浮動式催化劑成長法降低奈米碳管金屬間接觸電阻

Abstract

本篇論文研究在化學氣相沉積法(Chemical Vapor Deposition, CVD)成長奈米碳管(Carbon Nanotubes, CNTs)中，催化劑種類對於其產物與金屬間接觸電阻的影響。為取代銅做為三維積體電路(3DIC)中矽穿孔(TSV)的填充材料，奈米碳管與金屬接合點間的高接觸電阻一直都是需要被克服的難題之一。作為成長奈米碳管最普遍的方法，化學氣相沉積法，其原理為在高溫下利用催化劑將碳源氣體分解，並在催化劑表面成長出奈米碳管。而在矽基板上鍍上一層金屬催化層薄膜是最常見的催化劑類型，但此種催化劑類型會使矽基板與金屬催化層薄膜在預熱至奈米碳管生長溫度時發生交互作用，產生出金屬矽化物，此種金屬矽化物會毒化奈米碳管的成長，劣化奈米碳管的電性。

本篇論文提出以浮動式催化劑化學氣相沉積法(Floating Catalyst CVD, FCCVD )成長之奈米碳管能得到更低的與金屬間的接觸電阻。FCCVD方法藉由氣流將熱裂解的金屬催化奈米顆粒帶至矽基板上進行奈米碳管成長，避免了金屬與矽基板在預熱階段時的交互作用，預防金屬矽化物的產生，從而劣化奈米碳管的電性。實驗進行金屬催化層薄膜CVD與FCCVD方法成長之奈米碳管與不同金屬鉻(Cr)、銦(In)、銅(Cu)、鎳(Ni)、鎢(W)間的接觸電阻比較。藉由不同高度的金屬—奈米碳管—金屬結構與兩點探針系統測量電阻，可以推算出奈米碳管與金屬間的接觸電阻，而實驗也結果確實了以FCCVD方法成長之奈米碳管有著與金屬間更低的接觸電阻。此外，濕潤性佳的金屬還能提供更低的接觸電阻，如本篇論文選用的金屬鉍，測量到了與奈米碳管間的接觸電阻可以低至835Ω×μm2。此結果為解決金屬和奈米碳管間高接觸電阻提供了一個新的想法，使奈米碳管在3DIC結構中取代銅成為填充TSV的材料更進一步。

This work focuses on the effect of the catalyst type on the contact resistance between the metal and carbon nanotubes (CNTs) grown by chemical vapor deposition (Chemical Vapor Deposition, CVD).

In order to replace copper as the material for filling through-silicon vias (TSVs) in three dimensional integrated circuit(3DIC), the high contact resistance between CNTs and metal electrodes is one of the challenges that need to be overcome. The most common method of growing CNTs, CVD method, uses a catalyst to decompose the carbon source gas at high temperature, and grows CNTs on the surface of the catalyst, and a catalyst metal film on the silicon substrate is the most common type of catalyst, but this type of catalyst will produce metal silicides between the silicon substrate and the catalyst metal film during the heating stage, which will poison the growth of CNTs and lower the electrical properties of CNTs.

This work proposes that CNTs grown by Floating Catalyst CVD (FCCVD) can obtain lower contact resistance with metals. FCCVD uses gas flow to bring metal catalytic nanoparticles to the silicon substrate for CNTs growth, avoiding the generation of metal silicides. Experiments were carried out to compare the contact resistance between different metals (Cr, In, Cu, Ni, W) and CNTs grown by catalyst metal film and the floating catalyst, through the different heights of metal-CNTs-metal structure and the electrical measurement by two-probe method, we can obtain that the CNTs grown by FCCVD method have lower contact resistance with the metal. In addition, metals with good wettability can provide further low contact resistance, such as bismuth selected in this work, the contact resistance can be as low as 835Ω×μm2. This result provides a new idea for solving the high contact resistance between metal and CNTs, and it is a further step for CNTs to replace copper in the 3DIC structure as the material for filling TSVs.