Abstract
A Ni81W19 target was dc sputter eroded at constant target power density from a tiltable magnetron at different Ar pressures. The combination with a stationary mass-energy analyzer allowed investigating the abundance of different species within the plasma as well as the ion energy distribution functions of 40Ar+, 58Ni+, and 184W+ at any given angle θ between 0° and 90° from the target normal. Ar+ ions are detected at θ angles close to the target normal, whereas metal atoms are observed at larger θ angles. Ni is emitted at smaller θ angles compared to W. Both investigated metal ion energy distributions exhibit a high energy tail with energies up to 50 eV. Increasing the Ar pressure first affects the trajectories of Ni before W atoms. This can be understood by considering the smaller mass difference between Ni and Ar compared to W and Ar. This enables more effective energy transfer and larger scattering angles of Ni undergoing collisions with Ar compared to W. Subsequent film depositions on a spherical-shell substrate holder, covering angles between 0° and 80° from the target normal, allowed for a comparison of the angular dependent film- and plasma-compositions. This correlative analysis suggests that selective resputtering of Ni by energetic Ar neutrals, reflected from the target, leads to the observed difference between the target and film composition during sputter deposition from a multielement NiW target.
Highlights
Modern magnetron sputter deposited thin films often consist of multiple elements and are applied for a large variety of technological applications
This can be understood by considering the smaller mass difference between Ni and Ar compared to W and Ar
With the use of multiple elements with considerable mass differences in a single target, various challenges arise for the deposition of homogeneous thin films:[2] (i) Element-specific differences in sputter yield (Y), emission angles with respect to the target normal (θ), and energy distributions change the lateral composition of large-area coatings.[3,4,5,6,7] (ii) Depending on the mass of the target constituents, considerable amounts of Ar+ ions are reflected from the target as Ar neutrals
Summary
Modern magnetron sputter deposited thin films often consist of multiple elements and are applied for a large variety of technological applications. (i) Element-specific differences in sputter yield (Y), emission angles with respect to the target normal (θ), and energy distributions change the lateral composition of large-area coatings.[3,4,5,6,7] (ii) Depending on the mass of the target constituents, considerable amounts of Ar+ ions are reflected from the target as Ar neutrals These Ar neutrals have energies corresponding up to the target acceleration voltage of some 100 V and may lead to selective resputtering of the growing film.[8] (iii) Mass-dependent energy transfer coefficients (ε) and scattering angles (α) for collisions of sputtered species with background avs.scitation.org/journal/jva gas atoms influence the respective trajectories, energies, and the film composition.[2,5,7,9–14] (iv) The mass and charge state of the impinging species on the growing film surface and their respective ion energy distribution function (IEDF) determines the sticking coefficient of the film-forming species and the amount of selective resputtering.[2,3,10,12,15–17] (v) The substrate temperature influences the degree of selective thermal desorption of film-forming species as well as selective surface segregation, exacerbating the effect of selective resputtering.[1,3,18] (vi) The use of a substrate bias or reactive magnetron sputtering increases the complexity of the deposition process due to the contribution of highly energetic and/or reactive particles to film growth.[1,6,16]
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