Mitigating the geometrical limitations of conventional sputtering by controlling the ion-to-neutral ratio during high power pulsed magnetron sputtering

Abstract

High power pulsed magnetron sputtering has been used to grow thin chromium layers on substrates facing and orthogonal to the target. It is demonstrated that at low peak target current density, j T < 0.6 A/cm 2 corresponding to a low ion-to-neutral flux ratio, films grown on substrates facing the target exhibit in-plane alignment. This is due to the rectangular shape of the target that yields an asymmetry in the off-normal flux of sputtered species. With increasing j T the biaxial alignment degrades, as the major portion of the incoming flux (ions) can be effectively steered by the electric field of the substrate to remove asymmetry imposed by geometrical restrictions. Eventually, at j T = 1.7 A/cm 2 a fiber texture is obtained. For films grown on substrates orthogonal to the target, the large column tilt characteristic for growth at low j T , decreases with increasing ion content in the flux and almost disappears at the highest value of j T .The latter indicates that material flux to the substrate is highly ionized so that deposition takes place along substrate normal despite the high nominal inclination angle. Thus, in the limit of high j T the artifacts of conventional physical vapor deposition, resulting from the line-of-sight deposition, are effectively eliminated and the film growth proceeds more or less unaffected by the substrate orientation. Samples mounted orthogonally thus possess a similar texture, morphology, and topography as those facing the target.

Extended metastable Al solubility in cubic VAlN by metal-ion bombardment during pulsed magnetron sputtering: film stress vs subplantation

“…54 Typically, the ionization degree scales with the peak target current density. 55,56 Hence, during HIPIMS, the growing film surface is exposed to pulsed ion irradiation for 10-20% of the deposition time, where metal-ions constitute a significant part of the total ion flux. In contrast, during DC, ionization of sputtered species is negligible, as film growth proceeds from neutrals and the ion irradiation is due to gas ions (primarily Ar + , N2 + ), 57 however, throughout the 100% of the deposition time.…”

High power impulse magnetron sputtering discharge

“…41 As films grown by dcMS showed pronounced columns aligned toward the direction of incident material flux, the films grown by HiPIMS had columns growing normal to the surface. This effect has been further explored by Greczynski et al 188 for the growth of Cr films. They show that the Cr ion-to-neutral ratio in the flux incident onto the substrate depends on the peak target current density.…”

Tilt of the columnar microstructure in off-normally deposited thin films using highly ionized vapor fluxes

“…This trend is in agreement with previous reports. 24,25 The same behaviour is not seen for the Cr films, where no significant influnce of I Tpd on the column tilt is observed. The increase of I Tpd from 0.02 to 2.2 Acm À2 during the growth of Cu films resulted in a decrease of the film growth rate by about 30%.…”

“…24 Similar observations were made for off-normally deposited Cr films where it was found that the tilt of the columns approached the substrate normal as the degree of ionization of the sputtered material was increased by appropriate tuning of the HiPIMS process parameters. 25 The importance of these findings for technologically relevant applications has manifested itself in the uniform filling of nanometer-to micrometer-sized trenches by various metallic films 26,27 as well as in the growth of uniform ceramic coatings on cutting tools of complex geometry. 28 The ability to control column tilt when employing highly ionized fluxes in an off-normal deposition arrangement was explained by the deflection of ions closer to the substrate normal as a result of the high negative bias potential of several tens or hundreds of volts that was applied to the substrates in the aforementioned studies.…”