HIGH-PRECISION LARGE-AREA PLD OF X-RAY OPTICAL MULTILAYERS

To realize high quality X-ray optical multilayer stacks on large areas a double-beam PLD source was integrated into a commercial MBE system. Optimization of ablation conditions and film growth regime, resp., fo r various kinds of homogeneous thin films and multilayer systems has b een realized by a reproducible variation of pulse energy and repetitio n rate of each of the two Nd:YAG-lasers. In addition, the lasers can b e independently controlled by a predetermined pulse delay. Thus, plasm a parameters of two plumes generated from locally separated origins ca n be influenced by the pulse delay of the Nd:YAG-lasers, too. The infl uence of laser parameters and pulse delay on thin film growth is inves tigated by the deposition of Ni/C layer stacks. Optimum irradiation co nditions are zero delay and moderate pulse energies. Multilayer interf ace roughnesses on the order of sigma(R) approximate to 0.1 nm are ded uced from high resolution electron microscopy (HREM)-micrographs. The interface roughness increases with higher pulse energy. For changing t he pulse delay from tau = 0 ns to tau = 2.5 ms, a destruction of the l ayer stack is observed. Laterally graded Ni/C multilayers showing X-ra y optical activity were synthesized with these optimized deposition pa rameters in the period thickness range from 3 to 5 nm. Average values of thickness gradients typically Delta t/Delta x approximate to 2 x 10 (-8) for 4'' substrate length in maximum and period thickness variatio ns on the order of sigma(1) approximate to 0.1 nm are confirmed by gra zing incidence X-ray reflectometry end HREM. (C) 1998 Elsevier Science B.V.