Sanghak Yeo

Effect of annealing temperature on dielectric constant and bonding structure of low-k SiCOH thin films deposited by plasma enhanced chemical vapor deposition

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.

Significant improvement of electrical and thermal properties of low dielectric constant plasma polymerized paraxylene thin films by postdeposition H2+He plasma treatment

Electrical and thermal properties of plasma polymerized paraxylene (PPpX) thin films were significantly improved by postdeposition H2+He plasma treatment. Plasma treatment decreased dielectric constants and increased thermal stability. As the plasma treatment time increased from 0 to 6 min, the relative dielectric constant k decreased from 3.23 to 2.77. Suppression of C=O and O–H group formation and increase of C–H groups in the PPpX film were thought to contribute to the reduction of the k values. Plasma treatment enhanced the thermal stability of PPpX thin films. While the untreated PPpX thin film was stable only to 400 °C, plasma-treated films were stable up to 450 °C. H2+He plasma treatment did not increase the leakage current through the PPpX films notably and did not degrade the surface smoothness, either.

Effects of Deposition Pressure on the Properties of a Low-Dielectric Constant Cyclohexane-based Plasma Polymer

The effects of deposition pressure on the properties of cyclohexane-based plasma polymer (CHexPP) thin films were investigated. Deposition of CHexPP thin films at higher deposition pressures was associated with lower deposition rates and produced thin films with lower k-values, lower thermal stabilities and higher etching rates. It is considered that the higher deposition pressure decreases the energies of the charged reactive species generated by the plasma from the precursor molecules, resulting in less dense and less well cross-linked plasma polymer thin films.

Surface characterization of plasma-polymerized cyclohexane thin film

A plasma-polymerized cyclohexane (PPCHex) thin film was characterized by using Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry along with a principal component analysis (PCA). The PPCHex thin film was deposited onto a silicon substrate by using an inductively coupled plasma chemical vapor deposition method and cyclohexane as a precursor. The chemical composition of the PPCHex surface was controlled in a reproducible manner as a function of substrate bias plasma power. A PCA of the TOF-SIMS data also gave systematic insight into the surface chemical compositions and molecular cross-linking on plasma-polymerized thin films as a function of substrate bias plasma power. PPCHex thin film made at 100W plasma power had the least amount of oxygen functional groups such as the C–O–H form on the surface than the one made at 10W plasma power.

Sensitivity enhancement of carbon nanotube based ammonium ion sensors through surface modification by using oxygen plasma treatment

We have shown that the sensitivity of carbon nanotube (CNT) based sensors can be enhanced as high as 74 times through surface modification by using the inductively coupled plasma chemical vapor deposition method with oxygen. The plasma treatment power was maintained as low as 10 W within 20 s, and the oxygen plasma was generated far away from the sensors to minimize the plasma damage. From X-ray photoelectron spectroscopy analysis, we found that the concentration of oxygen increased with the plasma treatment time, which implies that oxygen functional groups or defect sites were generated on the CNT surface.