Abstract
Diffusion of boron in compressively strained Si1 –xGex alloy layers grown by rapid pressure chemical vapor deposition has been studied as a function of the composition for 0.0006 ≤ x ≤ 0.15 and annealing temperature. The comparison of the Si1 –xGex samples to the Si samples after rapid thermal and furnace annealing revealed a retarded B diffusion inside the strained Si1 –xGex layers. The influence of the Ge content on the dopant diffusion was also measured and simulated, demonstrating that the diffusion of B was found to decrease with the Ge alloy content and annealing temperature. A simple empirical expression for the B retardation is presented and incorporated into a diffusion model for dopants in heterostructures. Good agreement between the measured and simulated diffusivity that includes the model for strain and chemical effects are obtained. By comparing with experimental values, our extracted (by using experiment and simulation) B diffusivity predicted a lower value (retardation).
Highlights
Silicon Germanium (SiGe) HBT BiCMOS is a new promising technology that offers the possibility of integrating very high performance HBTs with state-of-the-art CMOS
Moriya et al [2] and Cowern et al [3] compared the diffusion in strained SiGe with that in relaxed Si and neglected any chemical effects
Kuo et al [4] have made a detailed comparison of the B diffusion in compressively strained SiGe with that in relaxed SiGe of the same composition and in tensile-strained Si with that in relaxed Si
Summary
Diffusion of dopants in a crystalline Si and Ge is an example where controlled experiments in pristine material have led to complex, phenomenological models These models, limited in their absolute prediction of diffusivity, do provide a guide for predicting the change of diffusivity with certain material properties including Ge fractions, chemical effects etc., and physical parameters including temperature etc. The present diffusion model accurately simulates the measurement profiles over the given range of Ge fractions, and box-type and graded Ge profiles that were selected as experimental conditions involved in the present study. With the present models and simulations it has been possible for the first time to the knowledge of the authors to separate chemical effects (alloy effect) as well as strain (with f factor) from effects arising from strain in interstitial-mediated diffusion of B in strained Sil_xGex epitaxial layers, 2. De is the boron diffusivity, Ce is the boron concentration, Nr is the net doping (NAND), n is the electron concentration and ni is the intrinsic carrier concentration for SiGe
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