鎢化鈦與鈦鎢氮化物薄膜應用於銅金屬化之擴散阻障層特性研究

Abstract

摘 要 在目前極大型積體電路的發展中，以銅作為導線引起越來越多人的注意，且進入深次微米製程，以銅取代鋁，做為金屬導線材料已成為必然的趨勢。為了克服銅與矽基材間相互擴散的問題，必須在銅與矽間鍍上具有低電阻係數、高熱穩定性及良好界面附著性的擴散阻障層。本實驗主要是在探討以TiW與TiWN薄膜做為銅與矽之間擴散阻障層的反應，由擴散、相變化的觀點來討論其變化。所採用的鍍膜結構如下： Si3N4(20nm)/Cu(100nm)/TiW(20nm)/SiO2(20nm)/Si Si3N4(20nm)/Cu(100nm)/TiWN(20nm)/SiO2(20nm)/Si Si3N4(20nm)//TiWN(20nm)/SiO2(20nm)/Si 在改變的氮/氬比例下以濺鍍法來沉積阻障層，再濺鍍銅膜，並利用PECVD沉積一層Si3N4，目的是避免退火過程中造成銅表面的氧化。對試片做450~800℃/ 30分鐘的氮氣氣氛退火處理，以四點探針量測片電阻，掃瞄式電子顯微鏡（SEM）用來觀察銅膜表面型態，歐傑電子能譜儀（AES）做成分縱深分析，X光繞射儀（XRD）做相的鑑定，並利用穿透式電子顯微鏡（TEM）做鍍膜截面的觀察，分析各層結構的變化。 研究結果顯示這幾種不同的結構在退火後有不同的行為，Cu/TiW/SiO2/Si結構與Cu/TiWN/SiO2/Si 結構（Ar-10%N2）分別在650℃與800℃/30分鐘退火後片電阻值明顯上升，約為976 與1116 mΩ/□，阻障層與銅膜產生銅-鈦析出物，顯示阻障層已經失去了阻絕銅擴散的能力。Cu/TiWN/SiO2/Si結構（Ar-16.6%N2與Ar-30%N2）在700℃退火後片電阻值有明顯的上升，其原因為表面銅膜產球化不連續的結團所導致。 由實驗結果可知Cu/TiWN/SiO2/Si 結構（Ar-16.6%N2），電阻值低，且具有高的熱穩定性。因退火過程中，TiWN阻障層產生變化，其變化原因將於本文中討論，氮元素在其中扮演了重要的角色。

Abstract Copper has attracted a lot of attention as a promising interconnect material in the fabrication of deep sumbmicro devices of ultra-large scale integration circuit devices due to its lower resistivity and better properties than conventional Al alloys. Since Cu diffuses fast in Si and forms deep-level trap defects, a proper diffusion barrier is needed. The barrier should have low resistivity, high thermal stability, and good adhesion with Cu and substrate. In this study, we investigate the diffusion barrier properties of TiW and TiWN thin films for Cu metallization in ULSI circuit device. The following structures are used: Si3N4(20nm)/Cu(100nm)/TiW(20nm)/SiO2(20nm)/Si Si3N4(20nm)/Cu(100nm)/TiWN(20nm)/SiO2(20nm)/Si Si3N4(20nm)//TiWN(20nm)/SiO2(20nm)/Si Copper and barriers were deposited by DC sputtering. The barriers were deposited by varying the N2/Ar ratio. Subsequently, a Si3N4 was deposited by plasma enchanced chemical vapor deposition (PECVD), in order to prevent the Cu surface from reacting with oxygen during annealing process. Annealing was carried out in nitrogen ambient at temperatures from 450 to 800 ℃ for 30 min. Sheet resistance was measured by a four-point probe method. Copper surface morphplogy（AES）was inspected by scanning electron microscopy（SEM）. Auger electron spectroscopy was used to evaluate the inter-diffusion across the interface by the compositional depth profile. The phase identification of layers was performed by XRD. The microstructure was investigated by cross-sectional transmission electron microscopy（TEM）with X-ray energy dispersive spectroscopy（EDS).Sheet resistance measurement and microstructural characterization showed that these structures have different behaviors after annealing. The barriers of Cu/TiW/SiO2/Si and Cu/TiWN/SiO2/Si structures deposited at the condition Ar-10%N2 mixtures were failed after annealing at 650℃ and 800℃ for 30 min due to the formation of copper-titanium related precipitate in Cu film. Sheet resistances of Cu/TiWN/SiO2/Si structures fabricated at the conditions of Ar-16.6%N2 and Ar-30%N2 after 700℃ annealing due to the spheroidization of Cu films. From these results, the structure of Cu/TiWN/SiO2/Si fabricates at the condition of Ar-16.6%N2 has low resistivity, high thermal stability. It is suggested that nitrogen plays important roles on the thermal stability.