Dear all,
I am currently trying to uniformly deposit organic semiconductor via thermal CVD at low pressure (around 10 Torr), but I sometimes get either no deposition or not homogeneous deposition on quartz and silicon slides, while it occurs everytime on Cu and glass. Someone has any hint to improve deposition on quartz and glass and can explain why?
thanks and best regards
Hi Paolo,
Could it be that some of your precursor molecules have low sticking coefficient on Si and SiO2? PECVD is a method where the reactions take place on the surface and sticking coefficient is important. Normal glass is SiO2 but CaO and NaO added to it. This might change the sticking behavior.
To improve the sticking coefficient you might try to change the substrate temperature or increase pressure (slowing down desorption). If this does not work, you need to consider a different substrate material to work on.
Check the substrate temperature distribution. Reduce gas pressure.These factors influence the deposition rate at some point, so checking these factors can enhance homogeneity. Also seeds can affect the homogeneity as Thomas mentioned.
Dear Paolo,
The most important thing is to enhance the nucleation of the organic materials on the intended substrate. This can be accomplished by creating atomic steps on the surface of the substrate to act as energetically preferable sites for the addition of the deposited molecules. You can enhance the mobility of the deposited molecules by heating the substrate at the highest possible temperature.
Other wise you can firstly deposit a very thin layer from a more suitable substrate.
Best wishes
Make sure that the cleaning process of Si is well done, as it involves organic materials, any residues may cause non uniformity or no deposition at some sites.
Temperature and pressure are factors as well.
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