具摻雜析離層蕭特基SONOS之元件製作與特性分析

Abstract

近年來，蕭特基電晶體被大量研究，主要是因為可以有效地微縮元件、低溫製造且擁有較低的寄生電阻。正因為如此，在未來的CMOS製程中蕭特基電晶體有機會取代p-n接面電晶體。然而因為蕭特基電晶體有幾乎定值的蕭基特能障落在源極端，造成驅動電流太小和Ambipolar效應。因此發展出用矽化物離子植入技術來製造出具摻雜析離層蕭特基電晶體,此電晶體是在源極和汲極接面做出摻雜的離子延伸，來抑制Ambipolar效應。 SONOS型記憶體逐漸成為非揮發性記憶體中的主流，主要原因是製程簡單、耗電量低而且可以做2 bit儲存等等優點。因此本文把具摻雜析離層蕭特基電晶體用在SONOS型記憶體上，並且探討具摻雜析離層蕭特基SONOS型記憶體，蕭特基SONOS型記憶體和量產型SONOS記憶體的特性比較，例如:寫入抹除速度、保持力(Retention)和耐久力(Endurance)。 從本研究中可發現，蕭特基SONOS型記憶體擁有比較大的記憶窗(Memory window)約為6V，量產型SONOS記憶體相較之下只有3.2V；而且也擁有快速的寫入的速度，在外加電壓10-4秒下約有3V的記憶窗，量產型SONOS記憶體相較之下只有1V的記憶窗；但是由於開關電流的比值(On-off ratio)太小，大約30.3，以至於很難分辨〝0〞和〝1〞。也因此使用具摻雜析離層蕭特基SONOS型記憶體來取代蕭特基SONOS型記憶體。本研究中可以發現具摻雜析離層蕭特基SONOS型記憶體在外加電壓10-4秒下約有2V的記憶窗；驅動電流為6.7×10-5A;導通電壓為4.38V，相較之下傳統型記憶體在外加電壓10-4秒下只有1V的記憶窗；驅動電流為6.8×10-7A;導通電壓為6.89V。而且相對於其他SONOS型記憶體，具摻雜析離層蕭特基SONOS型記憶體有較佳的持久力和耐久力。經本實驗可發現具摻雜析離層蕭特基SONOS型記憶體經過10年之後仍能維持3V的記憶窗，且對於經過寫入抹除 次的元件，10年之後也能維持1.3V的記憶窗。量產型SONOS記憶體相較之下，經過10年之後只有0.7V的記憶窗。

Schottky Barrier MOSFETs (SB-MOS) have been intensively studied recently for their capability, such as superior scaling down property, low thermal budget, and low parasitic resistance to outplace the doped source/drain MOSFETs in future CMOS technologies. Nevertheless SB-MOS devices suffer from approximate constant potential constraint on source side region that degrades the on-current, causing “ambipolar” effect. Therefore by using implant to silicide (ITS) technique to form dopant segregated Schottky barrier MOS (DSSB-MOS), which has the source drain extension to eliminate the ambipolar effect has been demonstrated in this work SONOS type memory plays an essential role in the nonvolatile memory market, due to less complexity of process, low power consumption and two bits storage ability. In this work, DSSB-MOS technique is used in SONOS memory devices. P/E speed, retention, and endurance characteristics of SB-SONOS, DSSB-SONOS and conventional SONOS memory devices are investigated and compared in this work. SB-SONOS device has largest memory window about 6V and provides fastest program speed for VTH shift about 3V with programming time of 10-4 seconds compared to conventional SONOS device which has memory window about 3V and program speed for VTH shift about 1V with programming time of 10-4 seconds. But SB-SONOS shows small on/off ratio around 30.3, causing difficult to differentiate between “0” and “1”. Therefore DSSB-SONOS device has been attempted to replace SB-SONOS device. For DSSB-SONOS device, it shows the better program speed for VTH shift about 2V with programming time of 10-4 seconds compared to conventional SONOS device. And for reliability, DSSB-SONOS device exhibits excellent retention and endurance performance compared to other SONOS memory devices. DSSB-SONOS devices retain 3V memory window after 10years and furthermore 1.3V memory window is obtained after subject to times of P/E cycles at room temperature.