用電子迴旋共振化學氣相沈積技術以矽烷，氧及四氟化碳成長低介電常數氟氧化矽層之研討

Abstract

在這篇論文中，我們將研討以氟氧化矽為主之金屬間隔介電物質。此氟氧 化矽層以電 子迴旋共振化學氣相沉積技術，用矽烷，氧及四氟化碳為反 應氣體來沉積。因為四氟化碳並不是直接參與氟化作用的原料，所以氟化 的機制將類似於四氟化碳電漿對矽氧層的蝕刻 。而此矽氧層的成長速度 視沉積和蝕刻反應的對比而定。此外，製程溫度對氟濃度的多寡 有相當 的影響。 從紅外線傅利葉轉換頻譜分析儀(FT- IR)和X光光電子頻譜分析儀(XPS)來看，我們發現沉積時增加四氟化碳和 矽烷的流量比(CF4/SiH4)，氟的含量將上升。而矽氟鍵結(Si-F) 亦將改 變矽氧層的性質。由FT-IR 譜線來看，矽氧鍵(Si-O)頻率位置的偏移跟矽 氟鍵和矽氧鍵的比例(Si-F/Si-O)有線性的正比關係。此關係亦反應在隨 矽氟鍵和矽氧鍵比例(Si-F/Si-O)的上升而降低的氟氧化矽層密度。此外 ，由電容(C-V)的量測中，我們發現 氟的攙入將導致較低的介電常數。這 是這篇報告的主要目的和根源。在此報告中，當氟濃 度在4.5原子百分比 時，達到我們最低的介電常數 - 約3.1。此外氟氧化矽層(FxSiOy)的 漏 電及應力現象和氟濃度跟沉積溫度有著有趣的關係。除了追求較低的介電 常數，我們也發現氟氧化矽層的熱穩定性和防水性跟沉積時的溫度，氟濃 度有著密切的關係。而這些性 質在超大型積體電路的金屬間隔介電層上 的應用和世界性研討的主題上也是未來的潮流。在此，我們發現熱穩定性 和防水性將隨沉積溫度的提升而有明顯的改善，然而較高溫度下的沉積也 導致較高介電常數和介面應力。另外，電子迴旋共振化學氣相沉積氧化 層(沒有添 加四氟化碳)，甚至在室溫沉積時，也有防水性。在用薄電子 迴旋共振化學氣相沉積氧化層包裹後，低溫沈積氟氧化矽層的吸水性可有 明顯的改善。因此，用高溫沈積來增強防水性的必要性可以避免。 In this work, the inter metal dielectric (IMD) material using fluorinated silicon oxide (FxSiOy) is fabricated and studied. These FxSiOy films were deposited in the electron cyclotron resonance (ECR) chemical vapor deposition system with SiH4,O2 and CF4 as the reaction gases. Because CF4 is an indirect fluo rinating source,the fluorinating mechanism will be simialar to that of theetching of oxide by fluorocarbon plasma. The growth rate of FxSiOy filmdepends on the competition between the species deposition and the etching reac tion. Besides, the process temperature will strongly affect incorporated fluor ine concentration. From the investigations by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoemission spectroscopy (XPS),we can find that by increasing the CF4/SiH4 flow ratio during the deposition, the fluorine concentration in thefilm will increase. The formation of Si-F bonds will change the oxide properties. Fromthe FTIR spectrum, the shift of absorbance peak position for Si-O bonds is found to have a linear positive relation with the absorbance ratio ofSi-F over Si-O. This reflects in the less dense of oxide network. On the other hand, from the C-V measurements, we can find that this incorporation of flu orine results in a lower dielectric constant. This is the most important purpose and the main spring of this study. In this work, the lowest dielectric constant is about 3.1 and the maxmium fluorine con centration is about 4.5 at. %. Besides, the leakage performance of FxSiOy film shows an interesting correlation with the incorporated fluorine concentration and the deposition temperature. Except chasing for the lowest deielectric constant, we also found that the thermal stability and moisture resistance of FxSiOy films strongly correlate to the deposition temperature and fluorine concentration. These are also the critical requirements for the VLSI circuits IMD applications and main subjects of studies in the world. Here we found that the thermal stability and moisture resistance are greatly improved by increasing the deposition temperature. Unfortunately,the high deposition temperature will result in a high compressed stress and dielectric constant. On the other hand, the ECR-oxide (without CF4 addition), even deposited at room temperature, is shown to have water resistance. After capped by a thin ECR-oxide, the moisture absorption of FxSiOy film deposited at low temperature can be improved. Thus, the necessity of high deposition temperature for moisture resistance is avoidable.