Plasma damage to low k dielectric materials was investigated from a mechanistic point of view. Low k dielectric films were treated by plasma Ar, O2, N2/H2, N2 and H2 in a standard RIE chamber and the damage was characterized by Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS), X-Ray Reflectivity (XRR), Fourier Transform Infrared Spectroscopy (FTIR) and Contact Angle measurements. Both carbon depletion and surface densification were observed on the top surface of damaged low k materials while the bulk remained largely unaffected. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. A downstream hybrid plasma source with separate ions and atomic radicals was employed to study their respective roles in the plasma damage process. Ions were found to play a more important role in the plasma damage process. The dielectric constant of low k materials can increase up to 20% due to plasma damage and we attributed this to the removal of the methyl group making the low k surface hydrophilic. Annealing was generally effective in mitigating moisture uptake to restore the k value but the recovery was less complete for higher energy plasmas. Quantum chemistry calculation confirmed that physisorbed water in low k materials induces the largest increase of dipole moments in comparison with changes of surface bonding configurations, and is primarily responsible for the dielectric constant increase.
Carbon doped silicon oxide SiO(C, H) low k thin films (k∼2.9) deposited by the plasma enhanced chemical vapor deposition technique from trimethylsilane (3MS) and oxygen (O2) have been studied. Two types of chemical vapor deposition process recipes, namely CVD1 and CVD2 were applied for film deposition. CVD1 is an initial recipe that resulted in films with a uniform deposition rate irrespective of film thickness and a low dielectric constant of about 2.9. However, it suffers from extraordinarily high post particle counts. CVD2 is a modified recipe adopted to address this issue. The main difference between the two recipes is that a pump down step immediately before the film deposition has been omitted in recipe CVD2, and this has successfully reduced the particle counts to a satisfactory level. However when using recipe CVD2, the deposition rate is nonuniform and the dielectric constant is slightly above 3.0, attributed to the residual oxygen in the process step prior to film deposition. In this study we investigate the effects of oxygen incorporation on the properties of SiO(C, H) films. Surface defects and their element composition, film thickness, refractive index, dielectric constant, and chemical bonding analysis of the films have been carried out. The chemical composition and structure of films deposited by recipes CVD1 and CVD2 show very slight differences, and are also slightly nonuniform along the film depth. Although the nonuniformity does not have much effect on the dielectric constants of the SiO(C, H) films, it may pose a potential challenge for these low k films in terms of advanced integration.
We have carried out direct diffusion measurements of Cu into Ta and Ta into Cu. Thin films of 50nm thickness of Cu were grown onto a thick Ta layer of 1 μm by Ionized Metal Plasma. Samples were annealed in a rapid thermal system from temperatures ranging from 400°C to 800°C for periods of 60s and 180s. The diffusion profile was performed using Secondary ion mass spectroscopy. The Cu diffusion coefficients in Ta can be described by 3.0246 × 10-15 exp(-0.1747eV/kT) at 60s and 2.7532 × 10-15 exp(-0.1737eV/kT) at 180s. The Ta diffusion coefficients in Cu can be described by 2.7532 × 10-15 exp(-0.1773eV/kT) at 60s and 2.1271 × 10-15 exp(-0.1753eV/kT) at 180s. To assure reliability, the extent of both diffusions should be considered in device design and processing.
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