Evaluation of Deteriorations on Process-induced Damage of Cu/low-k Interconnect Structure
Low-k films are more susceptible to structural and chemical changes during manufacturing processes such as dry etching, ashing, and barrier metal deposition. These processes cause deteriorations and lead to an increase in dielectric constants and/or degradation in hygroscopic properties. Such types of damage have adverse effects on the performance and reliability of Cu/low-k interconnects.
Electron energy-loss spectroscopy (EELS) method equipped with a scanning transmission electron microscope (STEM) is used for damage analysis in low-k interconnect dielectrics, and the decrease in the carbon of the trench walls due to the dry etching was reported. However, the results included less information about detailed chemical bonding information, and it is difficult to apply to low-k materials without electron beam damage.
On the other hand, FT-IR analysis easily reveals the structure of porous low-k films in a quantitative manner, and it has no effects on the film properties during the measurement. It is important to get knowledge for the quality and origin of the process-induced damage and for where the damage occurred in order to improve the manufacturing process. FT-IR is also effective tools to depth profile analysis of a blanket low-k film processed via various plasma treatments. We have carried out the line analysis by the microscopic IR method against the inclined surface formed by special pretreatment. We have obtained the chemical bonding structure in the depth direction. Information on bonding structure changes and the depth at which they occur is useful for manufacturing improvement. However, low-k film is processed into a trench structure in actual process. The main damage might occur in the low-k film trench side wall. The process-induced damage on the blanket film and on the side wall in the Cu/low-k interconnect structure might differ even under the same plasma conditions. The process-induced damage assessment was tried.
In the present study, a suitable measurement method has been explored for characterizing process-induced damage by the microscopic FT-IR method for a Cu/low-k interconnect structure. Damage analysis was carried out for samples with lines and spaces of various widths and various line heights. We have revealed the locations where process-induced damage occurs and its mechanisms for the Cu/low-k interconnect structure for the first time.
We have found that the FT-IR spectra mainly reflect structural changes in the sidewalls of the low-k films, and the mechanism of generating process-induced damage involves the generation of OH groups in the low-k film when Si-CH3 bonds break during the fabrication processes.