Electron-beam-induced deposition of 3-nm-half-pitch patterns on bulk Si

Abstract

This paper demonstrates electron-beam-induced deposition of few-nm-width dense features on bulk samples by using a scanning electron-beam lithography system. To optimize the resultant features, three steps were taken: (1) features were exposed in a repetitive sequence, so as to build up the deposited features gradually across the entire pattern, and thus avoid proximity effects; (2) an additional delay was added between exposures to permit diffusion of reactants into the exposed area; and (3) the exposures were phase-synchronized to the dominant noise source (the 50-Hz line voltage) to minimize the effect of noise. The reasons these steps led to significant improvements in patterning resolution are discussed. KEYWORDSElectron-beam-induced-deposition, EBID, lines and spaces, Scanning Electron Microscope 2 MANUSCRIPT TEXTElectron-beam-induced-deposition (EBID) is a direct-write lithographic technique that uses a focused electron beam to make small material deposits [1][2][3][4][5] . By dissociating precursor molecules adsorbed on a surface, two-and three-dimensional structures can be created. The size of these structures can range from single-digit nanometer scale to several micrometers.The minimum feature size possible with EBID is smaller than 1 nm, as has been demonstrated by using finely focused beams in Scanning Transmission Electron Microscopes 6,7 . However, it is more convenient to use the much more user-friendly and widely spread platform of the Scanning Electron Microscope (SEM). We recently demonstrated that EBID can be used to create 3 nm dots in an SEM 8 . However, deposition was done on a thin membrane and imaging was done using a transmission detector, which, for such small structures, provides better contrast than a secondary electron detector. It was also found that, when decreasing the separation between deposits, they became broader. This broadening is due to proximity effects. There are two proximity effects that play a role here. First, the angular dependence of the secondary electron (SE) yield, which causes the growth rate to increase when the beam irradiates the slope of the deposit 9,10 . This results in non-linear growth when writing EBID lines. Second, during deposition of a line, secondary electrons escaping from that line may dissociate precursor molecules on the neighboring line, causing it to grow further 11-13 .The challenge we address now is to pattern lines and spaces, as densely as possible, on bulk material as opposed to a membrane. This challenge is important for applications in the fields of mask repair and circuit edit, as well as nano-scale prototyping. Working on bulk material forces us to use secondary electron (SE) detection for imaging the patterns, and to develop a 3 strategy to deal with the proximity effects. We will demonstrate the fabrication of dense patterns on a sub-10 nm scale on bulk silicon substrates using EBID.The EBID setup we used is an FEI Quanta 3D FEG Dual Beam machine, with a 30 keV electron beam energy and a smallest specified probe size of ~1...

Sub-20 nm silicon patterning and metal lift-off using thermal scanning probe lithography

“…In t-SPL 10 nm half-pitch patterns were demonstrated having a patterning depth of 3-4 nm 7 . In particular for SPL but also for other lithographic techniques such as electron beam lithography (EBL) 8 , electron beam induced deposition (EBID) 9 , or He-Ion lithography 10 highest resolution patterning is often accompanied by a low ( < ∼ 10nm) thickness of the produced features. Thus, further processing of the patterns for device fabrication is challenging and the number of publications is limited.…”

Size and shape control of sub-20 nm patterns fabricated using focused electron beam induced processing

“…This allows for single pass serial exposure, which is preferred over multiple pass parallel exposures for throughput reasons. The proximity effects that were noticed in the previous experiments 21 performed in the precursor limited regime were not noticed here. It must be noted that the line patterns presented here were not at such small spacing as the results in Ref.…”

“…It must be noted that the line patterns presented here were not at such small spacing as the results in Ref. 21 and shown in Fig. 2.…”

“…So the concentration of deposited atoms due to the BSEs is really low when growing nanostructures. Van Oven et al 21 succeeded in depositing 3-nm dense lines and spaces on a bulk Si wafer, and imaged the structures using SE detection (see Fig. 2).…”

Pattern transfer into silicon using sub-10 nm masks made by electron beam-induced deposition

“…The high spatial resolution of EBID has been demonstrated by Van Dorp et al, who patterned dots of 1 nm diameter in a 200 kV Scanning Transmission Electron Microscope (STEM), using the W(CO) 6 precursor on a 30 nm thick Si 3 N 4 membrane [1]. Using an SEM, van Oven et al patterned 2.9 nm FWHM lines on a silicon bulk substrate using the MeCpPtMe 3 precursor [2]. However, electron beam lithography techniques are serial writing techniques and therefore inherently slow.…”