Thermal stability of supersaturated carbon incorporation in silicon

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题名:	Thermal stability of supersaturated carbon incorporation in silicon
作者:	林侑鋌;Lin,Yu-ting
贡献者:	物理學系
关键词:	過飽和矽碳合晶;supersaturated carbon incorporation in silicon
日期:	2013-07-15
上传时间:	2013-08-22 11:47:20 (UTC+8)
出版者:	國立中央大學
摘要:	由於碳原子與矽原子的大小不匹配，矽碳合金(Si:C)常被應用於n型金氧半場效電晶體(n-MOSFET)的源極(source)與汲極(drain)來對載子通道產生一個張應變(tensile strain)，藉此來提升電子在通道中的漂移率(mobility)。此外，碳原子的參雜也能有效的調整矽基板的能帶結構以及阻止其他參雜原子的暫態增強擴散效應(transient enhanced diffusion)。然而，較高的張應變能也限制了碳原子在矽基板中的溶解度且導致了較低的熱穩定性。先前的研究指出，矽基板中碳原子的濃度越高則系統的熱穩定性就越低(應變鬆弛)。應變鬆弛(strain relaxation)主要有四種途徑:沉澱(precipitation)、錯位(dislocation)、去活化(deactivation)和體積補償(volume compensation)。在這個實驗中，我們使用兩種不同濃度的矽碳合金來測試與驗證上述的結果。矽碳合金是以離子佈植及固相磊晶成長(solid phase epitaxial regrowth)的方式來製作，其濃度最大值分別為0.813% (CL系統)及1.131%(CM系統)。我們藉由高解析度X光繞射儀(HRXRD)與動態模擬(kinematic simulation)來研究系統的張應變隨著熱能增加的進展及雜質的溶解度。我們也藉由傅立葉轉換紅外光譜儀(FTIR)來研究系統應變鬆弛的物理機制。我們發現在CL與CM系統中，在熱退火(post-annealing)的初始階段系統的總張應變都會有明顯的增加。此應變增加的行為是一個新穎的物理現象，它可以被歸因於間隙碳原子的再活化效應(re-incorporation effect)。隨後我們也發現系統的張應變會隨著熱退火時間的增長或熱退火溫度的增加逐漸的鬆弛。然而，此熱退火條件卻遠低於先前研究(需高溫加熱並以β-SiC沉澱析出的形式來釋放張應力)的條件。傅立葉轉換紅外光譜儀的量測結果顯示出CL系統和CM系統的張應變鬆弛的原因並非源於晶格位置上的碳原子被置換或β-SiC的形成，而是源於晶格位置上的碳原子能有效的吸引與限制住表面氧化效應產生的大量間隙矽原子，進而使體積增大應變鬆弛。藉由動態模擬我們也發現間隙碳原子的量與張應變鬆弛是有關連的，這代表著間隙碳原子在張應變鬆弛的過程中扮演著重要的角色。根據上述，我們認為系統的張應變鬆弛主要是源於晶格位置上的碳原子較佳的吸引及限制間隙原子的能力。此外，我們也確認矽基板中碳原子的濃度越高則其熱穩定性就越低。 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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