Depth Profiles of High-energy Recoil Implantation of Boron into Silicon
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Depth profiles of high-energy recoil implantation of boron into silicon Lin Shao, Xinming Lu, Jianyue Jin, Qinmian Li, Irene Rusakova, Jiarui Liu, and Wei-Kan Chu Department of Physics, and Texas Center for Superconductivity, University of Houston, Houston, TX 77204-5932 ABSTRACT We have studied boron profiles by using the ion beam recoil implantation. A boron layer was first deposited onto Si, followed by irradiation with Si ions at various energies to knock the boron. Conventional belief is that the higher the implantation energy, the deeper the recoil profiles. While this is true for low-energy incident ions, we show here that the situation is reversed for incident Si ions of higher energy due to the fact that recoil probability at a given angle is a strong function of the energy of the primary projectile. Our experiments show that 500-keV high-energy recoil implantation produces a shallower B profile than lower-energy implantation such as 10 keV and 50 keV. The secondary-ion-massspectrometry (SIMS) analysis shows that the distribution of recoiled B atoms scattered by the energetic Si ions agrees with our calculation results. Sub-100 nm p+/n junctions have been realized with a 500-keV Si ion beam. .
INTRODUCTION As complementary metal-oxide-semiconductor device dimensions continue to shrink, junction depth requirements have now reached the 50-70 nm level. Fabrication of such submicron junctions has thus become increasingly difficult for standard ion implantation in the ultra-large scale integration technology. Currently available implanters modified for sub-keV implantation still face many challenges, with low beam current due to the space-charge effect being the most prominent. The search for alternative techniques has continued for many years, among them, recoil implantation from a solid dopant source has been employed to make n+p and p+n junctions [1-3]. By implantation of inert ions such as Ar+, Kr+, and Xe+, or heavy ions such as Si or Ge, dopants can be introduced into the substrate through ion-mixing to form a shallow junction. It has been reported that [4], the concentration profile C(x) can be well approximated by an exponentially decaying function C(x)=Ae-x/L in the central region of recoil distribution, where x is the distance from the surface, A is a prefactor, and L is the characteristic decay length. L is approximately a linear function of incident ion energy E0 . A commonly perceived picture is that the recoiled dopant profile will be deeper for higher implantation energy. In order to get shallow junctions, much effort was thus focused on low energy recoil implantation [3]. In this work, however, we show experimentally that boron recoil implantation by 500-keV Si ions produces a shallower boron profile than that of lower energy recoil implantation, such as 10 keV and 50 keV. While surprising, this agrees with our calculations based on the interatomic potential suggested by Wilson et al [5] in the LSS approximation [6,7]. EXPERIMENTAL
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A boron layer (0.4 nm) was first deposited by e-beam e
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