Frank Voss

High-average-power excimer lasers

A review of recent achievements and new tendencies in the development high energy, high repetition rate excimer lasers will be presented. The paper mainly focuses on the features of KrF, XeCl lasers with different combinations of output energy x pulse repetition frequency, for example: 1 J X 600 Hz (KrF); 3 J X 200 Hz or 10 J X 100 Hz (XeCl), which have been developed as candidates for industrial applications.

Excimer lasers for material ablation cross the 1.5 kHz mark

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.

Advanced F2 lasers for microlithography

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.

Recent developments of industrial excimer laser technology

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.

Advanced F2-lasers for 157-nm lithography

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.

Recent results on long-life 1-kHz excimer laser development

A new high repetition rate laser module on the basis of our latest metal-ceramic laser tube technology is developed. This laser can be operated up to 1 kHz with practically constant output energy of 30 mJ at 248 nm and up to 15 mJ for ArF and XeF. Gas lifetime and window cleaning interval can be extended to 500 million pulses. We present our latest test results for ArF, KrF, and XeF operation. All industrial applications require excellent pulse energy stability. In order to meet this demanding feature we modified the power supply and the high voltage circuit with respect to pulse energy stability. We achieved excellent pulse energy stability at all important laser wavelength with our new high repetition rate laser module, for example a pulse energy fluctuations of Sigma 0.8% at 1 kHz KrF operation.

High-power high-repetition-rate F2 lasers for 157-nm lithography

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.

Optimization of high-power excimer laser for TFT annealing

The flat panel display market is presently experiencing an annual growth rate of over 20%, and shows no signs of slowing down. Polycrystalline-silicon (poly-Si) thin film transistor (TFT) devices offer both improved quality and decreased cost over amorphous silicon displays, and will undoubtedly capture an ever increasing share of this market. However, producing poly-Si TFTs in high volume has presented a number of practical challenges. One of these challenges is transforming an amorphous silicon layer into poly-Si. For several years, researchers have investigated using excimer lasers for this purpose. In excimer laser annealing, a high-power excimer laser beam is scanned across the surface of a substrate coated with amorphous silicon. The intense UV light causes the silicon to melt, leading to subsequent recrystallization in polycrystalline form. This process is very non-linear, and places tight tolerances on laser beam parameters such as energy stability and beam uniformity. Furthermore, for this technique to be successfully integrated into a high volume production line, the laser must exhibit extremely high reliability, minimum downtime and low cost of ownership. In the past few years, excimer laser manufacturers have made significant technical improvements, leading to products that can successfully meet the rigorous demands of industrial TFT production. As a result, major display manufacturers in Japan, Korea and Europe have now adopted this technology for mass production.

Optimization of 200-W excimer laser for TFT annealing

Polycrystalline-silicon TFT technology is opening the door to highly reliable, high-resolution, high-performance, large AMLCDs that will be inevitable for HDTV and other advanced applications. For formation of polycrystalline silicon, excimer laser annealing has shown to be superior to all other techniques with respect to quality, reliability and economy. In excimer laser annealing a high-power laser beam is scanned over the surface of the substrate, coated with amorphous silicon. The amorphous silicon is heated up within a few nanoseconds, melts and recrystallizes into polycrystalline silicon. The pronounced nonlinearity of the annealing process, the high quality requirements and the high process speeds in production lines make high demands on the laser beam parameters such as energy stability and beam uniformity, and on laser output power. This presentation will discuss the results of recent development in high-power excimer lasers for annealing, and their impact on production of AMLCDs.

High-power excimer lasers for 157-nm lithography

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.