Mechanism of photoresist shrinkage investigated by single-line scan of electron beam

Abstract

Shrinkage behavior caused by a single-line scan of an electron beam over a photoresist line was studied, including shrinkage distribution in the photoresist-line direction. As single-line scan is the minimum unit of controllable electron-beam irradiation during scanning-electron-microscope-image (SEM-image) processing, the minimum amount of shrinkage should be observed in the condition. A new method for evaluating the minute amount shrinkage and the shrinkage distribution caused by a single-line scan was developed. According to the results of evaluations with this method, the shrinkage of a 50-nm-wide photoresist line caused by a single-line scan is less than 0.1 nm under landing energies of 200, 300, and 500 eV and probe current of 8 pA. This shrinkage is more than ten times smaller than the typical amount of shrinkage caused by a standard two-dimensional scan. This result indicates the possibility of a significant reduction of photoresist shrinkage during SEM measurements. The evaluations also show that the shrinkage caused by a single-line scan distributes more than about 30 nm in the photoresist-line direction, which is wider than the simulated electron-scattering range. Moreover, the evaluations show that the shrinkage distribution is narrower at higher position of the photoresist-line. This tendency suggests that the wide shrinkage-distribution does not stem from the distribution of the back-scattered electrons (BSEs) which enter the side wall of the photoresist line from the spaces nearby, because the incidents of BSEs distribute wider at higher position of the photoresist-line. Hence, shrinkage occurs in a wider region of the photoresist line than the region where electrons (including directly incident electrons and BSEs) reach. This result suggests that in order to interpret the photoresist-shrinkage mechanism it is important to clarify how the microscopic volume-reduction caused by electron-molecule interactions is integrated into macroscopic photoresist-pattern deformation. An elastic deformation is a plausible mechanism for this macroscopic photoresist-shrinkage process.