鎢在鋁/障礙層/p+n二極體的效應

Abstract

本論文探討Al/W/p+n結構的熱穩定性。鎢膜是以矽烷(SiH4)還原六氟化 鎢(WF6)方式選擇性地成長在矽基板上。對於具100nm厚度的鎢之 Al/W/p+ n二極體而言，該元件可承受450℃的熱處理30分鐘而不會有任何特性上的 劣化發生。但在500℃熱處理後即發現有劣化現象，並且XRD分析也顯示 WAl12的出現。如使用300nm的鎢膜，則Al/W/p+n二極體的穩定溫度可提 高50℃，不過，劣化仍然發生在550℃以上的高溫熱處理之後。在鋁和鎢 之間置入一層50nm的氮化鈦可成功地阻礙鋁與鎢的交互擴散和WAl12的形 成，即使熱處理溫度提高到575℃仍然具備有效的擴散阻止能力。再者， 藉由在化學氣相沉積成長的鎢膜上作氮氣電漿處理來自動對準地形成一層 WNx，並進而做成Al/WNx/CVD-W/p+n二極體的結構，經各種證據顯示可有 效地壓制WAl12的形成，並使該接面二極體之熱穩定度提高到575℃。 This thesis studies the thermal stability of W contacted p+n junction diodes using the selective CVD W with the silane reduction process. For the Al/W/p+n diode with a W layer of 100nm, the device was able to sustain a 450℃ anneal for 30min without causing any degradation to the device's characteristics. Degradation occurred when the device was annealed at 500 ℃, and the XRD analysis showed the appearance of WAl12 phase. With a thicker W layer of 300nm, the Al/W/p+n diode was able to raise the stable temperature by about 50℃, but the diode degraded when it was annealed at 550℃.The insertion of a 50 nm TiN layer between Al and W successfully retarded Al-W interdiffusion and WAl12 formation, resulting in excellent barrier capability up to 575℃. In addition, a simple self-aligned formation of WNx layer on the W surface by post CVD-W in situ N2 plasma treatment resulted in another thermally stable contact system of Al/WNx/W /Si structure. Various evidence has shown that this post CVD-W N2 plasma treatment efficiently suppressed the formation of WAl12 and resulted in an improvement on thermal stability of the W contacted junction diodes up to 575℃.