Pulsed laser deposition of nitride films

Abstract

The present research is aimed at using Pulsed Laser Deposition (PLD) method to fabricate epitaxial cubic TiN and TaN thin films on MgO(001) and Si(001). Crystalline TiN and TaN layers have been deposited under a base pressure of-10-6 Torr and at substrate temperatures ranging from 550C to 750C. Epitaxial TiN films of cube-on-cube grown on Si(001) in a 4-on-3 mode (Volmer-Weber type) at 600C and in a 5-on-4 mode (Stranski-Krastinov type) at 600C have been obtained. The resistivity of these epitaxial TiN film is about 44 u峏 cm at room temperature. They show a typical positive dp/dT characteristics of a metal. Epitaxial TaN(001) films, on the other hand, have been successfully grown on MgO(001) single crystal and TiN(001) buffered Si(001) substrates. Very good crystalline TaN films with cube-on-cube <001>TaN <001>MgO heteroepitaxy are obtained. In spite of the ball-shaped particles, a very sharp TaN/MgO interface is observed. The room temperature resistivity is about 600 u峏 cm with negative dp/dT. TaN films grown on TiN(001) buffered Si(001), however, show a mixture of TaNx (with x <= 1) components. Although the (001)-oriented TaN is always present prominently, the nitrogen deficient TaNx components are often co-existed in the films and show up as a broad peak in the X-ray diffraction profile. Stoichiometric and single phase TaN(001) films can only be obtained in a narrow temperature window at around 550C and heteroepitaxial relationship of <001>TaN <001>TiN <001>Si has been demonstrated. An interesting finding is that this bi-layer structure could produce a nearly flat R-T curve with dp/dT close to zero. The crystallinity and surface morphology of the epitaxial STO films with underlying TiN layer are also presented. All the STO films are cube-on-cube grown on the TiN/Si substrates over a wide temperature range (550 to 750C). The substrate temperature dependence growth modes of the TiN can change the orientation relationship of the STO films. It changes from (001) to (101) oriented at elevated temperature. It is suggested that better crystallinity STO films can be achieved by improving the quality of the TiN buffer layer. The fundamental mechanical properties of epitaxial nitride films have been studied. TiN films grown at optimum temperature of 650C under 4 x 1O-6 Torr, yields a hardness (H) value of about 25 GPa and a Young's modulus (E) of 375 GPa. The lack of crystallinity and decrease in hardness (20 GPa) for TiN films grown at 550C appear to be related to the low processing temperature. The H value for single-layered TaN is 22 GPa and E is about 313 GPa. A remarkably increase in hardness for the TaN/TiN bi-layer films were also obtained.