TRUMPF Laser Amplifier

The High Power Seed Module (HPSM) consists of two seed lasers – which generate output pulses of just a few watts, as well as of a variety of active and passive optical components, which form the laser beam and ensure an optimal pulse duration. An initial amplifier is used to pre-amplify the light to a magnitude of 100 W. The seed lasers have protection mechanisms that provide optimum protection against back-reflections, which significantly increases the stability of the entire system and enables the required continuous EUV power to be achieved.

The High Power Amplification Chain (HPAC) is made up of four resonators designed for increasing power, which are interconnected with beam guiding elements. Each resonator is optimised to the relevant amplification level (e.g. blower, RF excitation, gas mixture and beam guidance). In this process, three different cooling circuits make sure that the system has the required level of stability. Short pulses ensure an extremely high peak output power in the MW range. Comprehensive online metrology provides the starting point for the ongoing measurement of the beam.

The Beam Transport System (BTS) – consisting of an assembly board, periscope and mirror – transports the laser beam up to 30 metres in the direction of the droplet chamber. To ensure low absorption and contamination, it is essential that the system remains mechanically stable under the significant power load and that the beam guidance is targeted enough. The mirrors have a special coating, so that the amount of laser light that is absorbed is as low as possible.

The FFA consists of two components: an optics platform and a focussing unit. To generate the ideal plasma flash, the laser pulse has to hit almost 100% of the tin droplet. However, as the tin droplet is smaller than the diameter of the laser beam, a pre pulse and main pulse are separated in the optics platform and formed for optimum EUV generation. The pre pulse initially hits the tin droplet with a low pulse power, which causes the droplet to swell into a disc-like shape and the surface area to increase in size. The following main pulse is absorbed by the resulting liquid film, thereby forming the actual plasma that generates EUV radiation. This method enables the 40 kilowatts of laser power to be used efficiently and ensures that the plasma flashes for laser exposure are generated in a reliable manner. The focussing unit ensures that the laser light directed onto the tin droplet is as focussed as possible.