Cleaning and Restoring k Value of Porous MSQ Films

摘要

Planned increases in IC performance, such as faster clock speeds and lower power consumption, require the use of low-k materials for interconnects in chip manufacturing. Dense low-k materials with k values in the range of 2.8-3.0 are in manufacturing at the 90 nm node. The International Technology Roadmap for Semiconductors (ITRS) indicates that porous low-k materials with k<2.4 will be required for the 65 nm node by 2006. Patterning of porous low-k materials exposes the film to plasma etching, plasma ashing for resist stripping, liquid chemicals for etch residue removal, and water for final rinsing. Typical ash processes result in carbon depletion and modification of the surface properties from hydro-phobic to hydro-philic, thereby increasing the moisture sensitivity of the low-k material. The patterning of low-k materials, such as porous methylsilses-quioxane (MSQ), typically results in damage by causing changes in the chemical structure and/or by leaving absorbed chemical residues in the porous matrix. These effects can lead to an increase in k value, poisoning of photoresist in subsequent patterning processes, formation of voids after copper deposition and annealing, as well as reduced adhesion of barrier layers. The uptake of moisture is generally believed to be the cause of the increase in k after etching and ashing due to differences in dielectric constant between the low-k material and water, which are 2.2 and 78, respectively.