利用電漿輔助化學氣相沉積系統製備低介電碳氮化矽薄膜之研究

Abstract

本論文致力於研究與發展低介電碳氮化矽薄膜，作為銅導線後段內連接製程的擴散阻障層或蝕刻終止層以進一步降低等效介電常數來迎合先進半導體製程上的需求，並且針對其緻密的與多孔性的碳氮化矽薄膜在不同沉積溫度下之物理特性、電性量測和孔洞形貌進行一系列的探討，另外也對該薄膜結構與性質間的關係進行深入研究。 首先，利用電漿輔助化學氣相沉積系統於低電漿功率密度以及不同沉積溫度的環境下選用具有Si-N-Si環狀結構和三個乙烯基的單源前驅物1,3,5-trimethyl-1,3,5-trivinylcyclotrisilazane (VSZ)來沉積低介電碳氮化矽薄膜。薄膜的結構與性質的關係最主要是受到沉積溫度的影響，在低沉積溫度時，因為碳氮化矽薄膜中保有大部分VSZ的環狀結構，致使該薄膜具有較低的薄膜密度(1.60-1.76 g/cm3)、低的介電常數(k~3.6-3.9)以及22.0-25.0 GPa的彈性模數，而當沉積溫度提高時，Si-N-Si的環狀結構會轉變為較緻密的結構並伴隨著CHx鍵結的脫附而導致薄膜具有較高的密度(2.0 g/cm3)、4.6的介電常數以及卓越的彈性模數(65.2 GPa)。此外，根據低掠角小角度X光散射(Grazing-incidence small-angle X-ray scattering)實驗分析顯示，該碳氮化矽薄膜含有奈米孔隙度並且在低沉積溫度會有短程有序的排列。 接下來，我們為了要進一步的探討多孔性的低介電碳氮化矽薄膜，因此額外添加了孔洞劑(porogen) epoxycyclohexane (ECH)進入VSZ前驅物的進氣流中，實驗得知，孔洞劑的流量、沉積溫度以及經退火處理後的薄膜收縮率都是控制其薄膜孔隙率以及孔洞尺寸的關鍵因素，進而該孔洞形貌也會主導著薄膜的特性 (例如：介電常數以及彈性模數)，在本研究之中的最佳參數可以得到具有19.8%的孔隙率、3.7nm的孔洞大小、3.18的介電常數以及7.7GPa的彈性模數之低介電多孔性碳氮化矽薄膜。

In this thesis, novel low dielectric constant (low-k) silicon carbonitride (SiCxNy) films were developed and fabricated as the diffusion barrier/etch-stop layer for copper backend interconnects application. The objective is to reduce the effective dielectric constant in order to meet the requirements of advanced technology nodes as the device scales according to Moore’s law. In addition to film deposition of dense and nanoporous SiCxNy films at various temperatures, their film densities, dielectric properties such as dielectric constant, dielectric breakdown and leakage behavior, mechanical property such as elastic modulus, and pore morphology were characterized. The structure-property relationship of low-k SiCxNy films was also examined. In specific, low-k SiCxNy films were prepared by radio frequency plasma-enhanced chemical vapor deposition at 25 to 400oC under low power density of 0.15 W/cm3, using a single source precursor, 1, 3, 5-trimethyl-1, 3, 5-trivinylcyclo- trisilazane (VSZ), which has cyclic Si-N-Si linkages and three pendent vinyl groups. Relationship between structures and properties of the SiCxNy films were predominantly affected by the deposition temperatures. At ≤ 200oC, most cyclic VSZ structures were preserved in the SiCxNy films, resulting in a lower density (1.60-1.76 g/cm3), a lower dielectric constant (k~3.6-3.9) and a fairly good elastic modulus of 22.0-25.0 GPa. When the deposition temperature was raised, the cyclic Si-N-Si linkages were reformed to a dense Si-N structure, with the desorption of CHx bonds, resulting in higher density (2.0 g/cm3), a dielectric constant of 4.6, and an excellent elastic modulus of 65.2 GPa. Moreover, according to grazing-incidence small-angle X-ray scattering analysis, the SiCxNy films possessed nano-porosity with pore sizes of 3.3-4.9 nm, and a short-range pore ordering arrangement was observed only at low deposition temperatures. Next, a sacrificial porogen, epoxycyclohexane (ECH) was added to the feed stream of the VSZ precursor in order to explore and fabricate nanoporous low-k SiCxNy films with higher porosity. We found that the porogen loading, deposition temperatures, and film shrinkage upon the removal of porogen during post anneal were critical in determining the porosity and pore size of SiCxNy films. Subsequently, the film properties (e.g. dielectric constant and elastic modulus) depended mainly on the pore morphology. Optimized processing parameters facilitated the fabrication of low-k porous SiCxNy films exhibiting 19.8% porosity, 3.7-nm pores, a k value of 3.18, and an elastic modulus of 7.7 GPa.