Characterization and optimization of magnetron sputtered Sc/Si multilayers for extreme ultraviolet optics

Scandium/silicon multilayers have been deposited by magnetron sputtering and characterized by several techniques. Experimental peak reflectances of 0.22 and 0.37 have been measured respectively at wavelengths of 40 nm and 46 nm, for 10° incidence angle. The corresponding theoretical values for a perfect Sc/Si structure are respectively 0.38 and 0.57. In order to explain these differences between calculated and measured reflectivity, thin film and multilayer characterizations have been done. Effects of multilayer imperfections on the reflectivity have been estimated independently by means of simulation. Based on these results, a new design of Sc/Si multilayer is proposed with top layer thickness optimization. With this design, the experimental peak reflectance reaches 0.46 at a wavelength of 46 nm. PACS 78.67.Pt; 78.66.-W; 81.15.Cd     

Limiting step involved in the thermal growth of silicon oxide films on silicon carbide

Thermal growth of silicon oxide films on silicon carbide in O2 was investigated using oxygen isotopic substitution and narrow resonance nuclear reaction profiling. This investigation was carried out in parallel with the thermal growth of silicon oxide films on Si. Results demonstrate that the limiting steps of the thermal oxide growth are different in these two semiconductors, being diffusion limited in the case of Si and reaction limited in the case of SiC. This fact renders the growth kinetics of SiO2 on SiC very sensitive to the reactivity of the interface region, whose compositional and structural changes can affect the electrical properties of the structure.     

A 13C isotopic tracing study of a-C:H thin-film growth

The growth mechanisms of amorphous carbon (a-C:H) thin films obtained by the decomposition of methane gas in a multipolar plasma set up were studied using ¹³C as a tracer. Hydrogenated carbon films first grown in a methane plasma with natural isotopic composition (¹²C) were further grown in highly enriched ¹³C methane discharge (experiments were also carried out with the reverse order). ¹³C profiles were obtained by resonant nuclear reaction depth profiling using the narrow (FWHM<100 eV) resonance at 1747.6 keV, in the ¹³C(p, )¹⁴N nuclear reaction. Plasma conditions were varied so as to vary the energy of particles arriving at the sample surface from 30 eV to 500 eV. In all cases, a system of two layers was observed: a pure ¹³C film overlaying a pure ¹²C film (or the reverse order) with a rather sharp interface between the two layers. These results suggest layer by layer amorphous hydrogenated carbon film growth with minimal mixing or interdiffusion of the isotopic layers induced by the ionic bombardment during the growth.     

Artificially nanostructured Cu:Al2O3 films produced by pulsed laser deposition

The processes leading to the formation of Cu:Al₂O₃ composite films on Si (001) with a well defined nanostructure by alternate pulsed laser deposition (a-PLD) in vacuum are investigated. Alternately amorphous Al₂O₃ layers and Cu nanocrystals nucleated on the Al₂O₃ surface are formed, according to the PLD sequence. The Al₂O₃ deposited on the Cu nanocrystals fills in the space between them until they are completely buried, and subsequently, a continuous dense layer with a very flat surface (within 1 nm) is developed. The nucleation process of the nanocrystals and their resulting oblate ellipsoidal shape are discussed in terms of the role of the energetic species involved in the PLD process and the metal–oxide interface energy. Received: 4 July 2000 / Accepted: 5 July 2000 / Published online: 13 September 2000