- 學位論文
電漿改質低介電常數材料及其表面特性分析
Characterization of Plasma Effects on Low-k Film
摘要
隨著半導體產業蓬勃發展，在半導體元件繁瑣的製程步驟中，電漿製程已然成為不可缺少的一部分。然而，在目前文獻中甚少有提及低介電常數材料經過電漿處理後，材料表面化學結構變化的詳細探討。因此，本研究主要探討在不同電漿蝕刻條件下，低介電常數材料表面化學結構變化，所使用的電漿氣體分別為C2H2F4/CF4、CF4。而在半導體蝕刻製程之後，通常會再進行post-etch treatment(PET)來清除蝕刻後的殘餘物，在此一步驟本研究所選用的電漿氣體為N2/H2。最後經由X射線光電子能譜儀(XPS)、傅立葉轉換紅外線光譜儀(FTIR)、接觸角量測儀(CA)、場發式電子顯微鏡(FE-SEM)等儀器，分析晶圓表面經過C2H2F4/CF4、CF4、N2/H2 電漿處理後，物理性質及化學性質之變化。 經由研究結果發現，使用C2H2F4混合CF4電漿，膜材表面增加了大量的碳、氟元素，推測其原因為C2H2F4混合CF4之後，降低了整體的氟碳比，因此有助於在樣品表面上沉積氟碳膜，在升高C2H2F4的比例之後，此一情況更加明顯。反觀直接以純CF4電漿對膜材進行蝕刻，膜材表面不再沉積一層氟碳膜，發現電漿蝕刻時間為5秒、10秒時，皆只有在材料表面1、2奈米的地方有被氟化的情形。藉由氟元素的比例與被氟化的深度推斷其機制與CF4混合C2H2F4的長膜機制不同，應為電漿蝕刻機制。 找到CF4電漿蝕刻的最佳操作條件之後，逐以N2/H2電漿進行post-etch treatment步驟。經實驗結果發現，進行完PET之後膜材表面的碳、氟元素被大量的移除，氟元素更是幾乎消失殆盡，而隨著H2比例的增加，去碳能力也隨之上升。實驗最後進行一系列XPS分峰探討，觀察材料表面經過電漿處理後的化學結構變化。
並列摘要
Plasma technology is extensively used in the etching of low-dielectric constant (low-k) materials in semiconductor industry. However, the low-k films are vulnerable to the damaged by plasma species during dry etching and ashing. This study focuses on gaining fundamental understanding on damage mechanism of low-k films under different plasma treatments. Detailed chemical analysis of the plasma-modified surface with depth profile was characterized by X-ray Photoelectron Spectroscopy (XPS) to investigate the change of molecular structure on the surface of SiOCH low-k films after plasma treatment. First, low-k films were treated by C2H2F4/CF4 and CF4 plasma to simulate the fluorinated surface which formed on low-k film after plasma etching. Then, an optional post-etch treatment (PET) step utilizing N2/H2 plasma was applied to re-condition the low-k film and create a fluorine-free and hydrophilic surface which is required for post-etch residue removal (PERR). After C2H2F4/CF4 plasma treatment, the results revealed that it gained a large amount of carbon and fluorine elements on the low-k film surface. With an increase of C2H2F4 ratio, the content of carbon and fluorine increased. Thus C2H2F4/CF4 plasma deposited a thin layer of fluorocarbon film on the low-k film surface. In contrast, it was found that a small amount of fluorine element was formed with a depth of several nanometers on low-k film surface by CF4 plasma treatment. Judging from the content of fluorine and the depth of fluorinated surface, we suggested that CF4 plasma created a fluorinated low-k film surface by etching/doping mechanism. After PET step, it showed that a large amount of carbon and fluorine elements on the low-k film surface were removed, and moreover, the content of fluorine almost disappeared. Furthermore, the content of carbon decreased with an increase of H2 ratio in N2/H2 plasma.