Growth and characterization of thin sio2 and ta2o5 dielectric layers nd : yag laser oxidation


Thesis Type: Doctorate

Institution Of The Thesis: Middle East Technical University, Faculty of Arts and Sciences, Department of Physics, Turkey

Approval Date: 2005

Thesis Language: English

Student: Gülnur Aygün Özyüzer

Supervisor: RAŞİT TURAN

Abstract:

Our aim was to establish a methodology for laser assisted oxidation of semiconductor and metal surfaces. One advantage of laser oxidation is the fact that radiation is heavily absorbed in a thin surface layer of the sample and the other is its ability for local oxidation. In addition to this, laser beam can be directed into some areas that other processes cannot reach. For these reasons, Nd:YAG pulsed laser working at 1064 nm wavelength is used for the oxidation purposes of Si and Ta films. First, SiO2 layer was obtained for various O2 pressures and laser powers. The thickness, refractive index, structural, dielectric, electrical and optical characteristics of the SiO2 layers have been determined. We have established that there exists an interval of laser power in which the oxidation occurs without surface melting. The oxidation process is controlled by the laser power rather than by the substrate temperature (673 ا 748 K). It was found that better film quality is obtained at higher substrate temperatures and laser power greater than 3.36 J/cm2. Second, rf-sputtered Ta films were oxidized by laser, because Ta2O5 appears to be a good promising candidate to replace SiO2 because of its high dielectric constant, high breakdown voltage and relevant small leakage current values. It was found that the substrate temperature is an important parameter to obtain denser layers with reduced amount of suboxides and the most suitable substrate temperature range is around 350 C to 400 C. β-orthorhombic crystal structure was obtained when the substrate temperature is 350 ا 400 C for thinner films (up to 20 ا 25 nm) and 300 ا 350 C for thicker films (40 nm). The refractive index values of laser grown thin tantalum oxide films were between ~1.9 and 2.2 being close to those of bulk Ta2O5 (2.0 ا 2.2). Oxide thicknesses in uniform Gaussianاlike shapes were measured as around the twice of