Dear Karyn,

Very familiar problem you have there. Once plasma chambers are contaminated with fluorine, it is extremely difficult to get rid of F, HF (see Chapman, glow discharge processes).  Since nobody is using F-samples your suspicion about the Teflon is right. In plasma's it does not get sputtered off but Teflon reacts with oxygen species in the plasma and creates besides CO2 also fluorine and HF. It is my own experience from semiconductor technology that especially in oxygen plasma's teflon components degrade. You won't see chars but eventually the Teflon will become rough and will start to shed particles. Since the memory effect of fluorine in plasma systems is large, try to get rid of the teflon plate first by exchanging it for a different material, stainless steel, glass or ceramic and then do multiple vent/pump/O-plasma runs to get rid of the HF absorbed to the chamber walls. Hope this advice helps.

regards,

Peter 

At our lab we are also using the thick teflon plate as a dielectric layer. With RF you have to use thick dielectric plates, so often the teflon is used as a cheap and easy adjustable dielectric. We never experience the problem with Fluorine contamination  during  the O2 treatment or due thin film deposition. Perhaps you have some shorting on the teflon, but definitely it can be fixed, just open the electrode and check it.  I got a feeling that it is more probable that sometime before, your reactor was used for C2F6 or SF6 teratment and your walls still have contaminations. You can deposit SiO2 layer from HMDSO plasma in order to coat the contaminating part and easily check this possibility. If after deposition of 300-500 nm of SiO2 layer you will detect the F again, definitely you have problems with RF electrode. Good Luck.

Yep, it's definitely the teflon. If you don't have much thermal expansion to fear, you can substitute the teflon insulator with one made of MacorTM, which a machinable glass ceramics (it can even stand much higher temperatures than teflon but it is more rigid - that's why you have to take care that not too much thermal expansion is taking place).

That should solve your problem.

It is defuinitely teflon contamination. Very well known problem. Just substuitute the teflon plate with Alumina or Macor.

Thanks everyone for your useful suggestions. Replaced the Teflon disc with an acrylic one, and the F contamination decreased to 2 %. Now to get rid of the residual F in the reactor! Currently looking at getting a permanent replacement for the Teflon made from Macor. 

Hi Karyn,

Good to hear it worked. One last remark, If you cleaned out the system and did multiple O2-runs and you still find fluorine think about changing the pump oil (or do it preventively). With rotary pumps the oil probably also got contaminated and you usually get some oil back diffusion into the chamber, expecially when you pump the chamber to low pressure (idle situation) and leave it for longer times unused. If there is no N2 bleed on the pumping line (which prevents back diffusion) you will get that back diffusion in some degree.

kind regards,

Peter

 I am sure that the flourine is highly electro negative its value is -4 which is too high and in the high temperature its ionization potential is low then the flourine is free for deposit or move to its original position. Please weigh the or calculate the amount of flourine before and after. U can use the material in place of flourine you can use Bromine coating also.

Pls tell me your observations if u get help of my idea.

Thanks & Regard

Kamran Ahmed