Remote plasma enhanced chemical vapor deposition of fluorinated silicon oxide films using 1,2bis(methyldifluorosilyl)ethane and triethoxyfluorosilane.

摘要

The deposition characteristics of fluorinated silicon dioxide (SiO xFy) films using two fluorine-containing precursors, 1,2bis(methyldifluorosilyl)ethane (FASi-4) and triethoxyfluorosilane (FTES) were investigated in a custom-built remote microwave plasma enhanced chemical vapor deposition (PECVD) micro-reactor system. These studies were motivated by the finding that incorporation of fluorine in the oxide films reduces the dielectric permittivity of the films. Statistically-designed experiments were performed to identify significant independent parameters and their interactions, and to determine preferred operating windows; subsequent one factor at a time experiments were performed to better understand the effects of important single variables. Complementary film characterization methods including Rutherford Backscattering Spectroscopy (RBS), Fourier transform infrared transmission spectroscopy (FTIR), and scanning electron microscopy (SEM) were used to investigate and quantify film physical, chemical and electrical properties.; Arrhenius-type plots for the dependence of the deposition rate on substrate inverse temperature show that the FASi-4 sourced process is mildly activated with an apparent activation energy of 0.17 eV at a pressure of 0.4 Torr and 0.05 eV at a pressure of 0.1 Torr. Single factor experiments indicate that the deposition rates exhibit maxima at 0.1 Torr and 0.31 Torr for FASi-4 and FTES, respectively. The deposition rate maxima occur at lower pressures than the corresponding maximum observed for PETEOS deposition (∼0.6 Torr). Deposition rate maxima were also observed as a function of oxygen to source gas flow ratio. The deposition rate maximizes at 108 A/min with an oxygen: FTES flow ratio of 12:1. The deposition rate with TEOS, on the other hand, maximizes at over 400 A/min at an oxygen: TEOS flow ratio of 3:1.; RBS data indicate that decreasing O2:FASi-4 ratio from 15:1 to 8:1 increases the fluorine content in the deposited fluorinated silicon oxide films from 2 to 8 at.%. Fluorine incorporation decreased the dielectric constant from ∼4 for pure silicon dioxide to 3.6 with 8 atomic percent of fluorine incorporation. FTIR spectra show Si-O absorption band shifts from ∼1060 cm-1 for pure PECVD silicon dioxide to 1084 cm-1 for the fluorinated structure, indicating that the bonding structure is modified by fluorine incorporation. No measurable moisture absorption was observed.; Scanning Electron Microscopy (SEM) cross-section images indicate that the film conformality in deep trenches for fluorinated silicon oxide films deposited with FASi-4 was improved for a temperature increase from 250°C to 400°C. This result is consistent with the results that the deposition process is only mildly thermally activated at oxygen: FASi-4 flow ratio of 15:1. For such behavior the ballistic transport rate enhancement with increased temperature is greater than the reaction rate enhancement, and hence the effective reactive sticking coefficient decreases with increasing temperature. In contrast, SEM images with films deposited from FTES indicate that the conformality was slightly degraded when temperatures increase from 250°C to 350°C; this result may be attributed to the relative contribution of the oxygen atom recombination reaction, which creates oxygen radical concentration flux gradients in the features.