Titanium Nitride Formation by Low Energy Ar Ion Bombardment and UV-Light Irradiation During Deposition
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ABSTRACT Titanium nitride films were produced by a newly developed photon and ion beam assisted deposition system (PHIBAD system). With an electron beam evaporator titanium was deposited on silicon substrates in a controlled nitrogen environment. The growing 8-TiN films were bombarded with argon ions and illuminated with UV-light. The results demonstrate that the impurity content, the nitrogen to titanium ratio of the films, the microstructure and the crystal alignment are changed using UV-light irradiation during ion assisted deposition.
INTRODUCTION The rare gas ion bombardment during deposition of thin films provides the advantage of composition, structure and morphology control. Titanium nitride is a material which is well studied and well known in thin film technology due to its advantageous mechanical and electrical properties. It has been reported that films deposited under low energy ion bombardment show a lower impurity content (mostly oxygen and carbon) [1 ] and a modified microstructure [2] than films reactively evaporated at room temperature. This effect was ascribed to the energy transfer from the ions to the sample. Another means of transferring energy to the near surface region of the sample is irradiation with energetic photons during deposition and ion bombardment. As the reflectivity of metals decreases with decreasing wavelength, UV-light is very suitable for this application. Its penetration depth is about 10 nm. In this paper the chemical composition and the structure of thin titanium nitride films, produced by reactive evaporation (RE), ion beam assisted deposition (IBAD) and photon and ion assisted deposition (PHIBAD) are compared. In the reported experiments, the argon ion energy, the ion current density, the temperature during deposition, the substrat material, the conditions of titanium deposition, the partial pressure of nitrogen in the environment atmosphere and the UVlight intensity are constant. 491
Mat. Res. Soc. Symp. Proc. Vol. 396 ©1996 Materials Research Society
EXPERIMENT
The titanium nitride films were prepared by a PHIBAD system (details see ref. [3]). It consists of a 4 kW electron beam evaporator, a filamentless rf-excited broad beam ion source and a 500 W mercury arc lamp outside the vacuum chamber. The ion beam impinges the sample perpendicular to the surface. The UV-light enters the chamber through a sapphire window. This results in an integral illumination intensity (wavelength between 230 and 400 nm) of about 650 mW/cm 2 at the sample, measured by a combination of an UV-light sensitive photo diode and a grey filter to prevent nonlinearities of the photo diode under high intensity illumination. The sample, mounted on the top flange of the preparation chamber, is usually cooled to room temperature by water. The sample temperature is monitored by thermocouples and controlled by a PID-regulator. Titanium was deposited on Si (100) substrates with a constant deposition rate of 0.33 nm/sec and was simultaneously irradiated with argon ions in a defined nitrogen environment.
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