Now, I'm analyzing the composition ratio of Cu8GeS6(Cu: 53 at%, Ge: 7 at%, S: 40 at%) varying the power, after using the sputtering deposition at following the base pressure, 9*10^-7Torr.
However, compared to the composition ratio of the Cu8GeS6 target, there are different results that Ge ratio is high and S ratio is low.
So, I plan to increase the base pressure by 1*10^-6Torr, but I wonder if this value affects the deposition ratio of each material in the target.
I knew that ratio is decreased and quality is increased when lowering the pressure, How much is it affected?
I want to know how I can increase deposition ratio of Sulfide, lowering Germanium. Also, Are there another variations?
Thank you very much if you reply my question.
Base pressure usually affect the deposition rate. For your sample , first you have to optimize the base pressure. Other parameters like sputtering power, gas flow rate and substrate temperature also affect the film's properties.
Dear Seo Shem,
I'll assume the base pressure you refer to is the pressure in the chamber before deposition, while the sputtering itself is performed at a higher pressure approx E-3 torr under an Ar atmosphere or the like?
The base pressure should then only impact your stoichiometry in terms of impurities (higher base pressure could f.e. result in oxyde formation, depending what residual gas is responsible for the high pressure).
If you want to investigate changes in deposition stoichiometry you can alter the processing pressure (pressure during deposition), substrate temperature and power. However, I don't know of a way to precisely predict the impact of these settings for your target.
If you want to change the stoichiometry in a controlled fashion one normally uses co-sputtering, where you have multiple different sputter targets with individually controlled power aimed at the same sample. This will give you MUCH more control if you have the experimental setup.
Cheers
Dear Seo Shem,
As much as I know, the base pressure doesn't affect compositional transfer from target to substrate, except some absolutely unusual cases (and anyway even in these cases the base pressure is much higher than the one you use, ~1e-4 mbar or something).
With your situation: I guess three effects could be responsible. First, the target sputtering can be non-uniform. This is cured by proper choice of processing pressure and by "training" of the target (prolonged sputtering to stabilize the surface composition of target). This is simple :), just don't forget to keep the target as cold as possible (RT cooling water usually is enough).
Much more complicated is selective scattering on the way from target to substrate. This effect can be diminished by increasing (or sometimes decreasing) processing pressure, but you cannot completely suppress it. Usually the effect is not very strong, try to use as big target as possible (compared to the sample size).
Finally, the deposited material can be selectively re-sputtered (or re-evaporated) from the substrate. Again, it is very difficult to completely get rid of this effect, try to decrease sputtering power or increase target-substrate distance to remove the substrate from the glowing area.
If you are lucky, one of these processes acts against two others... But this is quite rare. In general, it is almost impossible to get exact transfer of (multicomponent) target composition to the substrate when using sputtering processes.
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