Effect Of Pressure On Boron Diffusion In Silicon

Abstract

We are studying the effect of pressure on boron diffusion in silicon in order to better understand the nature of the point defects responsible for diffusion. Si homoepitaxial layers deltadoped with boron were grown using molecular beam epitaxy. Diffusion anneals were performed in a high temperature diamond anvil cell using fluid argon as a pressure medium. Diffusivities were deduced from B concentration-depth profiles measured with using secondary ion mass spectrometry. Preliminary results indicate that pressure enhances B diffusion in Si at 850 ˚C, characterized by an average activation volume of -0.125±0.02 times the atomic volume, and thus appear consistent with an interstitial-based diffusion mechanism. Results are compared with previous hydrostatic-pressure studies, with results in biaxially strained films, and with atomistic calculations of activation volumes for self diffusion. INTRODUCTIONBecause understanding and controlling diffusion related phenomena become increasingly important as semiconductor device dimensions decrease, diffusion in semiconductors has been heavily studied. Despite this emphasis there remains no consensus about the relative concentrations and mobilities of the point defects involved in the diffusion of many substitutional elements in Si [1]. A study of the dependence of the atomic diffusivity, D, on pressure, p, can provide valuable information to help elucidate the atomistic mechanism(s) of diffusion. The pressure-dependence of the diffusivity is characterized by the activation volume, ∆V*:

Pressure and Stress Effects on Diffusion in Si

“…A study of the dependence of the diffusivity, D, on pressure, p, and stress, σ, can provide valuable direct information to help elucidate the atomistic mechanism(s) of diffusion [3,4]. It can permit conclusions to be drawn about the predominant point defect mechanism independent of the assumptions inherent in the currently used kinetic models.…”

Pressure measurement at high temperature using ten Sm:YAG fluorescence peaks

“…This is the worst YAG spectrum that was acquired in our high-T and high-p semiconductor anneal experiments and was apparently caused by an anneal duration too short to permit optimization of the Sm:YAG signal/background ratio. 4 Even though this is far from the typical situation, we need to address it to have a fitting routine that is robust, even for poor spectra. Routine 3.…”

“…Simultaneous high-p and high-T applications usually require in situ control over pressure, and in turn require a pressure measurement technique that can be used to quickly determine p. For quick and accurate p determination, the x-ray diffraction method needs a very strong, well collimated x-ray source, such as synchrotron radiation, which is not available in most laboratories. Moreover, the likelihood that metallic pressure calibrants, which tend to touch the sample during the experiment, may contaminate or be contaminated by the sample at high T further precludes the use of these x-ray pressure calibrants in many experiments, including measurements on diffusion in semiconductor materials 3,4 where an inert and clean environment is vital. For high p work with the DAC, ruby is the most commonly used optical pressure calibrant and the associated spectroscopic pressure calibration method is a standard technique.…”