X-ray reflectivity: a new metrology alternative for DUV ARCs

X-Ray Reflectometry (XRR) is a glancing angle technique to characterize thickness, density, and surface/interface roughness of thin stacks of transparent and opaque materials. XRR does not require prior knowledge of n and k, from which thickness values are derived using optical techniques. This study examines the effects of process parameters (including gas flows, RF power, deposition time, and pressure) on bulk and surface film properties using XRR. The films comprised of single-/multi- station deposition of SiON films with post-deposition surface treatment in an N2O plasma for anti-reflective coating (ARC) applications in UV/photolithography. The understanding of ARC films and the treatments used to reduce the nitrogen content in the skin film portion of the ARC is critical for minimizing the amount of residual photoresist or "footing" seen after develop(1). Multi-site measurements were done on a commercial x-ray reflectometer(2) designed for high-volume production processes. The results from these measurements describe the sensitivity of the XRR technique to interfacial/skin layers and explore this method as an alternative to conventional optical techniques. The ability to identify minute differences within the same film (for example, in a multi-station deposition process) using XRR offers advanced process control failure analysis possibilities.