High k / Metal Gate 金氧半場效電晶體

Abstract

在本論文中，我們利用多種量測方法(charge pimping, split C-V, DC Id-Vg, and pulse Id-Vg)來分析並研究具有高介電係數(HfO2)與金屬閘極(TiN)的金氧半場效電晶體(MOSFETs)。我們發現當n-MOSFETs金屬閘極中的鈦含量增加時，臨界電壓會明顯地下降。藉由對平帶電壓的分析，可發現金屬功函數隨著鈦含量的增加而減少是造成臨界電壓下降的主因。另外，我們也觀察有效載子移動率隨溫度(100K~300K)改變的趨勢，其結果指出不論在n型或p型電晶體中，高介電係數絕緣層中的remote phonon scattering會隨著鈦含量減少而增加，此因素將造成移動率下降。然而，我們亦發現閘極漏電流與金屬閘極中的氮含量有相當強烈的關係。我們利用pulse IV證實高介電係數絕緣層內的缺陷會被氮所修復，所以由Frenkel- Poole機制主導的漏電路徑將會減少，因此造成閘極漏電下降。最後，我們分別研究p型電晶體中的負偏壓不穩定性與n型電晶體中的熱載子效應。我們發現由於鈦含量的變化造成電性的改變，因此可靠度測試的結果也呈現出與金屬閘極的相關性。

The electrical characteristics and reliability of HfO2/TiN gate metal-oxide- semiconductor field effect transistors (MOSFETs) are investigated by analyzing experimental data from charge pumping, split C-V, DC Id-Vg, and pulse Id-Vg measurements. We have found that the threshold voltage (Vth) has a significant decrease as titanium increases in metal gate for n-MOSFETs. By examining flat band voltage, we found the Vth shift was resulted from metal gate work function (Φm) which became smaller as titanium increased in metal gate. In addition, the dependence of effective mobility on temperature from 100K to 300K was fully analyzed, which indicated HfO2 remote phonon scattering as the dominant cause of the mobility degradation in n- and p-MOSFETs when titanium decreased. However, the gate leakage current is also strongly dependent on the nitrogen in metal gate. It is proved that the nitrogen can passivate the traps in HfO2 by pulse I-V, leading to the decrease in gate leakage dominated by Frenkel- Poole mechanism. Finally, the reliability analysis including negative bias temperature instability and hot carrier effect are performed for p- and n-MOSFETs, respectively. The results show that the reliability will be strongly affected by the ratio of titanium in metal gate due to the change in electric characteristic.