利用溫度效應實驗分析奈米級超薄介電層場效電晶體之遠距散射機制

Abstract

由近年研究可得知，元件尺寸縮減時電子遷移率會伴隨遞減，這也指出了有額外的碰撞機制存在，並且此機制會對下一世代的元件造成很大的影響。因此本篇論文主旨係利用實驗萃取額外遷移率之溫度係數，進而探討Ｎ型超薄介電層場效電晶體下的遠距離散射機制。研究方法主要藉由一系列有系統的實驗與平面場效電晶體量子模擬器的搭配，由溫度效應去探討近年倍受爭議之遠距離庫倫散射的來源，並分辨造成遷移率大幅下降的主要碰撞機制為表面電漿子或遠距離聲子散射。而研究結果主要有以下兩點：(1). 即使改變表面粗糙度係數，其實驗萃取額外遷移率得到的溫度係數皆為負值，這說明了遠距離庫倫散射的主要來源是多晶矽空乏區中的表面電漿子。(2). 由近年的發表文獻可得知，表面電漿子之溫度係數約為-1.0，遠距離聲子散射的係數為-2.2左右。而在此實驗萃取額外遷移率得到的溫度係數皆落於-1.0附近，故我們認為表面電漿子是造成遷移率大幅下降的主要碰撞機制。

Electron mobility degradation is currently frequently encountered in highly scaled devices. This means that additional scattering mechanisms exist and will become profoundly important in next generation of devices. The aim of this work is to experimentally distinguish these remote scatterers particularly concerning the controversial arguments over remote Coulomb scatterers (RCS). To clarify whether Coulomb drag or surface optical (SO) phonons mode is responsible for the degraded electron mobility in n+-polysilicon ultrathin gate oxide nMOSFETs, we apply a novel temperature-dependent experimental method to obtain corresponding mobility component in high effective field regions. The results are remarkable: (i) in a considerable range of surface roughness amplitudes (Δ), the temperature coefficient exhibits a negative value, confirming interface plasmons in poly depletion region to be dominant remote Coulomb scatterers; and (ii) a new criterion is created with which one can experimentally distinguish interface plasmons from SO phonons: if a power-law temperature exponent □ is close to -1.0, additional scattering with interface plasmons dominates, while for scattering with SO phonons, □ lies around -2.2. In this work, we obtained □ whose value remains around -1.0. Hence we reasonably argue that Coulomb drag due to interface plasmons is responsible.