Paper AS-TuA11
Process Qualification and Monitoring of Interconnect Etch Processing using In-Line Total Reflective X-ray Fluorescence Spectroscopy

Tuesday, October 21, 2008, 5:00 pm, Room 207

Process qualifications and monitoring serve important functions in a high volume semiconductor production environment for insuring process control and product yield. Conventional production qualifications generally involve etch rate, defect characterization and final image critical dimension metrics and generate relatively little quantification of actual etch process excursions in the process chamber. Specifically, elevated levels of chlorine-based residual etch by-productions after interconnect etch can drastically increase the probability of corrosion of conventional Al-Cu (0.5%) metal interconnects. A new multiple parametric qualification (MPQ) has been developed that provides baseline surface composition for interconnect etch and clean process excursion detection using Total Reflective X-ray Fluorescence Spectroscopy (TRXFS). The 180nm technology node qualification includes automatic defect characterization (ADC) and electrically testable metal bridging structures for verification of electrical parametric versus interconnect design rules. TRXFS provides total chlorine content and spatial surface concentration profiling of the qualification wafers to levels of 100ppm range. In this study, total chlorine content after interconnect metal etch and clean has been correlated with high moisture atmosphere exposure tests to determine trigger levels for the start of corrosion of metal interconnect lines via HCl chemical reaction with the aluminum interconnect sidewall. Spatial surface concentrations of chlorine provide wafer maps to detect and investigate process tool variations in wafer backside helium cooling gas, process gas distribution and liquid solvent clean application. The chemical composition results have been correlated with Liquid Phase Ion Chromatograph and Secondary Ion Mass Spectroscopy to verify surface species concentrations. The TRXFS methodology provides definable metrics to compare chamber to chamber process performance and map process space. Furthermore, this surface sensitive protocol can replace cumbersome and time consuming high moisture atmosphere wafer exposure methodologies. Examples of semiconductor production excursions and process improvement investigations will be presented to illustrate the utility of the TRXFS qualification in comparison to conventional production monitoring.