Chemical and Thermal Stability of Fluorinated Amorphous Carbon Films for Interlayer Dielectric Applications
- PDF / 856,037 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 12 Downloads / 253 Views
XPS.
EXPERIMENT Fluorinated amorphous carbon (a-C:F) films were deposited by co-sputtering a graphite (DC 350W) target and a polytetrafluoroethylene (PTFE)/(RF 100W) target in a magnetron sputtering system. Argon was used as the sputtering gas at a pressure of 3 mTorr with the sample temperature held at room temperature to 400'C without substrate bias. The deposition 117
Mat. Res. Soc. Symp. Proc. Vol. 565 © 1999 Materials Research Society
rates under these conditions were 10 - 50 nm/min. The fluorine concentration in the film was varied from 2-55% by adjusting the relative power inputs to the two targets used. X-ray photoelectron spectroscopy (XPS) was used to determine the composition and chemical states of the a-C:F films. A monochromatic Al Kct (1486.6eV) X-ray source was used with a hemispherical detector, with a pass energy set at 23.5 eV with an 0.10 eV step. The photoelectron take-off angle with respect to the sample surface was 45'. In situ heating of the sample up to 500'C at a rate of 20°C/min was performed in the XPS chamber to determine the thermal stability of the a-C:F films. A Leybold Inficon Transpector® gas analysis system with a quadrupole mass spectrometer was used to measure the volatile CF, fragments desorbed from the a-C:F filrns upon heating, and mass spectra were recorded at each 50'C increment. It is worth noting that significant out-gassing from sample holder and the heating stage is observed, with H20, CO, C0 2, and C desorbed and detected by the mass spectrometer. The chemical stability of the a-C:F film with respect to a barrier material, TaN, was determined by depositing an approximately 4 nm thick TaN film on the a-C:F sample. A nitrogen (0.35 sccm) and argon (100 sccm) plasma at a pressure of 22 mTorr was used to sputter a tantalum target, the substrate temperature was held at 150'C and the deposition rate was approximately 8nm/min. The sample was then transferred through a gate valve under high vacuum to the XPS chamber for surface analysis. The thickness of the sputter deposited tantalum nitride films was comparable to the photoelectron escape length, therefore the interface between tantalum nitride and fluorocarbon film could be analyzed directly and non-destructively. The deposited TaN contains 15-20 at. % oxygen due to the background oxygen in the sputtering chamber. The bulk stoichiometry (excluding oxygen) of the tantalum nitride sample is determined to be TaN 0 .7 using Rutherford Backscattering Spectrometry with 2MeV He' ions on a 500 nm thick sample. X-ray Diffraction analysis using Cu Kcc radiation of the same sample indicates a tantalum rich TaNo.8 phase at around 20=35'.
RESULTS The carbon photoemission spectra, C(l s), from a series of samples deposited at room temperature with fluorine content ranging from 2 to 55 at.% are shown in Figure 1. The integrated intensities of the C(ls) spectra are normalized. The C(ls) binding energy is fixed by setting the F(ls) energy to 686.8 eV, and shifting the C(ls) spectra accordingly. Four components of the C(ls) spectra are e
Data Loading...
