When Cu wafers are exposed to H2/N2 plasma, hillocks are formed on the Cu wafer surface by a plasma cleaner with a surface wave plasma source. Plasma cleaning is divided into the initial stage and the rising temperature stage. Under a supply of H2/N2 gas and with the plasma power turned on, the H radicals first restore native copper oxide to pure copper. The N radicals then compete with the H radicals, and diffuse to the Cu grain boundary, which is the initial stage. During the rising temperature stage, plasma energy is absorbed by the Cu surface, and the wafer temperature increases rapidly. Consequently, plasma-enhanced compressive stress leads to the formation of Cu hillocks. For a plasma with a higher N/H radical ratio, more N radicals diffusing to the Cu grain boundary results in more Cu-N compounds, which make up the main source of stress during H2/N2 plasma cleaning. Experimental results indicate that using a plasma cleaner with an inductively coupled plasma source can achieve a lower N/H radical ratio, thus avoiding the formation of Cu hillocks.
|Journal||Journal of the Electrochemical Society|
|Publication status||Published - 2004|
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry