Igor Bragin

Excimer laser for 157-nm lithography

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.

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.

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.

ArF excimer laser for 193-nm lithography

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.

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.