| Summary: | 碩士 === 國立中央大學 === 物理學系 === 101 === Due to large size mismatch between carbon (C) and silicon (Si), silicon carbon alloy (Si:C) is used as the stressors in the source and drain (S/D) of n-type metal-oxide-semiconductor field effect transistor (n-MOSFET) to improve the electron mobility. In addition, it was shown that the incorporation of C in Si substrate leads to band structure modification and reduction in dopant transient enhanced diffusion. Nonetheless, the large strain energy also limits the solubility of C in Si substrate and causes lower thermal stability. Previous researches suggested that higher C concentration in Si substrate usually results in lower thermal stability by strain relaxation. There are four main pathways of strain relaxation such as precipitation, dislocation, deactivation and volume compensation. In this experiment, we used two concentrations of carbon-implanted silicon to test the models above. The peaks of their concentration are 0.813% (CL system) and 1.131% (CM system) respectively. After the thermal annealing treatment at 635oC for full recrystallization, post-annealing treatments were performed to study the thermal stability. High resolution X-ray diffractometer (HRXRD) rocking curve measurement and kinematic simulation were used to determine the strain evolution and impurity solubility layer by layer. Furthermore, Fourier transform infrared spectrometer (FTIR) observation was used to investigate the mechanism of strain relaxation. We found that the strain increased at the initial stage of post-annealing treatment for both CL and CM systems. It is a novel phenomenon and can be ascribed to the occurrence of C re-incorporation. We also found that even though the thermal budget applied is far below the threshold for β-SiC formation, almost complete strain relaxation is found without significantly substitutional carbon (Csub) loss. FTIR results revealed the strain relaxation is related to volume compensation by Csub-interstitial complex formation through oxidation injection of interstitial. By multilayer HRXRD kinematical simulation, we found correlation of the enhanced strain relaxation to interstitial C amount, implying interstitial C also play an important role in the observed strain relaxation during post-annealing treatment. We therefore suggested a model for the observed strain relaxation based on the good interstitial gettering capability of carbon. Furthermore, we also make sure higher C concentration in Si substrate usually results in lower thermal stability.
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