We performed an initial evaluation of 157-nm immersion lithography. The 157-nm immersion fluid needs to have both a high refractive index and high transmittance at a wavelength of 157 nm. This paper focuses on the transparency of the fluid. We evaluated the transparency of straight-chain perfluoroalkane and perfluoroether using a semi-empirical molecular orbital method. We found that perfluoroether has lower absorption at 157 nm than perfluoroalkane, and increasing the amount of ether bonds in perfluoroether can further reduce the absorption. Moreover, we found that designing the molecular structure with ether bonds so that the number of successive CFx is balanced should further improve transparency. Although the commercial perfluoropolyether BARRIERTA® J25V contains a trifluoromethyl group in one of its side-chains, it satisfied the above conditions and achieved high transmittance of 1.0 cm-1 at 157 nm. The sensitivity characteristics of the XP2332C and F-SSQ resists were evaluated by dry and immersion exposure using BARRIERTA® J25V immersion fluid, and no noticeable changes were seen in the development contrast for either exposure condition for either of these two resists. To perform 157-nm immersion exposures, we constructed a Michelson interferometric exposure tool, which let us create an interference pattern with sufficient optical contrast. We obtained a resolution of 60-nm line-and-space pattern having a good rectangular shape by immersion exposure using this interferometric exposure tool, F-SSQ resist, and BARRIERTA® J25V immersion fluid without using a top-coat.
A two-beam interference lithography system based on a line-selected F2 laser has been developed. Resist patterns with a 60nm line and space (L&S) resolution were produced by the interferometer by F2 immersion lithography. The F2 laser performance had been especially optimized for this application. The spectral emission at the 157.53nm line was less than 1% of the main line emission at 157.63nm. The main line had a deconvolved spectral bandwidth of 0.84 pm (full width at half maximum (FWHM)). The degree of horizontal linear polarization was above 0.73 and the visibility of spatial coherence was larger than 0.83 at a pinhole distance of 0.1mm.
In this paper, we present an evaluation system for F2 laser lithography masks and resists and we report preliminary test results. The evaluation system has two subsystems that are based on very accurate measurement technology. One subsystem is used for mask evaluation, the other subsystem for resist evaluation. The mask subsystem consists of two units. One unit evaluates real size 6025 binary masks placed horizontally as inside steppers. This unit measures three parameters: 1) the real time in-situ transmittance at 157nm during F2 laser irradiation, 2) the in-situ VUV transmittance using a VUV spectrophotometer and 3) the deformation of the pellicle. The precision of transmittance measurement at 157nm is +/-0.5%. The precision of the pellicle deformation measurement is +/-0.1μm. The second unit of the mask subsystem collects samples of the mask outgassing and analyzes them in a gas chromatograph mass spectrometer. The resist evaluation subsystem consists of three units. 1) One unit determines negative effects of outgassing resist contaminants on the transmittance of optical materials under F2 laser irradiation, 2) the second unit analyzes the outgassing from resists and 3) the third unit examines the effectiveness of exposure tool purge nozzles to reduce outgassing contamination.
We have evaluated the outgassing products and the in-situ transmittance of a contaminated CaF2 substrate for monocyclic fluoropolymers with four protecting groups: methoxymethyl (MOM), tert-butoxycarbonyl (t-BOC), menthoxymethyl (MM), and 2-cyclohexylcyclohexyloxymethyl (CCOM). We have also evaluated the same type of fluoropolymer with seven kinds of photo-acid generators (PAGs) added to a base fluoropolymer solution. We found little correlation between the total amount of outgassing from the polymer and the decreasing rate of the CaF2 substrate transmittance caused by outgassing adhesion. Although the MOM protecting group generated the largest amount of outgassing products, the most substantial decrease in the transmittance was observed for the t-BOC protecting group. Also, the outgassing products due to use of a PAG did not greatly reduce the absorption coefficient of a CaF2 substrate regardless of the kind of PAG. Therefore, the absorption coefficient of the outgassing-contaminated CaF2 substrate appears to be more sensitive to the type of protecting group, especially the t-BOC protecting group including a t-butyl unit, rather than the type of fluoropolymer or PAG. We analyzed the substrate surface contaminant due to the t-butyl unit by x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and time-of-flight secondary ion mass spectrometry (TOF-SIMS), and found that increasing amounts of organic compounds, containing mainly C- and H-atoms, were adhered to and deposited on the substrate surface with an increasing irradiation dose. We speculate that the contaminants on a CaF2 surface with or without an anti-reflective coating were formed not only through mere physical adsorption, but also through certain chemical combinations. We conclude that in terms of material design of the fluoropolymer resist for 157-nm lithography, we need to pay attention to the protecting group of polymers, especially the t-BOC or t-butyl protecting group, which generates isobutene product during 157-nm irradiation.
F2 laser lithography at 157nm is the most promising candidate of post-ArF excimer laser lithography. A major concern, however, is the deterioration of 157nm optics due to contamination under F2 laser irradiation. An evaluation of outgassed products of 157nm resist and their effect on optical materials and is therefore indispensable for F2 laser lithography. Semiconductor Leading Edge Technologies Inc. (Selete) and Komatsu Ltd. designed and constructed a resist outgassing evaluation system in order to develop exposure tools and resists for 157nm lithography. The system determines the negative effects of outgassing resist contaminants on the transmittance of optical materials under F2 laser irradiation. The system has two units. One unit collects resist outgas and analyzes sampled gas in a gas chromatograph mass spectrometer (GC-MS). The other unit is a resist outgassing adhesion unit, which measures the transmittance change of optical materials due to contamination adhesion in real-time. Our analysis showed that most outgassed products were from the resist protecting groups and photo acid generators (PAG) including small hydrocarbons like isobutene, benzene derivatives and dimethoxymethane. After irradiating a 157nm lithography resist with a total dose of 30J/cm2 the transmittance of a calcium fluoride (CaF2) substrate decreased from initially 90% to 85%. This was due to adhesion contamination as x-ray photoelectron spectroscopy (XPS) analysis showed an organic contamination deposition of over 5nm thickness on the CaF2 substrate.
F2 laser lithography (wavelength:157 nm) is a candidate of post-ArF excimer laser lithography. In order to test the characteristics of vacuum ultraviolet (VUV) materials for F2 laser lithography, we developed an evaluation system consisting of a 1 kHz F2 laser, an in-situ real-time transmittance measurement unit and an in-situ VUV spectrophotometer. The precision of the real-time transmittance measurement is +/- 0.5%. The precision of the VUV spectrophotometer measurement is +/- 0.5% for scanned wavelengths (140 - 300 nm) and +/- 0.1% for a constant wavelength (at 157.6 nm). Due to F2 laser irradiation cleaning, the transmittance of uncoated calcium fluoride (CaF2) substrates and of F2 laser coatings at first rapidly and then gradually increased. Thereafter the transmittance remained constant. Results of the real-time transmittance and the VUV spectrophotometer measurement were almost identical. In addition, durability tests of CaF2 substrates and of F2 laser coatings were performed with a 4 kHz F2 laser for more than 10 billion pulses (Bpls). After the initial transmittance increase of CaF2 substrates, no change in transmittance was observed during more than 10 Bpls. In order to maintain the CaF2 substrate transmittance, silicon compounds have to be removed from the purge gas and from the irradiation chamber where optical materials are placed. F2 laser coating quality varied enormously between suppliers.
The 157nm molecular fluorine laser is regarded as the next generation light source for semiconductor exposure technology in the vacuum ultraviolet (VUV) region. Research for high performance F2 laser optical materials is therefore indispensable. In this paper, we describe methods and results of evaluating optical materials used in the 157nm region. In order to evaluate F2 laser optical materials, we have developed in-situ system, which measures the real-time transmittance at 157nm during laser irradiation and the transmittance in the vacuum ultraviolet (VUV) region directly after laser irradiation to avoid airborne contamination. The system is purged with high purity nitrogen gas during irradiation to reduce laser light absorption and to keep contamination at a minimum. Due to F2 laser irradiation cleaning, the transmittance of uncoated calcium fluoride (CaF2) samples initially rapidly then gradually increased during 50 million pulses (Mpls). Thereafter the transmittance remained constant. In addition, durability test results of CaF2 substrates and coatings are also presented. Especially coating quality varied enormously between suppliers.
The 157 nm molecular fluorine laser is regarded as the next generation light source for semiconductor exposure technology in the vacuum ultraviolet (VUV) region. Research for high performance F2 laser optical materials is therefore indispensable. In this paper, we describe methods and results of evaluating optical materials used in the 157 nm region. We have developed an in-situ VUV evaluation system, which can measure the transmittance in the deep ultraviolet (DUV) and the VUV region directly after laser irradiation and the temporal transmittance during 157 nm-laser irradiation without airborne contamination. The system consists of a 2 kHz F2 laser, an in-situ VUV irradiation system and a specialized VUV spectrophotometer. Laser irradiation and measurements were carried out under high purity nitrogen gas. During the first phase of F2 laser irradiation (0 approximately 0.7 million pulses), a rapid transmittance increase (87% yields 89%) of calcium fluoride (CaF2) substrates was observed and this change took almost place within one minute after starting the irradiation. It is assumed that this effect is due to surface cleaning by the F2 laser beam. Surface polishing has been excluded because the sample surface roughness measured with an atomic force microscope (AFM) showed no difference before and after irradiation. After an irradiation of 0.1 million pulses, the fast initial increase of the transmittance slowed down and finally reached about 89%. The slower increase might be correlated with a reduced chemical bonding of hydroxyl groups on the surface, because the transmittance change at 157 nm was in good agreement with the measured VUV transmittance below 170 nm. This is corresponds with the hydroxyl absorption band below 170 nm. The transmittance and reflectance of high reflection coated substrates were examined as well. Obvious damage and a huge reflectivity loss (82.4% yields 47.4%) were observed after 1.5 billion irradiation pulses. The information obtained during this work is very useful in devising optical F2 laser components.
The F2 Laser (wavelength 157nm) is becoming the most promising candidate of light source for next generation optical micro-lithography below the 100nm-technology node. We have developed VUV optics evaluation system, which is able to measure the transmittance between DUV and VUV region right after laser irradiation and the temporal transmittance during 157nm-laser irradiation. This system structured by Ni-plated Aluminum and stainless steel. The inside of chamber is purged of any laser light absorption gas away with high purity nitrogen gas during the irradiation. Using this system, we can measure the characteristics of the irradiated sample without exposing to the air of other contamination sources. So this system has +/- 0.5% accuracy result in repeated measurement. In the in-situ transmittance measure system, the transmittance can be monitored during F2 laser irradiation. And we evaluated characteristics of VUV optical materials in the early period of F2 laser irradiation by this in-situ transmittance measure system.
ArF excimer lasers are the light source of choice for the next generation of micro-lithographic tools enabling structures below the 130nm technology node. For these lithographic mass production lines Komatsu successfully developed an ArF excimer laser, named G20A, which has a 2kHz pulse repetition rate, 10W average power and 0.5pm (FWHM) spectral bandwidth. G20A has three significantly improved important items: (1) the high resolution line narrowing module, (2) the high power and high repetition rate solid state pulse power module, and (3) the Xe added laser gas yielding an improved overall laser performance. ArF laser spectra were determined with out newly developed high-resolution spectrometer. The instrument function of the spectrometer was measured with a 193nm coherent light source jointly developed with the University of Tokyo. The laser gas composition is one key parameter of excimer laser performance. The deteriorating effect of impurities on ArF performance is e.g. ten times larger than on KrF performance. We observed that added Xe gas, however, has a beneficial effect on the pulse energy and the energy stability at high repetition rates. Experimental results of a currently developed 4 kHz ArF laser are also reported.
We have succeeded in the commercialization of the world's first kHz ArF excimer laser for microlithography application. The ArF laser is expected to be the light source for the DUV lithography tools for sub-0.13 micron geometry semiconductor production. In this paper, we present the performance and advanced technologies of the newest model of the ArF excimer laser, which achieves 10W of output power with 0.5 pm bandwidth at 2 kHz. The pulse-to-pulse energy stability, 3 sigma is less than 10 percent and integrated energy stability is within +/- 0.3 percent. The durability performance is extended to 5 billion pulses, which provides affordable CoO for volume production.
Highly narrowed Argon Fluoride excimer laser for practical refractive exposure system with high NA and wide field size lenses is developed. The laser realizes 0.6 W at 400 Hz. The spectral bandwidth is less than 0.75 pm, the stability of central wavelength is within +/- 0.25 pm and the concentration of energy within 3- pm band is more than 95%. The gas lifetime is more than 1 X 107 pulses without gas purifier. By the one gas life performance test and the short term performance test, we confirm this laser is useful for the development of microlithography process.
New KrF excimer laser for microlithography KLES-G7 with a new simple solid state pulsed power circuit (SPC) is developed. This SPC has several advantages such as less maintenance cost and the higher reliability. The laser realizes 7.5W with 0.8 bandwidth, 600 Hz, 10mJ. The performance and the stability of the laser is demonstrated. The maintenance interval of the SPC is more than 10 X 109 pulse. The KLES-G7 reduces 20 percent of the photon cost compared with the old model. It will accelerate the mass production of after 64Mbit DRAM.