Samir Ellwi

EUV emission from Kr and Xe capillary discharge plasmas

Kr and Xe plasmas are very intensive emitters in the spectral range of 100-150 A, which is relevant for a number of applications (for example microlithography). We present investigations of the extreme utraviolet (EUV) emission from a slow capillary discharge with Kr and Xe fillings. The emission of Kr ions (Kr VIII to Kr XI) within the range of 70-150 A consists of three bands of lines of about 10 A width with maxima at 116, 103 and 86 A. Xe emission bands of about 15 A width have their maxima at 136 and 115 A (Xe IX to Xe XII). The radiation duration in this spectral range is ~150 ns for both elements. At the optimum conditions, the Kr emission at 103 A is 2-3 times more intense than the Xe emission at 136 A. The measured spectral energy of Kr radiation is about 0.1 J sr-1 A-1. Experimental results are compared with numerical modellings of the dynamics and emission of the capillary discharge plasma, which enables the determination of plasma parameters and the future use of the codes as additional instruments for plasma diagnostics.

X-ray lasing as a result of an induced instability in an ablative capillary discharge

We report lasing of the CVI Balmer-α line at 18.22 nm using the new technique of an induced MHD instability in an ablative capillary discharge. A large spike of this line during the second half-cycle of the discharge is observed. The spike is identified as amplified spontaneous emission (ASE), and enhancements are derived for capillaries of lengths between 15 and 50 mm. We explain the ASE as a result of charge exchange processes which occur between ions produced in the neck of the MHD instability and low temperature ions present in the same plasma column. To emphasize this instability, we implemented a new method by using a straight capillary with a waved structure imprinted inside. The results are encouraging and an exponential gain length is achieved with GL = 4.5 for a 40 mm length capillary. Other evidence to support the observation is realised when a plane multilayer mirror with reflectivity < 30% is introduced resulting in amplification.

In-band EUV radiation of ablative capillary discharges in PVC

A study of the performance of an ablative capillary discharge through a PVC capillary is reported. It is shown that the PVC capillary is capable of producing strong in-band 13.5 nm EUV radiation. This band of radiation is produced by transition arrays of multiply ionised heavy metal ions (Sn, Zn, etc.) that are constituents of various chemical additives in commercial PVC grades. A low concentration of radiating ions, good thermalisation of the capillary plasma and plasma homogeneity along the capillary axis produce well-defined bands with little line radiation outside the band of interest. Two interesting cases are discussed, both producing band radiation with a full-width at half-maximum of around 1 nm and maxima near 10, 13.5 and 15.5 nm, respectively. The plasma spectra are not very sensitive to input discharge voltage, but in some cases the amount of energy in the band of interest can be controlled by it. The most serious problem of such discharges still remains the amount of macroscopic debris produced by the capillary ablation.

Time resolved diagnostics of plasmas in polyacetal ablative capillary discharges

The dynamics of the plasma in an ablative capillary discharge made of polyacetal has been studied by time resolved XUV pinhole imaging and spectroscopy. Pinching of the plasma column occurring shortly after the current maximum is observed and characterized. A waved structure imprinted into the capillary wall stabilizes ablation and makes pinching more reproducible.

A SIMPLE XUV SOURCE AT 13.5 NM BASED ON ABLATIVE CAPILLARY DISCHARGE

A XUV source that produces a strong emission band at the wavelength of 13.5 nm with a FWHM of 0.6 nm and a duration of about 100 ns is described. In particular this wavelength has attracted the attention of many scientists working in the field by being a good candidate for the development of XUV lithography. The source was generated by using an ablative capillary discharge where the capillary was made of PVC (polyvinyl chloride). A remarkable burst of radiation at the above wavelength was recorded, the intensity of the radiation being higher by a factor of 10 in the spectral region of interest, as compared to usually used capillaries made of POM (polyacetal), or to recently developed capillary discharges in noble gases. Total XUV radiation energy of up to 50 mJ per pulse seems to be possible with such a device. Due to its simplicity, the described capillary discharge is a good candidate for a simple incoherent XUV source at 13.5 nm.

Debris free high brightness light source based on LPP for actinic EUV microscopy and metrology applications

The progress of EUVL and the introduction of HVM scanners demands advanced actinic metrology especially for the EUV mask supply chain. For stand alone field use reliable metrology sources for EUV inband emission around 13.5 nm are critically needed. For nanometer resolution the effective “inband brightness” is extremely important. Laser produced EUV sources (LPP) are cost effective with efficient energy use thus providing a reliable approach for real-life industrial applications. However, apart from the Cymer/ASML LPP scanner source no such source is available. One reason is that realizing a reliable tin droplet target is beyond the technical and financial scope of a metrology source. In this paper, we propose a path to make industrial laser produced plasma based EUV sources reliable and with easy renewable targets a reality.