(607b) Inertial Gas Admixtures in Pecvd for Uv Absorbing Thin Films of Titanium Dioxide on Polymers

Titanium dioxide (TiO₂) films have versatile
applications, which include: ultra-thin film high-k insulators in integrated
circuits and surface passivation, as well as biocompatible coatings availing
their chemical and thermal resistance. Due to its high refractive index, it is
commonly used for antireflection coatings. Moreover, it appears to be a
material for effective UV absorption.

This is of special interest for the protection of polymers, which
suffer photo-degradation. Thus, thin amorphous films, mainly, consisting of TiO₂
, as discussed in an earlier work [1], were deposited at temperatures of 70°C
on films of polycarbonate, polyethylene-terephthalat and on quartz as reference
material.

Therefore, a low pressure rf discharge was operated in oxygen,
oxygen/nitrogen and oxygen/argon with small admixtures of
titanium(IV)isopropoxide (TTIP) at an input power of 200 W for 5 min. By
changing the flow rate of oxygen, the oxygen-to-TTIP ratio q was varied for all
types of discharges gas mixtures for q = 10 to 45. Besides the variation of the
deposition rate (i.e. film thickness), the behaviour of the spectral
transmittance of visually transparent films was determined in the range from
200 to 500 nm. Furthermore, the absorptance of films has been derived at
characteristic spectral positions of the transmission spectra of the films.
Accordingly, the cut-off wavelength of the films was found to be a subject of
variation depending on the ratio q for gas mixtures containing nitrogen or
argon. But, for mixtures of pure oxygen and TTIP, it appeared to depend on q
only slightly. Furthermore, at 310 nm, the spectral absorption coefficient
(extinction coefficient x concentration) was 13x10⁶ m^-1 for
q = 44 in oxygen/argon and marginally lower for oxygen/nitrogen (12x10⁶ m^-1)
as well as for oxygen (11x10⁶ m^-1). However, with
decreasing value of q a drastic decrease of the absorption coefficient (toward
8x10⁶ m^-1) was witnessed for the oxygen/TTIP mixture. In
contrast, the coefficient decreases only slightly (by 10⁶ m^-1)
for nitrogen and argon containing mixtures.

[1] A. Sonnenfeld, R. Hauert, Ph. Rudolf von Rohr, UV
Absorptance of Titanium Dioxide Thin Films by Plasma Enhanced Deposition from
Mixtures of Oxygen and Titanium-Tetrakis-Isopropoxide, Plasma Processes and
Chemistry, DOI: 10.1007/s11090-006-9022-6, online at Springer-Link, 2006