Ion Energy Distributions in Magnetron Sputtering of Zinc Aluminium Oxide

Abstract

Ion energy distributions have been measured with an energy‐dispersive mass spectrometer during magnetron sputtering of Al doped ZnO. A d.c. and a pulsed d.c. discharge have been investigated. Different positive ions from the target material have been observed with low energies in d.c. and a second energy peak of about 30 eV in pulsed d.c. with only weak additional energy due to the sputter process. Negative ions are mainly O− with energies corresponding to the target voltage of several 100 eV. They originate from the target and barely from the (O2) gas and hit the substrate opposite the race track. In pulsed d.c., due to the varying target voltage, energies of up to 500 eV have been observed. With increasing pressure, negative ions at the substrate are reduced exponentially in their density but not in their energy.

In situ analyses on negative ions in the indium-gallium-zinc oxide sputtering process

“…21 Moreover, a shoulder is clearly observed in the high-energy edge of the energy distribution functions of the O À ions. Similar behaviors have been also found, [22][23][24] which may be due to (1) the collision cascades in the target during sputtering 23 momentum exchange at high energy, which gives rise to a loss of the negative charge on collision, so that the collided ion would be completely removed from the observed distribution. 24 In summary, we investigated the energy distribution of the negative ion generated from an IGZO ceramic target in a dc magnetron sputtering process by in situ analyses.…”

On performance limitations and property correlations of Al-doped ZnO deposited by radio-frequency sputtering

“…The spatial distribution of the O − ion flux density was investigated in several works, which generally found a larger flux density near x e , corresponding to the largest plasma density or, equivalently, to the strongest magnetic field at the target [9,28,41]. It is difficult to extract quantitative trends, because the flux density distribution depends on the age of the target [9,42], the strength of the magnetic field in the magnetron [10], the type of excitation [9] (RF or DC), and energy-dispersive measurements are typically affected by the limited acceptance angle of the probe [9,15]. However, it can be assumed that increasing deposition pressure leads to a reduction in the flux density gradient due to a larger contribution from species with an off-normal incidence angle caused by more frequent collisions.…”

“…Mainly two explanations exist for this phenomenon: 1) bombardment of the film by inhomogeneously distributed energetic particles during deposition [7]; 2) inhomogeneity in the amount and activity of oxygen reaching the substrate, which results in non-optimal oxygen stoichiometry in certain regions of the film [8]. According to hypothesis (1), O − and O − 2 ions (the former being more abundant) [9,14,15] are formed at the target and accelerated through the cathode sheath up to an energy corresponding to the target DC bias voltage. Upon leaving the cathode sheath, such a collimated beam of energetic ions travels mostly perpendicular to the target surface with a small collision cross section with the working gas [16].…”

Ion distribution measurements to probe target and plasma processes in electronegative magnetron discharges. II. Positive ions

“…In most cases Ar and the sputtered species from the target have been measured (see e.g., Refs. [10][11][12][13][14][15][16]. With the advent of high power impulse magnetron sputtering (HIPIMS) in the last years, especially for metals and oxides, also such high-energy density discharges have been investigated, partly also time-resolved.…”