Sputtering requires a considerable amount of pressure within the deposition chamber, though I fail to understand why. For example, in DC sputtering, the atoms or ions coming off the target after ion bombardment, can anyway reach the substrate if it is maintained at the right bias. So why is there a need to create high pressure, hence sustain the plasma?
You have to ionize some of the gas that you will use for sputtering process. Although you will get some ions produced as a result, many will "die" instantly as they collide with the deposition chamber, only a small minority will be left to ionize more gas (and sustain the plasma).
As such you need to ensure the pressure of the sputtering gas is high enough that there is a good probability that one of your "re-sputtered" ions will actually collide with, and ionise further gas atoms before it reaches the walls of the chamber itself.
By way of reference see:
https://vacaero.com/wp-content/uploads/2018/08/Fig-2.gif
At 10-5mbar the mean free path is about 1m (so assuming our "re-sputtered" ion doesn't feel any immediate electrostatic attraction, at this pressure it can travel 1m before it encounters a gas molecule that it might have a chance to ionize).
As you stated correctly, the ions are the actors that actually do the sputtering process. Now, if you want a sustainable, continuous sputtering process, you also require a continuous stream of ions which need to be generated all the time because once an ion hits the chamber wall, it loses its charge. That's why you need the high pressure.
The second point for continuity is that the ions must be generated somewhere. If you use sputtering for surface purification, this is achieved by an electron beam from a filament while in your case that's the role of the plasma: a plasma is a phase that consists of ionized species in various states which also make it conducting. These ions in turn ionize other gas atoms thus providing an "ionization-charge loss-equilibrium" which enables the continuous operation.
You have to ionize some of the gas that you will use for sputtering process. Although you will get some ions produced as a result, many will "die" instantly as they collide with the deposition chamber, only a small minority will be left to ionize more gas (and sustain the plasma).
As such you need to ensure the pressure of the sputtering gas is high enough that there is a good probability that one of your "re-sputtered" ions will actually collide with, and ionise further gas atoms before it reaches the walls of the chamber itself.
By way of reference see:
https://vacaero.com/wp-content/uploads/2018/08/Fig-2.gif
At 10-5mbar the mean free path is about 1m (so assuming our "re-sputtered" ion doesn't feel any immediate electrostatic attraction, at this pressure it can travel 1m before it encounters a gas molecule that it might have a chance to ionize).
The sputtering in magnetron is performed by ions from the plasma, generated above the target. The ion sputtering is a specific process, which can be characterized by sputtering rate (nm/s) and sputtering yield (atom/ion). For low energy sputtering (the ion energy less than 1keV), realized in most magnetron, the sputtering rate and yield are quite low. So, if you want a high sputtering efficiency and, as a consequence, a high deposition rate, you need increase the number of ions, or ion current. One way is to increase the ionization efficiency in plasma: this is a reason for using of magnets in magnetron. In magnetic field electrons of the plasma moves by cycloid trajectories (spirals) and the ionization probability (electron impact ionization of argon) increases. Another way is to increase the gas atom concentration (pressure) to get a higher ionization and a higher ion current.
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