Boron Implantation into Silicon Subject to Hydrogen Plasma
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Boron Implantation into Silicon Subject to Hydrogen Plasma Sanjay Rangan, Mark Horn, S. Ashok Electronic Materials and Processing Research Laboratory, The Pennsylvania State University, University Park, PA 16802.
Abstract Alleviating transient enhanced diffusion (TED) is one among several issues that has to be solved to realize deep sub-micron CMOS. In this paper we present the influence of hydrogen plasma on TED of boron, along with deep level transient spectroscopic (DLTS) studies on defect evolution as a function of anneal temperature. The studies reveal that TED monotonically increases as a function of anneal temperature up to 650oC, where maximum TED occurs. Further increase in anneal temperature reveals TED reduction. The DLTS reveals a corresponding increase in defect density up to 650oC and then decreases when annealed at 850oC for the same amount of time.
Introduction The National Technology Roadmap for Semiconductors indicates that 0.1µm CMOS technology requires 20-40nm deep source and drain junctions [1]. Processing of 40nm junction depth requires precise control of implant energy, annealing time and annealing temperature to minimize dopant diffusion. TED is the enhanced diffusion of dopants during activation anneals due to the presence if excess interstitials [2]. However, the enhanced diffusion is observed only during the initial period of anneal. For example, the tail of implanted boron when annealed at 800oC for 35 min diffuses over 700Å, while the equilibrium diffusion is only 25 Å. Several techniques have been used to reduce/eliminate TED. Some of them are: reduction in the implant energy [3], amorphizing silicon before implanting boron, carbon implantation [4] and reducing the thermal budget [5]. Currently, the reduction of implant energy and thermal budget seem to be the techniques of choice. There are other techniques that show some promise but have not been actively studied, probably because they are not compatible with conventional CMOS process. One such technique is the use of atomic hydrogen in the formation of shallow junctions. Some experimental and theoretical studies have shown that hydrogenation can reduce the thermal budget for activation anneals, along with enhancing dopant activation [6,7]. This has been attributed to lattice relaxation, which occurs because of the termination of silicon dangling bonds by hydrogen and charge screening. It has been shown for example that, for an interstitial phosphorus dopant, the reduction in the activation energy is almost 3.0eV (depending on the configuration of hydrogen and the vacancy) [6]. An earlier study involving the implantation of hydrogen into the region implanted with phosphorus showed a 10% increase in dopant activation when compared to an un-hydrogenated (UH) implanted case. A recent study on the influence of hydrogen co-implantation with boron revealed that shallower junctions could be realized in hydrogen-implanted (H) samples [8]. However, in this study, furnace anneals were done at 1000oC for 30 min. The results from furnace anneal
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