無柵極離子束沉積法低介電常數類鑽碳薄膜之研究

Abstract

隨著小型化、高速化積體電路技術急速進步及條件嚴格要求，為了 提升積體電路的積集度，因此，多層金屬內連線系統的研究發展，成為 本世紀初重要的課題。由於線寬、線路間距、以及線與閘極間距縮小會 導致電阻-電容時間延遲(R-C time delay)現象，影響元件中的訊號傳 遞速度。減少R-C time delay有兩個解決方法：一是使用電阻值較低的 金屬導線，另一是使用低介電常數材料做為金屬導線間的介電層，以降 低寄生電容值。 類鑽碳（Diamond-Like Carbon，DLC）為碳元素的一種型式，其結 構主要為sp3和sp2鍵結的混合體，化學性質安定，且具有高硬度、低摩 擦係數、與抗磨耗等優點，在低溫或室溫下即可沉積，易相容於現今半 導體技術而製成元件。 本研究採用無柵極離子束沉積法（Gridless Ion Beam Deposition ，IBD）製備非晶質類鑽碳薄膜，並且對沉膜進行熱退火試驗，探討DLC 薄膜之物理性質對介電性質之影響。物理性質方面，利用拉曼光譜儀來 分析DLC薄膜之鍵結結構，以及利用RBS來進行DLC薄膜之密度和孔隙度 分析。電性方面，主要是利用I-V、C-V量測，探討DLC薄膜之漏電流與 介電常數值。 拉曼光譜分析結果顯示，DLC薄膜的ID/IG比值隨著退火溫度增加而 漸增，表示DLC薄膜中的sp2鍵結增加，使薄膜趨向於”石墨化”。RBS 分析結果顯示，DLC薄膜的密度隨著退火溫度增加而有增加的趨勢，孔 隙度則有下降的趨勢，原因可能是由於溫度提昇時，DLC薄膜中的氫鍵 會被打斷形成較多的sp2鍵結；而電性量測結果顯示，在真空中退火時 ，隨著退火溫度增加，MIS電容結構的漏電流即大幅增加；但在氮氣氣 氛下進行退火，由於可以消除薄膜表面放電現象，故漏電流可以獲得改善。至於氫氣電漿表面處理，當處理的時間增加時，漏電流有明顯下降 的趨勢。介電常數計算結果顯示，未做任何處理前，DLC薄膜的介電常數 值為3.8，經退火處理後，DLC薄膜的介電常數值會隨著退火溫度的升高 而有明顯下降的趨勢，當400℃時，介電常數值為2.9。

For the needs of scaling down the feature sizes and increasing the circuit speed for IC manufacturing, the trend toward increasing interconnect packing density has driven the development of multilevel interconnect system. As interconnect lines shrink and move closer together, the resistance-capacitance (RC) delay will produce and directly limit device speed. The semiconductor industry has been prompted to adopt new materials and architectures: low-k dielectric / copper damascene and dual-damascene replacing traditional SiO2 / aluminum subtractive etch architectures and processes. Diamond-like carbon (DLC) is one structure of carbon elements. It is primary a mixing structure of sp3 and sp2 bondings that its chemical property is stable. DLC films are developed for future application with the advantages of high hardness and low coefficient of friction. Because DLC films can be deposited at low temperature or at room temperature, they are easily suitable for IC manufacturing. In this study, gridless ion beam deposition has been adopted to prepare amorphous diamond-like carbon films. We took thermal annealing tests on DLC films and investigated the relationships between physical properties and dielectric properties. For the studies of physical properties, DLC films were analyzed by Raman spectroscopy for chemical bonding and by RBS for film density and porosity. For the studies of electrical properties, I-V and C-V measurements were used to evaluate the leakage current and dielectric constant of DLC films. By Raman spectrum, it was found that Raman ID/IG ratio increases with annealing temperature increasing which indicates higher sp2 content in the films. The evident indicate the films are more “graphite-like”. By RBS spectrum, the density of DLC films increases while the porosity decreases with annealing temperature increasing. The results are due to the broken of the hydrogen bonds and the formation of more sp2 bondings for DLC films with increasing temperature. For the electrical characteristics of DLC films, it was found that the leakage current of MIS capacitor increases with increasing temperature annealed in vacuum while decreases in N2 ambience. The leakage current decrease is due to the reduction of surface charging by N2 annealing. By H2 plasma post-treatment, the leakage current strongly decreases with increasing treating time. The dielectric constant of DLC films was found to degrade from 3.8 (as-deposited) to 2.9 (400℃ annealed) with increasing temperature annealed whether in vacuum or in N2 ambience.