動態臨界電壓金氧半電晶體之特性及可靠性研究

Abstract

在本論文中，吾人先討論了在不同閘極材質和厚度下的nMOSFETs。在利用動態臨界電壓的模式下操作，吾人發現所有在動態臨界電壓模式下操作的元件，不管其厚度或閘極材質，其臨界電壓皆趨近於0.7V，和厚度或閘極材質無關。這是由於基底效應被消除的原因。而且其臨界電壓和次臨界擺幅的公式亦被提出來解釋此特別的現象，次臨界擺幅的模擬結果亦同時被提出。接下來，吾人將探討製作在SOI 晶片上的pMOSFETs，且操作在動態臨界電壓模式下，對不同的結構的閘(T 型或H 型)且在不同溫度下的熱載子效應。操作在動態臨界電壓的模式下，在可靠性測量以後，臨界電壓的偏移量會降低，但是其最大的轉導和驅動電流在室溫下確有更惡化的趨勢。特別是T 型結構。操作在動態臨界電壓模式下的轉導放大效應和T 型結構下的電位不均勻是被認為造成Ｔ型閘極元件更加惡化的原因。 將逆向的Schottky 位能障製作在動態臨界電壓電晶體的基底接觸點上，使其可以操作在高電壓和高溫下，亦在本論文中討論。藉著這種製作在基底接觸點的Schottky 位能障，動態臨界電壓電晶體可以操作在高電壓下，且高溫下亦呈現出理想的次臨界擺幅值，較低的臨界電壓和較大的驅動電流。另一方面，這種結構的pMOSFETs 亦在本論文中討論，而且操作動態臨界電壓模式下的NBTI 的特性亦被首次討論。因為一般的p 型動態臨界電壓電晶體僅能操作在-0.7V 以下，以 避免基底和源極間的接面二極體的啟動。另一方面，值得注意的是，在NBTI 的量測以後，操作在動態臨界電壓模式的pMOSFETs，其臨界電壓的偏移量有大幅下降的趨勢。 此外，在附錄中，吾人亦對pMOSFETs 不同的區域佈植不同劑量的氮離子，進而研究NBTI 的效應。高劑量的氮離子，不論是佈植在通道或是源極/汲極的延伸，皆會造成嚴重的NBTI 效應。而且本論文亦研究動態NBTI 和基板熱載子效應。大量的氮離子佈植不僅會造成嚴重的NBTI 效應且會加速基板熱載子效應的進行。 最後，本論文最後附錄，將研究製作在(100)或(111)晶片上且具有超薄氧化層的pMOSFETs，關於其閘極氧化層厚度，載子遷移率和氮離子劑量之效應。製作在(111)矽晶片的pMOSFETs 可以把原本製作在(100)矽晶片上的pMOSFETs 之轉導提升約64％。吾人亦發現，氮離子的佈植可以增加(100)矽晶上pMOSFETs的載子遷移率，但是會降低(111)矽晶片上pMOSFETs 的載子遷移率。另一方面，因為二維的應變效應，在(111)矽晶片上的pMOSFETs 呈現出對長寬比的高度相關性，且在(111)矽晶片上的pMOSFETs 對溫度有比較大的靈敏度。

We discuss dynamic threshold MOS (DTMOS) operations for nMOSFETs ofdifferent dielectric types and thicknesses. We found that, under the DT mode of operation, all devices exhibit a threshold voltage close to 0.7 V, independent of the thickness and gate dielectric type of the device. This is due to the diminished influence of the body effect factor. Formulations of threshold voltage and subthreshold swing of DTMOS are developed to gain insights into this unique phenomenon, and simulation of the subthreshold swing is also provided. Then, we compared the hot carrier effects of T-gate and H-gate SOI pMOSFETs operating under DT-mode and conventional mode at various temperatures. By operating under DT-mode, the threshold voltage shift is reduced. However, enhanced degradations in maximum transconductance and drive current are observed when operating under DT-mode at room temperature, especially for the T-gate structure. The transconductance enlargement effect for devices operating under DT-mode, together with the non-uniform potential distribution in T-gate structure, are believed to be responsible for the observed enhanced degradations. The applications of DTMOS with reverse Schottky barrier on substrate contacts for high voltage and high temperature were presented. By this reverse Schottky barrier on substrate contact, DTMOS can be operated at high voltage, and exhibits excellent performance at high temperature in terms of ideal subthreshold slope, low threshold voltage and high driving current. In addition, the characteristics of DT-pMOSFETs using the reverse Schottky substrate contacts are also discussed. Furthermore, the NBTI effects of DTMOS were also reported for the first time. This is because DTMOS could operate just below 0.7V of VG due to the diode turn-on behavior. It is interesting to note that the shift of the ΔVTH of pMOSFETs under NBTI measurement was significantly alleviated in the DT operating mode. Furthermore, NBTI effects of pMOSFETs with different nitrogen dose implantation and regions were investigated in the appendix A. High nitrogen dose implantation in the channel or source/drain extension results in serious NBTI degradation. Both the dynamic NBTI effects and substrate hot holes effects were also discussed in this dissertation. Larger nitrogen dose not only results in serious NBTI effects but also serious substrate hot holes effects.. Finally, gate dielectric thickness, carrier mobility, and nitrogen dosage effects on pMOSFETs with ultra-thin gate dielectric on Si-(100) and Si-(111) were investigated in the appendix B. PMOSFETs on Si-(111) show about 64% improvement of carrier mobility than that on Si-(100) counterparts. We found that the nitrogen incorporation enhances the carrier mobility on Si-(100), but degrades on Si-(111). In addition, compared to Si-(100), pMOSFETs on Si-(111) show a strong dependence with aspect ration effect due to 2-dimensional strain effect. Finally, pMOSFETs on Si-(111) show slightly large sensitive for temperature dependence.