以溶膠凝膠法製備含二氧化鋯薄膜電容之特性研究

Abstract

傳統上，半導體廠是以物理氣相沉積法(PVD)或化學氣相沉積(CVD)鍍膜，但此種沉積方法所遭遇到的困難為薄膜均勻度不佳，或製備成本太高。隨後發展的原子層沉積(ALD)技術具有大面積、高階梯覆蓋率、高厚度均勻性、低溫製程及原子級膜厚控制等優點，可以有效解決超薄高介電材料鍍膜需求，但成本仍然過高。 我們在此提出以溶膠-凝膠法(sol-gel method)，利用四氯化鋯(ZrCl4)當前驅物來製備二氧化鋯(ZrO2)薄膜。溶膠-凝膠技術有以下的特點：使用溶膠-凝膠法製備薄膜，會先將所有的前驅物溶解在液體中形成真溶液，此時反應物在溶液中是以分子級混合，所以會得到高度均勻的薄膜；另外由於是在低溫環境下進行製程，可以避免一些易揮發成分元素的散失及高溫製程時所產生不必要的擴散現象。 在這篇論文中，先將前驅物四氯化鋯粉末溶解在去離子水(DI water)中，產生二氧化鋯化合物後，以旋塗(spin coating)方式覆蓋在矽基板上，過程中設計了以下的四個條件：薄膜後氧電漿處理、薄膜旋塗速率、薄膜前氧電漿處理、不同薄膜濃度共四個實驗來觀察薄膜表面粗糙度的變化。再藉由原子力顯微鏡(AFM)和掃描式電子顯微鏡(SEM)的觀察薄膜表面型態，以找出無裂痕、連續且無結晶的二氧化鋯薄膜，並決定二氧化鋯薄膜的最佳製成參數。我們也進一步製備金屬-絕緣體-金屬(metal-insulator-metal)電容並量測其I-V與C-V特性，利用電容公式 算出介電常數k值。這些薄膜的材料特性和元件的電性表現證明了在低溫的電漿製程下，也可展現出電容的效能。

Traditionally, the semiconductor factory prepared thin films by physical vapor deposition (PVD) or chemical vapor deposition (CVD). But those methods have involved several problems, such as the uniformity of the thin films and the preparation cost. The next technology which called atomic layer deposition (ALD) has the advantages of large area and stepped coverage fraction, good thickness and uniformity, low temperature process and controllable film thickness under atom grade. ALD can also meet the necessary of ultra thin high k material film preparation, but the cost is also too high. We provide sol-gel method in this paper, and use ZrCl4 powder as precursor to prepare ZrO2 thin films. Sol-gel method has the advantages as below: all precursors are dissolved in solvent completely and formed molecular grade materials, so can prepare the good uniformity thin films; besides, the low temperature process can avoid the loss of volatile elements and the diffusion phenomenon caused by high temperature process. In this paper, ZrCl4 powder is dissolved in DI water and then formed ZrO2 compounds. Subsequently, film is spun coated on the silicon substrate. We designed four experiments including: O2 plasma treatment on the thin film, the spin rate of spin coating, O2 plasma treatment on silicon substrate, and different thin film concentrations. The surface morphology of the ZrO2 film is investigated by using scan electron microscope (SEM) and atomic force microscope (AFM) to find out the flat and smooth thin films. We also prepared the metal-insulator-metal (MIM) capacitor according to the best thin film parameters. I-V and C-V measurements of the films are realized by MIM capacitors. From the experimental results and formula as , we calculate the dielectric value (k) of different thin films. This paper indicates that the O2 plasma reaction is effective process for the complete oxidation of the sol-gel precursor at relatively low processing temperature.