Investigation on the Interfacial Stability of Copper/Tantalum Nitride/Dielectrics Multilayered Systems

• Main Authors: Ching-Chun Chang, 張景鈞
• Other Authors: Jen-Sue Chen
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/53194692128455136559

博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 94 === In this study, the characteristics of various Cu/Ta-N/dielectric /<Si> structures before and after heat treatment were explored. Dielectric materials with low dielectric constants used in this study were fluorinated silicate glass (FSG) and organosilicate glass (OSG). The FSG and OSG films were deposited onto silicon wafers in a single-wafer CVD chamber. Ta, Ta-N and Cu layers were then deposited sequentially on the dielectric layers by magnetron sputtering. The Ta-N films prepared with 1% and 5% of nitrogen flow ratio (N2/(N2+Ar)) are amorphous TaNx~0.5 and polycrystalline TaN, respectively. After deposition, all the specimens were annealed in vacuum at various temperatures for 60 min to investigate their thermal interactions. The experimental results indicate that the ability of the amorphous TaNx~0.5 film, to prevent copper and fluorine from diffusing, is superior to that of the polycrystalline TaN upon annealing at 800 oC in vacuum. However, TaNx~0.5 film degrades seriously after annealing at 900 oC. It is caused by the tensile stress produced as the Ta2N grains grow. On the other hand, bubble-like topography was observed on the surfaces of the Cu/Ta-N/Ta multilayers deposited on FSG but not seen for the multilayers deposited on OSG. It should be attributed to the significant stress produced by the release of moisture from the FSG film. The cross-sectional TEM bright-field micrographs of the Cu/TaNx~0.5/Ta/FSG/ <Si> show that voids were formed at the interface between TaNx~0.5/Ta bi-layer and FSG film after post metallization annealing. It is caused by the evolution of moisture from the FSG film. The formation of tantalum fluoride, lowering the adhesion strength of the Ta/FSG interfaces, can be observed by using X-ray photoelectron spectroscopy. The experimental results show that both of FSG and OSG are “stabilized” by pre-baking treatment (400 oC/30 min, in N2) before metallization. It means that the unstable Si-F bonds in the FSG film can be eliminated by thermal treatment. It is noticed that the dielectric constant of FSG film will decrease after annealing at 400 oC in vacuum for 60 min. By comparing the k values of as-prepared FSG with/without water-soaking treatment, it is clear that the main factor altering the k values of FSG is the moisture content. Pre-baking (400 oC in N2 ambient for 30 min) treatment is effective to drive the moisture out of the dielectrics and the water-soaking process brings the moisture back. Nevertheless, the 400 oC/60 min annealing further reduces the k values to be even lower than that of as-deposited FSG. It may be due to the loss of fluorine and/or the instability of the FSG structure. Therefore, the further reduction in the dielectric constant of the 400 oC/60 min-annealed FSG films is attributed to the decrease in the film density of the FSG dielectric layers upon annealing. On the other hand, the OSG possesses better water resistance and thermal stability. The functional groups incorporated in the OSG film will not be released upon annealing to 400 oC. In summary, this study investigates the influences of the moisture and unstable fluorine in the FSG dielectric layer on the integrity of the Cu/Ta-N/Ta/FSG/<Si> multilayer structure. In comparison, the specimens with the Cu/Ta-N/Ta/OSG/<Si> structure were also investigated. The results indicate that the moisture absorbed in the FSG film increases the dielectric constant drastically. Furthermore, leakage current density of the FSG dielectric layer is affected by the moisture content in the dielectric layer, too. This study shows that the outgassing from dielectrics might deteriorate the performance of the IC devices. Therefore, baking the FSG dielectric adequately prior to the subsequent metallization is essential.