Calculation of the Ga+ FIB Ion Dose Distribution by SEM Image
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XVIII INTERNATIONAL SYMPOSIUM “NANOSTRUCTURES: PHYSICS AND TECHNOLOGY”, MINSK, REPUBLIC OF BELARUS, SEPTEMBER, 2020. NANOSTRUCTURE CHARACTERIZATION
Calculation of the Ga+ FIB Ion Dose Distribution by SEM Image M. I. Mitrofanova,*, G. V. Voznyuka,**, S. N. Rodina,***, W. V. Lundina,****, V. P. Evtikhieva,*****, A. F. Tsatsulnikovb,******, and M. A. Kaliteevskic,******* a
Ioffe Institute, St. Petersburg, 194021 Russia R and E Center, RAS, St. Petersburg, Russia c ITMO University, St. Petersburg, 197101 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] ****e-mail: [email protected] *****e-mail: [email protected] ******e-mail: [email protected] *******e-mail: [email protected]
b SHM
Received June 23, 2020; revised July 23, 2020; accepted July 27, 2020
Abstract—A new approach for calculating the ion dose spatial distribution of the focused ion beam is proposed. The approach is based on the analysis of the secondary electron microscopy image of the area irradiated by the focused ion beam. Keywords: FIB, focused ion beam distribution, ion beam lithography DOI: 10.1134/S1063782620120246
INTRODUCTION Ion dose is one of the key parameters of focused ion beam (FIB) nanolithography. Ion dose is the quantity of ions absorbed by a medium. It is commonly used to estimate etching rate or material removal rate [1]. Ion dose has units of ions/cm2 and is computed from several technological parameters: ion beam current, time of exposure and step size or pixel distance. In FIB etching parameters investigations, ion dose is generally estimated for the area that is much larger than the ion beam diameter (typically submicron). However, during FIB lithography of nanostructures both the real diameter of ion beam and the ion dose distribution should be taken into account as the structures size is comparable to the ion beam diameter. In early studies on the formation of windows for selective epitaxial growth, significant broadening was observed during etching of micron and submicron strips [2]. Ion beam diameter is estimated as a full width at half maximum of Gaussian ions flux density distribution [3]. Experimentally the profile of ion beam distribution is estimated by atomic force microscopy (AFM) topography of the etched hole or trench, or by the rise distance method on the knife-edge of the sample [3, 4]. However, the rise distance method has several sources of error, which should be kept in mind.
This method can only be used for the low current ion beams due to destruction of the knife-edge of the sample. AFM topography estimates only etched area and does not includes tails of implanted ions. In our research, we had used rather large working currents of the FIB to form the windows for selective epitaxy, so that we had not obtain enough information by usual methods to estimate the broadening of the etched windows. To resolve this issue, we have developed a new approach for the experimental estimation of the beam parameters on the sample surface. Figure 1 show
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