טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAbelev Esta
SubjectElectrochemical Behavior of Copper in Aqueuos Solutions for
Chemical-Mechanical Planarization Applications
DepartmentDepartment of Materials Science and Engineering
Supervisors Professor Eugen Rabkin
Professor Yair Ein-Eli


Abstract

Copper is used as a replacement for aluminum in integrated circuit interconnections. However, there are several problems that must be resolved before copper can be fully used in integrated circuit technologies. One of them is planarization which involves fine copper lines patterning. The most perspective technique for copper line patterning is the chemical-mechanical planarization (CMP). Different media, such as ammonium hydroxide, (NH4OH), peroxide, (H2O2), ferric nitrite (Fe(NO3)3,) and nitric acid (HNO3), with and without the presence of inhibitors, were suggested as slurry solution in copper CMP. In this work we studied the compatibility of these media with CMP requirements. Our work indicates that these solutions (both basic and acidic media) did not satisfy the conditions for a conventional CMP process. Copper is actively dissolved in all of these solutions and in some of them with high dissolution rate.  We found that copper active dissolution is conducted through deep intergranular penetrations that could result in the deterioration of thin Cu connectors. This study also shows that the use of benzotriazole (BTA) or other inhibitors is not suitable for a metal CMP process.

In this work we studied copper passivity features in aqueous solutions. Especially, we focused our study on the electrochemical behavior of copper in sodium hydroxide solutions. Our interest was focused on copper passivity at potentials near open circle potential (OCP) and above it. We established that copper oxide morphology in potential region above 0.3 V is strongly dependent on the initial electrochemical pre-treatment. We found that above the potential of 0.3 V a thin protective oxide layer covering the copper surface is formed, leading to a major suppression of copper dissolution.