矽基板上矽奈米柱的形成與特性分析

Abstract

在本論文中，我們成功地利用二氧化矽薄膜當緩衝層，使得鎳的奈米顆粒成功地快速凝聚在矽的基板上。因為矽的高熱導148 W/m-K造成熱快速散逸，所以奈米鎳顆粒很難直接地聚集在矽的基板上。藉由厚度200 Å且熱導只有1.35 W/m-K的二氧化矽當緩衝層，阻止了NiSi2化合物的產生，和讓奈米鎳顆粒因為在鎳和矽界面之間吸附力減小與熱的累積，更容易形成自我凝聚。因此，奈米鎳顆粒可以加速形成，退火時間大大縮短到22秒。奈米顆粒的大小和密度平均是30奈米和7□1010 cm-2。利用鎳在二氧化矽層上自我凝聚成的奈米粒當奈米遮罩，經過活化離子式蝕刻後，可以在矽的基板上製造出大面積的矽奈米針陣列，而針的大小可以被控制到小於50奈米。在我們的實驗中，矽奈米針的最理想高寬比是8。此時，針的平均大小和高度分別是40奈米和400奈米。去除掉在矽的基板上的奈米粒和二氧化矽後，從矽奈米柱發出的光激發可以發現到400到600奈米的可見波段和750奈米的近遠紅外波段。400奈米到600奈米的可見波段主要源自於氧的弱鍵結（WOB）、中性的氧化缺陷（NOV）與E’缺陷。更進一步地，因為矽奈米針持續氧化產生在光激發譜上的藍位移現象和產生在變功率光激發譜上的強度飽和現象，所以成功地證實750奈米波段是量子侷限效應。其他在電性上，相較於矽的靶材，矽奈米針擁有較快的充放電速度、較低的電阻和超低漏電流，而在光性，則明顯有較低的反射率。

In this essay, rapid self-aggregation of Ni nanodots on Si substrate covered with a thin SiO2 buffered layer is investigated. Ni nanodots are hard to self-aggregate on highly heat dissipated Si substrate with a thermal conductivity of 148 W/m-K. Adding 200Å-thick SiO2 buffer with an ultralow thermal conductivity of 1.35 W/m-K prevents the formation of NiSi2 compounds, facilitates the self-assembly of Ni nanodots from enhanced heat accumulation and released Ni adhesion with Si. Formation of Ni nanodots can therefore be accelerated with size and density of 30 nm and 7□1010 cm-2, respectively, under an annealing time greatly shortened to 22 sec. With the advantage of the self-assemble Ni/SiO2 nano-dots based nano-mask, a large-area Si nano-pillar array with rod size of <50 nm can be formatted on Si substrate through the induced coupled plasma reactive ion etching (ICP-RIE) procedure. In our experiment, the optimum aspect ratio of the Si nanopillars is 8 with the average diameter of 40 nm and the average height of 400 nm. After removing Ni dots and the SiO2 film on the Si substrate, both the visible 400 nm-600 nm and near infrared 750nm photoluminescence from the Si nano-pillar sample were observed and analyzed. The visible emission 400 nm to 600 nm mainly originated from the weak oxygen bond (WOB) the neutral oxygen vacancy (NOV) defects, and the E’ defects. Moreover, the peak wavelength of 750 nm is emitted from the quantum confining centers proven by the blue shift of the oxidizing Si nanopillars in the μPL and the saturating peak intensity in the power dependentμPL. Comparing to the bulk structure, the Si nanopillars owned the high charging and discharging speed、low resisters and no leakage current in electrics and the low reflectance in optics.