A Study on Electrochemical and Physical Properties of Tantalum Ruthenium and Cobalt-based Materials as Multi-purpose Diffusion Barrier for Next-generation Cu Metallization

Abstract

As the gate length of semiconductor devices shrink down to 45 nm and beyond the width of metal connects shrink at the same time and the impact of RC delay become increasingly serious The first part of this study is discussing the method of improving the step coverage of barrier layers and lowering their resisvitiy at the same time in narrow damascenes opening In order to improve the step coverage of physic vapor deposition (PVD) process a new method called ionized metal plasma PVD is widely used as an alternative to conventional PVD method In this study we found that great improvement in step coverage can be obtained through changing substrate bias voltage by radio frequency (RF) power For Tantalum-based (Ta-based) materials Tantalum nitride (TaNx) is served as a copper diffusion barrier by its amouphous structure and Ta is ued as a wetting layer of Cu This stack structure with TaN first and than Ta deposit becomes a well solution for a Cu barrier layer In this work creating substrate bias voltage after TaN deposition is used to generate plasma bombardment on TaN films As the level of bombardment increase the sequentially deposited Ta wetting layer will change from high-resistivity ? phase to low-resistivity ? phase Meanwhile we found that increasing nitrogen (N2) content makes TaNx change from Ta-like column structure to amouphous structure As TaNx films are deposited with higher N2 flow sequentially deposited Ta layers can form low-resistivity ? phase with lower level of plasma bombardment The second part of the study is to discuss the interaction of sequential Cu deposition and chemical mechanical polishing (CMP) on Ta barriers with different preferred orientation Cu seed layers deposited on ?-Ta shows a weaker Cu (111) out of plane orientation than ones deposited on ?-Ta With regard to the lattice correlation ?-Ta with loose structure will not limit the growth of PVD Cu seed out of its plane orientation On the contrary ?-Ta constrains the growth of Cu seed and lead to formation of such mismatch structure For Cu gapfilling previous research have pointed out that Cu twin structure can effectively prevent electromigration In this work we demonstated a simple method to insert an interlayer within the ECP Cu film and form Cu twin structure The interlayer deposited in the condition of low plating current and high rotaional speed shows carbon-rich (C-rich) charateristic This kind of interlayer suppresses the rate of Cu self-annealing and further induces the formation of Cu twin structure The third part of this study is focused on novel materials for seed-less barrier layers which should demonstrate good thermal stability and wetting ability at the same time The physical and electrochemical properties of N-doped Ru and W-doped Co with different atomic ratio were investigated Results show that RuN demonstrates no Cu diffusion into silicon Electrochemical studies by impedence spectroscopy and cyclic voltammetry show that both Ru and RuN are suitable for Cu direct-plating However we found that Co is easy to be dissolved in acidic Cu-plating bath By adding W into Co the anti-corrosion capability of Co-based material is dramatically improved thus making it a possible solution as a multi-purpose barrier for next-generation Cu metallization

Date of Award	2014 Jul 25
Original language	English
Supervisor	Wen-Shi Lee (Supervisor)