ICMCTF2007 Session B4: Laser-Assisted and Ion Beam Coatings and Technologies

Recent results of thin film deposition by means of ion beam sputtering or UV laser beam ablation of solid targets for depositing multilayered coatings for x-ray, EUV, and optical applications are summarized. In particular, the large area deposition of Mo/Si multilayers for EUV lithography masks by ion beam sputter deposition using a new ion beam sputter deposition tool are reviewed. The concept ideas of the tool to fulfill the requirements of homogeneity and low particle generation are pointed out and the selected results of the multilayer characterization are mentioned. The influence of the deposition parameters on the film properties are discussed in terms of the film properties, e.g. the film stress. Further examples concern the deposition of Ni/C and Cu/C multilayers by PLD and oxidic multilayers by IBS.

Finally, the interaction of these multilayers with ultrashort laser pulses are presented. The basics of laser-matter interactions of such thin film multilayers with ultrashort pulses are discussed and measurements on the damage threshold of optical multilayers presented.

Thin films of lanthanum monosulfide (LaS) have been successfully deposited on Si and MgO substrates by pulsed laser deposition. Films grown on Si substrates at room temperature in vacuum were mostly amorphous with small (5-10 nm) crystalline regions and exhibit very broad Raman features. Films grown on MgO at elevated substrate temperatures in a background gas of H₂S were polycrystalline with varying grain size dependent on temperature and pressure. The Raman spectra of these LaS/MgO films are all similar and exhibit intensity variations from sample to sample consistent with changes in grain size. These spectra resemble that of polycrystalline bulk LaS showing a number of sharp and also broader features with the main peaks at 101, 148, 178, and 262 cm^-1 due to disorder-induced first-order scattering from acoustic and optic phonons¹. Spectroscopic ellipsometry¹ shows a sharper optical band edge in the LaS/MgO films compared with LaS/Si films consistent with an increased crystallinity. Scanning anode field emission microscopy (SAFEM) reveals that an increase in film crystallinity leads to an increase in the total emitted current. The mostly amorphous La/Si films emit up to 0.5 µA for a cathode surface of 200 µm² before a burnout occurs due to thermally induced phase change in the emitting nanocrystallites. A polycrystalline LaS/MgO film with a 40 nm grain size emits up to 40 µA /200 µm² with no burnout, a result that is consistent with the patchwork field emission behavior of the LaS/Si films.² LaS thin films could potentially be used for cathode materials in vacuum microelectronic devices.

¹ M. Cahay, K. Garre, X. Wu, D. Poitras, D. J. Lockwood, and S. Fairchild, JOURNAL OF APPLIED PHYSICS 99, 123502 (2006)

² V. Semet, M. Cahay, Vu Thien Binh, S. Fairchild, X.Wu , D.J. Lockwood, JOURNAL OF VACUUM SCIENCE AND TECHMOLOGY B 24(5), Sept/Oct 2006 .

Thin-film MoS₂ coatings have been been studied for a number of years as a self-lubricating wear-resistant film for a number of applications.² The addition of metals such as Ti has been observed to improve such tribological properties as friction and wear behavior. The metals have typically been added to sputtered coatings by either dual sputtering or by interlayering using alternate sputtering targets. We are investigating the microstructure, friction, and wear performance of MoS₂/metal films formed by high-power ion beam ablation of one or more targets. These experiments are carried out on the 750 kV RHEPP-1 facility at Sandia National Laboratories. An intense ion beam of up to 10 J/cm² fluence is used to ablate either a composite MoS₂/metal target, or ablate alternately two discrete targets. The deposited layer from each pulse can be between 5-20 nm in thickness. Although Ti is the primary admixed metal, other metals such as Ni may be investigated. Due to the high-power nature of the process (similar to PLD), the film texturing is likely to be different from that formed by either RF or DC-magnetron sputtering. The pulsed nature may lead to new metastable phases due to the rapid quench, and with much higher deposition rates than PLD. We will form and investigate pure MoS₂, MoS₂/metal composite, and MoS₂/interlayered metal films. Pin-on-disk testing, SEM, and XTEM of selected layers is planned.

¹Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Co., under US DOE Contract DE-AC04-94AL85000.

²N.M. Renevier, J. Hampshire, V.C.Fox, J. Witts, T.Allen, D.G. Teer, Surf. Coat. Tech. 142-144 (2001) 67-77.