MICRO: Materials Integration

Abhay Ramrao Deshmukh, National Semiconductor he planarization of interlevel dielectric (ILD) is critical to the success of multilevel metallization processes. In multilevel metallization, patterned conductors and dielectric layers at one level can create severe topography problems for the layers at the next level. Topography problems can produce opens in the interconnects or voids in the dielectric layers because of step coverage issues associated with deposited dielectrics. Topography-related lithography issues can also cause shorts between adjacent lines. The purpose of planarizing multilevel metallization layers is to eliminate or smooth out the topographic undulations caused by conductors, dielectrics, contacts, and vias. Planarization ensures that metal, at any level, is deposited on a flat surface, preventing step coverage issues. ILD layers are primarily planarized with spin-on glass (SOG) to avoid processing problems such as poor step coverage of deposited metal or void formation in deposited dielectric films. However, the use of SOG is not without drawbacks. Gel or SiO particles can easily form in the SOG solution. Even in sealed bottles, SOG has a finite shelf life because of the danger of particle formation. Extended sit times, even at room temperatures, can lead to high particle levels in SOG materials. Although SOG is shipped from manufacturer sites with very low particle counts, shipping, material storage and handling, and manufacturing processes can affect the material. Particulation becomes even more pronounced after an SOG bottle is opened, since solvent evaporation enhances particle formation. A more troublesome source of particle generation is that excess SOG spun onto the walls of the spinner bowl dries quickly and forms particles. Ever-shrinking device geometries mandate increasingly stringent defect-reduction goals to decrease the sizes and numbers of particles, pinholes, and microbubbles created during the manufacturing process. Consequently, improvements in the quality of semiconductor process materials, such as SOG, are necessary. This