具獨立雙閘極之P型聚集模式多晶矽奈米線電晶體的製作與特性分析

Abstract

在本篇論文中，我們成功製作出操作在聚集模式(accumulation mode, AcM)下，具獨立雙閘極之P型多晶矽奈米線電晶體。此元件在通道中擁有高濃度的摻雜，且由於具有極小的奈米線尺寸，因此閘極可以有效的控制並開關元件。另外，此種元件的電性表現，包含基本特性以及次臨界特性，都將與操作在加強模式(inversion mode, IM)下，具有無摻雜通道的傳統元件做個比較。 在整個多晶矽通道導通的情況下， AcM元件明顯具有較IM元件大的電流驅 動力。此外，在兩個獨立閘極所提供多元操作的彈性下，我們將這兩種元件間不同的傳導機制成功地做區隔，並利用TCAD的模擬結果來做驗證。其次，由於AcM元件所提供的表面空乏區使得實質閘極介電層厚度的增加，因此具有較差的短通道效應。另一方面，我們也將討論元件跨導的特性，並利用其結果探索閘極耦合效應對兩種元件的影響。最後，我們也發現在同樣的閘極驅動下，AcM元件在閘極氧化層與通道的接面上具有較小的垂直電場，且由於AcM元件的實質通道涵蓋整個奈米線，使得載子受到表面粗糙與介面缺陷散射的影響較小，因此對於AcM元件而言，其跨導隨閘電壓增加而衰退的現象會比IM元件來得輕緩。

In this thesis, we have successfully fabricated p-type accumulation-mode (AcM) independent double-gated poly-Si nanowire (NW) transistors which contain a high doping concentration in the channel and can be effectively turned off on account of the ultra-small feature size of NW. In addition, the electrical characteristics are well compared to the conventional devices with undoped channels which operate in the inversion mode (IM). Owing to the current conduction through the whole channel, the Ion characteristics are obviously better for the AcM devices, so do the output characteristics. Moreover, due to the flexibility in device operation by the two independent gates, the differences of conduction mechanisms between the two types of devices can be clarified, and are also confirmed by the TCAD simulation results. We also found that short channel effects (SCEs) are more severe for the AcM devices, which is ascribed to the additional effective oxide thickness (EOT) contributed by the surface depletion layer. The Gm characteristics are also characterized and compared between the two types of devices, from which the influences of gate coupling effect for each device are well discussed. On the other hand, the AcM devices have a smaller electric field at the interface at the same gate overdrive, and the carriers also inherently suffer less from the scattering of the surface roughness and the interface traps on account of the whole channel conduction. Thus, the Gm degradation with increasing gate overdrive is more severe for the IM devices.