ZnO/Al2O3 nanolaminates fabricated by atomic layer deposition:: growth and surface roughness measurements

Nanolaminates are unique nanocomposites that allow various thin film properties to be tuned by changing the composition and interfacial density. ZnO/Al2O3 nanolaminates allow the surface roughness to be controlled because ZnO is crystalline and Al2O3 is amorphous at low deposition temperatures. ZnO/Al2O3 nanolaminates were grown using atomic layer deposition (ALD) methods. The ZnO and Al2O3 films were deposited at 450 K using alternating diethyl zinc/H2O exposures and trimethyl aluminum/H2O exposures, respectively. The growth rate and surface topography of the pure oxide films were examined using ex situ ellipsometry, stylus profilometry and atomic force microscopy (AFM) techniques. The ZnO ALD films grew at 2.01 Angstrom/cycle and roughened significantly versus film thickness because of the presence of ZnO nanocrystals. In contrast, the Al2O3 ALD films grew at 1.29 Angstrom/cycle and remained remarkably smooth versus film thickness because of their amorphous structure. In situ quartz, crystal microbalance measurements were employed to study the ZnO/Al2O3, nanolaminate growth. The individual ZnO and Al2O3 nanolayers nucleated and grew easily on each other with minimal interfacial effects. ZnO/Al2O3 nanolaminate films were prepared where the number of ZnO/Al2O3 interfaces was varied but the total thickness remained constant at similar to1250 Angstrom. Using AFM techniques, the RMS roughness of the nanolaminates was observed to decrease substantially with increasing ZnO/Al2O3 interfacial density. The Al2O3, nanolayer interrupts the ZnO crystal growth and forces the ZnO nanolayer to renucleate on the Al2O3 surface. AFM measurements revealed that a single trimethyl aluminum/H2O reaction cycle was sufficient to reduce markedly the surface roughness of the ZnO/Al2O3 nanolaminate films. ZnO/Al2O3, nanolaminates should be useful to fabricate a surface topography with a controlled surface roughness. (C) 2002 Elsevier Science B.V. All rights reserved.