Effect of flux clusterization on the thickness of films deposited by magnetron and pulsed laser sputtering of metal oxides

Abstract

231The deposition of films of multicomponent chem ical compounds is usually accompanied by clusteriza tion, whereby the parameters of clusters are clearly related to the main structural types of the deposited material [1][2][3][4]. In the volume of deposited layers, the formation of clusters, which possess an intermediate order [1] and significantly influence the structure and properties of samples, is determined by the substrate type and temperature and stimulated by local internal stresses [5][6][7]. The clusterization is more pronounced in systems susceptible to phase separation [8,9].However, the formation of clusters during the dep osition of films from the gas phase is frequently observed before the onset of film growth. This is espe cially clearly manifested when the deposition process is based on the sputtering of targets and the formation of clusters takes place in the flow of sputtered material moving from the target to substrate. In this case, the clusterization is clearly revealed in deposited films with amorphous structure deposited onto cold glass substrates, where the clusters appear as "frozen" local atomic configurations incorporated into the amor phous matrix. These configurations are nucleated in the flow as a result of collisions and chemical interac tions of the sputtered components with each other and with atoms (ions) of a working gas [10,11]. Simulta neously, these collisions in low pressure gaseous media lead to a decrease in the ion energy and account for losses of the material moving from the target to substrate, thus affecting the deposited film thickness. Therefore, the gas phase collisions influence both the thickness of deposited layers and cluster formation, thus determining their possible interrelation.We have studied the relation between clusterization in the flux of a substance and the thickness of depos ited films obtained by the sputtering of La 0.7 Sr 0.3 MnO 3 (LSMO) and YBa 2 Cu 3 O 7 -δ (YBCO) targets. Both these metal oxides are known to be high susceptible to cluster formation [2, 5, 6, 10]. In amorphous YBCO, clusters are conveniently revealed by optical tech niques [10][11][12]. For determining the concentration of clusters in LSMO, a more acceptable approach is based on magnetic methods [13]. In this study, we have also compared the technologies of pulsed laser sput tering [2, 5, 10-12] and magnetron sputtering of mul ticomponent metal oxide targets.The magnetron sputtering of an LSMO target with a diameter of D = 4 cm was performed at a current of 140 mA and an interelectrode voltage of 350 V in a mixture of argon (84 at. %) and oxygen (16 at. %)at a total working gas pressure of 6 × 10 -3 Torr. A distance from the target to the edge of a glass substrate (oriented perpendicular to the target) was 0.5 cm (Fig. 1a). Dur ing the pulsed laser sputtering of an YBCO target, the film was deposited onto a glass substrate oriented along the direction of predominant plasma expansion in the laser plume (Fig. 1b) [14]. The YBCO target was sputtered in oxygen at a pressure of 2 ×...