I use RGA to scan my sputtering chamber and the pressure of H2 is 10-8 torr, which makes it very hard to further pump down the chamber. I know that oxygen can be removed by sputtering some Ta, but how about hydrogen?
And also it looks like that my MgO target abosrbs some water when exposed to air. After sputtering some MgO, the pressure of hydrogen and water is very high in the chamber. Does anyone have some idea on solving this?
High Jiacheng,
This is a very typical but not solved completely problem for all vacuum systems.
First, there is a quite low concentration of H2 in air, so, the main source of hydrogen in vacuum chamber is water.
If you reach 10-9 Torr by using a turbo pump, you can find up to 90% of hydrogen among all residual gases - this is the result of low efficiency of turbo pumps for hydrogen removing. For 10-8 Torr the water desorption from all internal surfaces still form the hydrogen background.
So, there are different solutions depending on your actual situation.
To remove water vapor, you can make a back-up of your system: 180oC for 24-48 hours is a standard for MBE system, but this is necessary for 10-11 Torr. For your system 24 hours at 100oC will be enough.
Another option is to use a cryo pannel with LN to remove water.
If it will be enough but you need
Jiacheng Shi
I think there's a different scenario - hydroxyl (- OH) groups on the surface of the MgO rather than free water or H2. MgO (and Mg) react with water to produce Mg(OH)2. I think that you need to argon ion etch for 10 - 15 atomic layers to remove the reacted Mg(OH)2 and get to the free MgO.
Thermal outgassing or high temperature bake out in inert atmosphere may help in removing hydrogen from sputtering chamber.
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