Dear fellow researchers,
I am currently trying to build thin film tantalum pentoxide integrated capacitors. I use 8''/200mm silicon wafers with a 100nm thick silicon oxide layer. I sputtered 200nm of TiW and on top of that 1 µm of copper. This I want to use as the bottom electrode. I then sputtered 250nm of tantalum and anodized it in a mixture of distilled water, tartaric acid and ethylene glycol at 120V and 80mA.
Now to my problem: I encountered a lot of defects on the tantalum pentoxide layer which I am not sure why (pictures are attached). My first guess was that maybe copper diffuses into the oxide layer during anodization, and causes these defects. This is why I then tried a slightly different setup. Everything was the same except that I now sputtered another 200nm TiW layer between the copper and tantalum layers. I now don't see these defects any more.
My question is if anyone else encountered this problem because I can't find any papers about copper diffusion during anodization. Also, I am not sure if it was copper diffusion or maybe a breakdown of the oxide layer or any other reason. I would find the diffusion of copper quite unintuitive because I read that tantalum is being used as a diffusion barrier for copper.
I would appreciate any ideas or confirmation of my theory.
Andrei Costina The issue with the anodization of thin film tantalum pentoxide integrated capacitors may be due to copper diffusion causing defects in the pentoxide layer. To resolve this, chemical analysis, alternative barrier layer materials, and anodization parameters adjustments can be implemented.
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- Ezhilvalavan, S., & Tseng, T. Y. (1999). Preparation and properties of tantalum pentoxide (Ta 2 O 5) thin films for ultra large scale integrated circuits (ULSIs) application–A review. Journal of Materials Science: Materials in Electronics, 10, 9-31.
- Duta, L., & Grumezescu, V. (2024). The Effect of Doping on the Electrical and Dielectric Properties of Hydroxyapatite for Medical Applications: From Powders to Thin Films. Materials, 17(3), 640.
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