I would like to know what kind of materials should be avoided in sputtering processes. I deposit evacuating the chamber around 10^-6/-5 mbar and at working pressures around 1x10^-3 mbar. By the moment I am considering using new materials to deposit different alloys, and because of that I would like to know what materials could generate outgassing around those values. The vacuum chamber is not intentionally heated and therefore the temperatures used are around 60 ºC.
The list of materials is infinite (practically), so it is unreasonable to ask for it. You have to check vapour pressure of the materials you are intending to use. Look at manufacturer's specs: if they are vacuum compatible you will find vapour pressure tables as a function of pressure. If you really need to know then fit a quadrupole to your chamber, add the materials you want to test and look directly at the outgassing species.
Dear Chris, thank you for your response.
In order to narrow this matter I would like to ask specifically for metals that should not be used in sputtering processes. As I said before, I want to deposit alloys and Im not aware of metals that should be avoided for those ranges. As you said I could measure it, but in this moment I dont have the resources to do it. As I want to test and calibrate some properties of alloys containing metals with high relative thermal expansion coefficients, I would like to know experiences you already had with metals as Cd, Zn and Sb on this ranges.
The most dangerous are materials with high vapour pressure at your process temperature; the most common of them is Zn and Zn alloys like brass which are deadly even at room temerature. Not only the working atmosphere is contaminated but all the inner walls of the chamber from where the material will reevaporate during the following processes ==> if you want to work without that zinc you have to clean your equipment completely.
Other bad materials are the porous ones - works as a virtual leak. Similar for laminated materials and rough surfaces. Really, the list is pretty long as Chris said.
The first question to be answered is : what is the tolerable outgassing rate? for this you should determine the outgassing of your basic system (vessel+ancilliaries) i.e. the limit pressure after a given pumping time multiplied by the pumping speed at the gauge position. This will give you the tolerable extra outgassing: 1%, 10%...(your choice) of the basic outgassing. This divided by the area of the extra material introduced gives the tolerable specific outgassing rate. The most popular vacuum text book show the specific outgassing rate of many materials in use in vacuum systems.
As mentioned before high vapour pressure metals (Cd, Zn..) must be avoided, the possible excessive outgassing problem with alloys of these metals is more questionable (e.g. brass) and depend on the application. Avoid all porous materials (and weld!!!) (a limit for the pore size is difficult to determinate) but all elastomers are porous and widely used in vacuum systems.
Finally perhaps as much as the material itself, the preparation (cleaning) of the surface is determinant for the outgassing rate.
I can only agree that between the metals, zinc is the worst for vacuum enviroment. Many years ago I had a problem with sample holder made from brass, which was heated in uhv. The chamber was practically coated with Zn and the cleaning process (mechanical) was very long and boring.
Zn and floating including this element (brass) because it have maximum of sputtering yield!
Google "rca vapor pressure charts" to get numbers for the vapor pressure of the elements as a function of temperature. You should be able to find charts describing the vapor pressure of compounds as well, though compounds are not included in Honig's (i.e., RCA) charts.
I once came across this useful resource from Agilent Technologies (no affiliation). See the section on "Materials". It is not an 'infinite list' (vapor pressures of donuts and my keyboard are not included), but it does include many common materials that could be questionable for UHV.
Disclaimer: This handbook was originally accessed and available online via google search.
it's a general question and for different material are difference. for annealing all of the material, first u need calculation absolute melt point, because after this point you have evaporation, It can contaminate in your chamber. if your sample has more different melt point, u need to use quartz tube for avoiding from this kind of problem. during the annealing also u have sublimation.
You are planning to use those metals that have bad vapour pressures. So there is no way to avoid these materials since you want their alloys. So you need larger pumping system to maintain good vacuum. If you are wanting to study the alloys of certain metals that you have mentioned you need to use them!!!!!..
Only way is to optimize the system. Use small targets and large pumping system.
To Dunja Popovic:
Can you explain me what is your UHV chamber contaminated with?
Hello,
I wouldn't call the system with an operation pressure of 10^-6/-5 mbar an UHV one. This is a rather "medium" high vacuum, and even Zn and brass are not so bad in it unless you heat them above some 50-100 Celsius degrees (for more precise values, please see the vapor pressure dependencies).
There are definitely much-much worse materials like Sb, As and Hg, but I'm pretty sure you're not going to deposit them :)
what about materials containing sulfur, posfur, boron, and halides, does the copper o'rings compatible with such materials?
Just avoid like the plague or pest Selenium. I did not understand 30 some years ago why nobody in th eLab I was working wanted to deposit thin films containing selenium; fast forward 10 years ago we ran a Selenium beam for the NSCL Lansing cyclotron program, and it stayed with us ever since; mercifully the cyclotron was decomissioned last november !
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