A Study on Electrochemical and Barrier Properties of Cobalt-tungsten Alloy as multi-purpose diffusion barrier for Next-generation Cu metallization

論文翻譯標題: 鈷鎢合金多?能阻障層應用於次世代金屬銅製程之電化學及阻障特性研究
  • 曾 煒翔

學生論文: Master's Thesis


As integrated circuits (ICs) are scaled down to deep submicron regime the impact of interconnect RC delay is becoming increasingly serious One of the realistic methods to solve the issue is using Cu as the conductor for multi-level interconnects to reduce the resistance However Cu has high diffusivity To prevent Cu from diffusing into dielectric materials under high electric fields and temperature a barrier layer is needed Moreover wetting layers deposited on barriers are commonly used to enhance the Cu electroplating ability on the barrier layers In this study we try to find out whether the cobalt-tungsten (CoW) alloy can be used as a combination of the barrier layer the wetting layer and the direct electroplating layer which we call a “3 in 1 layer” to replace the traditional metal stack To investigate its material properties the CoW thin films were deposited by sputtering Different W/Co content ratio was controlled by various W RF power In this study the plating ability was investigated The behaviors of direct Cu electroplating on different barrier metal including thin Co CoW W and Ta/TaN films were investigated We demonstrated that Cu could be electroplated on the CoW films with more uniform distribution of Cu nuclei The Cu nucleation behaviors on the CoW substrates changed with the sputtering RF power Potentiodynamic sweep methods including potential dynamic curves (Tafel plot) and cyclic voltammetry stripping (CVS) curves were used to help interpret the electroplating results The wetting ability was also investigated in this study The SEM images of the Cu/Ta/SiO2 Cu/Co/SiO2 Cu/CoW/SiO2 Cu/W/SiO2 structure after annealing for 30 min at 400 °C shows that pure Co has the best wetting ability to Cu There are less pin holes on the surface of pure Co compared to those of CoW substrates With W adding into the Co the wetting ability degraded due to smaller adhesion coefficient of W The amount of pin holes on the surface of Cu/CoW/SiO2 structure with W RF power of 60 W is still comparable to the surface of Cu/Ta/SiO2 structure Finally the anti-diffusion ability of the CoW films was investigated The change in sheet resistance versus time and temperature of the Cu/CoW/Si films were used to monitor the formation of Cu3Si It is shown that with W RF power of 50 W and 60 W the CoW films is able to prevent Cu diffusion until annealing temperature higher than 600 °C The SEM images of the Cu/CoW/Si films after annealing 30 min at 400 °C also indicated that W with 60 W RF power the formation of Cu3Si can be avoided
獎項日期2014 八月 19
監督員Wen-Shi Lee (Supervisor)