Temperature Dependence of the Intrinsic Stress and Biaxial Modulus of Plasma Deposited Silicon Nitride and Silicon Oxynitride Films

Abstract

The intrinsic stress and biaxial modulus of thin films of amorphous silicon nitride (0.5μm) and silicon oxynitride (1.5 to 2.5 μm) were measured following deposition (T_s=260 to 610°C), and then at discrete intervals throughout an annealing cycle. The biaxial modulus and intrinsic stress of the silicon nitride films increased from 110 GPa and 130 MPa, respectively, to 180 GPa and 680 MPa as the deposition temperature increased from T_s=340°C to T_s=610°C. The elemental composition was unaffected by the deposition temperature. Annealing at 1100°C increased the intrinsic stress to ≃ 1.8 GPa, as nitrogen and hydrogen were lost. Films with “near-stoichiometric” compositions (SiN_1.1; H = 12 at.%) did not crack.

Adding oxygen to form silicon oxynitride lowered both the biaxial modulus (20-30 GPa) and the intrinsic stress (-50 to 100 MPa). All the silicon oxynitride compositions (SiO_0.3N_1.0 to SiO_1.7N_0.5) were unstable when annealed above the deposition temperature (260°C). Films grown using mostly nitrous oxide (R = N₂O/(N₂0+NH₃) < 0.5) oxidized at 350°C to form silica. Simultaneously, the biaxial modulus and intrinsic stress increased to 100 GPa and 170 MPa, respectively. Films grown from mostly ammonia (R <0.5) lost nitrogen and hydrogen and cracked when the temperature exceeded the deposition temperature by 40 to 90°C. The stress induced by the elemental loss was ≃ 600 MPa.