Hello

i got this issue in the past; We called them polysilicon filaments or "worms". We traced it back to the equipment exhaust pipes which were not 316 stainless steel as specified. The metallic contaminants were able to backstream into the deposition chamber.Once the exhaust pipes were changed, the issue disappeared.

Hope this helps;

Hervé

Thank you  Hervé. Any information is welcome. I will try to go further  in  the  investigation  using  your  input.

Regards

Mohamed