The relentless demand for smaller and lighter products with faster and more powerful processing capabilities continues to be the overarching trend across nearly every sector of the electronics market: from telecom systems to medical sensors, image processing, and of course smart phones and devices. Today, advanced package integration (API) is arguably the key technological enabler supporting this trend, with a focus on vertical stacking platform – so-called 2.5D and 3D architectures – or fan-out wafer level packaging (FOWLP) as preferred in high bandwidth memory (HBM). An example of a true 3D package is where two (or more) thinned chips are stacked on top of each other in the same molded package, such as several memory chips or the combination of a logic chip and a memory chip. Excimer laser structuring offers multiple advantages in advanced packaging applications including ablation of vias and trenches, seed layer removal, and debonding. This technology is proven to provide a cost advantage for both current and future packaging applications. Whereas lithographic patterning involves photographic exposure of a resist, the excimer laser pulses directly remove material with virtually no peripheral thermal effects. A proven means to increase achievable field size is overlaying time-synchronized combined beams. Therefore, a sensitivity analysis of applying 308-nm excimer laser double pulses using various pulse delays on the key ablation parameters has been conducted.
While applications such as drilling μ-vias and laser direct imaging have been well established in the electronics industry, the mobile device industry’s push for miniaturization is generating new demands for packaging technologies that allow for further reduction in feature size while reducing manufacturing cost. CO lasers have recently become available and their shorter wavelength allows for a smaller focus and drilling hole diameters down to 25μm whilst keeping the cost similar to CO2 lasers. Similarly, nanosecond UV lasers have gained significantly in power, become more reliable and lower in cost. On a separate front, the cost of ownership reduction for Excimer lasers has made this class of lasers attractive for structuring redistribution layers of IC substrates with feature sizes down to 2μm. Improvements in reliability and lower up-front cost for picosecond lasers is enabling applications that previously were only cost effective with mechanical means or long-pulsed lasers. We can now span the gamut from 100μm to 2μm for via drilling and can cost effectively structure redistribution layers with lasers instead of UV lamps or singulate packages with picosecond lasers.
Average power scaling of 308nm excimer lasers has followed an evolutionary path over the last two decades driven by
diverse industrial UV laser microprocessing markets. Recently, a new dual-oscillator and beam management concept for
high-average power upscaling of excimer lasers has been realized, for the first time enabling as much as 1.2kW of
stabilized UV-laser average output power at a UV wavelength of 308nm. The new dual-oscillator concept enables low
temperature polysilicon (LTPS) fabrication to be extended to generation six glass substrates. This is essential in terms of
a more economic high-volume manufacturing of flat panel displays for the soaring smartphone and tablet PC markets.
Similarly, the cost-effective production of flexible displays is driven by 308nm excimer laser power scaling. Flexible
displays have enormous commercial potential and can largely use the same production equipment as is used for rigid
display manufacturing. Moreover, higher average output power of 308nm excimer lasers aids reducing measurement
time and improving the signal-to-noise ratio in the worldwide network of high altitude Raman lidar stations. The
availability of kW-class 308nm excimer lasers has the potential to take LIDAR backscattering signal strength and
achievable altitude to new levels.
The growing demand for laser micro fabrication drives further requirements on higher production speed per part and
lower manufacturing costs. A newly developed 1.2 kW 308 nm excimer laser addresses both micro-manufacturing and
high production throughput.
Solid state UV laser sources usually cannot emit UV laser radiation directly. The inherently required frequency
conversion limits the total output power to several 10 Watts below 350 nm. Furthermore these UV-conversion- modules
limit the long term reliability of high power UV solid state lasers significantly because of the wear of the conversion
crystals. Excimer lasers, however, overcome these issues by direct emission at 308, 248, or 193 nm. By now up to 540
Watts at 308 nm are established in production. With the new laser we have more than doubled the available output power
to 1.2 kW.
The combination of short wavelength and highest available UV laser power makes it ideal for processing of small
features or to modify thin surfaces. Furthermore, pulsed UV laser radiation is very suitable for removing delicate
electronic devices from manufacturing substrates.
High-power UV laser systems are capable of processing large areas with resolution down to several microns in one
single laser ablation step without using multiple lithography and wet chemical processes. For instance, laser Lift-Off and
large area annealing have proven to be very efficient manufacturing techniques for volume production. In this paper, a
novel 1.2 kW excimer laser will be presented and discussed.
Stable, high energy excimer lasers providing pulsed output energies ranging from 100 mJ up to over 1000 mJ in the ultraviolet region with photon energies as high as 5 eV (248 nm), 6.3 eV (193 nm) or 7.9 eV (157 nm) lend maximum flexibility to laser microprocessing, since virtually every material is amenable to accurate, high resolution material ablation without subsequent cleaning. Due to the UV photons provided with no up-conversion required as direct output by excimer lasers, output powers of many hundred watts are easily achievable and are key to high throughput, and up-scaling capability of manufacturing processes. Most important for reproducible production results is a temporally and spatially stable behavior of consecutive laser pulses as well as utmost lateral homogeneity of the on-sample energy density (fluence). These requirements constitute the superiority of excimer lasers over other pulsed UV laser sources such as lamp-pumped Nd:YAG lasers. Pulse-to-pulse stabilities of less than 1 %, rms as easily provided by excimer laser systems which cannot be achieved with frequency converted Nd:YAG. Laser systems. In particular, the large flat-top excimer laser profile is well-suited for most efficient parallel processing of two and three dimensional microstructures. Spectral properties, temporal pulse and laser beam parameters of state of the art UV excimer lasers and beam delivery systems will be compared with frequency converted, flash-lamp pumped Nd:YAG lasers.
Today's excimer lasers are well-established UV laser sources for a wide variety of micromachining applications. The excimer's high pulse energy and average power at short UV wavelengths make them ideal for ablation of various materials, e. g., polyimide, PMMA, copper, and diamond. Excimer micromachining technology, driven by the ever-shrinking feature sizes of micro-mechanical and micro-electronic devices, is used for making semiconductor packaging microvias, ink jet nozzle arrays, and medical devices. High-power excimer laser systems are capable of processing large areas with resolution down to several microns without using wet chemical processes. For instance, drilling precise tapered holes and reel-to-reel manufacturing of disposable sensors have proven to be very cost-effective manufacturing techniques for volume production. Specifically, the new industrial excimer laser-the LAMBDA SX 315C-easily meets the high demands of cost-effective production. The stabilized output power of 315 watts at 300 Hz (308 nm) and its outstanding long-term stability make this laser ideal for high-duty-cycle, high-throughput micromachining. In this paper, high-power excimer laser technology, products, applications, and beam delivery systems will be discussed.
Laser annealing has become the primary method for producing the Low-Temperature-Poly-Silicon (LTPS) panels used in the Flat Panel Display (FPD) industry. Thin Film Transistor (TFT) backplanes based on LTPS substrates for Active Matrix Liquid Crystal Displays (AMLCD) offer substantial advantages over TFT backplanes based on amorphous silicon. The trend to higher pixel density, the integration of more driver and logic ICs on the glass, and the advent of Active Matrix Organic Light Emitting Displays (AMOLED) all have lead to significant interest in the laser annealing process. Currently, there are several different approaches to the annealing process based on excimer lasers, cw-green DPSS lasers, modelocked-green DPSS lasers and Q-switched Nd:YAG lasers. This paper reviews the various laser technologies and annealing techniques, such as the line beam method and Sequential-Lateral-Solidification (SLS). These approaches will be compared in terms of crystal quality, electron mobility, throughput, yield and operating cost.
We report performance parameters of a robust, 50 W, high repetition rate amplified ArF excimer laser system with FWHM bandwidth of less than 0.25 pm, 95% energy content bandwidth of less than 0.55 pm, and ultra-low ASE level. Proprietary design solutions enable stable operation with a substantial reliability margin at this high power level. We report on characterization of all the key parameters of importance for the next generation microlithography tools, such as spectrum and dose control stability, in various operating modes.
According to the ITRS-Roadmap, the 157 nm wavelength of the F2-laser is the most likely solution to extend the optical lithography for production of ICs with critical dimensions below 70 nm down to the 50 nm node. This requires high power, high repetition rate F2-lasers with highest reliability, operating in the power range of more than 40 W at repetition rates of at least 4 kHz. In the recent three years strong efforts have been done in order to investigate and develop all kind of materials, technologies and devices which are necessary to introduce the 157 nm lithography for high volume mass production in the year 2004/5. Towards this road Lambda Physik has developed a 4 kHz line selected F2-laser with an output power of 20 W meeting the spectral performance requirements and therefore suitable for pilot 157 nm scanner. In order to reach an output power of 40 W under retention of the required spectral performance, we are now concentrating on the output power increase which comprises a new tube design, a modified discharge and charging circuit. In this paper the laser performance data which has been verified and measured by existing and improved 157 nm metrology as well as new findings on general F2-laser properties at high repetition rate, high power operation will be discussed. The prototype 4 kHz line selected F2-laser gains benefit from the outstanding long term reliability of the resonator optics. The field proven NovaLine F2020 optics modules are only slightly modified for 4 kHz operation. Lambda Physik will present appropriate reliability data which had been confirmed from field application showing laser tube and optical modules life times passing 5 Bio shots at 2 kHz repetition rate operation.
Excimer lasers are widely used as the light source for microlithography scanners. The volume shipment of scanner systems using 193nm is projected to begin in year 2003. Such tools will directly start with super high numerical aperture (NA) in order to take full advantage of the 193nm wavelength over the advanced 248nm systems. Reliable high repetition rate laser light sources enabling high illumination power and wafer throughput are one of the fundamental prerequisites. In addition these light sources must support a very high NA imaging lens of more than 0.8 which determines the output spectrum of the laser to be less than 0.30 pm FWHM. In this paper we report on our recent progress in the development of high repetition rate ultra-narrow band lasers for high NA 193nm microlithography scanners. The laser, NovaLine A4003, is based on a Single Oscillator Ultral Line-narrowed (SOUL) design which yields a bandwidth of less than 0.30pm FWHM. The SOUL laser enables superior optical performance without adding complexity or cost up to the 4 kHz maximum repetition rate. The A4003's high precision line-narrowing optics used in combination with the high repetition rate of 4 kHz yields an output power of 20 W at an extremely narrow spectral bandwidth of less than 0.30 pm FWHM and highest spectral purity of less than 0.75 pm for the 95% energy content. We present performance and reliability data and discuss the key laser parameters. Improvements in the laser-internal metrology and faster regulation control result in better energy stability and improved overall operation behavior. The design considerations for line narrowing and stable laser operation at high repetition rates are discussed.
According to the ITRS-Roadmap, the 157nm wavelength of the F2-laser is the most likely solution to extend the optical lithography for production of ICs with critical dimensions below 70nm down to the 50nm node. The introduction of the 157nm lithography for high volume mass production requires high power, high repetition rate F2-lasers operating in the power range of more than 40W or at repetition rates of more than 4kHz. To meet the narrow time gap for an introduction of the full-field 157nm-scanner systems for real production in the year 2004/5 the community have to solve several challenging issues even in the laser section. F2-laser systems are needed which completely fulfill all specifications of a lithography light source, either for a refractive or a catadioptic projection optics. Verification and precise measurement of the key laser parameters in the VUV usually requires a specific development of the metrology, necessary for this task. In this report we present the progress which had been achieved in the development of high repetition rate high power single-line F2 lasers for catadioptic lithography application. The key features of a F2-laser > 4kHz will be demonstrated. We will also review the main parameters and the performance data from the field of the standard lithography-grade F2020 a 2kHz system which is already applied for pilot scanner tool design. Some improvements of these systems with regard to single line power, dose stability, polarization and gas life will be shown and reliability data from the field will be reviewed. Critical dependence of the spectral properties of the F2-laser emission at 2 kHz and 4 kHz will be discussed. Some new investigations on the coherence properties of the Fluorine laser are also implemented.
Capital costs and economical efficiency is becoming the most important criteria for any decision on lithography tools for an advanced IC fabrication facility. Each lithography wavelength has to compete for productivity, cost efficiency and return of investment. Reliable high repetition rate laser light sources enabling high illumination power and wafer throughput are one of the fundamental prerequisites. In this paper we report on our recent progress in development of high repetition rate ultra-narrow line and semi-narrow band ArF lasers for advanced 193nm lithography. These lasers are designed for high NA refractive and catadioptic scanner tools targeting the 100 nm node and below. We present key performance data of our high repetition rate ArF- lasers which currently operate at 4 kHz with a spectral bandwidth of < 0.35 pm or 25 pm, and 20 W or 40 W, respectively. Improvements in the laser-internal metrology and faster regulation control result in better energy and wavelength stability, dose control and improved overall operation behavior. Ultra-narrow bandwidth emission combined with an extra ordinary high spectral purity E(95%) < 0.8 pm is achieved by a new design of the optical line narrowing module implemented into the A4005. Improvements in the tube design support a laser operation with repetition rates of greater than > 4kHz and with 75% duty cycle. Data on the main laser parameters in dependence on repetition rate are presented. These results indicate the robust performance of the A4005 for all operation conditions and suitable reliability and lifetime of the modules.
High output power and ultra-narrow bandwidth has been the development goals for the 193 nm lithography excimer lasers in the last years to support the throughput and requirements of advanced 193 nm wafer scanner. Cost of ownership comparable to current 248 nm lithography wafer scanner is one of the important prerequisites for the economic implementation of 193 nm lithography in production. In this paper we present the performance results of our new high power ArF lithography excimer lasers with repetition rate of 4 kHz. The laser delivers a stabilized output power of up to 40 W. The spectral laser output is matched to the requirements of high NA catadioptric imaging lenses with a bandwidth of less than 25 pm, FWHM. The new laser delivers energy dose stability of less than 0.35% for a 50 pulse dose window. Second part of the paper gives the status of the ultra-narrow bandwidth 193 nm excimer laser for refractive imaging lenses. A spectral bandwidth of less than 0.35 pm, FWHM, has been achieved with a spectral purity of less than 0.95 pm. Results from the laser operating at 2 kHz are presented. The performance characteristics at of he line-narrowed 193 nm laser with 4 kHz repetition rate are presented. Finally an outlook on the achievement of ultra-narrow-bandwidth 193 nm excimer lasers for micro-lithography will be given.
According to the SIA-Roadmap, the 157 nm wavelength of the F2 laser is the most likely solution to extend the optical lithography for chip production from the critical dimensions of 100 nm down to the 50 nm node. The introduction of the 157 nm lithography for high volume mass production requires high power, high repetition rate F2 lasers operating in the power range of more than 40 W or at repetition rates of more than 4 kHz. These leading specifications are combined with other challenging laser specifications on dose stability and bandwidth which must be realized within a very aggressive time line for the introduction of the full-field scanner systems in the year 2003. According to this roadmap of the tool suppliers Lambda Physik has now introduced a 2 kHz lithography-grade F2 laser F2020 for further pilot scanner systems. In this report we present basic performance data of this single line 2 kHz F2 laser and some typical results on key laser parameters which had been measured with new and improved metrology equipment. We demonstrate for the first time precise measurements on the correlation of the natural bandwidth versus pressure which had been performed with an ultrahigh resolution VUV spectrometer. In addition a new compact and transportable high resolution VUV spectrometer was used for analyses of spectral purity and line suppression ratio of the laser emission. The experimental setup and result of an absolute calibration of a power meter, for the first time directly performed at the true 157 nm wavelength, are presented.
Results on the feasibility of highest repetition rate ArF lithography excimer lasers with narrow spectral bandwidth of less than 0.4 pm are presented. The current 193 nm lithography laser product NovaLine A2010 delivers output power of 10W at 2 kHz repetition rate with energy dose stability of +/- 0.5 percent. A novel 193 nm absolute wavelength calibration technique has ben incorporated in the laser which gives absolute wavelength accuracy better than 0.5 pm. Long-term results of optical materials, coatings and laser components give insight into estimated cost of ownership developments for the laser operation over the next years. Progress in pulse stretching approaches to achieve lower stress of the wafer scanner illumination optics and lens allow optimistic estimates of total system CoO. Initial results on the laser operation at 4 kHz in order to reach 20W output power are discussed.
According to the SIA-Roadmap, the 157 nm wavelength of the F2 laser emission will be used for chip production with critical dimensions of 100 nm down tot eh 70 nm node. Currently al basic technologies for 157 nm lithography are under investigation and development at material suppliers, coating manufacturers, laser suppliers, lens and tool manufacturers, mask houses, pellicle manufacturers, and resist suppliers.
We have developed a KrF excimer laser with ultra narrow linewidth and high repetition rate applicable for optical lithography using DUV wafer scanners with highest numerical aperture (NA) of more than 0.8. A laser bandwidth of less than 0.4 pm, full width half maximum, is achieved by our new design of the laser resonator, which is based on out patented polarization coupled resonator. The new resonator design increase the efficiency of ht laser optics and improves the wavelength stability. The laser tube and solid sate pulser have been adapted to the new laser resonator. As a result, another step in the reduction of the cost of operation is achieved. The laser operates with a repetition rate of 2 kHz and gives a large operation range with respect to wavelength and energy range. The characteristic performance of this new excimer laser is presented.
The demand of high throughput and good energy dose stability of DUV scanner systems result in the requirement of laser repetition rates above 2 kHz for lithography production tools at 193 nm and 157 nm. Also in 248 nm lithography, dose energy stability could be improved by higher repetition rates from the laser. We have investigated the possibilities and limits of high repetition rate performance of laser discharge units for DUV lithography lasers. A new chamber has been developed with electrode configuration, pre- ionization system and high speed gas flow system for very high repetition rate operation. Acoustic resonances in the frequency range of interest have been prevented by design. With new solid-state pulsed power modules which support long pulse gain modulation and high precision high voltage power supplies very high repetition rates have been demonstrated. For 248 nm lasers repetition rates above 5 kHz have been achieved, for 193 nm laser above 4.5 kHz. 157 nm lasers can be operated above 2.5 kHz. Data of the laser performance as e.g. power and energy stability are given for the various wavelengths.
Fluorine (F2) lasers emit at 157 nm, the shortest commercially available laser wavelength. Innovations such as NovaTubeTM technology have resulted in powerful, highly reliable and cost effective F2 lasers. This paper will discuss the most recent F2 laser developments, resulting in repetition rates up to 1000 Hz and pulse energies in excess of 25 mJ. The industry now considers F2 lasers to be the next step (after ArF at 193 nm) in key technologies such as lithography and micromachining.
With the transition of DUV lithography into mass production, the economics of the excimer laser light sources is getting more important. The efforts in the development are directed towards an increase of the laser's repetition rate and output power for higher wafer throughput and an improvement of the component lifetime in order to reduce the cost of laser operation. Here we describe advanced 248 nm and 193 nm laser systems which operate with repetition rates of 2 kHz to be used in conjunction with refractive, partially achromatic refractive and catadioptric lithographic lenses, respectively.
Optical deep UV (DUV) lithography is aiming to reach feature sizes of below 100 nm. The likely choice of the exposure wavelength will be 157 nm, which is emitted by the F2 excimer laser. Experience with this laser type in a variety of applications has been gained at Lambda Physik for the past 20 years. A major breakthrough in performance, in particular laser efficiency and durability, was achieved with the introduction of our metal ceramic laser tube in 1996. In this paper, we report on the progress in the development of the F2 laser light source. A major advance in narrowing the bandwidth of a 10W laser is the achievement of output spectral width of about 1 pm. With a newly developed NovaTube based F2 discharge chamber we show more than 19 million pulses gas lifetime without any additional gas actions. The laser achieves up to 1 kHz repetition rate. Energy stability sigma is 1 percent, dose energy stability 0.5 percent. The performance characteristics as temporal and spatial beam profile and the suitability the laser for microlithography are discussed. Typical lifetimes of the key components and a projection of the present and future cost of operation are presented.
Considerable progress has been made in the development of the major components for 193 nm lithography tools. Here we describe the parameters of a line-narrowed ArF excimer laser for microlithography. With a specified FWHM bandwidth of less than 0.7 pm, the laser is applicable for refractive steppers and scanners which utilize some degree of achromatization. Prototype lasers have been built to study the optimum parameters. The main challenge of the development was the achievement of high efficiency in the conversion from the laser's broadband emission into line-narrowed emission. The lasers are operated at up to 1 kHz repetition rate with a maximum power of 10 W. This paper provides an overview of the currently achievable power levels, energy stability and bandwidths and discusses future trends.
The ArF excimer laser light source will extend the optical lithography to below 0.18 micrometers design rules. Still under discussion is the most effective layout of the stepper or scanner imaging optics. The decision for an all-fused-silica lens, an achromatic lens using CaF2, or a catadioptric imaging system has great impact on the laser-bandwidth requirement. In addition, the potential performance and perspective of the laser must be considered in the system layout of the production stepper or step and scan tool. Cost effective operation of such a lithography tool requires a 193 nm excimer laser with high power and repetition rates in the order of 1 kHz or higher. Precise dose control of the exposure demands high repetition rate and excellent stability of the laser output energy. We have developed an ArF laser which can be operated with up to 800 Hz repetition rate based on NovaTubeTM technology. Optimized materials and discharge configurations have been used to achieve laser tube lifetimes above 109 pulses. Up to 4 X 109 pulses tube lifetime have been achieved in beta-site tests. Gas lifetime of several 107 laser pulses is obtained. A solid-state switch has been adapted for the reliable and cost efficient excitation of the 193 nm lithography laser. To achieve laser output of different bandwidths various resonator arrangements have been investigated. The paper gives an overview of the currently achievable power levels at different bandwidths and discusses future trends.
The paper reviews recent developments in high power excimer laser technology driven by industrial requirements. Technological achievements as NovaTubeTM laser tube technology and HaloSafeTM halogen generator technology are discussed. Experimental results are presented for various lasers at the most important excimer wavelengths 351 nm (XeF), 308 nm (XeCl), 248 nm (KrF), 193 nm (ArF) and 157 nm (F2) which have been designed for application in micromachining, thin-film-transistor annealing, marking as well as lithography.
Industrial applications of excimer laser include fabrication of multi-chip modules, ink jet nozzles and TFT annealing of flat panel displays. For more than a decade these applications and the deep-UV-lithography pushed the excimer laser technology to improved performance and lower cost. As a result, highly reliable laser systems have been developed, which utilize state of the art technologies like metal ceramic laser tubes, solid state switching circuits and solid state halogen generation.High repetition rate lasers are suitable for micromachining applications especially in the direct structuring mode. Depending on the processing parameter the throughput and operating cost of such a high repetition rate system will be advantageous compared to standard laser systems. In the absence of other process inherent limitations, the processing time both for 2D and 3D laser ablation are proportional to the lasers pulse repetition rate. While most industrial lasers are limited to 300 Hz repetition rate, the developed laser operates up to 1.5 kHz.
The year 1997 will become known as the 'year of commercial excimer lasers.' The number of installations on manufacturing and medical floors will be much higher than ever before. Besides the medical uses the most important applications are DUV lithography, TFT annealing for flat panel displays and microdrilling for nozzle arrays, especially for ink jet printer heads. Recently two very important breakthroughs were achieved. The first is in regard to the performance of the excimer laser itself. The second is a much more efficient way of using the UV photons. These are the main reasons for the actual success. Technology development by laser manufacturers has resulted in remarkable improvements of component lifetime, reliability, cost of ownership and ease of use. With gas and optics lifetimes in excess of 108 pulses, laser tube exchange intervals longer than 5 multiplied by 109 pulses and integration of internal halogen generators a quasi sealed-off excimer laser with hands-free operation is accomplished. The new generation NovaLineTM combines the experience of more than 4000 installed excimer lasers with a completely new laser engineering design. Progress in advanced UV optics will be demonstrated with two examples. In commercial production of very precise nozzle arrays, high-end optics allow the drilling of all nozzles simultaneously with an optical distortion of less than 0.5 micrometer over a full 0 18 mm processing field. For scanning applications as AMLCD annealing, the rectangular laser beam can be optically transformed into a very homogeneous line, up to 300 mm long and 0.5 mm wide.
In this paper we discuss several resonator designs in terms of bandwidth, efficiency and lifetime of the major optical components. Experimental data are presented for a resonator combining the advantages of a long lifetime grating and etalon elements. Moreover, the limitations of these elements are overcome through the outcoupling scheme, ensuring optimum feedback over gas and tube lifetimes. In addition to low cost-of-ownership, this same resonator provides for an extremely narrow bandwidth ArF excimer laser development, using a single oscillator.
Excimer lasers offer unique benefits for a wide range of applications, including industrial materials processing, scientific research and medicine. The benefits of the excimer laser stem from its high peak power output delivered in short pulses at a variety of UV wavelengths. In recent years, technical developments by laser manufacturers have lead to remarkable improvements in excimer performance, reliability and utility, as well as lower cost of ownership. As a result, the market for excimer lasers continues to grow and diversify. In this paper we examine some of the more recent advances, look at various industrial applications that are enabled by excimer lasers, and catch a glimpse of the future direction of this technology.
Advanced DUV lithography tools are adapting scanning methods in order to match the increasing demands on throughput, field size, and resolution. The demands on the laser source are changing for both the reflective and the refractive Step&Scan tools. The cost-effective operation of such lithography tool requires 248 nm excimer laser with high power and repetition rates of >= 1 kHz. Precise dose control of the exposure demands not only high repetition rates but also excellent stability of the laser output energy. The combination of the new NovaTube technology laser tube design with the LITHO line narrowing optics design allows 1 kHz operation of the excimer laser with high stability.
Excimer lasers are the most efficient and powerful sources for ultraviolet radiation. Our new laser cavity design NovaTubeTM is the result of many years of extensive material research. Several test runs with NovaTubeTM lasers at 193 nm (ArF) and 157 nm (F2) demonstrated excellent gas lifetime data when compared to conventionally designed lasers. For the first time a 50 W KrF laser was successfully operated sealed-off for more than 1 billion pulses. By this outstanding performance the operating costs can be cut 10 times using the new laser tube technology.
NovaTubeTM is the result of many years of extensive material research at Lambda Physik to develop a laser cavity of quasi sealed-off laser performance. As test data demonstrate the operating costs can be cut 10 times using the new tube. Test runs in the laboratory have culminated in 109 shots operation on a single gas fill achieved with a 50 W KrF laser.
KrF lasers with up to 500 Hz repetition rate and a bandwidth of about 1 pm are in use for DUV-microlithography. Increasing resist sensitivity demands even higher repetition rate in order to allow precise dose control. In some cases step & scan exposure tools apply reflective optics instead of refractive ones. This diminishes the bandwidth requirements by about two orders of magnitude, but a high polarization degree of >= 98% is a basic requirement for the laser light source. Dose control and statistics define the second basic requirement for the laser. A dose accuracy of less than 2% demands small energy increments, i.e., for pulse energy in the 10 to 20 mJ range. Throughput requires 10 to 20 W of average laser power. Therefore, the repetition rate must be in the 1 kHz range.
The paper presents the features of the Lambda Physik 248 LEX KrF DUV-Lithography laser for spectral performance, reliability, and system integration. The 248 LEX is based on Lambda Physik's series of `LAMBDA' industrial lasers. Data of 5 years field experience with the LAMBDA high power industrial lasers are used to discuss reliability of the laser in and economic aspects of the laser application in terms of cost-of-ownership. Results of an endurance test program for lithography lasers are used to given an outlook on system performance and component lifetime. Based on these data the cost-of-ownership is projected for the coming years and multiple system installations. An update of Lambda Physiks' R&D effort and recent progress is given.