Extreme ultraviolet mask surface cleaning effects on lithography process performance

Abstract

Extreme ultraviolet mask substrate surface roughness effects on lithographic patterning J. Vac. Sci. Technol. B 28, C6E23 (2010); 10.1116/1.3502436The effects of oxygen plasma on the chemical composition and morphology of the Ru capping layer of the extreme ultraviolet mask blanks Cleaning of extreme ultraviolet lithography optics and masks using 13.5 nm and 172 nm radiation Extreme UV ͑EUV͒ masks are expected to undergo cleaning processes in order to maintain the lifetimes necessary for high volume manufacturing. For this study, the impact of repetitive cleaning of EUV masks on imaging performance is evaluated. Two high quality industry standard EUV masks are used, with one of the masks undergoing repeated cleaning and the other one kept as a reference. Lithographic performance, in terms of process window analysis and line edge roughness, was monitored after every two cleans and was compared to the reference mask performance. Surface analysis by atomic force microscopy did not show changes in the midspatial frequency roughness measured after each clean. After a total of eight cleans, minimal degradation is observed in the lithographic performance of the mask. From these observations, the authors conclude that the cleaning cycles completed thus far did not damage the mask multilayer or the absorber structures. The cleaning cycles will be continued until significant loss in imaging fidelity is found.

Secondary electron deposition mechanism of carbon contamination

“…), and become fixed to surfaces as a carbonaceous layer when irradiated with ionizing radiation. 2,5,8,11,12,[15][16][17] The results are sometimes mixed, 8,9,12 but in certain cases the reflectance can be fully recovered, 15 and an optic can survive multiple cleaning cycles. The carbonaceous deposits are often highly undesirable as they can degrade the transmissive or reflective properties of optics, introduce spectroscopic artifacts, and/or decrease the efficiency of detectors.…”

“…This phenomenon is common to diverse technologies that involve high energy radiation (electron microscopy, [3][4][5] x-ray photoelectron spectroscopy, 6 synchrotron and free electron laser beamlines, [7][8][9] space-based telescopes [10][11][12][13] ). 17 In practice, the contamination processes can be mitigated, 5,7,18 but often cannot be totally eliminated, and cleaning processes entail some instrument downtime, which ultimately reduces productivity. With regards to EUV lithography, the carbonaceous layer has been observed to decrease reflected intensity, distort the wavefront, 14 and change the optical path length, 9 all conceivably capable of introducing defects in the devices produced and reducing throughput.…”