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Viviparous reproduction has evolved independently more than 100 times in the evolutionary history of Squamata (lizards and snakes). Adaptation to cold climates is the dominant hypothesis explaining...

The jaws of vertebrates display a striking diversity in form and function, but they typically open and close like a trapdoor rather than sliding like a saw. Here, we report unique feeding behaviour in the blunt-headed snail-eating snake, Aplopeltura boa (family Pareidae), where the snake cuts off and circumvents the indigestible part (the operculum) of its prey in the mouth using long sliding excursions of one side of the mandible, while the upper jaws and the mandible on the other side maintain a stable grasp on the prey. This behaviour, which we call ‘mandibular sawing’, is made possible by extraordinarily independent movements of the jaw elements and is a surprising departure from usual feeding behaviour in vertebrates., ヘビが顎をノコギリのように使うことを発見 --ボルネオ島での爬虫両生類の生態調査で--. 京都大学プレスリリース. 2020-07-31.

ArF lithography is still applied to the majority of critical layers, even with increasing of extreme ultraviolet lithography in leading-edge production. As wafer design shrinks, conventional 6% phase shift mask (PSM) becomes hard to meet the ArF lithography requirements especially for array dot on mask (hole on wafer). Therefore, transmission dependency was evaluated by mask 3D simulation, and it was found that 30% transmission has the best lithographic performances for array dot. Based on these results, mask blank and mask making process for new 30% PSM were developed. Wafer printability test using negative tone development demonstrated that new 30% PSM has better process window and mask error enhancement factor (MEEF) than conventional 6% PSM for array dot (hole on wafer). To investigate further application of new 30% PSM, lithography performances of various patterns were evaluated by mask 3D simulation and aerial image measurement system (AIMSTM). The results indicated that new 30% PSM has larger lithography margin than 6% PSM for iso dot, iso line and logic pattern. Additionally, wafer printability test demonstrated that new 30% PSM has better process window than 6% PSM for iso dot. Defect control is also an important factor in high volume manufacturing. Therefore, it is necessary to evaluate the repairability and printability of the defects on new 30% PSM. We repaired various types of defects by electron-beam repair tool and confirmed the repairability by AIMS. And the defect printability of new 30% PSM and 6% PSM to critical dimension (CD) on wafer was evaluated by program defect mask that has pin dot, extrusion and intrusion defects.

Even with the increase in need for next-generation lithography, immersion ArF lithography is still applied to the majority of critical layers. However, as circuit designs shrink, conventional 6% phase-shift mask (PSM) will become difficult to meet the lithography requirements for dense dot pattern compared to dense line pattern. To enhance immersion ArF lithographic performances for dot pattern, high-transmission PSM (High-T PSM) is attracting attention because the transmission of PSM has a significant impact on lithographic performances. From results of transmission dependency evaluated by mask three-dimensional (3D) simulation, it was found that 30% transmission has the best lithographic performances for dense dot. Based on these results, mask blank and mask making process for the new 30% PSM were developed. The results showed good cross-section profile, mask pattern resolution, and defect repairability. In addition, the durability against chemical cleaning and ArF irradiation were also improved. Wafer printability test using negative tone development demonstrated that new PSM has advantages in process window and mask error enhancement factor for dense dots (holes on wafer). Finally, the potential for further application of new PSM was investigated by mask 3D simulation. The results showed that new PSM has lithographic benefits not only for dense dots but also other patterns.

Gunung Mulu National Park (GMNP) in northwestern Borneo is marked by high species diversity and diverse environments. We present one new amphibian and ten new reptile records from GMNP and its surrounding area. In the records, Asthenodipsas jamilinaisi and Garthius chaseni were newly recorded in the Sarawak State. We also present the first record of Cyrtodactylus muluensis from outside of GMNP and the second record of Opisthotropis typica from the park. Combined with previous information, a total of 108 amphibians and 104 reptiles are known from GMNP, and their preferred habitat types are diverse. Furthermore, observed male-male combat of Dopasia buettikoferi is the first detailed description of the genus. Two color morphs of D. buettikoferi had an identical ND2 haplotype and appeared to be the same species. The present study provides new information about Bornean amphibians and reptiles, and also emphasizes the importance of continuous monitoring.

Even with the increasing need for next-generation lithography, ArF lithography is still applied to the majority of critical layers. However, as wafer design shrinks, conventional 6% phase shift mask (PSM) becomes unable to sufficiently meet the lithography requirements for dense dot pattern compared to dense line pattern. To enhance ArF lithographic performances for dot pattern, high-transmission phase shift mask (High-T PSM) is attracting attention because the transmission of PSM has a significant impact on lithographic performances[1-4]. From the evaluation results of transmission dependency by mask 3D simulation, it was found that 30% transmission has the best lithographic performances for dot pattern. Based on these results, mask blank and mask making process for the new 30% PSM were developed. The result showed good cross-section profile, mask pattern resolution and defect repairability. In addition, the durability against chemical cleaning and ArF irradiation were also improved. Wafer printability test using negative tone development demonstrated that new PSM has advantages in process window and MEEF for dense dots (holes on wafer). Finally, the potential for further application of new 30% PSM was investigated by mask 3D simulation. The results showed that new 30% PSM has lithographic benefits not only for dense dots but also for other patterns. The new 30% PSM is a strong candidate capable of enhancing ArF lithographic performances for 5nm node or hp 1Xnm and beyond.

Toads are chemically defended by cardiotonic steroids known as bufadienolides. Resistance to the acute effects of bufadienolides in snakes that prey on toads is conferred by target-site insensitivity of the toxin’s target enzyme, the Na+/K+-ATPase. Previous studies have focused largely on the molecular mechanisms of resistance but have not investigated the physiological mechanisms or consequences of exposure to the toxins. Adrenal enlargement in snakes often is associated with specialization on a diet of toads. These endocrine glands are partly composed of interrenal tissue, which produces the corticosteroids corticosterone and aldosterone. Corticosterone is the main hormone released in response to stress in reptiles, and aldosterone plays an important role in maintaining ion balance through upregulation of Na+/K+-ATPase. We tested the endocrine response of select species of snakes to acute cardiotonic steroid exposure by measuring circulating aldosterone and corticosterone concentrations. We found that Rhabdophis tigrinus, which specializes on a diet of toads, responds with lower corticosterone and higher aldosterone compared to other species that exhibit target-site resistance to the toxins but do not specialize on toads. We also found differences between sexes in R. tigrinus, with males generally responding with higher corticosterone and aldosterone than females. This study provides evidence of physiological adaptations, beyond target-site resistance, associated with tolerance of bufadienolides in a specialized toad-eating snake.

Foraging behavior of a diurnal gecko, Lygodactylus tolampyae, was observed during the night in the field in Ankarafantsika National Park, Madagascar. An adult L. tolampyae was observed to stay near the nest of an ant, Aphaenogaster swammerdami. The gecko attacked a worker ant carrying a pupa and ate only the pupa by robbing it from the worker. This observation suggests that typically diurnal geckos may shift foraging time to the night under natural conditions.

We conducted a radio-tracking study on Rhabdophis tigrinus to assess its spatial ecology in the Ashiu Forest Research Station, Kyoto, Japan from 2009 to 2010. The study site is located in a temperate mountain area and includes forests, grasslands, a river, open riverbanks, and small brooks. We estimated the width and area of home ranges for 11 and 10 individuals, respectively. Home range size showed a large individual variation, with home range width ranging from 97 to 997 m and area ranging from 1.3 to 11.0 ha. We did not find obvious sexual differences or effects of body size on home range size. Tracked snakes tended to aggregate in riverside areas in spring, although females were sometimes found away from the river. Compared to spring, snakes in summer and fall were relatively dispersed and more likely to be located in brookside areas or places apart from water bodies. Eight individuals moved from riverside areas to brookside areas in summer. We located hibernation sites of nine individuals. ...

The mean-square radius of gyration 〈S2〉, second virial coefficient A2, and intrinsic viscosity [η] were determined in methanol at 25.0 °C for two kinds of poly(N-isopropylacrylamide) (PNIPA) synthesized by radical polymerization in tert-butanol and benzene by the use of azobis(isobutyronitrile) as an initiator. In all cases of the three quantities, it is found that the value is smaller for the PNIPA synthesized in benzene than for that synthesized in tert-butanol and the difference between the two kinds of PNIPA increases with increasing the weight-average molecular weight Mw. The average chain dimension of the former PNIPA should then be smaller than that of the latter. Since the two kinds of PNIPA were shown to have the same stereochemical composition (and also the same chain end group), the difference in the average chain dimension may be regarded as arising from the difference in the primary structure, i.e., the number of branch points. Considering the fact that the average dimension of a given polymer chain in general decreases with increasing the number of branch points, it may be concluded that the number is larger in the former PNIPA than in the latter. The behavior of the interpenetration function Ψ and the Flory–Fox factor Φ as functions of Mw is also examined, confirming the conclusion.

The cloud point was determined for aqueous solutions of four kinds of poly(N-isopropylacrylamide) samples synthesized by radical polymerization in methanol, tert-butanol, benzene, and 1,4-dioxane by the use of azobis(isobutyronitrile) as an initiator, in the range of the weight fraction of the sample from 0.5 to 10%. It has then been found that the cloud points so determined for the samples synthesized in benzene and 1,4-dioxane are definitely lower than those for the samples synthesized in methanol and tert-butanol, although all the samples have almost the same stereochemical composition and the same end group. The observed deviation may be regarded as arising from the difference in the primary structure between the samples.

The control of critical dimension uniformity (CDU), especially intra-field CDU, is an important aspect for advanced lithography, and this property must be controlled very tightly since it affects all of the exposure fields. It is well known that the influence of the mask CDU on the wafer intra-field CDU is becoming dominant because the mask error enhancement factor (MEEF) is quite high for low-k1 lithography. Additionally, the abovementioned factors impact the CDU through global (field-level) and local (grating-level) variations. In this paper, we analyze in detail CDU budgets by clarifying the impact of local CD variation. The 50-nm staggered hole features using Att-PSM showed a mask global CDU of 1.64 nm (3sigma at the mask level) and a wafer intra-field CDU of 2.30 nm, indicating that the mask global CDU was a major part of the intra-field CDU. By compensating for the contribution of the mask CD, the wafer intra-field CDU can be reduced to 0.986 nm. We analyzed the budgets of wafer intra-field CDU, which is caused by local CD variation (mask and process) and measurement noise. We determined that a primary cause of the wafer intra-field CDU after applying a mask CD correction was these local CD variations, which might disturb the proper use of dose correction for the mask CD. We demonstrated that the impact of mask local CD variation on the correction flow can be greatly reduced by averaging multiple point measurements within a small area, and therefore discuss the optimum conditions allowing for an accurate intra-field CDU determination. We also consider optimization of the CD sampling scheme in order to apply a dose correction on an exposure system to compensate for the mask CDU.

In this paper we compare the imaging properties of lithographic test structures formed on test masks with different reticle absorbers for use in1.35 NA immersion lithography. We will look into different aspects like process windows and CD fingerprints. Beyond that we look into the topographic effects caused by the different absorbers, the mask 3D effects. We will study the interaction between the different masks and immersion scanner. Special attention is given towards the correctability of the intrafield CD fingerprint by mask and scanner applying dose corrections.

For sub 20nm features, IC (integrated circuits) designs include an increasing number of features approaching the resolution limits of the scanner compared to the previous generation of IC designs. This trend includes stringent design rules and complex, ever smaller optical proximity correction (OPC) structures. In this regime, a new type of mask, known as opaque MoSi on glass (OMOG), has been introduced to overcome the shortcomings of the well-established phase shift masks (PSM). This paper reviews the fundamental aerial imaging differences between identically designed PSM and thin OMOG masks. The masks were designed for scanner qualification tests and therefore contain large selections of 1D and 2D features, including various biases and OPCs. Aerial critical dimension uniformity (CDU) performance for various features on both masks are reported. Furthermore, special efforts have been made to emphasize the advantages of aerial imaging metrology versus wafer metrology in terms of shortening scanner qualification cycle time.

As half pitch shrinks to sub 20nm dimensions, the latest hybrid IC (integrated circuit) designs include a greater number of features that approach the resolution limits of the scanner than in the previous generation of IC designs. This trend includes stringent design rules and complex, ever smaller optical proximity correction (OPC) structures. In this regime, a new type of mask, known as opaque MoSi on glass (OMOG), has been introduced to overcome the shortcomings of the well-established phase shift masks (PSM). As for lithography, scanner and mask determine ultimate intra-field performance as one approaches scanner resolution limits. Holistic lithography techniques have been developed to optimize the interrelated mask and scanner effects on critical dimension uniformity (CDU) and common process window (PW) for the most demanding sub 20nm node features. This paper presents an efficient and production worthy methodology for evaluating the CDU, PW, and 3D effect fingerprints of the latest immersion scanner and thin OMOG masks, and minimizing them using high-order optimizers of the latest holistic ArFi lithography.

High-order harmonic (HOH) beam generated from the intense femtosecond laser pulse always propagates coaxially with the fundamental laser field. Thus, we need to separate the fundamental laser field from the HOH beam whenever we apply the HOH to spectroscopies. Conventional thin foil metal filters can completely eliminate visible or infrared fundamental laser light, while the thin foils are very fragile and easily damaged with the intense fundamental laser pulse. We have already demonstrated that a silicon or silicon carbide plate is useful for splitting the fundamental and HOH beams thanks to the Brewster incident angle to the fundamental laser beam. Nevertheless, the silicon or silicon carbide (amorphous) beam splitter (BS) is not fully satisfactory for the application because the BS is opaque for visible light. Hence, we cannot reuse the transmitted light. Thermally induced effects such as deformation of the surface may not be negligible under the high-power irradiation of the laser field. Thus, we have searched for transparent materials for visible light which should be suitable for the BS of the HOH beam.

In the semiconductor technology using the 193nm ArF excimer laser, the problem of radiation damage on photomask becomes more serious. This phenomenon is regarded as serious issue for semiconductor device fabrication. Some approaches have been tried to prevent the radiation damage. One of reports indicates that the radiation damage can be reduced by using an exposure tool with ultra clean extreme dry air [1]. However, it is difficult to adopt dry air into all exposure tools due to high cost. In our previous work, two facts were ascertained; radiation damage is caused by MoSi film oxidation, and depends on MoSi film composition [2]. In this paper, radiation damage was tried to decrease by MoSi film modification of att. PSM. MoSi film composition for PSM is optimized in consideration of cleaning durability, mask defect repair and processability. The new PSM is named AID (Anti Irradiation Damage). Radiation damage of AID PSM can be improved by 40[%] from conventional PSM. Cleaning durability can be also improved by AID PSM. The other evaluation items such as CD performance, cross section, defect level and repair, are equal between the AID PSM and conventional one. Additionally, the lithography performances by simulation of AID PSM are equivalent with that of conventional PSM. Therefore, it can be expected that there is no difficulty in converting conventional PSM into AID PSM. From these evaluation results, development of AID PSM was completed, and preparation for production is now going.

The exposure tools have been advanced for finer patterns and higher throughput. However, it causes the increase of accumulation of exposure dose on mask, which induces the mask CD growth. This issue has been reported as the radiation damage and brought the low yield of device chips [1, 2, 3]. As the solution, the radiation damage can be reduced by the ultra extreme dry air in exposure tool [4]. It is difficult to adopt dry air to all exposure tool due to cost. In this work, we tried to solve the radiation damage from photomask making approach. The attenuated phase-shift mask (att. PSM) was chosen for this evaluation because its damage is severest. The test plates of att. PSM were exposed by ArF laser, and the amount of CD degradation and the composition change in damage area were investigated. By the analyses of TEM and EDX, it was confirmed that the root cause of radiation damage is oxidation of MoSi film. Therefore, the approaches from mask process and material were tried to prevent MoSi film from oxidation. As a result, the approach from mask material, especially modification of MoSi film is effective. And the characteristics of new MoSi film, such as CD performances, cross section, and cleaning durability, were compared with conventional att. PSM. These results show the characteristics of two masks are equivalent. Att. PSM with new MoSi film is promising solution to improve radiation damage.

The miniaturization of pattern size on photomask is advanced year by year. It becomes more important to improve Line Edge Roughness (LER) and resolution because of their impacts on lithography performances. When miniaturization is advanced, high sensitivity inspection is also indispensable. Therefore, LER becomes the key factor to reduce the nuisance defect for high sensitivity mask inspection. Basically, LER originates from resist materials and EB writer. If resist pattern LER is good, final pattern LER can be good too. One of the easiest solutions for LER is using thick resist. Thick resist can vertically smooth down the LER. However, it deteriorates resolution due to the high aspect-ratio. Another solution for LER is using low sensitivity resist. Low sensitivity resist needs many electron exposures by EB writer. Therefore, electronic density of EB pattern increases and pattern edge becomes clear. However, it deteriorates throughput, which is essential to production. Only by mask resist, it is difficult to satisfy all items, that is mask LER, resolution and throughput. In this study, the improvement of LER without deterioration of resolution is tried by dry etching process. It is found that remaining resist after Cr etching has its limitation for mask LER. And Cr over etching and source power of Cr and MoSi etching are effective factors for mask LER. On the basis of these results, the optimal etching process is determined. It is confirmed that mask LER can be improved without deterioration of resolution by the optimal etching process.

Q-switching of a Pr∶LiYF 4 laser at three visible wavelenghths pumped by a high-power GaN laser diode is demonstrated. The highest laser peak power of 79 W with a pulsewidth of 50 ns is obtained for 639 nm at 7.7 kHz

For 45nm and 32nm node technology, the challenges for resolution and CD control of mask patterns become the steeper mountain path. Especially, Sub Resolution Assist Feature (SRAF) is the smallest pattern on mask and amplifies the difficulty of mask fabrication. In order to improve the resolution of fine patterns, the influence of wet processing cannot be neglected, because it causes the pattern collapsing. Wet processing of mask-making can be divided into resist development and cleaning. In this study, the root causes of pattern collapsing are investigated at each wet processing. It is confirmed that thin resist can enhance the resolution limit of resist pattern and hard-mask blank, such as OMOG: Opaque MoSi On Glass, is suitable for thinner resist under 1500A. The pattern collapsing of OMOG is compared with that of Att.PSM at the cleaning before and after Cr stripping. Mask inspection finds that pattern collapsing can be suppressed by OMOG at both cleanings. It is because OMOG has lower cleaning stress than Att.PSM due to lower aspect-ratio. This benefit is demonstrated by cleaning stress simulation. Additionally, it is found that the SRAF size of OMOG can be wider than Att.PSM by optical simulation. From these results, OMOG has much advantage of fine pattern fabrication and is the optimal blank for 32nm node and beyond.

The verification of not only two-dimensional feature but also three-dimensional feature, sidewall angle (SWA), has been becoming increasingly important in NGL mask fabrication. The OMOG (Opaque MoSi on Glass) mask for ArF immersion lithography with double patterning and the reflective type mask for EUV (Extreme Ultra- Violet) lithography are especially in need of it. There are several metrology tools e.g. SEM, AFM, and Scatterometry for sidewall angle (SWA) measurement. We evaluated a new SWA measurement method using white-band width (WBW), which is equivalent to mask pattern edge width, by CD-SEM. In general, WBW correlates with SWA. It narrows as SWA becomes steeper. However, the correlation deteriorates when SWA is vertically near. This is due to the resolution limit of electron beam diameter used for measurement. We analyzed the new approach to measure SWA by CD-SEM to solve this problem. And the analysis revealed that WBW changes proportionately electron beam current value. The amount of width change depends on SWA. In this paper, we will describe the new SWA measurement method and its evaluation results as well as SWA measurement results of OMOG and EUV masks.

Current flash memory technology is facing more and more challenges for 45nm and 32nm node technology. To get good CD and yield control, optimized RET, OPC modeling and DFM techniques have to be applied [1]. To enhance process window (PW) and better CD control for main features, assist features (SB) have to be used. Simulation and wafer evaluation show that the SB CD performance is very critical. Based on OPC simulation, we can get a very good prediction about the CD size and placement of assist features. However, we can not always get what we want from mask suppliers. For 45nm node technology and beyond, The SB CD size (~ 20nm at 1X) has almost pushed to the current mask process limit. Wafer fabs have a very big concern about the stability of linearity signatures from different suppliers and different products in order to keep high accuracy of OPC models. Actually the CD linearity signature varies from one mask supplier to another and also varies from product to product. To improve the SB CD control, the ideal goal is to make "flat" linearity for all mask suppliers. By working closely with TPI mask supplier, we come up solutions to improve SB CD control to get "flat" linearity. Also technology development is causing more severe SB printability, we proposed a methodology to use AIMS for predicting SB printability. Wafer results proved the feasibility for these methodologies.

The development of semiconductor process for 32nm node is in progress. Immersion lithography has been introduced as an extension of 193nm lithograpy. In addition, DPL (Double patterning lithography) is becoming a strong candidate of next generation lithography. The extension of optical lithography increases more mask complexity and tighter specification of photomasks. CD performance is the most important issue in the advanced photomask technology. However, it is expected that conventional mask cannot satisfy the required mask specifications for 32nm node and beyond. Most of CD errors are contributed to the dry etching process. Mask CD variation is greatly influenced by the loading effect from dry etching of the absorber. As the required accuracy of the mask arises, Cr absorber thickness has been gradually thinner. CD linearity with the thinner Cr absorber thickness has better performance. However, it is difficult to apply thinner Cr absorber thickness simply under the condition of OD > 3, which is needed for wafer printing. So, we adopted MoSi absorber instead of conventional Cr absorber, because MoSi absorber has less micro and global loading effect than that of Cr absorber. By using MoSi absorber, we can reduce Cr thickness as a hardmask. The thinner Cr hardmask allows for reduce resist thickness and become same condition for conventional EB resist lithography. The lithography performances were confirmed by the simulation and wafer printing. The new MoSi absorber mask behaves similar to the conventional Cr absorber mask. The adoption of super thin Cr as a hardmask made it possible to reduce resist thickness. By the application of the thin resist and the latest tools, we'll improve the mask performance to meet the 32 nm generation specification.

As the required accuracy of the mask arises, Cr shading film thickness has been thinner gradually. CD linearity with the thinner Cr film thickness has better performance. However, it is difficult to apply thinner Cr film thickness simply under the condition of OD > 3, which is needed for wafer printing. So, we tried to develop new shading film. We adopted MoSi film, because MoSi film has almost no micro loading effect compared with Cr film. MoSi shading film with att.PSM satisfied OD > 3 at 193nm wavelength with good resist profile. But the issue was dry-etching selectivity, because shading layer material was the same of att. PSM layer material. Therefore super thin Cr etching stopper was inserted between MoSi shading layer and MoSi att.PSM layer. The mask CD performance of new blank was evaluated for CD linearity, CD through pitch, and global loading effect. This blank and mask process reduce loading effect, therefore the mask CD performance is improved remarkably. In conclusion, the mask manufacturing process margin was able to be expanded by this new blank and method, and it is expected that we can achieve the required specifications for att.PSM in 45nm node and beyond.

For 45 nm node and beyond, the alternating phase-shift mask (alt. PSM), one of the most expected resolution enhancement technologies (RET) because of its high image contrast and small mask error enhancement factor (MEEF), and the binary mask (BIM) attract attention. Reducing CD and registration errors and defect are their critical issues. As the solution, the new blank for alt. PSM and BIM is developed. The top film of new blank is thin Cr, and the antireflection film and shielding film composed of MoSi are deposited under the Cr film. The mask CD performance is evaluated for through pitch, CD linearity, CD uniformity, global loading, resolution and pattern fidelity, and the blank performance is evaluated for optical density, reflectivity, sheet resistance, flatness and defect level. It is found that the performance of new blank is equal to or better than that of conventional blank in all items. The mask CD performance shows significant improvement. The lithography performance of new blank is confirmed by wafer printing and AIMS measurement. The full dry type alt. PSM has been used as test plate, and the test results show that new blank can almost meet the specifications of pi-0 CD difference, CD uniformity and process margin for 45 nm node. Additionally, the new blank shows the better pattern fidelity than that of conventional blank on wafer. AIMS results are almost same as wafer results except for the narrowest pattern. Considering the result above, this new blank can reduce the mask error factors of alt. PSM and BIM for 45 nm node and beyond.

The attenuated phase-shift mask (att. PSM) is one of resolution enhancement technologies (RET) and has been widely adopted for several device layers. And the high-transmission att. PSM, which has various structures and transmittances, can be expected to have the advantages in process window. In this paper, the lithographic performances (Contrast, MEEF and DOF) of high-T att. PSM were evaluated by using the 3D electro-magnetic field simulator. The results showed that high-T att. PSM has better MEEF and partially better DOF than those of 6%-transmission MoSi type. As the transmittance is getting higher, the smaller line CD is needed for OPC adjustment especially at narrow pitch. In respect of film structure, it is found that there is no large difference among three high-T att. PSMs except for MEEF at specific pitch. Remaining chrome on the high-T films causes the trade-off between contrast and MEEF. The simulation results are compared with AIMS results measured by AIMS TM 45-193i of Carl Zeiss. The AIMS results of actual masks agree with no-Hopkins mode simulation very well, while they do not agree with Hopkins mode simulation especially at narrow pitch. Because the azimuthal polarization does not cause contrast loss, the differences between AIMS mode (conventional) and Scanner mode (vector effect emulation) are small.

Alternating Aperture Phase Shift Mask (AAPSM) is one of the most effective approaches to improve the resolution of logic gate structures for ArF lithography of the 65nm half-pitch node and beyond because AAPSM shows good performance due to the high image contrast and the small mask error enhancement factor (MEEF). For AAPSM, the issue of intensity imbalance between pi-space and zero-space is well known. In order to solve this issue, several kinds of AAPSM, such as single trench with undercut, single trench with bias are used in production application. The fabrication of single trench with bias AAPSM requires that the quartz dry etch satisfies many conditions. The etched quartz features must not only show excellent depth uniformity but also good etch depth linearity across a wide range of feature sizes. However, in defocus conditions, the through-pitch image placement error becomes worse even with good quartz etch depth linearity. The reason is that the phase error caused by mask topography is different depending on the pitch. In this work, we minimize the phase error through-pitch and through-focus by rigorous 3D mask simulations. Based on the results, we have fabricated two masks with opposite quartz depth linearity signatures to estimate the imaging impact of phase errors and used them for exposures on an ASML XT:1250Di immersion scanner. We discuss the feasibility of this method by comparison of through-focus and through-pitch image placement errors between wafer printing, AIMS, and simulation.

Chromeless Phase Lithography (CPL) is one of resolution enhancement technologies (RET) for 65nm node and beyond. CPL has various advantages such as no necessity of double exposure, and small pattern displacement and CD error caused by the intensity imbalance. The high resolution lithography can be expected with the combination of high NA and off-axis illumination (OAI) in 193nm lithography. It is known that CPL can flexibly change structure through gate pitch. There are various kinds of structure, such as pure CPL, Zebra, Rim, and Stripe. And there are also various kinds of scattering bar depending on the gate pitch. In this paper, we estimated normalized image log-slope (NILS), mask error enhancement factor (MEEF), depth of focus (DOF) and phase shift depth for each CPL structure by rigorous 3D mask electro-magnetic field (EMF) simulation on mask topographies. And it was found that Zebra and Stripe can improve NILS, and Stripe is most effective to improve MEEF for narrow pitch. There is no large difference in DOF between all structures, and DOF for all structures with wide pitch can be expanded by the addition of chrome scattering bar. We evaluated the impact of phase shift depth and found that the optimal phase shift depths of all structures are larger than 180degrees. The improvement of mask-making accuracy becomes more important to achieve better mask pattern resolution. Therefore, we focused on the defects of the sub-resolution chrome feature and chrome scattering bar. It was found that the defects of sub-resolution chrome feature have big influences on the lithography performance. And the defects of scattering bars become more sensitive with closer to the main feature.

The phase shift mask (PSM) is one of the most effective approaches to improve ArF lithography performance. Recently, the quartz dry etching technology plays an important role to fabricate the PSM, such as space bias type Alternating (Alt.) PSM and chrome-less phase lithography (CPL) mask. The quartz etching profiles seems to be affected the lithography performance. In this paper, preliminary, we evaluate the nominal influences of quartz profile by rigorous electromagnetic field simulation. Then influence of the quartz profile is investigated by measuring the real masks. In this experiment, we intentionally fabricate Alt. PSM and CPL masks with the tapered side-wall and deeper micro-trench. Lithography performances of the real masks are measured by the aerial image measurement system (AIMS fab193). We compare the result of AIMS with simulation. We investigate the AIMS measurement well corresponds to the simulation. Side-wall angle and corner rounding strongly affect the lithography performance. However, micro-trench doesn’t affect a lot.

The alternating phase-shift mask (alt. PSM) is one of the most effective approaches to improve a resolution of the 65nm logic gate structure in ArF lithography. Previously we have studied the optimization of alt. PSM in 180nm gate-pitch. In this study, we evaluated various alt. PSM in the case of 160nm gate-pitch. Using a rigorous electro-magnetic field simulation of light scattering in 3D mask topographies, we evaluated CD difference between π-phase and 0-phase space size (the π-0 CD difference), resist CD through pitch and normalized image log-slope (NILS). The parameters for our simulation were mask structure (shallow trench depth (ST), undercut size (UC), space bias, Chrome (Cr) CD, pitch, phase shift depth) and ArF exposure condition (NA, sigma, defocus). From the results of simulation, it turned out that single trench structures with UC and/or space bias showed the good intensity balance through defocus. We compared the simulation results with the AIMS fab193 (Carl Zeiss) results and found there was no large difference. The combination of UC and space bias could be chosen as suitable structure for 160nm gate-pitch.

We have investigated novel beam splitter (BS) materials to relax thermal issues under irradiation of a high-average-power visible and near infrared (VIS–NIR) laser beam. The material should efficiently reflect a high-order harmonic beam in the extreme ultraviolet (XUV) spectral region and transmit a VIS–NIR fundamental laser beam at a Brewster incidence for the latter beam. We have investigated optical and thermo-mechanical properties of crystalline silicon carbide (SiC), diamond, and rutile since they exhibit high transparency and high index of refraction for a VIS–NIR light. We also address thermal issues of conventional opaque BS materials by measuring their thermal distortion. We have shown that crystalline SiC is the most promising candidate among the other materials because of a high reflectivity for XUV light, as well as an ignorable thermal distortion. The surface flatness of a crystalline SiC plate must be improved to realize an applicable BS in the XUV spectral region.

We demonstrate pulse laser operation of a Pr:LiYF4 laser pumped by InGaN laser diodes (444 nm) using an acousto-optic modulator. We obtained a maximum laser peak power of 167 W (4 μJ/pulse) with a pulse width of 24 ns at an 11 kHz repetition rate for a 63 nm wavelength. Employing an 8 mm long lithium triborate nonlinear crystal in the laser cavity, we obtained a maximum peak power of 55 W (2.7 μJ/pulse) at 320 nm, which corresponds to a conversion efficiency of 69% with respect to the fundamental laser energy. The UV laser pulse width was 36 ns.