碳基介電薄膜的製備與其應用在ULSI連線技術之特性評估

Abstract

本實驗嘗試以無柵極離子束沉積法(gridless ion beam deposition，GIBD)及電漿輔助化學氣相沉積法(plasma-enhanced chemical vapor deposition，PECVD)分別製作非晶質碳及碳化矽薄膜，並且探討其漏電流及介電常數等特性及其應用在銅製程中蝕刻阻止層的可能性評估。 首先利用GIBD法在常溫下以乙炔(C2H2)及氬氣(Ar)混合氣體沉積非晶質碳膜，並加以退火及氫電漿處理來改變薄膜特性。經拉曼分析結果顯示，ID/IG強度比及D特徵峰波數(wavenumber)皆隨著乙炔流量的增加而減小，乙炔流量增加至60 sccm時有類鑽石(diamond-like)化的最佳條件，因此我們利用此條件所形成的DLC膜再分別作真空退火及氫電漿處理，探討其對DLC膜之特性影響，結果顯示DLC膜隨著退火溫度增加，ID/IG強度比逐漸地增大，同時薄膜密度也由3.44 g/cm3減小到2.89 g/cm3，而退火溫度從200℃至300℃時漏電流密度會逐漸的增大，推測此現象可能是因退火時造成薄膜中的碳逐漸石墨化所致。另外經氫電漿處理後的DLC膜則隨著處理時間的增加而漏電流逐漸減小，經氫電漿處理6分鐘後的漏電流密度為3×10-7 A/cm2 (在1 MV/cm的電場下)，明顯低於未經處理之DLC膜(1×10-4 A/cm2)，介電值為3.4也明顯低於未經氫電漿處理的DLC膜介電值(3.83)。 其次，利用PECVD法來沉積碳化矽薄膜時，以矽烷(SiH4)及甲烷(CH4)之混合氣體作為反應氣體源，基材溫度保持在250℃下沉積含氫非晶質碳化矽(a-SiC:H)薄膜。並分別以薄膜測厚儀及汞探針電性量測系統量測薄膜的厚度及介電常數，結果顯示，隨著甲烷流量的增加，薄膜的沈積速率、折射率及介電常數皆明顯的減小。以5%的矽烷濃度最佳條件下所形成的碳化矽(C/Si:68/25)膜的折射率為1.76、介電常數為3.6、漏電流1.79×10-8 A/cm2 (在1MV/cm的電場下)為最小及沉積速率為1.32 Å/s。再將此碳化矽薄膜分別施以氫(H2)及氨(NH3)電漿表面處理，結果經氨電漿表面處理後的薄膜除了表面粗糙度較氫電漿處理的表面粗糙度大外，薄膜表面會形成氮化層，致使薄膜漏電流密度明顯的降低，而經氫電漿表面處理後的薄膜表面碳含量皆隨著處理時間的增加而減少的同時漏電流密度亦有降低的趨勢。

The purpose of this work is research the dielectric properties of a-C and a-SiC:H films, deposited respectively by using gridless ion beam deposition (GIBD) and plasma-enhanced chemical vapour deposition (PECVD), to evaluate the possibility for using in the etching-stop layer of copper interconnect technology. Amorphous hydrogenated carbon (a-C:H) films were deposited from gas mixtures of acetylene (C2H2) and argon (Ar) in a GIBD system supplied with dc power. Vacuum annealing and hydrogen plasma treatment were performed on the a-C:H films and their effects on the physical and electrical characteristics of the films were investigated. The structure and properties of the film were investigated as functions of the C2H2 flow rate, using Raman spectroscopy. The Raman spectra revealed that the Raman ID/IG ratio and D peak position decreases with C2H2 flow rate, indicating more diamond-like character of the films. Otherwise, the annealed a-C:H films exhibited that the Raman ID/IG ratio increases with annealing temperature, but the film density decreases simultaneously, indicating more graphite-like character for the annealed films as the annealing temperature was increased. The dielectric constant of the annealed a-C:H films was reduced from 3.8 to 2.9, but the leakage current density was obviously increased while the annealing temperature was increased from 200℃ to 300℃. However, the leakage current density and dielectric constant of the hydrogen-plasma-treated a-C:H films were clearly lower than those of the as-deposited a-C:H films. Amorphous SiC:H films were deposited from a mixture of silane and methane gases, using PECVD. Reducing the ratio of the silane flow rate decreased the deposition rate of the a-SiC:H films, decreasing the refractive index and dielectric constant, but increasing the optical band gap and the hydrophobicity of the surface. It has a minimum refractive index (1.76), dielectric constant (3.6), leakage current density (1.79×10-8 A/cm2 at the electric field of 1MV/cm) and deposition rate (1.32 Å/s) for the concentration of silane, which is 5% in the mixture gas. XPS data indicate that the carbon concentration of the a-SiC:H films declined as the methane flow rate increased, but the silicon concentration increased. Carbon-rich films were treated with hydrogen and ammonia plasma for various periods, but were then converted into films with higher silicon content. Increasing the ammonia or hydrogen plasma treatment duration roughened the surface, even though the original film had a smooth surface, with a roughness of 0.231 nm. Ammonia plasma treated film has larger roughness (1.741 nm) than that of by using hydrogen plasma treated films (0.829 nm). The ammonia ionization species reacted with Si to promote the formation of silicon nitride. Accordingly, the leakage current density of a-SiC:H films declined as the ammonia plasma treatment time decreased, but the dielectric constant slightly increased. As expected, the leakage current density and the dielectric constant of a-SiC:H films declined as the hydrogen plasma treatment period increased.