Control of reactive sputtering processes

The method of reactive gas control during reactive sputtering strongly influences the deposition rate and film properties of the compound being deposited. Flow control of the reactive gas is the simplest method, but since reactive sputtering is typically done in the compound or poisoned mode of the target, the deposition rate is low compared to the rate from the elemental target. In addition, the film properties produced by flow control reactive sputtering are less than optimal. Partial pressure control of the reactive gas is more complex than flow control because it requires active feedback control, but it allows operation of the process in the transition region between the elemental and poisoned states of the target. By operating in this region, higher deposition rates compared to flow control are achieved, and the film properties are improved. Reactive sputtering of insulating films requires the use of the right type of power to prevent arcing on the target, which is detrimental to the quality of the deposited films. Both pulsed dc and mid-frequency ac power prevent arcing during the reactive sputtering of insulating films. Arc prevention eliminates droplet ejection from the target and allows the reactive deposition to occur without large fluctuations in the reactive gas partial pressure, often a result of uncontrolled arcing. Ternary or quaternary compounds can be reactively sputtered using dual magnetron set-ups and multiple reactive gases. Multiple reactive gases present an additional control problem in that one of the reactive gases can trap the target in the poisoned mode unless the partial pressures of both reactive gases are individually controlled. Reactive sputtering with high power pulsed magnetron sputtering, which provides a high degree of ionization of the sputtered species, is possible for insulating films as long as the partial pressure of the reactive gas is controlled and arc detection and suppression is available on the power supply.

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