Controlling energy deposition during the C 60 + bombardment of silicon: The effect of incident angle geometry Joseph Kozole *, Nicholas Winograd Department of Chemistry, Penn State University, University Park, PA 16802, USA 1. Introduction Atomic primary ion beams, such as Cs + , are routinely used for semiconductor depth profiling in secondary ion mass spectro- metry (SIMS) [1]. For the experiments, the effect of incident energy and incident angle on the quality of the data obtained is well established [1,2]. Typically, a depth profile with 1 nm depth resolution can be acquired using a low energy (1 keV), glancing incidence (508 with respect to sample normal) ion beam [1,2]. The emergence of cluster primary ion beams, such as C 60 + , has provided an alternative approach to SIMS depth profiling [3]. Because each C atom in a C 60 + projectile carries 1/60th of the total energy, the depth at which the energy is deposited into the solid is substantially smaller than an atomic counterpart [4]. Since the depth resolution of the experiment is directly related to the altered depth, C 60 + is a promising projectile for obtaining ultra-high depth resolution (1 nm) during erosion experiments. To date, the application of C 60 + to semiconductor depth profiling has been restricted by the occurrence of artifacts when Si is bombarded with C 60 + [5]. The artifacts, which include the deposition of a C layer and the formation of topographical features, severely limit, and in some cases eliminate, the ability of C 60 + to erode the Si solid. Investigations have shown that the undesired effects can be minimized by increasing the incident energy of the C 60 + to 15 keV or higher [5,6]. However, increasing the kinetic energy of the projectile decreases the depth resolution of the experiment [1,2,5]. The effect of changing the incident angle of the C 60 + on the erosion of Si has yet to be examined. Molecular dynamics (MDs) simulations suggest the C 60 + incident geometry is critical to the location at which the energy is deposited into a solid, a factor important in the determination of sputter yield and altered depth [6–8]. Additionally, a study on the effect of C 60 + incident angle on the bombardment of a molecular solid finds that sputter yield does not increase with a 1/cos u relationship, a behavior quite different than what is observed for atomic projectiles [9,10]. The objective of this research is to determine if the unique energy deposition process observed during C 60 + bombardment can be manipulated in a way that the formation of artifacts during the erosion of Si is avoided and the prospect for performing ultra-high resolution semiconductor depth profiling is retained. Here, we report that the choice of incident energy and incident angle of the C 60 + projectile strongly influences the Si sputtering yield, the C deposition probability, and the formation of topography. The results show that the 10 keV, 408 incident C 60 + erosion of Si is limited by the deposition of a C layer and that the artifact can be Applied Surface Science 255 (2008) 886–889 ARTICLE INFO Article history: Available online 18 May 2008 Keywords: SIMS C 60 + Silicon Depth profiling ABSTRACT The profile of the energy deposition footprint is controlled during the C 60 + erosion of Si surfaces by varying the incident energy and/or incident angle geometry. Sputter yield, surface topography, and chemical composition of the eroded surfaces were characterized using atomic force microscopy (AFM) and secondary ion mass spectrometry (SIMS). The experiments show that the 10 keV, 408 incident C 60 + erosion of Si results in the formation of a C containing, mound-like structure on the solid surface. We find that the occurrence of this C feature can be avoided by increasing the incident energy of the C 60 + projectile or by increasing the incident angle of the C 60 + projectile. While both strategies allow for the Si samples to be eroded, the occurrence of topographical roughening limits the usefulness of C 60 + in ultra-high resolution semiconductor depth profiling. Moreover, we find that the relative effect of changing the incident angle geometry of the C 60 + projectile on the profile of the energy deposition footprint, and thus the sputter yield, changes according to the kinetic energy of the projectile and the material of the bombarded surface, a behavior that is quite different than what is observed for an atomic counterpart. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. E-mail address: jjk302@psu.edu (J. Kozole). Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.05.259