Effect of sputter heating in ionized metal physical vapor deposition reactors

Abstract

Ionized metal physical vapor deposition ͑IMPVD͒ is a process in which sputtered metal atoms from a magnetron target are ionized by a secondary plasma, accelerated into the substrate, and deposited with moderately anisotropic fluxes. The momentum and energy transfer from the sputtered metal atoms and ion-produced reflected neutrals to the background gas, sputter heating, produces rarefaction which influences the operating characteristics of the discharge. To address these processes, a model was developed to simulate the sputtering of metal atoms and their transport in IMPVD reactors. The model accounts for the ion-energy-dependent yield and kinetic energy of the sputtered and reflected atoms, and for sputter heating. The model was validated by comparing its results to experimentally measured metal atom densities and the ionization fraction of the deposition flux. Sputter heating as a function of auxiliary ionization and magnetron power in an inductively coupled plasma IMPVD reactor for Al deposition was then investigated. Sputter heating produces rarefaction of the buffer gas which results in a redistribution of Al species in the reactor compared to the absence of sputter heating. Consequently, the ionization fraction of the depositing metal flux decreases, while the magnitude of the flux increases. The minimum Ar density due to sputter heating is regulated by heat transfer to the target. The electron density increases significantly with the addition of a small amount of metal atoms to the plasma.

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

“…Kadlec [26] has used a Monte Carlo method to simulate the neutral particle flow during a HiPIMS pulse showing a strong rarefaction, heating of the background gas, and the formation of a shock wave. [39] These shock waves have been demonstrated experimentally by Hala et al [23]. These are clearly important processes for the operation of a HiPIMS discharge but are beyond the scope of this work.…”

“…The reaction set and rate coefficients for the argon discharge are listed in table 1. We assume that metal ions are created by electron impact ionization, by Penning ionization, by collisions of metal atoms with electronically excited argon atoms (Ar m + M → M + + Ar + e) with a rate coefficient k P = 5.9 × 10 −16 m 3 s −1 [39], and through charge exchange Ar + + M → M + + Ar with a rate coefficient k chexc = 1 × 10 −15 m 3 s −1 [39]. The rate coefficient for the electron impact ionization of aluminum is calculated from the electron impact ionization cross sections given by Freund et al [40].…”

Experimental study of a radio-frequency Ionized Physical Vapour Deposition process: Contamination by the internal coil

“…The gas flow rate is 175 sccm of argon and the pressure is regulated at 4 Pa. This pressure has been reported to allow a good compromise between the ionization efficiency and the deposition rate for a distance of approximately 10 cm between the magnetron and the substrate [11,[13][14][15]. The distance between the titanium target and the substrate holder is 14 cm.…”

MgO Erosion Profile in the High Pressure Coplanar Discharge

“…The sputtering yields [16,17] were obtained using TRIM assuming a surface binding energy at 10 eV [7]. TRIM provides the sputtering yield as a function of angle and energy of incident ions.…”