Study of Measurement Condition Optimization in Critical Dimension-Scanning Electron Microscope

Abstract

The critical-dimension scanning electron microscope (CD-SEM) is an essential tool for semiconductor fabrication process control because of its high resolution and high precision. However, in ArF lithography, the CD of resist changes during CD-SEM measurement due to shrinkage caused by the electron beam irradiation. This shrinkage can be reduced by measurement parameters; however, there is a trade-off relationship between shrinkage and precision. Thus, measuring the CD of an ArF resist pattern precisely with small shrinkage is difficult. The authors propose an optimization method using the Taguchi method. Four measurement parameters were chosen as control factors for an L18 orthogonal array: probe current, acceleration voltage, horizontal length of field-of-view, and number of image acquisitions. As a result, high prediction accuracy was obtained that is smaller than 0.2 nm for shrinkage and 0.1 nm for precision. Moreover, an optimum measurement condition that achieves 0.28 nm shrinkage and 0.37 nm precision was also obtained. Thus, the proposed method was demonstrated as a promising method to optimize CD measurement parameters.

Photoresist cross-sectional shape change caused by scanning electron microscope-induced shrinkage

“…7 Lowering the acceleration voltage and/or decreasing the irradiation dose density of the EB are effective ways to reduce the damage itself due to the EB irradiation. [8][9][10] In addition, phenomenological methods for calculating the shrinkage amount of simple patterns, such as the lines and holes, have been developed. 11,12 The original CD before SEM observation can be estimated using these methods, even though the shrinkage itself cannot be avoided.…”

Large Range Atomic Force Microscopy with High Aspect Ratio Micropipette Probe for Deep Trench Imaging

“…Other common methods that facilitate high-resolution measurements of CDs include the CD scanning electron microscope and CD transmission elctron mi-croscoTEM approaches. [19,20] However, electron microscopy results in poor imaging quality of insulators and encounters difficulties in characterizing deep trench features. Although CD-AFM [21,22] is a promising method of high-resolution characterization of irregular features, the imaging of deep trenches or steep sidewalls remains challenging for conventional AFM probes owing to the conflict among the short effective travel range, accuracy, and feedback bandwidth.…”

Precise Cross-Sectional Measurement of Photoresist Shrinkage Caused by Electron Beam Irradiation

“…As solutions to this problem, lowering the accelerating voltage of EB and decreasing the irradiation dose density of EB are proposed and found to be effective. [10][11][12][13] In addition, methods of estimating the amount of shrinkage to obtain the CD before observation are studied. 14,15) In spite of the fact that these practical solutions are successful, a detailed mechanism of photoresist shrinkage is still unclear.…”

“…Most studies on photoresist shrinkage so far have mainly focused on the phenomenology of linewidth slimming [10][11][12][13][14][15][16][17] or the microscopic mechanisms of local volume reduction in the second step, namely, the interaction between an electron and photoresist molecules. [18][19][20] Some recent studies examined the effects of electrons scattered from spaces between patterns [21][22][23][24] and elastic deformation on pattern shape.…”