Comparison of direct-total-reflection X-ray fluorescence, sweeping-total-reflection X-ray fluorescence and vapor phase decomposition-total-reflection X-ray fluorescence applied to the characterization of metallic contamination on semiconductor wafers

摘要

The issues related to the matching between the 3 modes of Total-reflection X-Ray Fluorescence available on the latest generation of commercial equipment: Direct-Total-reflection X-Ray Fluorescence, Sweeping-Total-reflection X-Ray Fluorescence and Vapor Phase Decomposition-Total-reflection X-Ray Fluorescence, are discussed for quantitative analysis of metallic contamination on Si wafers. Direct-Total-reflection X-Ray Fluorescence and Sweeping-Total-reflection X-Ray Fluorescence agrees very well (+/-20% for light elements, transition metals and heavy metals), but due to a poor surface coverage with Direct-Total-reflection X-Ray Fluorescence, the matching is correct on a whole wafer only for uniform contaminations. Vapor Phase Decomposition-Total-reflection X-Ray Fluorescence might agree with other Total-reflection X-Ray Fluorescence modes only if the collection of contaminants following the oxide decomposition step is 100% completed. This is not achieved for 2 situations: noble metals which plate on bare Si, and solid particles partially digested during the Vapor Phase Decomposition and collection protocol. Furthermore, even if the collection of contaminants is well completed, quantification after Vapor Phase Decomposition depends on the shape of the dried residues and the Total-reflection X-Ray Fluorescence incident angle. With the incident angle selected to maximize the signal to noise ratio for ultra trace applications, i.e. about 0.5 times the Si critical angle, an increase of the quantification by a factor up to 10 is often seen after Vapor Phase Decomposition because of particle-like shape of the metals against film-like shape for the initial distribution. Taking into account advantages and drawbacks of each Total-reflection X-Ray Fluorescence mode, a proposal for the use of Total-reflection X-Ray Fluorescence in advanced Integrated Circuit manufacturing is given and illustrated by practical results from a R&D pilot line and a mass production plant.