Effect of Annealing Temperature on Dielectric Constant and Bonding Structure of Low-k SiCOH Thin Films Deposited by Plasma Enhanced Chemical Vapor Deposition

Abstract

We investigated the effect of annealing temperature on the properties of SiCOH films deposited by plasma-enhanced chemical vapor deposition using or a mixture of Si–O containing and hydrocarbon precursors, decamethyl-cyclopentasiloxane (DMCPSO-C10H30O5Si5) and cyclohexane (CHex-C6H12). These SiCOH films were deposited at pressures of 0.6 and 1.5 Torr and the as-deposited SiCOH films were subjected to annealing temperatures from 25 to 500 °C in a furnace for 1 h in N2 ambient at a pressure of 1 atm. The relative dielectric constants, k, of the SiCOH films deposited at 0.6 and 1.5 Torr were 2.76 and 2.26, respectively, before the annealing process. The subsequent annealing of the SiCOH film at 500 °C further reduced the k values to as low as 2.31 and 1.85, respectively. Decreases in the refractive index, hardness, and modulus were observed as the annealing temperature increased to 450 °C. However, further increasing annealing temperature to 500 °C caused the refractive index, hardness, and modulus to increase again. Trends of decreases in both the hardness and modulus with increasing annealing temperature were found. The refractive index and the film thickness retention also decreased with increasing annealing temperature. The change in the k value as a function of the annealing temperature was correlated with the change in the Fourier transform infrared absorption peaks of C–Hx, Si–CH3, and Si–O related groups. As the annealing temperature increased, the intensity of both the CHx and Si–CH3 peaks decreased, respectively. In particular, the C–H2 (asymmetric and symmetric) peaks provide direct evidence of the presence of ethylene groups in the SiCOH films. Thus the decrease in intensity of the peaks corresponding to the CHx groups and Si–O cage structure in the SiCOH films was considered to be responsible for lowering they dielectric constant, refractive index, hardness and modulus of the films. The leakage current density of the SiCOH films at 1 MV/cm is obtained ∼10-8 A/cm2 with the 450 °C annealed films, which can be considered as an acceptable leakage current level for the interconnect application.