N型電晶體結合CESL應力結構之熱載子效應與應力分佈之關係

Relationship between stress distribution and hot-carrier effect for nMOSFETs with CESL stressor

徐鴻文(Hung-Wen Hsu)

指導教授 ： 黃恆盛 ； 劉傳璽

國立臺北科技大學/機電學院/機電科技研究所/博士(2013年)

摘要

如何有效增加MOSFETs效能是一項重要的議題，在許多方法當中，應變矽技術是能夠有效提升性能且省成本的方法。本篇論文中，討論了當MOSFETs結合了接觸蝕刻停止層與矽鍺通道後，元件的載子遷移率與效能的變化。電性特性方面量測了n型與p型電晶體的基本特性，其中包含了輸出特性、轉移特性、電子遷移率、次臨界特性與短通道效應。另外，也討論了停止蝕刻層對短通道效應的影響，如臨界電壓下滑、汲極引起的位能下降以及次臨界斜率。其次，透過ANSYS軟體，使用有限元素分析法來分析元件通道中應力的分佈也是本論文中重要的一部分。透過模擬得知，當接觸蝕刻停止層為壓應力或張應力時，對長通道到短通道產生的應力分佈會有反轉的現象。當短通道元件上覆蓋的接觸蝕刻停止層為伸張應力時，對通道引起的應力也是伸張應力，因此能夠有效提升電子的遷移率。相反的接觸蝕刻停止層為壓縮時會提升短通道元件中電洞遷移率。然而，在長通道時通道中的應力剛好與停止蝕刻層的應力是相反的。由基本電性量測與應力分析的結果比較後，印證了相同應力源在不同通道長度下所引起的應力是會反轉的。在了解基本特性之後，本論文中也討論了關於熱載子效應的可靠度議題。實驗中n-MOSFET結合了不同應力的停止蝕刻層來作熱載子測試。最後討論了基本特性、應力分析與熱載子可靠度，可以清楚了解接觸蝕刻停止層對元件的影響。

關鍵字

應變矽技術 ； 接觸蝕刻停止層 ； 矽鍺通道 ； 應力分析 ； 熱載子效應

並列摘要

In this thesis, metal-oxide-semiconductor-field-effect-transistors (MOSFETs) combining contact etch stop layer (CESL), SiGe channel, and Si cap were fabricated. The CESL structure, with varying stress and SiGe channel, was fabricated with 90 nm technology. The electrical properties of n-type MOSFET (nMOSFET) and pMOSFET devices, combining CESL and SiGe channel, were investigated. Short-channel effects, such as drain-induced barrier lowering, were also studied. Moreover, TCAD simulation results and electrical properties were investigated. CESL type (tensile or compressive) or channel length (short or long) significantly affects the channel stress distribution. The stress in the channel region affects carrier mobility as well as device performance. To verify the simulation results, electrical properties such as mobility and output characteristics (Id-Vd) were measured. According to the output characteristics, with a channel length of 0.11 μm, the tensile CESL can enhance the performance of nMOSFETs. However, the improved trend is inverted when channel length increases. Based on the experimental and simulation results, device performance is confirmed to be associated with the stress in the channel. In addition, the CESL stressor and the SiGe channel approach effectively improve the mobility of nMOSFETs and pMOSFETs. We also compared Vt roll-off and subthreshold swing (SS) for different structures. The results show that the devices exhibited more severe Vt roll-off when CESL is adopted and that SS degrades more when CESL is compressive. The hot-carrier reliability of SiGe-channel nMOSFETs with various CESL nitride layers was also extensively studied. The effect of stress induced by the CESL stressor and SiGe channel on the hot-carrier reliability of the strained nMOSFETs was analyzed through experimental investigation. The shift in threshold voltage (△Vth) versus stress time (t) under different stress temperatures was measured. According to the reliability results, both the interface states (Nit) and oxide-trapped charges (Not) increased after hot-carrier stress. As regards hot-carrier reliability, the degradation of strained nMOSFETs with compressive CESL stressor is more serious than those with tensile CESL stressor under all stress conditions. The nMOSFET devices with tensile CESL have better performance and hot-carrier reliability than those with compressive CESL. Therefore, the CESL-induced damages (Nit) located at the interface between the gate dielectric and underlying channel are responsible for hot-carrier reliability.

並列關鍵字

Strained-Si technology ； contact etch stop layer (CESL) ； SiGe channel ； stress simulation ； hot-carrier effect

參考文獻

[90] 李冠徵（2011）。具張或壓應力CESL應變矽nMOSFET之特性分析與熱載子效應。國立臺北科技大學卅機電整合研究所卅研究所碩士論文，未出版，台北。

[2] M. Copel, S. Guha, N. Bojarczuk, E. Cartier, V. Narayanan, V. Paruchuri,"Interaction of La2O3 capping layers with HfO2 gate dielectrics", Applied Physics Letters 95/21 (2009) p.p. 212903-212906.

[4] S. Thompson, S. Parthasarathy,"Moore's law: the future of Si microelectronics", Materials Today 9/6 (2006) p.p. 20-25.

[5] O. Moutanabbir, M. Reiche, A. Hahnel, W. Erfurth, U. Gosele, M. Motohashi, A. Tarun, N. Hayazawa, S. Kawata,"Nanoscale patterning induced strain redistribution in ultrathin strained Si layers on oxide", Nanotechnology 21/13 (2010) p. 134013.

[6] H.W. Hsu, K.C. Lin, C.C. Lee, M.J. Twu, H.S. Huang, S.Y. Chen, M.R. Peng, H.H. Teng, C.H. Liu, "Phenomena of n-type metal-oxide semiconductor field-effect-transistors with contact etch stop layer stressor for different channel lengths", Thin Solid Films (2013) in Press.