h, and in air while waiting for PEB. Further, such resists show a strong PEB temperature sensitivity of up to 8 nm/K. The multi-zone hotplate approach of the APB AFB 5500 bake system with its use prior temperature uniformity results in excellent global CD-uniformity already. However, all kinds of systematic large area effects of processes, e.g. blank coat/bake, exposure, PED, the PEB itself, etch loading, etc. may transfer in additional systematic CD-errors. Such systematic, repeatable errors can be reduced during PEB by superimposing an appropriate non-uniform temperature profile onto the regular, optimized uniform bake temperature profile, thereby compensating for such CD-non-uniformities. The required temperature profile can automatically be calculated from a suitable gobal CD measurement, determined in a typical process flow. The compensation of CD-errors resulting from vacuum PED and hotplate temperature characteristics is demonstrated here, by using automated temperature profile calculation. The global CD uniformity was improved significantly, the achieved results show a typical reduction of about 20-30%, from a total global range of about 9nm to about 6-7nm on leading-edge production photomasks.

The critical dimensions (CD) change by the process delay is the most critical issue to apply the chemically amplified resists (CAR) for photomask fabrication. In the photomask fabrication processes, the resist should have both post coating delay (PCD) and post exposure delay (PED) stability, while keeping higher sensitivity. To achieve this requirement, overcoat process has been examined for the purpose of CD stabilization in CAR process for photomask manufacture. The material, which consists of hydrophobic polymer and PAG, was used for the overcoat in this study. Consequently, it has become clear that pattern formations have been possible without unnecessary thickness loss. Moreover, it has been proved that the overcoat shows the effect of controlling CD change and improvement of CD uniformity. From these results, it is thought that the overcoat process is promising for the size stabilization in photomask manufacture for devices less than 90 nm.

Yucatan Mini-pigs were exposed on their flank to 0.5 milli second 1318 nm pulses of laser light. The ED50 damage threshold was determined for this laser exposure combination. The skin was assessed for injury immediately, at 1 hour, 24 hours and three days post exposure. Generally, at least 24 hours was required for visible lesions to form. It was found that as the duration between exposure and assessment expanded the injury was more easily visualized. Tissue samples were collected for histology at one hour, 24 hours and three days. Histologic sections will be presented in future work. It was also found that the topical application of mineral oil to the area of interest was found to greatly increase the ease of identification of injuries.

An increasing number of industries, to include military, medicinal, and technological arenas, are using 1.3 micron laser systems for which current skin and eye guidelines are identical. No skin threshold, ED50 or exposure data are available. The mechanisms of laser-tissue interaction with skin at 1.3 microns are unknown. Together, these facts necessitate increased research to prevent future laser accidents and injuries. This study examines the method of interaction of 1.3 microns laser light with tissue in the Yorkshire pig. Our research addresses laser-tissue interaction through delivery using a Nd:YAG with an intracavity filter producing 1.3 micron light at 0.5 millisecond exposure time and in the range of 137 to 475 J/cm 2 . Laser exposure to Yorkshire pigs was evaluated for dermal lesion development. Lesions were appraised for acute, one-hour and 24-hour post exposure presentation.

Yucatan mini-pigs and Yorkshire pigs were exposed on their flanks to 1318 nm, 0.5 ms laser pulses. Injuries were readily visible on the Yorkshire pigs immediately, one hour, and 24 hours post exposure but difficult to locate at 3 days post exposure. The Yucatan mini-pig injuries were not seen immediately or at one-hour post exposure, but at 24 hours and three days post exposure they were easily identified. The Yorkshire injuries were round red, well demarcated, with a circular pink area of edema. It is hypothesized that skin pigmentation has an effect on the mechanism of 1318 nm laser energy absorption in skin. Pigmentation may have a significant effect on how infrared laser injuries present, develop and heal.

The new capillary spin (CAP-Spin) coating principle, realized in the STEAG HamaTech ASR5000, was evaluated for mask making using chemically amplified resists. Basic correlations between coating parameters, resist thickness and film uniformity were figured out. We achieved a film thickness uniformity of close to 2% total range after a process optimization based on our investigation results with the positive tone resist JSR KRS-XE. Finally, the performance of ASR coated blanks was assessed on the basis of a binary mask making process using the Fuji FEP171 resist. The ASR5000 was integrated in an advanced tool set and the patterned reticles have met the requirements of the 100nm Technology Node in terms of resolution and CD-uniformity. No correlation between thickness and CD distribution could be observed. The evaluated post coating and post exposure delay influence of FEP171 also confirms the usability of the ASR5000 coated substrates for advanced mask making.

Writing fogging effect in chemically amplified resist process makes critical effect on global CD distribution in the advanced 90nm node photomask with higher pattern density and smaller geometries. High contrast feature of chemically amplified resist makes difficult to correct the global CD uniformity in resist develop process compared with conventional ZEP resist. In this paper we examine the fogging effect in the combination chemically amplified resist with 50KeV writing tool and the consequential problem for production mask with higher pattern density. We will present the feasibility of the global CD uniformity correction technique in post exposure baking process using gradient temperature hotplate.

CD-uniformity data of chemically amplified (CA) resists have been generated, by using a dynamically controlled multi-zone hotplate system, APB5000. The optimized baking procedure of the APB5000 system for Post Coat Bake (PCB) and Post Exposure Bake (PEB) is characterized by a maximum in the total temperature range on a 6025 mask substrate surface of 0.5 degree(s)C during the heat-up ramping and smaller than 0.2 degree(s)C at the set-point temperature of 90 degree(s)C. In this experiment CD-uniformity for isolated lines was improved to 7.8nm, compared to 13nm when using conventional baking systems. Additionally, a compensation method based on the baking processes is presented to further decrease the CD- uniformity range of CA-resists. Derived from CD-uniformity data measurements, a local temperature variation from the optimized baking strategy of the APB5000 system is used to compensate CD-errors caused by other process steps. In this experiment the result of such a measure showed a 40% improvement of the CD-uniformity range for dense lines from 14.2nm to 8.0nm.

Various resist develop models have been suggested to express the phenomena from the pioneering work of Dill's model in 1975 to the recent Shipley's enhanced notch model. The statistical Monte Carlo method can be applied to the process such as development and post exposure bake. The motions of developer during development process were traced by using this method. We have considered that the surface edge roughness of the resist depends on the weight percentage of protected and de-protected polymer in the resist. The results are well agreed with other papers. This study can be helpful for the developing of new photoresist and developer that can be used to pattern the device features smaller than 100 nm.

A new type of bake system for photomasks, APB5000, has been developed, using a dynamic and multiple zone approach, to enable more precise Post Exposure Bake (PEB) and Post Coat Bake (PCB) of conventional and chemically amplified resists (CAR). The principal equipment concept and the optimization strategies are presented. The baking performance of the APB5000 is demonstrated for several surface temperatures between 90 degree(s)C and 150 degree(s)C. The temperature uniformity ranges achieved at the resist plane are better than 0.25 degree(s)C after stabilization at the final temperature and better than 1.5 degree(s)C during the ramping period. The repeatability of the bake temperature is better than +/- 0.07 degree(s)C for the setpoint temperature.

In this study, the influence of the thermal history during post exposure bake (PEB) on the lithographic performance of a chemically amplified resist is examined using a reaction-diffusion model of the resist combined with an arbitrary time-temperature profile. The temperature profiles investigated in this study are either based on a simple heat transfer model or arbitrary time-temperature data. The heat transfer model allows variation of the rise time to the bake temperature, of the cooling process during transfer to the chill plate, and of the fall time to the chill plate temperature. Calculations of the dose-to-size for dense features and the iso-dense bias are presented for typical temperature profiles, and these results are contrasted with the lithographic responses for an ideal bake. Also, the lithographic response for a double bake is presented. For certain resist model parameters, the lithographic response for a higher temperature bake followed by a lower temperature bake can be significantly different from the response when the lower temperature bake precedes the higher temperature bake.

Completion of recent studies within our group indicates a breed-based difference in dermal response to 1540 nm 0.8 millisecond laser pulses. Laser exposure to Yucatan Mini- Pigs (highly pigmented skin) and Yorkshire pigs (lightly pigmented skin) demonstrate statistical differences between the ED50's of the two breeds. Laser delivery is accomplished using an Er:Glass system producing 1540 nm of light at millisecond exposure times and in the range of 5 to 95 J/cm2. Dermal lesion development was evaluated for acute, 1 hour, and 24-hour post exposure presentation. Our data contradicts the theory that water absorption is the sole mechanism of dermal tissue damage observed from 1540 nm laser exposures, as skin chromophores appear to play a role in lesion development.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A possibility of chemically amplified resist (CAR) process for mask production has been studied experimentally to solve the low throughput problem with a high voltage variable shaped e-beam system. The pattern fidelity of CAR for small patterns like serifs and scattering bars is comparable to the ZEP7000 resist that is the most popular e-beam resist nowadays. We estimated the amount of delay effect in vacuum that can be generated during a long writing time in the vacuum state. And it proved that critical dimension (CD) change occurred with an acetal type resist rather than an acrylate type resist. The effect of temperature fluctuation during post exposure baking (PEB) was also evaluated by measuring line-widths and line- width variations across the mask plate. Through our work, we have achieved CD non-uniformity of < 10nm in ?3 within 135 X 135 mm2 field showing a high possibility for CAR process to be applied to the mask production for device generations beyond 180nm.

One of the major problems for DUV resists is linewidth change owing to Post Exposure Delay (PED). Linewidth is mainly induced by acid diffusion during exposure and baking. Based on the mechanism of the neutralization of organic base and photo generated acid, a model had been generate din our previous study to describe the linewidth variation for different PED times. The derived equation can calculate the minimum elapse time, which will cause linewidth variation to exceed the specification of a specific CD. This work concludes that the smaller CD received a higher percentage of CD variation under PED for an isolated line pattern. Therefore, the minimum acceptable time for the smallest CD can be obtained based on +/- 10 percent of the nominal CD.

Single pulses in the near-infrared (800 nanometers) were used to measure retinal minimum visible lesion (MVL) thresholds in rhesus monkey eyes at a pulse width of 130 femtoseconds (fs) within both the macula and paramacula regions. We report the MVL thresholds, determined at 1 hour and 24 hours post exposure, which were obtained within the macula and adjacent paramacula. This data will provide a direct comparison of the sensitivities of different retinal areas to laser injury and provide additional insight to laser damage. These new data points will be added to the databank for MVLs for single pulses. The MVL-ED 50 threshold for the macula was measured to be 0.35 (mu) J at 24 hours postexposure, which compares with 0.43 (mu) J measured at 580 nm and the 0.17 (mu) J measured at 532 nm in our laboratory. Our measurements show that the retinal ED 50 threshold in the paramacula was larger by a factor of 1.6 than in the macula. This factor of 1.6 is in good agreement with the factor of 1.1 to 2.5 reported in previous studies.

This paper describes the formulation robustness of an 'ESCAP' type resist based on hydroxystyrene/t-butyl acrylate copolymer. The resist formation matrix consists of the polymer, a photo acid generator (PAG) and a base. The performance of the resist design was tested lithographically over 900 angstrom DUV-30 BARC as a function of variations in the PAG concentration and the base ratio to the PAG. The post exposure bake (PEB) temperature was also investigated as a third process variable in addition to the first two formation variables. The analysis of the results shows high performance tolerance to the formation variables. The resolution, focus latitude and exposure margin exhibited high tolerance to changes in the PEB temperature, PAG or base ratios.

As we enter the DUV lithography generation, the developmental phase of the photolithography process is becoming crucial due to the high costs associated with the lithography equipment. Improvements in the modeling of chemically amplified resists are necessary to extract the maximum possible information from the minimum amount of experimentation. The poor man's dissolution rate monitor (drm) method has been used successfully to extract the post exposure bake (PEB) and develop rate parameters for conventional I-line photoresists and some DUV chemically amplified photoresists (CARs). However, the original method suffers from some drawbacks such as locally optimized results due to the highly non-linear nature of the Mack development model and the need for visual inspection to detect convergence of the rate data. This paper used a simulated annealing optimization engine for global optimization and uses the deprotection induced thickness loss phenomenon for the conversion of dose to m. Post-exposure bake and develop rate parameters have been extracted for Shipley's UV-5 DUV photoresist.

We have developed a 3D practical lithography simulation system and realized the practical parameter optimization. A very fast 3D profile computation is performed by using the FFT algorithm in aerial images and the post exposure bake. The optimization system is developed by using object- oriented technology in order to reduce the computation time. The resulted computational time is less than one tenth of the conventional system. The total parameter optimization time is also reduced.

This paper examines the effects of latent acid formation and acid diffusion into dark regions of images in determining resist behavior during post exposure bake. Results of two new experiments, consisting of diffusion from an exposed into an unexposed resist film, the deliberate introduction of flare in patterned exposures, and re-examination of FTIR measurements of flood and patterned exposed samples show that a sharp diffusion front is the dominant mechanism determining resist image formation with post exposure bake times, and similar front velocities of 33 nm/min, 35 nm/min, and 31 nm/min were obtained for each experiment, respectively. In addition, quantitative modeling of toploss in unexposed samples due to acid diffusion from a top-to-top contact bake with an exposed sample show that Fickean diffusion cannot account for the experimental observations and suggest deprotection dependent diffusion fronts in positive DUV resists are important in modeling lithographic performance.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In PROMOTE processing of novolac-diazonaphtoquinone (DNQ) resists, a deep UV flood exposure is given under water-free conditions during the post exposure bake. When exposure is done under water-free conditions DNQ forms an ester with the novolac, which is insoluble in TMAH. Due to the high absorption of the resist for the DUV flood exposure wavelength, ester is mainly formed in the top of the formerly unexposed regions. With DRM measurements it is shown that PROMOTE can enhance both development contrast and, due to the ester gradient in the depth of the resist, profile slopes. Therefore, dyed resist processing benefits more from PROMOTE than transparent resist, especially when degradation of the top of the resist profiles is the limiting factor, i.e., near the resolution limit of the stepper/resist combination, PROMOTE is advantageous. When the development process is left unchanged, the improvement with PROMOTE is attained at the expense of a higher imaging dose. An alternative for a higher imaging dose is a more aggressive development process, which can be achieved by a longer development time or a higher normality developer. The best results with PROMOTE are obtained when a more aggressive development process is used.

Though simulations of PEB (Post Exposure Bake) on the basis of PAC diffusion mode! have been carried out by a number of researchers '' (2) , it has never been confirmed that those could predict experimental data caused by PEB' s effects accurately . Because no details of chemical reactions thernlly induced by PEB are known, fundamental parameters which determine PEB' s effects must be obtained experimentally. We have acquired the volume of changes of development rate function, RATE(M) by PEB with DRM monitoring for some types of photoresist . The values of diffusion length have been obtained by means of compareing experimental B (exposure ener) vs T (development time to clear) curves with simulated ones which is based on RATEOA) data. Their dependence on the baking time has been investigated with fixed FEB temperature and it has been proved that a progress of the diffusion saturates only in less than a few seconds when the diffusion length is about lO'-l5ncn, which is much shorter than the standing wave length(= 66nm, for G-line). Profiles of low contrast resist patterns can be improved by the decrease in development rate of slightly exposed areas by PEB. The effects on these resists depend on the baking time because the volume of the decrease grows with increasing FEB time. On the other hands, for high contrast resists PEB' s diffusion enhances their resolution while the decreases in development rate have little effect on them. Time dependence cannot be observed for these resists because the diffusion length remains constant with increasing FEB time.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.