FIB Damage in Silicon: Amorphization or Redeposition?

Abstract

The Focused Ion Beam (FIB) instrument has been utilized for site-specific specimen preparation for a wide range of analytical techniques due to its ability to achieve high spatial resolution imaging, milling, and deposition [1,2]. The understanding of FIB damage is important to ensure that the region being analyzed is indeed representative of the material, and is not due to a specimen preparation artifact. The interaction between the incident ions (e.g., Ga + ) and the target material during FIB operation (e.g., imaging or milling mode) may lead to surface damage and consequently limit the ability to achieve high quality high-resolution TEM images. Amorphization of a FIB milled crystalline surface may occur due to sufficient atom displacement within the collision cascade resulting in the loss of long-range order when the density of point defects reaches a critical value [3]. Redeposition of sputtered atoms has also been reported as a result of FIB milling [4]. The propensity for redeposition increases when FIB milling is performed in a confined and/or a high aspect ratio trench, or when FIB conditions are used that contribute to factors that increase the sputtering rate (e.g., using a higher beam current) [5]. Observations have shown that FIB milling with Ga at an energy of 30 keV will produce amorphization damage along a Si side-wall that is ~ 28 nm thick and up to 20 wt% Ga may be present within the damage region [6]. Previous work in our lab has shown that the side-wall damage thickness in Si varies with beam current [7]. In addition, while significant amounts of Ga were observed in the side-wall damage [8], Ga was not detectable in side-wall damage when Si was FIB milled using gas assisted etching (GAE) [9]. The following study was performed in an attempt to better understand FIB damage. In this study, three square trenches (2x2 µm 2 , 4x4 µm 2 , and 6x6 µm 2 ) were FIB milled to 1 µm in depth in a (100) Si wafer using an FEI 200TEM FIB workstation equipped with a Ga liquid metal ion source and an Omniprobe in-situ W probe. An accelerating voltage of 30 keV and a beam current of 1000 pA was used to mill the trenches. The specimen was removed from the FIB and sputter-coated with Cr to preserve the FIB milled damage layers. The specimen was put back into the FIB and the trenches were filled with CVD Pt deposition using a beam current of 100 pA. A cross-section TEM specimen was prepared across the trenches using the in-situ FIB lift-out method [10]. The specimen was observed using a Philips EM430 operating at 300 keV. A bright field (BF) TEM image of the trenches is shown as FIG. 1 (a). A BF image from the top of the wafer is shown in FIG. 1(b). A BF image from the side-wall of the middle trench is shown in FIG. 1(c). Note that the side-wall damage clearly consists of two regions with different contrast. This layer clearly indicates that the side-wall damage consists of two regions: (i) an amorphization layer and (ii) a redeposition layer. X-ray energy dispersive spectrometry (XEDS) results showed that significa...

Precise nanofabrication with multiple ion beams for advanced circuit edit

“…As the via aspect ratio increases and the feature size shrinks, precise endpoint detection during the milling procedure becomes very difficult because the secondary electron signal becomes weak and eventually can reach undetectable level compared with background noise levels. In addition, a Ga-FIB suffers the limitations due to large probe size, Ga implantation and high re-deposition rate [13]. A new method with a decreased beam probe size, improved signal collection, controlled material removal at nano scale and reduced re-deposition is needed.…”

Composite Materials Based on Shape‐Memory Ti2NiCu Alloy for Frontier Micro‐ and Nanomechanical Applications

“…The problem of amorphization, [11,12] redeposition, [13] and implantation [14] of a near-surface region with a local ion etching has been reported in a number of papers. FIB made it possible to create micron, submicron, and nanoscale structures without the use of optical or electron beam lithography.…”

“…FIB made it possible to create micron, submicron, and nanoscale structures without the use of optical or electron beam lithography. The problem of amorphization, [11,12] redeposition, [13] and implantation [14] of a near-surface region with a local ion etching has been reported in a number of papers. However, in almost all the studies, the damaged surface is considered to be undesired and hence should be minimized.…”

Introduction to Focused Ion Beams

“…There is a distinct difference between damage due to inherent ion-solid interactions and redeposition artifacts (Rajsiri et al, 2002). There is a distinct difference between damage due to inherent ion-solid interactions and redeposition artifacts (Rajsiri et al, 2002).…”