Properties of Al 2 O 3 films prepared by argon ion assisted deposition
- PDF / 1,382,458 Bytes
- 7 Pages / 576 x 792 pts Page_size
- 27 Downloads / 223 Views
G. N. Subanna Materials Research Center, Indian Institute of Science, Bangalore 560 012, India
K. Narasimha Rao and S. Mohan Instrumentation and Services Unit, Indian Institute of Science, Bangalore 560 012, India (Received 15 January 1994; accepted 17 May 1994)
Aluminum oxide films have been prepared by ion assisted deposition using argon ions with energy in the range 300 to 1000 eV and current density in the range 50 to 220 yu,A/cm2. The influence of ion energy and current density on the optical and structural properties has been investigated. The refractive index, packing density, and extinction coefficient are found to be very sensitive to the ion beam parameters and substrate temperatures. The as-deposited films were found to be amorphous and could be transformed into crystalline phase on annealing. However, the crystalline phases were different in films prepared at ambient and elevated substrate temperatures.
I. INTRODUCTION
II. EXPERIMENTAL
Aluminum oxide (A12O3) thin films have been extensively used in optical and electronic industries, as protective films for metal reflectors, laser mirrors, and as passivation layers in metal/oxide/semiconductor devices. Several techniques have been used to prepare these films. Ion assisted deposition (IAD) is used as a means to prepare films with better characteristics for a variety of applications.1"9 Oxide films deposited with simultaneous oxygen ion bombardment not only have higher packing density (increased refractive index), but also better stoichiometry.10"14 In our recent publication,15 we have reported the optical and structural properties of A12O3 films deposited using oxygen ion assisted deposition. However, the presence of oxygen ions at the hot filament of the ion source limits the life of the filament. This could be partly overcome by either using argon or a mixture of argon and oxygen for the deposition of oxide thin films. There is only very limited work on argon IAD of oxide films and the investigations on the effect of ion beam parameters on their optical and structural properties. In this paper, we report the optical and structural properties of AI2O3 films produced by electron beam evaporation with the growing film bombarded with argon ions in the energy range 300-1000 eV and current density range 50-220 /iA/cm 2 . The substrates were maintained at ambient, 100, 200, and 300 °C during deposition. The films were characterized for their refractive index extinction coefficient, packing density, and inhomogeneity. Films in their as-deposited condition and after post-annealing in air at 800 °C were studied for their structural properties.
The details of the evaporation system and the deposition conditions have already been discussed.15"18 A12O3 films were deposited by electron beam evaporation (ESV6, Leybold AG, Germany) of A12O3 (99.99% purity) onto optically polished fused silica and NaCl substrates. The substrates were precleaned with argon ions of energy 500 eV and current density 100 /zA/cm 2 for 3 min prior to deposition using a 3 cm Kaufman ion
Data Loading...
