Calculation of the effective gas interaction probabilities of the secondary electrons in a dc magnetron discharge

Abstract

In sputter magnetrons the electrons emitted from the target, the so-called secondary electrons (SE), can be recaptured by the target. As a result, not all emitted SE will interact with the discharge gas. The effective gas interaction probability (EGIP) is the probability that an emitted SE interacts with the discharge gas, and thus is not recaptured by the target. To calculate the EGIP an analytical model is developed. The model is verified by comparing its results with those of a Monte Carlo model.The EGIP of an individual SE is strongly, and in a complex manner, dependent on the electric and magnetic field to which the electron is subjected and on its initial starting conditions. Therefore, it is useful to introduce the average EGIP of the discharge which is a weighted average of the individual EGIP values. The influence on the EGIP of different parameters, such as the initial energy of the SE, the electron reflection coefficient and the electric and magnetic field is discussed. For typical discharge conditions at a pressure of 0.5 Pa values for the average EGIP in the range of 0.25–0.35 are found. This means that the recapture probability lies typically between 65% and 75%, showing that it is necessary to take into account this process to accurately model and simulate the magnetron discharge.

Electron Emission from Surfaces Induced by Slow Ions and Atoms

“…However, since the electron mean free path is inversely proportional to pressure, at the low gas pressures of a magnetron discharge [42,54,55], a significant number of these electrons can return to the cathode and be recaptured without producing ionizations. The effect of electron recapture on the argon discharge characteristics has been discussed in a simplified [54] and a detailed model of the dc planar magnetron [42].…”

“…The influence of different discharge parameters on the discharge voltage during magnetron sputtering has been recently discussed by Depla et al [55] who compiled a list of electron emission yields for several metals from experimental data and empirical formulas found in literature [47,56,57]. As seen in Fig.…”

“…It is noteworthy that, for some target materials (Al, Cr, Mg, Nb, Re, Ti) at low discharge current, the discharge voltage decreases with increasing current [55], possibly due to target contamination by residual gases during sputtering. Indeed, since water is the main species in the residual gas, its chemisorption on target surfaces cannot be ruled out, especially at low discharge current.…”

Correlation between electron and negative O− ion emission during reactive sputtering of oxides

“…3,4 Knowledge of the ion-induced secondary electron emission coefficient ␥ e and the ion-induced negative O − ion emission coefficient ␥ O − is also essential for the understanding and the modeling of the plasma sheath potential 5,6 and the magnetron discharge. 7 The secondary electron emission induced by low energy ions, i.e., up to a few hundred of eV, is already well understood for clean metallic surfaces. 8,9 In contrast, due to the complexity of the measurements, the mechanism responsible for electron emission of insulators and/or oxides is so far not yet fully understood.…”

The importance of an external circuit in a particle-in-cell/Monte Carlo collisions model for a direct current planar magnetron

“…13,22 When this happens, they can be reflected or absorbed depending on the reflection coefficient ͑RC͒, given as the number of electrons that are reflected back in the discharge versus the number of incident electrons, and which is thus given by a value between 0 and 1. It is shown that this recapture of secondary electrons has a great effect on the discharge characteristics.…”