低介電常數材料與銅之可靠性分析與製程整合之研究

Abstract

摘 要 本論文研究低介電常數材料MSZ (Methylsilsesquiazane)薄膜與多孔性的二氧化矽(porous methylsilsesquiazane)在此簡稱PPSZ薄膜，在積體電路（IC）製程整合的技術和可靠性分析。多孔性的二氧化矽（PPSZ-M）薄膜由於具有多孔的結構，介電常數將有效的降低，但是相對的機械強度一般來說都較緻密的材料差。由於在積體電路的製造技術中，光阻的去除常是利用氧電漿處理的方式來將光阻中的碳氫成份分解，達到光阻灰化的目的。本論文將探討兩種薄膜經氧電漿處理後對於不同金屬導線(銅和鋁)之可靠性分析，實驗結果顯示經氧電漿處理後MSZ與PPSZ的表面都會受到破壞並且有吸水的現象，漏電流上升的大小由吸水的多寡決定，高溫漏電流較小而室溫則較大，對於銅電極而言因為吸水會有較多的銅氧化形行氧化銅，因為大量的氧化銅存在導致高溫、高電場下BTS會有銅離子的擴散，其漏電流的傳導機制是Poole-Frenkel Transport，在此情況下漏電流除了吸水的效應外還需進一步考慮銅離子擴散，但對於鋁電極而言漏電流的上升則只有吸水的效應。PPSZ 薄膜固然有較低的介電常數但相對的由於其多孔性易受氧電漿之破壞與易吸水，所以銅的擴散導致漏電流的上升和可靠性的下降較非多孔性薄膜來的嚴重，但是若以CMP(chemical-mechanical polish) 有效的去除被氧電漿破壞並且吸水的薄層則其低介電常數的優勢又可再度展現出來.

Abstract In this thesis, we will investigate on reliability and process integration of low dielectric constant material MSZ (Methylsilsesquiazane) and PPSZ (porous Methylsilsesquiazane). The lower dielectric constant of porous low k material is due to porous structure. However, the mechanical strength of porous low-k materials is worse than that of dense materials. In the present IC manufacturing processes, photoresist stripping is commonly implemented with O2 plasma ashing. We will investigate the reliability of these two low-k material with copper and aluminum electrode after O2 plasma ashing. The experimental results show that a damaged layer was formed on MSZ and PPSZ surface after O2 plasma ashing. It will result in moisture absorption. The leakage current and dielectric constant of MSZ and PPSZ with O2 plasma ashing will effectively decrease after CMP process due to removing the damaged layer on the surface. CuxOy is formed between Cu and surface of MSZ and PPSZ. It will be ionized into Cu+ ion and diffuses into MSZ and PPSZ during high temperature and bias stress. The leakage mechanism of MSZ and PPSZ with O2 plasma ashing at high temperature after high temperature and bias stress are also Poole-Frenkel Transport. The dielectric constant increase and moisture absorption of PPSZ film are greater than MSZ film after O2 plasma ashing. Copper diffusion in PPSZ is greater than MSZ film in same O2 plasma condition and the reliability of PPSZ film is not as good as MSZ film. As a damaged layer formed on PPSZ surface can be effect removed by CMP (chemical-mechanical polish), the advantage of low dielectric constant will reappear.