Formation and metrology of dual scale nano-morphology onSF6 plasma etched silicon surfaces

Abstract

Surface roughness and nano-morphology inSF6 plasma etched silicon substrates are investigated in a helicon type plasma reactor as afunction of etching time and process parameters. The plasma etched surfaces are analyzedby atomic force microscopy. It is found that dual scale nano-roughness is formatted on thesilicon surface comprising an underlying nano-roughness and superimposed nano-mounds.Detailed metrological quantification is proposed for the characterization of dual scalesurface morphology. As etching proceeds, the mounds become higher, fewer and wider, andthe underlying nano-roughness also increases. Increase in wafer temperature leads tosmoother surfaces with lower, fewer and wider nano-mounds. A mechanism based on thedeposition of etch inhibiting particles during the etching process is proposed for theexplanation of the experimental behavior. In addition, appropriately designedexperiments are conducted, and they confirm the presence of this mechanism.