運用非晶化離子佈植與鐿介層調變矽化鎳之蕭特基能障高度

Abstract

金屬矽化物形成源極/汲極的蕭特基位障金氧半場效電晶體是22奈米以下之元件最有可能的結構之一，其優勢為源極/汲極串聯電阻小、製程較簡化、低熱預算，及不易受短通道效應的影響。但蕭特基電晶體常因不適當的位障高度而造成關閉狀態漏電流和低飽和驅動電流的問題。鎳矽化物是目前最具潛力的金屬矽化物材質，因為它比鈦矽化物和鈷矽化物有更大的優勢。由於NiSi的費米能階約位於矽能隙的中間，其蕭特基位障高度對電子（0.65eV）和電洞（0.45eV）都相當大。 已有幾項研究報導運用稀土金屬如鐿、鉺和鏑降低NiSi/Si介面對電子的蕭特基位障高度以提升元件性能。其結果顯示，在退火後稀土金屬析離至矽化鎳表面，而非堆積在矽化鎳/矽的介面，因此只有觀察到些微調變蕭特基位障高度的效果。 在本研究中，運用鐿介層調變NiSi/Si介面的蕭特基位障並製作出蕭特基二極體。藉由非晶化離子佈植矽基板的幫助，退火後鐿原子聚集至矽化鎳表面的現象受到抑制。在所有實驗條件中，N2+離子非晶化佈植後沉積TiN/Ni(5nm)/Yb(15nm)的結構透過500℃退火產生最佳的蕭特基位障高度調變效果。

The metal silicide source/drain (S/D) Schottky barrier (SB) MOSFETs are considered one of the most promising candidates for sub-22nm devices because of small series resistance of S/D, easy processing, low thermal budget, and excellent short channel effect immunity. However, SB MOSFETs usually suffer from a large leakage current at the drain in the off state and poor saturation drive current due to undesired high SB height (SBH). Ni silicide is the most promising silicide material because it has greater advantages than Ti silicide and Co silicide. Owing to the Fermi level of NiSi lies close to the middle of Si bandgap, the SBH of NiSi is rather large for both electron (0.65eV) and hole (0.45eV). Several studies have addressed decreasing the SBH for electrons at the NiSi/Si interface to improve device performance by incorporating rare earth (RE) metals such as, Yb, Er, and Dy into NiSi. The results show that the RE metals segregated at the NiSi surface rather than piled up at the NiSi/Si interface after annealing, therefore little modulation of SBH was observed. In this study, tuning the SBH at the NiSi/Si interface for a Schottky barrier diode using an Yb interlayer is proposed. With the aid of pre-amorphization implantation (PAI) to silicon substrate, it was found that aggregating of Yb atoms in the surface of NiSi after silicidation is suppressed. Among the splits, the TiN/Ni(5nm)/Yb(15nm) structure deposited after the pre-amorphization of Si by N2+ ions induced the greatest change in SBH after annealing at 500℃.