互補式金屬氧化物半導體元件之高電場效應研究與應用

隨著製程技術的進步，不論是元件的通道長度(Leff)以及閘極氧化層的厚度(tox)皆已進入深次微米的世代，而且隨著電路設計的需求，元件的幾何設計上也不再侷限為對稱型元件，因此大幅的提昇元件的速度與性能。但是受到工作電壓的限制，元件內所產生的電場強度遠高於從前，而高電場效應所衍生出的可靠性問題便顯得日益重要，這些高電場現象包括了熱載子注入、能帶對能帶穿透、以及氧化層的穿透所衍生出效應直接影響到元件的特性與生命週期，例如氧化層的傷害與功率的損耗。但由於高電場現象能夠將電子注入/移出閘極氧化層而被廣泛的應用在快閃記憶體，因此將針對非對稱閘極元件所面臨到的高電場效應進行研究。首先，定義出一非對稱閘極元件及其操作模式，探討其電場的分佈、撞擊離子化程度以及熱載子注入閘極氧化層的分析。其結果發現在窄端(forward)模式下，有較高的撞擊離子化程度與熱載子注入效應。在能帶對能帶穿透方面，將討論側向電場、汲極參摻雜濃度以及閘極氧化層厚度對穿透效應的影響，其結果發現側向電場將有助於加速載子而注入，垂直電場將助於電子電洞對的產生，此結果將不同於前述之熱載子注入效應，且較高的汲極摻雜濃度與較薄的閘氧化層厚度將有助於穿透電子的產生。在介電層的穿透電流方面，高介電係數材料(Al2O3)的穿透電流將與SiO2作一比較，因為SiO2 的電子能障高度約為3.1eV高於Al2O3的1.28eV，所以需要較高的穿透電場 ~ 6 MV/cm，而Al2O3 ~ 3 M V/cm。在相同電容值下，因為Al2O3有較厚的等效氧化層厚度，所以具有較小的漏電流。

關鍵字

F-N穿透效應；熱載子效應；能帶對能帶穿透效應；非對稱閘極元件

並列摘要

As processes technology improving, the channel length (Leff) and gate oxide thickness (tox) has already entered the submicron regime and in order to match up circuit design, the geometry shape of MOS devices is not symmetric rectangle any more. The performances of MOS devices are greater than before and the electric field in the device is substantially increasing. The high electric field effects include “CHE”,”BTBT” and “F-N tunneling” induced the reliability issues and become more and more serious. The effects degrade the lifetime and performance of devices such as oxide damage, power consumption …etc. Those high electric field effects are widely adopted in flash memory, because they can inject the electron into the gate oxide or pull it out. So the high electric field effects in MOS devices are investigated. At first, we will define an asymmetric gate device and analysis the electric field and impact ionization rate between different operating modes. It is found that the electric field and electron injection rate are higher in the forward mode. In BTBT effect, the lateral electric field, drain side doping concentration, and tunneling oxide thickness affect the tunneling mechanism will be discussed. It is found the vertical field contributes to generate the electron-hole pairs and lateral field contributes to hot electron injection. The thinner tunneling oxide and higher drain doping concentration also contribute to BTBT efficiency. The leakage current of high dielectric constant oxide layer Al2O3 is compared with SiO2. It is found the tunneling field of Al2O3 (~ 3 MV/cm) is smaller than the SiO2 (~ 6 MV/cm) because the barrier height for SiO2 was estimated to be 3.1eV and the Al2O3 was about 1.28eV. The large barrier height requires the high electric field for tunneling. At the same capacitor, the dielectric constant of Al2O3 is about 2.3 times of SiO2, so the dielectrics can be thick for the same stored charge. The leakage current of Al2O3 is smaller because the thickness of Al2O3 is thicker than SiO2.

並列關鍵字

BTBT ； CHE ； Asymmetric gate device ； F-N tunneling

參考文獻

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互補式金屬氧化物半導體元件之高電場效應研究與應用

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