Stress in ion-beam assisted silicon dioxide and tantalum pentoxide thin films

Sirotkina, N

Abstract

Ta205 and Si02 thin films, deposited at room temperature by ion-beam sputtering (IBS) and dual ion-beam sputtering (DIBS), and Si02 films, deposited by reactive e-beam evaporation and ion-assisted deposition, were studied. The energy (150-600 eV) and ion-to-atom arrival ratio (0.27-2.0) of assisting argon and oxygen ions were varied. Influence of deposition conditions (deposition system geometry, nature and amount of gas in the chamber, substrate cleaning and ion-assistance parameters) on films properties (stress, composition, refractive index njoonm and extinction coefficient ksoonm) was investigated.
A scanning method, based on substrate curvature measurements by laser reflection and stress calculation using the Stoney equation, was employed.
RBS showed that stoichiometric Ta205 films contain impurities of Ar, Fe and Mo. Stoichiometric Si02 films also contain Ta impurity. Argon content increases with ion bombardment and, at maximum incorporation, argon bubbles are registered by TEM. XPS studies are complicated by surface contaminations and preferential sputtering. Evaporated Si02 films show +100 MPa stress (+ is tensile, - compressive). With 300 eV Ar+ bombardment, stress changes to -200 MPa, n500nm decreases (1.56-1.49) and k50onm increases (1.4x1 O'4-1.8x 103).
Of all studied IBS conditions, stress in Si02 (-560 MPa) and Ta205 (-350 MPa) films depends only on sputtering gas species and oxygen entry point into the chamber.
With argon and oxygen bombardment stress in IBS Si02 films decreases to -380 MPa and below the stress measurement system resolution, respectively. While Ar+ bombardment of Ta205 films leads to increase in stress to -490 MPa, the effect of oxygen assistance depends on ion energy. The observed behaviour was related to the total recoil density.
In DIBS Si02 and Ta205 films nm„m varies in the region of 1.5-1.59 and 2.13-2.20 and ksoonm is below 5.5x10'3 and 8.5x1 O'3, respectively. The refractive index exhibits complex behaviour, while ksonnm increases after initially decreasing to a minimum. The origins of the observed behaviour are unclear.

Citation

Sirotkina, N. Stress in ion-beam assisted silicon dioxide and tantalum pentoxide thin films. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Sep 7, 2021
• Publicly Available Date: Sep 7, 2021
• Publisher URL: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272625
• Related Public URLs: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272625
• Award Date: Jan 1, 2003