Residual stress and thermal expansion behavior of TaO xN y films by the micro-cantilever method

Abstract

A micro-electro–mechanical system (MEMs) technique, the bilayer cantilever beam method was used to examine the residual stress and the thermal expansion coefficient (α) of TaO x N y films by measuring the changes in radius of curvature. Residual stresses of all the TaO x N y films RF-deposited onto SiO 2/Si (100) are compressive and varied from 2.5 to 12.5 MPa. The compressive stress is inversely proportional to the N 2/O 2 flow ratio except that appears at the flow ratio 0.5. However, the calculated α values, ranging from 7×10 −7 to 2×10 −5 °C −1, increase proportionally with the N 2/O 2 flow ratio, except the value appears at the flow ratio 2. Comparing the α values of ZnS/SiO 2 and Si 3N 4 films, the properties of TaO x N y films being optimizable by adjusting the N 2/O 2 flow ratios are obviously promising candidates in optical recording applications. Effects of other processing parameters on the α value and stress, such as the film thickness, RF power and reactive gas ratios during deposition, are also elucidated. Furthermore, a load-sensing nano-indentation method was used to examine the elastic property of the films. The obtained reduced elastic modulus E r values of TaO x N y films are nearly constant (∼200±15 GPa) at the N 2/O 2 flow ratio from 0.25 to 2.