Enhancement of Boron Activation in Shallow Junctions by Hydrogen
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Enhancement of Boron Activation in Shallow Junctions by Hydrogen A. Vengurlekar, S. Ashok, C. E. Kalnas*, N. D. Theodore** Department of Engineering Science, Pennsylvania State University, University Park, PA 16802 *Solid State Measurements Inc., Pittsburgh, PA 15275 ** Motorola Inc., Advanced Products R&D Labs, Tempe, AZ 85284 ABSTRACT The ability to activate greater amounts of dopants at lower temperatures is a persistent contingency in the continual drive for device scaling in Si microelectronics. We report on the effect of incorporating atomic hydrogen on the activation of implanted boron in shallow junctions. Hydrogen incorporation into the sample was carried out by exposure to an electron cyclotron resonance (ECR) hydrogen plasma. Enhanced activation was observed in hydrogenated samples for post-implantation annealing temperatures of 450oC and below, as measured by spreading resistance profilometry, and confirmed by identical boron atomic profile in hydrogenated and unhydrogenated samples. The enhancement in boron activation at lower temperature is attributed to the creation of vacancies in the boron-implanted region, the lattice-relaxation effect by the presence of atomic hydrogen, and the effect of atomic hydrogen on boron-interstitial cluster formation.
INTRODUCTION The scaling down of device dimensions and the resultant decrease in the depth and width of the MOSFET source and drain decreases the total number of free carriers present in these regions. The increase in device resistance needs to be counteracted with higher dopant concentrations [1]. Therefore, the ability to successfully activate greater numbers of dopant atoms, and to do this at lower temperatures, is an important challenge for junction technology. Previous efforts to achieve such activation include the creation of a vacancy-rich region around the boron profile by higher energy silicon implantation [2, 3], and subsequent absorption of self-interstitials by these vacancies. This approach was also used to reduce transient enhanced diffusion (TED) of boron [4-6]. Low-temperature activation of boron is limited by the formation of boron-interstitial clusters, and the presence of vacancies reduces the interstitial supersaturation [7,8]. Boron activation is more difficult to achieve in shallower junctions due to these clusters and due to higher concentration of boron [9]. The high temperatures currently used to activate boron (>1000 oC) result in increased junction depth, and problems with TED [10], however, lowering the annealing temperature results in decreased boron activation. Hence, attaining greater boron activation at lower annealing temperatures is a desirable goal. The enhanced activation of other kinds of dopants in silicon by the presence of atomic hydrogen has been previously reported [11]. Li et al. reported on the increase in boron activation due to the incorporation of other species in the Si lattice [12]. Theoretical calculations [13, 14] show that when a vacancy in crystalline Si is occupied by atomic hydrogen, substantial
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