Bright-field photomasks are used to print small contact holes via ArF immersion multiple patterning lithography. There
are some technical difficulties when small floating dots are to be measured by SEM tools because of a false imaging
shadow. However, a new scan technology of Multi Vision Metrology SEMTM E3630 presents a solution for this issue. The combination of new scan technology and the other MVM-SEM® functions can provide further extended applications with more accurate measurement results.
KEYWORDS: Scanning electron microscopy, Photomasks, Metrology, Electron beam lithography, Line scan image sensors, Electron beams, Lithography, Semiconductors, Capacitance, Absorption
As an alternative to EUV lithography, ArF immersion multiple patterning lithography has been heavily employed in
semiconductor fabrication. This situation has led to increase use of bright-field photomasks with floating small patterns.
Latest CDSEMs are equipped with various charge compensation features and applicable for devices with conductive
and insulating material. However, there remain some difficulties when floating small patterns are to be measured. One
of the specific examples is a floating dot on a via mask, dimension of which is around 200nm at the 45 nm process
node, scaling down to 100nm at the 22nm process node. Since the dot has very small capacitance, it is easily charged by
electron beam irradiation, and discharged in a short period. This kind of temporary voltage variation can affect the
secondary electron yield, causes degradation of the SEM image contrast. We have analyzed that the "edge effect",
which is the principle of SEM, has a primary role in small dot charging, and interchanging of scan line effectively
suppresses the voltage variation. Based on this concept, we have developed a new scan technology for our "Multi
Vision Metrology SEM" E3630, and improved the performance of image-based measurement. In this paper, the new
scan technology and evaluation results are presented.
Thin film hardmasks with 10nm or less are used in double patterning techniques to generate fine
patterns for 32nm-node and beyond. Using a conventional Mask CDSEM for ultra accurate
measurement of patterns on these thin film hardmasks is difficult due to weakness of the edge
profiles generated by a scanning electron beam. Additionally, the tones of a SEM image can be
reversed due to a charging phenomenon, which causes false recognition of lines and spaces. This
paper addresses ultra accurate measurement of thin film hardmasks using a new measurement
algorithm that is applied to profiles obtained from multiple detectors.
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