CRITICAL DIMENSION CONTROL OF HIGH-RESOLUTION METAL STRUCTURES BY BACKSCATTERED ELECTRONS

In this article a commercial e-beam lithography machine (Leica Cambridge EBMF 10 cs/120) is used in metrological mode for critical dimension control of metal features with size down to 100 nm. The experimental backscattered electrons signal, collected by a channel plate detector, is described by an analytical function which is the convolution of probe beam function, detector transfer function, and specimen absorption transfer function. The further data processing by means of a developed software algorithm, allowed the determination of the significant structure parameters as linewidth and sidewall angle. Metal test structures, as isolated lines and grooves with size down to 100 nm, fabricated on silicon wafers, are successfully inspected and measured by this method. The comparison between computed dimensions and scanning electron microscopy measurements shows a good agreement (within 5%) for structures of different dimensions, varying their aspect ratio and the sidewall angle at their edges. The effect of beam diameter (BD) value on the measurement was also investigated and accurate measurements have been obtained for BD less than the structure dimension. Finally, a repeatability test performed on a sub-200 nm gold feature showed a precision of 6 nm (3-sigma(S) value) on a sample of one thousand measurements.