具30奈米鰭寬度於砷化銦鎵鰭式電晶體及其元件特性暨鰭片側壁製程之研究

Abstract

在這篇論文中，我們研究磷化銦基板上磊晶50奈米厚砷化銦鎵及300奈米厚砷化銦鋁之N型三五族鰭式場效電晶體。為此我們成功展示砷化銦鎵鰭式場效電晶體，其擁有200奈米閘極長度及30奈米鰭片寬度，且閘極氧化層為高介電係數介電層。此元件開關電流比約為10的3次方。在量測條件為汲極電壓0.05伏特和絕對溫度300K時，陡峭之次臨界擺幅為157.86 mV/dec。 砷化銦鎵鰭式場效電晶體在低溫中能展現更理想的元件特性，因此我們更進一步地，在絕對溫度200K的環境下進行量測。其元件開關電流比提升為10的5次方。在汲極電壓0.05伏特下，陡峭之次臨界擺幅降至90.21 mV/dec。 緊接著我們運用材料分析方法，來討論砷化銦鎵鰭式場效電晶體中的非理想問題。從穿透式電子顯微鏡的觀察結果得知，我們元件上鰭式通道的側壁與基板之間夾角為51.51度，且側壁表面有明顯凹凸不平的現象。從而得知，我們在乾蝕刻製程上面臨兩個重大的挑戰：側壁與基板之間的夾角、側壁表面的平整性。 最後，我們運用TCAD模擬軟體，來討論不同側壁角度所導致的效應。鰭式結構若擁有垂直的側壁，能在關閉狀態下有較均勻的電流密度分布，且電場強度近乎於零。這個結果顯示著，垂直的鰭式側壁結構能增強閘極控制能力且更容易地將元件關閉，所以在鰭式場效電晶體之中是最理想的通道形狀。

In this thesis, we investigated N-type III-V FinFET with 50nm In0.53Ga0.47As channel and 300nm In0.52Al0.48As barrier layer on InP substrate. The 30-nm fin width and 200-nm gate length InGaAs FinFET with high-K gate dielectric has been demonstrated successfully. The on/off current ratio was about 103, and the subthreshold swing was 157.86 mV/dec at drain voltage of 0.05V and temperature of 300K. Further, the InGaAs FinFETs at low temperature had ideal characteristics. Thus, we measured the same device at temperature of 200K. The on/off current ratio increased to 105, and the subthreshold swing decreased to 90.21 mV/dec at drain voltage of 0.05V. Next, material analysis was used to discuss the non-ideal issue of our InGaAs FinFETs. From TEM images, our fin sidewall profile was angle of 51.51 degrees, and the surface of sidewall was too rough by half. Thus, we had two significant challenges in dry etching process that were roughness of sidewall surface and sidewall profile angle. Finally, we uses TCAD simulation to discuss the effect of fin profile with different angle. The vertical sidewall of fin structure had uniform current density distribution and nearly no electric field at off-state. Thus, vertical sidewall of fin structure was a better profile as channel, because it could improve gate control ability and turn-off the device more easily.