Strained silicon has been employed as a standard module in the source/drain (S/D) part of metal oxide semiconductor field effect transistor (MOSFET).The nMOSFET counterpart of the Si:Ge S/D in Pmosfet is Si:C S/D. While germanium is soluble in silicon, the equilibrium solid solubility of carbon is only at the order of 10¹⁷ cm⁻³. Non-equilibrium process such as ion implantation, chemical vapor deposition (CVD), or molecular beam epitaxy is needed to incorporate ∼ 1 atomic percent of substitutional carbon into silicon lattice in order to generate significant strain effect. Due to its non-equilibrium nature, its tolerance to post-process is in question. Furthermore, in order to form junction, dopants are conventionally introduced into S/D regions. Due to low parasitic resistance requirement, high doping is a must. The high doping has been reported to cause detrimental effect to Si:C S/D devices. The process window for highly doped Si:C S/D becomes narrower due to the above practical constraints. Therefore, understanding how implanted dopants interact with substitutional carbon (C_sub) during the post-processes is important for implementation of this tuning knob in future microelectronic device.

We have investigated the strain relaxation mechanism of P doped Si:C formed by solid phase epitaxial regrowth (SPER) and CVD. The origin of strain relaxation is investigated by Fourier transform infrared (FTIR) spectroscopy and high resolution x-ray diffraction (HRXRD). We find strong indication that interstitial phosphorus promotes the volume compensation by forming C_sub-interstitial complexes during the thermal treatment. We also find a peculiar carbon re-incorporation phenomena in CVD grown Si:C. Our current research efforts include study on improvement of the strain stability by utilizing carbon cocktail implantation process and strain distribution in regards to S/D length scale.

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