Structural investigations on ultrathin Mo layers in a-Si : H with emphasison the island-continuous layer transition

The structural properties of Si/Mo/Si triple layers with Mo-layer thickness es from 34.0 nm down to nominal 0.17 nm are studied by X-ray reflectometry (XRR), X-ray diffraction at glancing incidence and transmission electron mi croscopy (TEM). The Mo-layers, sputter deposited under various conditions, are sandwiched by 15 nm (bottom) and 18 nm (top) a-Si:H layers, which are p repared at 470 K by PCVD or magnetron sputtering in an especially developed three-chamber deposition apparatus, which is described. Depending on the d eposition conditions, the discontinuous-continuous layer transition detecte d by XRR occurs at nominal thicknesses of the intermediate layer between 0. 4 and 1 nm. In the sub-1 nm range, the density of the intermediate layer in creases with thickness and reaches a maximum, which amounts to 94% of the b ulk value, around 1 nm. As found by TEM, layers with nominal thicknesses ar ound 0.7 nm consist of ellipsoidal nanoclusters in contradiction with the r esults of XRR. With the increase of thickness to 20 nm, dense Mo-layers (93 % of bulk) with smooth interfaces (RMS roughness typically 1 nm) are grown for low pressure sputter deposition. Mo-layers prepared at increased argon pressure have a density of 62% and a porous structure with nanocolumns of t ypical 10 nm diameter. (C) 1999 Elsevier Science S.A. All rights reserved.