Mechanism Study and Process Optimization of Etching-Induced Ghost Patterns in Niobium Superconducting Thin Films

The Ali CMB Polarization Telescope (AliCPT) is China’s first and the only facility in the Northern Hemisphere dedicated to studying primordial gravitational waves. To achieve mass production of its tens-of-thousands-scale low-temperature superconducting detector array, process stability is particularly critical, where the quality of niobium (Nb) superconducting thin film deposition and etching directly determines the final device performance. Early studies found that under specific conditions, ghost patterns appear on niobium superconducting thin films after etching, severely affecting process stability and device quality. To investigate this mechanism, this paper comprehensively utilized methods including surface topography characterization, elemental composition analysis, and surface chemical state analysis, confirming the presence of photoresist residue with non-uniform thickness within the etched regions. The residual photoresist induced thickness variations in the carbon-fluorine passivation layer during the etching process, leading to mismatched etching rates across the region and ultimately forming the ghost patterns. By optimizing both the cleaning process and etching recipe, this study successfully suppressed ghost-pattern defects, laying the foundation for large-scale mass production of low-temperature superconducting detectors, it also provides a valuable reference for addressing common process issues such as particulate deposition.