Ionization of sputtered metals in high power pulsed magnetron sputtering

Abstract

The ion to neutral ratio of the sputtered material have been studied for high power pulsed magnetron sputtering and compared with a continuous direct current (dc) discharge using the same experimental setup except for the power source. Optical emission spectroscopy (OES) was used to study the optical emission from the plasma through a side window. The emission was shown to be dominated by emission from metal ions. The distribution of metal ionized states clearly differed from the distribution of excited states, and we suggest the presence of a hot dense plasma surrounded by a cooler plasma. Sputtered material was ionized close to the target and transported into a cooler plasma region where the emission was also recorded. Assuming a Maxwell–Boltzmann distribution of excited states the emission from the plasma was quantified. This showed that the ionic contribution to the recorded spectrum was over 90% for high pulse powers. Even at relatively low applied pulse powers, the recorded spectra were dominated by emission from ions. OES analysis of the discharge in a continuous dc magnetron discharge was also made, which demonstrated much lower ionization.

An ionization region model for high-power impulse magnetron sputtering discharges

“…It reaches 19% which is consistent with experiments [6,7]. n M + starts at low values because n M starts at zero, and increases more rapidly than n Ar + due to a combination of decreasing argon density due to gas rarefaction shown in curve (a) of figure 6(a), and an increasing accumulated neutral metal density (not shown).…”

“…The reason for this choice is that this particular magnetron sputtering discharge has been extensively studied [5][6][7][17][18][19][20][21][22]. It is driven by a Sinex I HiPIMS power supply from Chemfilt Ionsputtering, delivering 100 µs long discharge pulses at a repetition frequency of 50 Hz, with a peak current of 100 A, and a peak voltage of −800 V which decreases monotonically during the pulse (see figure 1(b)).…”

“…An important development in sputtering technology over the past decade is the high-power impulse magnetron sputtering (HiPIMS) discharge [1][2][3] which is achieved by applying the power to a conventional magnetron sputtering device in the form of intense short pulses. The result is an increase in plasma density by up to three orders of magnitude [4,5], and a high degree of ionization of the sputtered vapor [6,7] that opens a completely new perspective in the engineering and design of new thin film materials [2]. In the HiPIMS discharge the sputtered flux usually includes more ions than neutral atoms and thus the process can be considered as ionized physical vapor deposition (IPVD) [2,8,9].…”

An introduction to thin film processing using high-power impulse magnetron sputtering

“…34 Thus, given the high electron density in the HiPIMS discharge a significant fraction of the sputtered material is thereby ionized, which also has been verified in a great number of publications. 4,[35][36][37] Worth pointing out is that there are substantial differences in the degree of ionization of the sputtered material depending on what target material is used (from a couple of percent to almost fully ionized 36,38 ). The reason FIG.…”

Hysteresis and process stability in reactive high power impulse magnetron sputtering of metal oxides

“…This mode of operation allows for maximum target power density values during the pulse on-time (referred to as peak target power density) in the order of several kWcm -2 , while the average target power density is maintained in the order of several tens of Wcm -2 comparable to conventional magnetron sputtering processes [9]. The high peak target power densities in turn facilitate the generation of dense plasmas (electron densities up to 10 19 m -3 ) resulting in high degree of ionization for both gas and sputtered species [8][9][10][11][12]. These plasma conditions have been shown to allow for the deposition of films with superior properties as compared to those obtained by conventional magnetron sputtering techniques.…”