Vadim Berger

Prospects for very high repetition rate lasers for microlithography

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.

Ultranarrow-bandwidth excimer lasers for 248-nm DUV lithography

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.

High pulse energy excimer lasers for nanotechnology

Stable, high energy excimer lasers provide pulsed output energies ranging from 50 mJ up to 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). Shortest ablation wavelengths strongly couple with every material, deliver highest lateral and depth resolution and significantly reduce the size of particulates in the plasma. Most important for thin film reproducibility, next to shortest possible ablation wavelength, is a stable behavior of consecutive laser pulses as well as the homogeneity of the on-sample laser fluence. These requirements constitute the superiority of excimer lasers as pulsed UV laser sources when it comes to precision and reproducibility in surface treatment and micromachining. Spectral properties, temporal pulse and laser beam parameters of state of the art excimer lasers will be compared with frequency converted high pulse energy laser sources with regard to the requirements of applications in nanotechnology.Stable, high energy excimer lasers provide pulsed output energies ranging from 50 mJ up to 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). Shortest ablation wavelengths strongly couple with every material, deliver highest lateral and depth resolution and significantly reduce the size of particulates in the plasma. Most important for thin film reproducibility, next to shortest possible ablation wavelength, is a stable behavior of consecutive laser pulses as well as the homogeneity of the on-sample laser fluence. These requirements constitute the superiority of excimer lasers as pulsed UV laser sources when it comes to precision and reproducibility in surface treatment and micromachining. Spectral properties, temporal pulse and laser beam parameters of state of the art excimer lasers will be compared with frequency converted high pulse energy laser sources with regard to the requirements of applications in nanotechnology.