|M.Sc Student||Margalit Magi Nagar|
|Subject||Elucidating Advanced Inhibitors for Copper: K-Sorbate and|
K-Phosphate as Inhibitors in Copper CMP Slurry
|Department||Department of Materials Science and Engineering||Supervisor||Full Professor Ein-Eli Yair|
|Full Thesis text|
Chemical mechanical polishing (CMP) is a widely used technique for the planarization of metal and dielectric films to accomplish multilevel metallization (MLM). The rapid advances in the microelectronics industry require a decrease in the size of microelectronic devices and thus, fabrication of these defects-free small feature devices requires significant improvements in the CMP process. The success of CMP operations depends on the rate of material removal and the quality of the surface finish. During and after the CMP process, the copper surface needs to be passivated. Non-passivated copper surface would cause copper dissolution, which would eventually lead to the device failure.
The goal of this study was to perform a systematic study on the integration of advanced inhibitors in copper CMP slurry and eventually to relate CMP performance to the inhibitor concentration in the slurry.
Two inhibitors, namely potassium sorbate and potassium tri-basic phosphate were examined in H2O2-glycine based slurry. The integration of the two inhibitors in copper CMP slurry requires a deeper understanding of the material removal mechanism during polishing. In order to reach this goal, the specific role of each chemical constituent in the slurry should be elucidated at a fundamental level. Therefore, the study was performed in few stages: electrochemical studies, CMP on blanket wafers and CMP on patterned wafers.
CMP results obtained on patterned wafers illustrate the effect of the inhibitor concentration on CMP performance. In phosphate system: phosphate showed an ability to enhance copper passivation and to reduce dishing of copper lines in a specific range of concentrations (~0.43 M).
In sorbate system: CMP results with blanket wafers showed that an increased sorbate concentration provides lower roughness values. CMP results with patterned wafers showed that an increased sorbate concentration provides higher polishing uniformity and lower dishing values of copper lines. Dishing values of ~50 nm were obtained in slurry containing concentration of 1.7M sorbate. The high solubility of sorbate in water (up to 9 Molar) is a major advantage for CMP processing. Thus, further reduction of the dishing values can be expected in higher concentrations of dissolved sorbate in the slurry. Furthermore, it was found that increase in sorbate concentration leads to a reduction of silica particles adhesiveness at the copper surface. The ability of sorbate to provide both passivated and silica free copper surface can facilitate the post CMP cleaning.