鉻矽化物奈米線異質結構及其成長行為之動力學研究

Abstract

過渡金屬矽化物奈米線有許多良好的特性:低電阻、優秀的熱穩定性以及良好的機械強度，因此，在未來他們可望被應用在積體電路的內連接導線以及接觸材料上。 在本論文裡，我們成功地利用固態反應法合成出矽化鉻奈米線的異質結構。進一步利用原子層化學氣相沉積鍍覆氧化鋁(Al2O3)薄膜，增加其反應過程中的外加應力，探討壓應力於奈米尺度下之效應。實驗中使用三種不同條件的矽奈米線作為模板，第一種是表面無氧化層的矽奈米線，第二種是表面具有自生成SiO2殼層的矽奈米線，此兩種均合成Si/Cr3Si的異質結構。第三種是鍍覆Al2O3作為矽奈米線殼層，並合成Si/Cr5Si3的異質結構。在700 ℃下，藉由臨場穿透式電子顯微鏡觀察三種鉻矽化物奈米線生成的過程以及擴散機制，計算其成長速率，以及反應前後奈米線的膨脹率。在這三種奈米線中，我們均發現，矽化鉻奈米線在成長過程中，由於矽原子擴散速率大於鉻原子，因此會先產生一個富矽的過渡相，再形成Cr3Si或Cr5Si3的穩定相。另外，在引入外層氧化鋁後，我們發現殼層氧化鋁會改變擴散反應的行為，給予矽奈米線足夠的壓應力，將有效限制矽化鉻奈米線徑向的成長，並增加其軸向的成長速率外，也大幅減少矽化鉻奈米線的徑向膨脹率。加入氧化鋁殼層後，限制了富金屬相的Cr3Si產生，取而代之產生的是富矽相的Cr5Si3。此外，我們也研究了Cr3Si、Cr5Si3奈米線的晶體結構，利用球面像差修正掃描穿透式電子顯微鏡來進行其成分分析與結構鑑定，觀察到A15晶系之Cr3Si與D8m晶系之Cr5Si3。本研究成果，預期將對未來的奈米製程科技及相關應用帶來重要的參考價值與影響。

Transition metal silicide nanowires exhibit low resistivity, great thermal stability and excellent mechanical strength, thus can be applied as interconnect and contact materials for future integrated circuits devices. In this work, we successfully fabricated three kinds of chromium silicide/silicon heterostructure nanowires through solid state reaction ─ bare Si/Cr3Si nanowires, Si/SiO2 core-shell/Cr3Si nanowires and Si/Al2O3 core-shell/Cr5Si3 nanowires. The growth behaviors and diffusion mechanisms of these three kinds of silicide heterostructure nanowires were observed by in-situ TEM at 700℃, and calculate the growth rate and thermal expansion of these chromium silicide nanowires. During the growth of chromium silicide nanowires, Si-rich phase would form first in front of silicide nanowires. We also find that oxide-shell can control the diffusion process in silicon nanowire. When oxide-shell applied, suppression stress would restrain radial direction growth of chromium silicide and accelerate its axial direction growth rate. In addition, Al2O3 shell was found to reduce the radial expansion of chromium silicide nanowires and hinder Cr-rich phase, then Cr5Si3 eventually wins out as the first phase. Furthermore, we studied the crystal structure of Cr3Si and Cr5Si3 nanowires, and confirmed the single-crystalline A15 and D8m type structure of the intrinsic Cr3Si nanowires and Cr5Si3 nanowires respectively. In addition to fundamental science, the significant study would be helpful for future processing techniques in nanotechnology and related applications.