Search

Extreme Ultraviolet Lithography (EUVL) is a leading candidate for the future development of smaller and faster microchips with feature sizes of 32 nm or less. Tin laser-produced plasmas (LPPs) are one of the most promising sources of in-band radiation for EUV lithography and inspection applications. However, ions emitted from these LPPs may cause significant damage to components, specifically the collector optics. Tin-droplet targets have the ability to supply the minimum mass required to generate the EUV radiation, leading to substantial decrease in the amount of generated debris. Absolute intensity measurements of the EUV radiation formed using a droplet target, have been recorded. Measurements were recorded over 2 pi steradian with respect to the plasma. The droplet generator, a fully in-house developed system, was synchronized with a Nd:YAG laser operating at a frequency of 5 kHz. The laser pulse was focused to a power density of approximately 10 11 W/cm 2 to maximize in-band emission. EUV measurements were recorded at the Intermediate Focus of the High Brightness Source of the Laboratory for Energy Conversion. To complement the EUV measurements, out-of-band measurements were simultaneously recorded with a calibrated spectrometer from 300 to 1000 nm.

The next generation of semi-conductor devices will be manufactured using extreme ultraviolet lithography with a laser-produced plasma as a candidate 13.5nm light source. A primary challenge, particularly for metrology tools, is the stability and the brightness of the generated EUV at the intermediate focus. In the experimental facility at ETH a novel collecting system is studied to optimize brightness and stability, and to avoid contamination after the intermediate focus. Different experimental studies are shown to confirm the design's success for both the EUV beam quality and lack of contamination after the intermediate focus.

The leading candidate for the manufacture of next generation semi-conductor devices is extreme ultraviolet lithography, with laser-produced plasmas as a candidate 13.5nm light source. A primary challenge for continuous operation is elimination of the debris load on the collector, without compromising the radiation intensity at the intermediate focus. A novel combination of thermal management and debris mitigation is developed in order to reduce the deformation and degradation of collector optics. This patent-pending novel debris mitigation technique enables the continuous operation of the source. The paper shows atomic force microscope measurements of the collector surface deposition. The debris mitigation system run at 50% design operating condition gives 90% debris mitigation effectiveness. The average temperature of the cooled collector is 36.5°C at the design point, with a peak-to-peak difference of 0.8°C. The collector geometry, after being adapted to compensate the thermal deformation, yields a spot size of 30μm at IF. Computational simulations, using ETH's multi-scale computational tools, complement the presented experimental results.

Powerlase has made significant steps forward in developing reliable and cost-effective, kilowatt-class laser modules with short pulse duration and small footprint, for use as EUV drivers. These characteristics in parallel to EUV target requirements are essential for the generation of 115W of in-band EUV power at the intermediate focus. These laser modules can be coupled to the EUV target by using our flexible spatial and temporal multiplexing approach in order to scale up the laser average power on target. The multiplexing method developed by Powerlase is modular and optimised for maximum EUV collection angle. To further this goal we are currently evaluating target materials such as xenon in various phases and forms and also have a programme in place to investigate suitable tin targets.

Laser milling of diverse materials has been demonstrated with short pulse lasers ranging from microsecond to femtosecond pulse durations, and with wavelengths from the far infrared to vacuum ultra-violet. In all cases a balance between quality, throughput and cost of ownership must be struck in order to determine commercial relevance. Latest generation Q-switched Diode Pumped Solid State Lasers offer the potential to enable the industrial uptake of laser milling for a wide variety of materials including aerospace alloys, thermal barrier coatings, tool steels, diamond and diamond substitutes. This paper will investigate these practical applications of laser milling with reference to comparative laser and non-laser processes.

Laser milling of a variety of substrates is investigated with the intention of achieving high quality material removal to create three-dimensional shapes in the material. A high power Q-switched Diode Pumped Solid State Nd:YAG Laser at 1064nm is used in all cases. Materials investigated include Nickel Superalloys, Thermal Barrier Coatings, Steels, Tungsten Carbide and Polycrystalline Diamond. Multi-layer substrates are also considered. The effects of laser intensity, plasma formation, pulse duration, material properties, and resulting removal rate, recast and surface finish are explored for this process. This paper defines the findings of this study within the context of commercial imperatives.

Electrical to EUV conversion efficiency is a key parameter for systems scaled to EUV emission in the 100W regime. Improvement in efficiency of conversion from laser radiation at the EUV source, reduces the required laser power and as such can lend itself to reduced heat load and debris emission. Also, improvement in the electrical to laser conversion efficiency results in a direct reduction in cost of ownership. Laser solutions optimised for efficient conversion to high M 2 CW laser radiation are not optimised in design for efficient short-pulsed operation; the mode of operation required for EUV generation. Aspects of both EUV source and laser design are discussed, with a view to optimising conversion efficiency for scalable EUV solutions.